4  System structure

4.1 Available components

The HyEfRe Decision Support Tool allows you to configure your hydrogen infrastructure project by selecting different components through checkboxes in the System structure window. This section explains how to select components and which combinations are feasible.

4.1.1 Selecting components using checkboxes

When you open a scenario in the System structure view, you will see a panel with checkboxes that allow you to select which components to include in your analysis. The checkboxes are organized as follows:

1. Navigate to System structure: In the sidebar, expand your scenario and click on System structure.

2. Locate the checkbox panel: At the top of the main window, you will see “Step 1: Select your components” with a list of available components.

3. Enable/disable components: Click on a checkbox to include or exclude that component from your scenario:

   • Checked (enabled): The component will be included in the optimization
   • Unchecked (disabled): The component will not be considered in the analysis

The following components can be selected via checkboxes:

Component	Description
RESu	Renewable Energy Surplus - represents excess renewable energy that can be utilized
LREP	Local Renewable Energy Plant - dedicated renewable energy generation
PV	Photovoltaic (PV) system - solar electricity generation
WF	Wind Farm - wind-based electricity generation
BESS	Battery Energy Storage System - electrical energy storage
El. cons.	Fixed Electricity Consumption - baseline electricity demand
Electrolyser	Electrolyser - hydrogen production through water electrolysis
H2 sales	Hydrogen Sales - hydrogen product distribution
O2 sales	Oxygen Sales - oxygen by-product from electrolysis
Fuel cell	Fuel Cell - hydrogen-powered electricity generation
Waste heat	Waste Heat Utilization - thermal energy recovery and use

Note

Some components are present in the system but do not have checkboxes:

• Location - defines the geographic coordinates and local conditions
• Electrical grid connection - connection to the grid is always present
• Water supply - water input for the electrolyser (when Electrolyser is active)
• Financial parameters - economic settings for the analysis
• Simulation parameters - technical settings for optimization

4.1.2 Component dependencies

The DST enforces certain dependencies between components. Some components can only be selected if other components are already enabled. This ensures that the infrastructure configuration is technically coherent.

4.1.2.1 Electrolyser-dependent components

The Electrolyser is a central component in the hydrogen infrastructure. If you enable the Electrolyser, the following components become available:

• H2 sales (Hydrogen Sales)
• O2 sales (Oxygen Sales)
• Fuel cell (Fuel Cell)
• Waste heat (Waste Heat Utilization)

These components depend on the Electrolyser because they either:

• Use hydrogen produced by the electrolyser (H2 sales, Fuel cell)
• Use by-products from electrolysis (O2 sales)
• Utilize thermal energy generated during electrolysis (Waste heat)

4.1.3 Feasible component combinations

Below are examples of common and feasible infrastructure configurations. The DST validates component combinations based on three essential rules:

4.1.3.1 Validation rules

The system validates your component selection against the following rules:

1. Electrolyser dependency: If the Electrolyser is selected, at least one of the following must also be selected:

   • H2 sales (Hydrogen Sales)
   • Fuel cell (Fuel Cell)

   Rationale: The electrolyser produces hydrogen, so there must be a way to utilize or sell the hydrogen.

2. At least one electric source: The configuration must include at least one of:

   • El. grid (Electrical Grid)
   • LREP (Local Renewable Energy Plant)
   • PV (Photovoltaic system)
   • WF (Wind Farm)

   Rationale: The system needs at least one source of electricity.

3. At least one electricity consumer: The configuration must include at least one of:

   • Electrolyser (hydrogen production)
   • El. cons. (Fixed Electricity Consumption)
   • BESS (Battery Storage)

   Rationale: There must be a consumer for the electricity supplied by the sources.

4.1.3.2 Invalid combinations

If you try to select an invalid combination of components, the application will:

1. Reject the change: The component selection will not be updated
2. Maintain valid state: The previous valid configuration will remain active

For example, the following combinations are invalid:

• Electrolyser without H2 sales or Fuel cell: The electrolyser produces hydrogen that must be used somewhere
• No electric source: There must be at least one source of electricity (El. grid, LREP, PV, or WF)
• No electricity consumer: There must be at least one consumer (Electrolyser, El. cons., or BESS)

4.1.3.3 Automatic dependency handling

When you select a component that has dependencies, the application may automatically enable those dependent components. Similarly, when you deselect a component, dependent components may be automatically deselected.

For example:

• Selecting Electrolyser automatically enables H2 sales (if not already selected)
• Deselecting Electrolyser automatically deselects all components that depend on it (O2 sales, Fuel cell, Waste heat)

4.2 Component details

4.2.1 Location

Purpose
The backend uses the geographic coordinates for:

• Weather data which is used for rain collection in Water supply component
• Solar data which is used in PV component
• Wind data which is used in Wind farm component
• Detecting country which is used to set default parameters in:
  • Electricity grid connection
  • Electricity supply
  • Water connection

You can enter coordinates manually, choose one of predefined cities or choose location on a map.

4.2.1.1 Input parameters

Parameter	Description	How to input
Latitude/Longitude	Geographic coordinates	Click on map or enter manually
City	Predefined city selection	Select from dropdown list
Country	Automatic from coordinates	Auto-detected

Important Notes:

• Must be set before generating renewable production profiles

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4.2.2 Electrical grid connection

The Electrical grid connection component represents the interface between the renewable energy hub and the electrical grid. This component cannot be disabled.

It consists of 3 sections:

• Grid connection: the physical characteristics of the grid connection (e.g. grid fees, peak power pricing).
• Electricity supply: models and tariffs for purchasing electricity from the grid and feeding it into the grid.
• Advanced features: optional grid-related constraints.

Before the 3 sections, there is a parameter influencing both Grid connection and Electricity supply:

Show predefined values for the country (dropdown menu)

The country is automatically selected according to the site location, but it can be changed manually. Available countries are those that participated in HyEfRe project: Austria, Croatia, Czechia, Germany, Hungary, Italy, Poland, and Slovenia. If the selected location is in another country, the value of this parameter remains empty. With the selected country the tool offers grid connection and electricity supply types for that country, but any parameter can be entered manually.

4.2.2.1 Grid connection

The following parameters define technical and economic aspects of the physical grid connection. Depending on whether an existing connection is available, different cost calculation approaches are applied.

Parameter	Description
Use predefined connection type [dropdown menu]	Depending on the selected country, the tool offers predefined connection types. By selecting one of the connection types, all other parameters from this section (Grid connection) are populated. You can also enter data manually, even after selecting a connection type.
Grid connection already exists? [checkbox]	Whether the grid connection already exists at the location or not. It must be enabled if there is any other existing infrastructure.
Existing connection size [kW]	The size of the existing grid connection. The connection is assumed symmetrical, i.e. it has the same limit for both directions. The parameter is visible only if Grid connection already exists? is enabled.
Capacity price for grid connection enlargement [€/kW]	It represents the price for building and installation of the connection depending only on the capacity, i.e. size. It can be determined from existing projects: cost of the connection divided with the capacity of the connection.
Unit price for grid connection installation [€/(kW km)]	It represents the price for building and installation of the connection depending on the capacity and distance to the nearest connection point. A connection point represents a piece of infrastructure to which the renewable energy hub must be connected to, such as a substation. This parameter is used only for greenfield investments – it is visible only when Grid connection already exists? is disabled. It can be determined from existing projects: cost of the connection divided with the capacity and distance to the nearest connection point.
Distance to nearest connection point [km]	A connection point represents a piece of infrastructure to which the renewable energy hub must be connected to, such as a substation. This parameter is used only for greenfield investments – it is visible only when Grid connection already exists? is disabled. It is used to calculate the total price of the grid connection: Unit price * Distance + Capacity price
Start time of high tariff [0–24]	Hour of the day when high tariff for grid fees starts. If the tariff model has a single tariff, set it to 0, and enter your single tariff grid fee in Grid fee during high tariff.
Start time of low tariff [0–24]	Hour of the day when low tariff for grid fees starts. If the tariff model has a single tariff, set it to 24, and the model will use only Grid fee during high tariff as your single tariff grid fee.
Weekend tariff exists? [checkbox]	Whether there is weekend tariff for grid fees or not. If enabled, weekend tariff applies to every weekend, starting on Saturday at 00:00 and ending on Sunday at 23:00.
Grid fee during high tariff [€/kWh]	Grid fee, without taxes, during high tariff hours. Includes transmission and distribution fees, and any other fees paid to DSO and TSO, charged per amount of energy consumed.
Grid fee during low tariff [€/kWh]	Grid fee, without taxes, during low tariff hours. Includes transmission and distribution fees, and any other fees paid to DSO and TSO, charged per amount of energy consumed.
Grid fee during weekend tariff [€/kWh]	Grid fee, without taxes, during weekends (from Saturday at 00:00 to Sunday at 23:00). It is visible and applies only if Weekend tariff exists? is enabled. It includes both transmission and distribution fees, and any other fees paid to DSO and TSO, charged per amount of energy consumed.
Peak power price [€/kW/month]	Monthly charge based on the maximum recorded power demand. The fee is applied for each month included in the simulation period, regardless of the number of simulated days within that month. Even if the simulation lasts only 1 day in a month, it is assumed that the peak power happened that day.

4.2.2.2 Electricity supply

Electricity supply represents the only non-green electricity source for the hydrogen hub. The parameters in this section define the electricity purchase and feed-in prices, excluding grid fees, which are specified separately in the Grid connection section.

Electricity supply parameters can be defined in two ways, each available in a separate tab:

• Standard tariffs: defined through high, low, and optional weekend tariffs.
• Custom price profile: defined by importing external time-series data of electricity prices.

Parameters in Standard tariffs tab

Parameter	Description
Use predefined supply models [dropdown menu]	Select a predefined electricity supply model for the chosen country. When selected, all energy prices, feed-in prices, and additional fees in this section are automatically populated according to the selected model. Manual modification of individual parameters is possible after selecting a predefined model.
Start time of high tariff [0–24]	Hour of the day at which the high tariff period begins. If a single tariff model is used, set this parameter to 0 and define the energy price in Energy price during high tariff.
Start time of low tariff [0–24]	Hour of the day at which the low tariff period begins. If a single tariff model is used, set this parameter to 24. In that case, only the high tariff price is applied throughout the entire day.
Weekend tariff exists? [checkbox]	Indicates whether a separate tariff applies during weekends. If enabled, weekend tariff values apply from Saturday at 00:00 to Sunday at 23:00. If disabled, weekday high and low tariffs are applied during weekends as well.
Energy price during high tariff [€/kWh]	Energy price for electricity imported from the grid during high tariff hours. This price represents the supplier’s energy component only and excludes grid fees and taxes.
Energy price during low tariff [€/kWh]	Energy price for electricity imported from the grid during low tariff hours. This price represents the supplier’s energy component only and excludes grid fees and taxes.
Energy price during weekend tariff [€/kWh]	Energy price for electricity imported from the grid during weekend tariff hours. Visible and applied only if Weekend tariff exists? is enabled. This price excludes grid fees and taxes.
Feed-in price during high tariff [€/kWh]	Compensation received for electricity exported to the grid during high tariff hours. Defines the revenue per unit of exported electricity.
Feed-in price during low tariff [€/kWh]	Compensation received for electricity exported to the grid during low tariff hours. Defines the revenue per unit of exported electricity.
Feed-in price during weekend tariff [€/kWh]	Compensation received for electricity exported to the grid during weekend tariff hours. Visible and applied only if Weekend tariff exists? is enabled.
Additional fees during high tariff [€/kWh]	Additional supplier-related energy charges applied during high tariff hours. These may include supplier margins, balancing costs, or other contractual energy charges, excluding grid fees and taxes.
Additional fees during low tariff [€/kWh]	Additional supplier-related energy charges applied during low tariff hours. Excludes grid fees and taxes.
Additional fees during weekend tariff [€/kWh]	Additional supplier-related energy charges applied during weekend tariff hours. Visible and applied only if Weekend tariff exists? is enabled. Excludes grid fees and taxes.
Tax on electricity [%]	Percentage tax applied to the total electricity purchase price. The tax is calculated on the sum of: energy price, additional fees, and grid fees. Feed-in revenues are not subject to this tax.

GUI elements in Custom price tab

This option allows the user to define electricity purchase prices by importing a time-series dataset from a CSV file. The imported values represent electricity prices including VAT, but excluding grid fees. The custom price profile replaces the standard tariff definition and is applied throughout the entire simulation period. Grid fees from Section 4.2.2.1 are applied.

GUI element	Description
Custom profile of prices [text field]	Defines the name of the CSV file containing the electricity price time series. It is not possible to write in this field – it is automatically populated after clicking on button Browse….
Browse [button]	By clicking Browse, the user selects a CSV file from the local system. File format requirements: - File format: .csv - Single column - No header row Allowed number of rows: - 8,760 (hourly resolution) - 17,520 (30-minute resolution) - 35,040 (15-minute resolution) Each row must contain a numerical value representing the electricity purchase price in €/kWh, including VAT and excluding grid fees. The first value in the file corresponds to the beginning of the year (January 1st, 00:00), and the last value corresponds to the end of the year (December 31st, 23:00 for hourly resolution). If the dataset originates from a leap year (8,784 hourly values), one day of data must be removed to match one of the supported row counts. After selecting a file, a message is displayed indicating whether the data import was successful or if errors were detected.
Check imported data [button]	Opens a pop-up window displaying a chart of the imported electricity price profile. The chart is dynamic, meaning it can be zoomed in or out and moved around. This allows the user to visually verify data continuity, seasonal trends, extreme values, and possible data inconsistencies. The chart is for verification purposes only and does not modify the imported dataset. This button is visible only if data import was successful.
Percentage for feed-in remuneration [%]	Defines the percentage of the imported electricity purchase price used to calculate the feed-in price. The feed-in price is calculated as: feed-in price = imported electricity price × defined percentage. For example, if the percentage is set to 80%, the feed-in remuneration equals 80% of the corresponding purchase price at each time step.

4.2.2.3 Advanced features

This section provides additional constraints related to electricity import, export, and price behavior. Certain options are mutually exclusive and cannot be enabled simultaneously.

Parameter	Description
Electricity export is not possible [checkbox]	Enable this option if electricity can be imported from the grid but cannot be exported to it. When enabled, the model does not allow feed-in of surplus electricity to the grid. All locally generated electricity must either be consumed on-site or curtailed. This option is applicable in cases where grid injection is not permitted by the DSO or contractual arrangements. If enabled, the following options are automatically disabled: Electricity import is not possible, Energy export limited to the imported amount
Electricity import is not possible [checkbox]	Enable this option if electricity can be exported to the grid but cannot be imported from it. When enabled, the system cannot purchase electricity from the grid. This is typically relevant when optimizing a generation plant with storage, where charging from the grid is not permitted by the DSO. If enabled, the following options are automatically disabled: Electricity export is not possible, Energy export limited to the imported amount.
Energy export limited to the imported amount [checkbox]	Limits total exported electricity to the total imported electricity over the simulation period. This reflects regulatory or contractual conditions where feed-in remuneration is restricted to the amount of previously imported energy. Such schemes are designed to ensure that the prosumer remains primarily a consumer rather than a net producer. If enabled, the following options are automatically disabled: Electricity export is not possible, Electricity import is not possible.
Price of electricity cannot be negative [checkbox]	Prevents the effective electricity purchase price from becoming negative. When using custom electricity price profiles (e.g., day-ahead market data), negative prices may occur. In practice, however, retail consumers purchasing electricity through a supplier are typically not remunerated for consumption during negative price periods. If this option is enabled, any negative energy price is set to zero. It is recommended to keep this option enabled when electricity is purchased or sold through a supplier rather than directly on wholesale energy markets.

4.2.2.4 Optimization output

After running the optimization, the tool calculates the optimal technical and economic values for the defined scenario. This subsection shows what variables are tied to the Electrical grid connection component, while the results are presented in Results (Chapter 5).

Variable	Description
Grid connection enlargement	If the existing grid connection capacity is insufficient to satisfy the optimized power flows, the model determines the required: - Grid connection capacity enlargement [kW] - Investment cost of enlargement [€] The investment cost is calculated according to the parameters defined in Section 4.2.2.1 – capacity price and/or distance-based cost components. If no enlargement is required, the investment cost is zero.
Electricity import from supplier	The optimization determines the time-dependent profile of electricity purchased from the supplier. Results include: - Electricity import profile as mean powers for each time step [kW] - Operating cost of imported electricity [€] The operating cost is calculated using: energy prices, additional fees, and taxes. If the total operating cost is negative, it indicates that revenue from electricity export exceeds the cost of electricity import during the simulation period. In that case, the hydrogen hub generates net income from electricity production.
Electricity flow through the grid connection	The tool also provides the time-dependent profile of electricity flowing through the physical grid connection. This profile represents the actual power exchange at the connection point and may differ from the electricity purchased from the supplier. The difference occurs because the RESu component (Section 4.2.3, if enabled) acts as a secondary supplier. Therefore, grid fees are calculated based on the total electricity flowing through the connection. Outputs include: - Electricity flow profile as mean powers for each time step [kW] - Total cost of grid fees [€]
Monthly peak power	For each month included in the simulation period, the model determines peak import power [kW] and peak export power [kW]. Peak values are used to calculate capacity-based charges according to the defined peak power price. The resulting output includes: - Monthly peak values [kW] - Total peak power cost over the simulation period [€] If the simulation covers only part of a month, the peak power charge is still applied for that month, according to the defined pricing rules.

NoteTime resolution and profile length

All resulting time-series outputs (electricity import, export, and grid flow profiles) are generated according to the Simulation parameters – sampling time, start date, end date. The length of the output profiles therefore directly corresponds to the simulation settings.

4.2.2.5 Related components

• Location, as the predefined models of Grid connection and Electricity supply depend on the selected country.
• RESu, as its electricity flow contributes to the total grid fee cost.

4.2.2.6 Troubleshooting

Common issues and solutions

WarningExisting connection size and payoff period limit

If you are using any existing infrastructure, most commonly Electricity consumption (Section 4.2.8), make sure the Existing connection size (see Section 4.2.2.1) is large enough to cover current energy needs.

If the existing connection is too small, the tool will automatically enlarge it, regardless of whether the investment is economically viable. This enlargement incurs an investment cost, which means that it is not possible to limit the payoff period in the Financial parameters (Section 4.2.8) if the existing connection capacity is insufficient.

The tool calculates the minimum required connection size needed to enable the payoff period constraint. If this minimum is not reached, an error message is displayed.

WarningUsing RESu and limiting electricity import

Under the Advanced features of the Electrical grid connection (see Section 4.2.2.3), it is possible to forbid electricity import. If this option is enabled, the RESu component (Section 4.2.3) cannot be used.

This restriction is intended for scenarios such as power plants where grid import is not allowed.

If this combination is enabled, the tool will notify the user with adequate error message.

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4.2.3 Renewable energy surplus

The Renewable Energy Surplus (RESu) component represents excess energy available in the power distribution or transmission grid. This component allows the optimization to utilize renewable surplus energy that would otherwise be curtailed or wasted.

In the HyEfRe DST, the RESu component serves as an alternative electricity source that can reduce grid electricity imports. When activated, the optimization algorithm can choose to use this surplus renewable energy (at the specified price) instead of purchasing electricity from the grid.

4.2.3.1 Input parameters

Basic parameters

Parameter	Description
HPM output file	The Hydrogen Potential Model (HPM) output file containing renewable surplus data. The file needs to be a CSV file, formatted as 2 columns and 8760 rows (no header). Currently, this option is not yet fully implemented.
File with RESu profile	A custom CSV file containing yearly renewable energy surplus profiles. The custom RESu needs to be in a CSV file, formatted in a single column and 8760, 17,520, or 35,040 rows (no header), where values represent renewable energy surplus in kWh. If the data in the file is for a leap year, please remove 1 day of data to match 8760, 17,520, or 35,040 rows. The first value in the file corresponds to the beginning of the year, while the last value corresponds to the end of the year.
Energy price [€/MWh]	Price at which the surplus of renewable energy is bought from the grid. Grid fees from Electrical grid connection are added to this value. Default value is 0 €/MWh.

4.2.3.2 Optimization output

Variable	Description
Used power [kW]	Power used from the renewable energy surplus. This represents the actual amount of surplus energy utilized in each time step, limited by the available surplus.
Total cost of buying surplus energy [€]	Operational costs associated with using the renewable energy surplus. Calculated as the energy price multiplied by the power used.

The optimization model determines how much of the available renewable surplus to use in each time step.

4.2.3.3 Interface options

The RESu component provides a tabbed interface with two data input methods:

1. From HPM tab: Import renewable surplus data directly from the Hydrogen Potential Model (HPM) output file. Click Browse… to select the HPM output CSV file. Note: This feature is not yet fully implemented.

2. From tabular tab: Import a custom renewable surplus profile from a CSV file. Click Browse… to select the CSV file containing the RESu profile. Additionally, you can set the energy price at which the surplus renewable energy is bought from the grid.

3. Check renewable energy surplus button: After loading a RESu profile (from either source), click this button to visualize the renewable energy surplus data as a time series chart. This helps verify that the data has been correctly imported and shows the profile over time.

Data format requirements:

• HPM output file: 2 columns, 8760 rows (hourly data for non-leap year)
• Custom RESu profile: 1 column, 8760 rows (hourly), 17,520 rows (30-min), or 35,040 rows (15-min)

4.2.3.4 Related Components

• Electrical grid connection - grid fees are added to the RESu energy price

4.2.3.5 Troubleshooting

Common issues and solutions:

• HPM output file is not defined: When using the From HPM tab, ensure you have selected an HPM output file. Note that this feature is currently not fully implemented. Use the From tabular option instead.

• File with RESu profile is not defined: When using the From tabular tab, ensure you have imported a valid CSV file with the RESu profile. Click Browse… to select a properly formatted CSV file.

• Invalid file format: The custom RESu file must be a single-column CSV with no header. Ensure your file meets this requirement.

• Incorrect number of rows: The RESu profile file must contain exactly 8760, 17,520, or 35,040 rows. If your data is from a leap year, remove one day of data to match the expected row counts. Common row counts: 8760 (hourly), 17520 (30-min), 35040 (15-min).

• RESu and LREP combination error: If you have both RESu and LREP active with the payoff period limit enabled, the optimization will fail. Disable the payoff period limit or remove one of these components from your configuration.

• Grid import required: When using RESu, electricity import from the grid must not be disabled in the Electrical grid connection settings. Ensure import is allowed if you want to use RESu.

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4.2.4 Local renewable energy plant

A local renewable energy plant (LREP) is considered as an existing plant that does not require any additional investments, i.e. this component is a source of renewable electricity that is not sized by the optimization procedure. The LREP can represent various renewable energy sources, such as wind, solar PV, hydro, biomass, biogas, and geothermal, but also a combination of those.

The user can specify multiple energy plants (REPs), each with its own production profile. A REP is added by clicking on Add new REP button.

By right-clicking on a REP’s node, a pop-up menu appears with the following options:

• Rename REP – change the name of the REP.
• Delete REP – delete the REP.

Production profile of each REP can be parametrized in two ways:

• by selecting a generic power production profile available in the tool, or
• by importing a custom power production profile from a file.

The price for electricity export is set in Electrical grid connection.

NoteDisclaimer

The electricity production of LREP is used for green hydrogen production and therefore must comply with Article 3 of EU regulation 2023/1184.

4.2.4.1 Input parameters

Generate data

Parameter	Description
REP type [dropdown menu]	A generic production profile of the selected type is used and scaled to match the Annual energy production.
Annual energy production [MWh]	Amount of electricity produced by the REP in a year. This value is used to scale the generic profile.

Import data

GUI element	Description
File with the production profile [text field]	Defines the name of the CSV file containing the electricity production time series. It is not possible to write in this field – it is automatically populated after clicking on button Browse….
Browse [button]	By clicking Browse, the user selects a CSV file from the local system. File format requirements: - File format: .csv - Single column - No header row Allowed number of rows: - 8,760 (hourly resolution) - 17,520 (30-minute resolution) - 35,040 (15-minute resolution) Each row must contain a numerical value representing the electricity production power in kW. The first value in the file corresponds to the beginning of the year (January 1st, 00:00), and the last value corresponds to the end of the year (December 31st, 23:00 for hourly resolution). If the dataset originates from a leap year (8,784 hourly values), one day of data must be removed to match one of the supported row counts. After selecting a file, a message is displayed indicating whether the data import was successful or if errors were detected.

Check the production profile
A button that opens a pop-up window displaying a chart of the electricity production profile, based on the active tab. The chart is interactive and can be zoomed and panned. This allows the user to visually verify data continuity, seasonal trends, extreme values, and possible data inconsistencies. The chart is for verification purposes only and does not modify the data.

4.2.4.2 Optimization output

Variable	Description
Electricity production profile [kW]	Time-dependent profile of electricity production expressed as average power per time step, since every REP’s output can be curtailed. A single profile is used for all REPs together. The electricity produced can be used within the renewable energy hub, or it can be exported to the grid. The exact power routing cannot be determined because all electricity is balanced through a common bus.

4.2.4.3 Interface options

Production profile of each REP can be parametrized in two ways, each with its own tab:

1. Generate data: the user selects the type of the REP (PV, Wind, or Hydro), and enters annual energy production. The tool scales the profile accordingly.
2. Import data: the user imports a CSV file with a possible power production profile.

4.2.4.4 Related components

• Electrical grid connection, where prices for electricity export are defined.

4.2.4.5 Troubleshooting

An error is displayed if the button Check the production profile is clicked on and:

• Generate data tab is active and a REP type is not selected, or
• Generate data tab is active and Annual energy production is zero, or
• Import data tab is active and no CSV file has been imported.

WarningUsing RESu and LREP together

It is not possible to use both RESu and LREP in the same configuration while also limiting the payoff period.
If such a configuration is optimized, the tool displays an error message and the optimization is not executed.

In general, using both RESu and LREP in the same scenario is not recommended.

4.2.5 Photovoltaic system (PV)

The Photovoltaic (PV) component models solar power generation systems within the HyEfRe DST. It enables the design and optimization of PV arrays by either generating production profiles from PVGIS (Photovoltaic Geographical Information System) or importing custom production data.

The PV system can consist of multiple arrays, each with different orientations, inclinations, and specifications. During optimization, the algorithm determines the optimal installed capacity for each array within the specified constraints, considering the available area, financial parameters, and the production profile.

4.2.5.1 Input parameters

Basic parameters

Parameter	Description
Orientation angle [°]	Orientation angle, or azimuth, is the angle of the PV modules relative to the direction due South. -90° is East, 0° is South and 90° is West.
Inclination angle [°]	Inclination angle, or slope, is the angle of the PV modules from the horizontal plane. 0° means horizontally placed PV modules, while 90° means vertically placed PV modules.
Available area [m²]	Total area available for placement of new PV modules. For example, if it is a roof, then enter the surface area of the roof.
Installed power for reference [kWp]	Installed peak power of the system for which the data is imported.

Advanced parameters

Technical parameters

Parameter	Description
PV size per m² [Wp/m²]	Amount of PV modules that is possible to install per unit of surface area, including obstacles. For example, if a 500 Wp panel covers area of 2.5 m², this parameter should be less than 200 Wp/m² because not all surface could be covered with PV panels.
Limit PV size directly [checkbox]	The limit of the PV array is posed by the available surface area and then calculated into the limit of installed power. With this option you can limit the maximum installed power directly.
Maximum PV size [kWp]	Upper limit on the size (installed power) of the PV array. It is calculated according to ‘Available area’ and ‘Solar PV panel power per area’, but it can be also entered manually.
Minimum PV size [kWp]	Lower limit on the size (installed power) of the PV array. If this value is greater than zero, ‘Maximal payoff period’ and ‘Maximum investment’ parameters are disabled.

Financial parameters

Parameter	Description
PV system [dropdown menu]	Choose a PV system from the application’s database and its financial parameters will be filled automatically. Afterwards you can change any of its parameters.
Investment price [€/kWp]	Investment price, per unit of installed power, includes all necessary elements (PV modules, inverter, cables, etc.), materials, labor (design, mounting, commissioning, etc.), and financing until full operation.
Maintenance price [€/kWp]	Estimated annual operation and maintenance (O&M) price per installed power. O&M includes cleaning of PV modules, insurance, administration costs, and replacing broken components. O&M does not include degradation of the system.
Replacement price [€/kWp]	Same as investment price, but after the lifetime of the system, i.e. the future investment price. The main difference from the investment price is that the subsidy does not apply to the replacement price.
Lifetime [years]	Number of years after which the PV system needs to be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

4.2.5.2 Optimization output

Variable	Description
Installed capacity [kWp]	Optimized installed power capacity for each PV array.
Total installed capacity [kWp]	Sum of installed capacities across all PV arrays.
Power production [kW]	Actual power production in each time step, optimized by the model.
Available power [kW]	Maximum potential power production based on installed capacity and irradiance profile.
Investment cost [€]	Total investment cost for all PV arrays.
Maintenance cost [€/year]	Annual operation and maintenance costs.
Degradation cost [€/year]	Annual cost accounting for system degradation over its lifetime.

The optimization model determines the optimal installed capacity for each PV array within the specified minimum and maximum size constraints. The power production is constrained by the available irradiance profile and the installed capacity.

4.2.5.3 Interface options

The PV component provides a tabbed interface with two data input methods:

1. Generate data tab: Create PV production profiles using PVGIS (Photovoltaic Geographical Information System).
   • Set orientation and inclination angles for the PV array
   • Specify the available area for PV module placement
   • Use Check generated data to visualize the production profile
2. Import data tab: Import custom PV production profiles from a CSV file.
   • Click Browse… to select a CSV file with production data
   • Specify the peak power of the system for which the data was generated
   • Set available area and existing PV parameters
   • Click Import power profile to process and save the data
   • Use Check imported data to visualize the imported profile

Data format requirements for import:

• Single column CSV file with no header
• 8760 rows (hourly), 17,520 rows (30-min), or 35,040 rows (15-min)
• Values represent mean production power at the output of the PV inverter [kW]
• For leap year data, remove one day to match expected row counts

4.2.5.4 Related Components

• Location - Geographic coordinates are used for PVGIS data generation

4.2.5.5 Troubleshooting

Common issues and solutions:

• PV production profile is not yet generated: Before running optimization, you must either generate a production profile from PVGIS or import one from a file. Use the “Generate power profile” or “Import power profile” button.

• PVGIS API connection failed: Check your internet connection. The PVGIS service may be temporarily unavailable.

• Invalid file format for import: The CSV file must have exactly one column with 8760, 17,520, or 35,040 numeric values and no header row.

• Available area must be positive: If “Limit PV size directly” is not checked, the available area must be greater than zero. Enter a valid surface area for PV placement.

• Minimum size too large for available area: The minimum PV size cannot exceed the maximum possible size calculated from the available area and power per area ratio. Either reduce the minimum size or increase the available area.

• Reference power must be larger than 0: When importing production data, you must specify the peak power of the system for which the data was generated.

• Coordinates not set: PVGIS data generation requires location coordinates. Ensure the location is properly set in the Location component.

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4.2.6 Wind farm

The Wind farm (WF) component represents a wind power installation consisting of one type of wind turbine. Once the location of the wind farm is defined, the power production profile for a specific installed capacity can be generated. The tool then scales this profile to determine the optimal size of the wind farm. The scaling factor of the production profile is multiplied by the reference capacity to calculate the optimal capacity for installation.

4.2.6.1 Input parameters

Basic parameters

The basic parameters are organized in two tabs, allowing users to either generate data from an API or import their own reference power profiles.

Parameters in Generate data tab

Parameter	Description
Hub height [m]	The height of the turbine’s tower, that is, how far the blades are centred above the ground. Hub heights are limited to between 10 and 150 m.

Parameters in Import data tab

This option allows the user to define the wind power production profile by importing a time-series dataset from a CSV file.

Parameter	Description
File with the production profile [text field]	The custom profile of production power needs to be in a CSV file, formatted in a single column and 8760, 17,520, or 35,040 rows (no header), where values represent hourly, half-hourly, or 15-min mean power in kW, respectively. If the data in the file is for a leap year, please remove 1 day of data to match 8760, 17,520, or 35,040 rows. The first value in the file corresponds to the beginning of the year, while the last value corresponds to the end of the year.
Reference power [kW]	The installed capacity, i.e. power, of the wind power plant from which the data was collected.

Advanced parameters

Parameter	Description
Minimum capacity [kW]	Lower limit on the installed capacity. If this value is greater than zero, “Maximal payoff period” and “Maximum investment” parameters are disabled.
Maximum capacity [kW]	Upper limit on the installed capacity.
Type of the wind turbine [dropdown menu]	Choose the type of the wind turbines used in the wind farm. The parameters will be filled with predefined values. After selection, you can change any of the parameters.
Investment price [€/kW]	Investment price of the wind farm, per unit of power, includes wind turbine(s), all auxiliary materials, labour (mounting, commissioning, etc.), and financing until full operation.
Maintenance price [€/kW]	Estimated annual maintenance price per unit of power. It does not include degradation of the wind turbine(s).
Replacement price [€/kW]	Same as investment price, but after the lifetime of the wind turbine(s), i.e. the future investment price. Also, it is not influenced by the subsidy.
Lifetime [years]	Number of years after which the wind turbine(s) needs to be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. It does not apply to the replacement cost.

4.2.6.2 Optimization output

After running the optimization, the tool calculates the optimal technical and economic values for the defined scenario. This subsection shows what variables are tied to the Wind farm component.

Variable	Description
Optimal installed capacity	The optimization determines the optimal installed capacity of the wind farm [kW]. This value is calculated by scaling the reference production profile to minimize the total cost while meeting the energy demands of the hydrogen hub.
Power production profile	The time-dependent profile of electricity generated by the wind farm. Results include: - Power production profile as mean powers for each time step [kW] - Total energy produced over the simulation period [kWh]
Investment cost	The total investment cost for the optimal wind farm capacity [€]. This includes the wind turbine(s), all auxiliary materials, labour, and financing. If a subsidy is defined, it is deducted from this cost.
Annual maintenance cost	The estimated annual maintenance cost based on the optimal installed capacity [€/year].
Replacement cost	The future investment cost for replacing the wind turbine(s) after their lifetime [€].

4.2.6.3 Interface options

The Wind farm component provides a tabbed interface with two data input methods:

1. Generate data tab: Automatically generate a wind power production profile based on the location and hub height. The tool uses the renewables.ninja API to fetch typical wind power production data for the specified location and turbine configuration. After setting the hub height, click “Check power production” to generate and visualize the profile.

2. Import data tab: Import a custom wind power production profile from a CSV file. This is useful when you have site-specific measurements or want to use data from a particular wind turbine model. After importing the file and setting the reference power, click “Check power production” to visualize the profile.

Data format requirements for custom profiles:

• File format: .csv
• Single column (no header row)
• Allowed number of rows:
  • 8,760 (hourly resolution)
  • 17,520 (30-minute resolution)
  • 35,040 (15-minute resolution)
• Each row must contain a numerical value representing the mean power output in kW
• The first value corresponds to the beginning of the year (January 1st, 00:00)
• The last value corresponds to the end of the year (December 31st, 23:00 for hourly resolution)

4.2.6.4 Related components

• Location, as the generated wind power profile depends on the geographic coordinates..

4.2.6.5 Troubleshooting

Common issues and solutions:

• Hub height out of range: Ensure the hub height is between 10 and 150 m. Values outside this range will cause an error.

• Production profile is not defined: When using the “Import data” tab, ensure you have imported a valid CSV file and set the reference power. Click “Browse…” to select a properly formatted CSV file.

• Reference power must be greater than 0: When importing custom data, the reference power must be a positive value representing the installed capacity of the wind power plant from which the data was collected.

• Invalid file format: The custom production profile file must be a single-column CSV with no header. Ensure your file meets this requirement.

• Incorrect number of rows: The production profile file must contain exactly 8,760, 17,520, or 35,040 rows. If your data is from a leap year, remove one day of data to match the expected row counts.

• API connection failed: If generating data fails, check your internet connection. The tool requires access to the renewables.ninja API to fetch wind power production data.

• Minimum capacity greater than maximum capacity: Ensure the minimum capacity is not greater than the maximum capacity. This will cause a validation error.

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4.2.7 Battery energy storage system

The battery energy storage system (BESS) consists of:

• a battery pack, which determines the energy capacity of the BESS [kWh], and
• a power converter, which determines the charge/discharge power of the BESS [kW].

4.2.7.1 Input parameters

Basic parameters

Parameter	Description
BESS already exists? [checkbox]	Whether there is an existing battery energy storage system at the site or not. If enabled, existing capacity and power parameters are shown.
Existing capacity [kWh]	Rated capacity of the existing battery pack. It is visible only if BESS already exists? is activated.
Existing power [kW]	Rated power of the existing power converter. The rated power is assumed to be bidirectional, i.e. the same power is considered for both charging (rectifier mode) and discharging (inverter mode) of the battery. It is visible only if BESS already exists? is activated.

Advanced parameters

Parameter	Description
Minimum battery pack capacity [kWh]	Lower limit on the battery pack capacity. If this value is greater than zero, the options Maximal payoff period and Maximum investment under Financial parameters must be disabled.
Maximum battery pack capacity [kWh]	Upper limit on the battery pack capacity.
Minimum power rating [kW]	Lower limit on the power converter’s nominal power. If this value is greater than zero, the options Maximal payoff period and Maximum investment under Financial parameters must be disabled.
Maximum power rating [kW]	Upper limit on the power converter’s nominal power.
Battery system type [dropdown menu]	A battery system from the application’s database. Once selected, all parameters below are automatically populated. The user may modify any parameter afterward.
Charging efficiency (overall) [%]	Overall efficiency of the BESS during battery charging. It includes both the power converter efficiency and the battery efficiency.
Discharging efficiency (overall) [%]	Overall efficiency of the BESS during battery discharging. Includes both the power converter efficiency and the battery efficiency.
Number of cycles [-]	Number of charging-discharging cycles that the battery is rated for without significant drop in capacity. Usually, the number of cycles is presented together with depth of discharge in datasheets of battery packs.
Depth of discharge [%]	Percentage representing the portion of the battery capacity that can be repeatedly discharged without significantly affecting battery health. Usually, the number of cycles is presented together with depth of discharge in datasheets of battery packs.
Maximum charging rate [1/h]	The maximum charging rate defines the upper limit of charging power relative to the battery energy capacity. It represents the C-rate at which the battery can be charged. A charging rate of 1 means the battery can be fully charged in one hour, 0.5 means it takes two hours, and 2 means it can be charged in half an hour.
Maximum discharging rate [1/h]	The maximum discharging rate defines the upper limit of charging power relative to the battery energy capacity. It represents the C-rate at which the battery can be discharged. A discharging rate of 1 means the battery can be fully discharged in one hour, 0.5 means it takes two hours, and 2 means it can be discharged in half an hour.
Investment price (battery) [€/kWh]	Investment price of the battery pack, per unit of energy capacity. It includes the battery pack itself, all auxiliary materials (cables, mounting brackets, etc.) and labour (mounting, commissioning, etc.) required to bring the system into full operation.
Maintenance price (battery) [€/kWh]	Estimated annual maintenance cost per unit of energy capacity. Battery degradation is not included.
Replacement price (battery) [€/kWh]	Same as investment price, but after the lifetime of the battery pack, i.e. the future investment price. After the battery has degraded, it will be replaced with this price. Degradation depends on battery usage, number of cycles, and depth of discharge. The replacement cost is not affected by the subsidy.
Investment price (converter) [€/kW]	Investment price of the power converter, per unit of power. It includes the power converter itself, all auxiliary materials (cables, mounting brackets, etc.) and labour (mounting, commissioning, etc.) required to bring the system into full operation.
Maintenance price (converter) [€/kW]	Estimated annual maintenance price per unit of power. Power converter degradation is not included.
Replacement price (converter) [€/kW]	Same as the investment price, but applied after the converter lifetime has expired, i.e. the future investment price. Also, it is not influenced by the subsidy.
Lifetime (converter) [years]	Number of years after which the power converter needs to be replaced.
Subsidy [%]	Percentage deducted from the investment cost. The same subsidy applies to both the battery pack and the power converter. It does not apply to replacement costs.

4.2.7.2 Optimization output

Variable	Description
Battery storage capacity [kWh]	Optimized nominal energy capacity of the battery pack. It represents the required usable storage size that enables the selected operational strategy and economic constraints.
Battery power converter [kW]	Optimized nominal bidirectional power of the battery’s power converter. It defines the maximum charging and discharging power available for battery operation.
Battery charging profile [kW]	Time series of battery charging power over the simulation period. Positive values indicate charging from the electrical system, subject to converter limits, constraints, and battery availability.
Battery discharging profile [kW]	Time series of battery discharging power over the simulation period. Positive values indicate energy supplied from the battery to the electrical system, respecting converter limits and state-of-charge constraints.
Battery state-of-charge (SoC) [kWh]	Time series of the battery’s state of charge during the simulation. It represents the available stored energy.

4.2.7.3 Interface options

The BESS parameters can be predefined by selecting one of the available BESS types from the database. Any parameter can still be manually modified after selection. By default, the first BESS type in the list is used.

4.2.7.4 Troubleshooting

• Existing sizes: The existing capacity and power must respect the ratio defined by Maximum charging rate and Maximum discharging rate. Otherwise, the optimization may fail.

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4.2.8 Fixed electrical consumption

The Fixed electricity consumption component represents all existing electricity consumers at the location. It contains a power profile of all the existing electricity consumers, which can be imported directly or simulated with specific consumer types from the application’s database.

This component defines the baseline electricity demand that must be supplied by the electrical grid connection or other electricity sources in the system.

4.2.8.1 Input parameters

The component offers two methods for defining the electricity consumption profile:

• Generate profile: Create a profile by selecting consumer types from the database.
• Import data: Import an existing consumption profile from a CSV file.

Parameters in Generate profile tab

Parameter	Description
Consumer type [dropdown menu]	Choose a consumer type from the application’s database.
Annual electrical energy consumption [MWh]	Annual energy consumption of selected consumer. The profile selected by Consumer type will be scaled so that total energy is equal to this number.

GUI elements in Import data tab

This option allows the user to import an existing electricity consumption profile from a CSV file.

GUI element	Description
Browse [button]	The power consumption profile needs to be in a CSV file, formatted in a single column with 8,760, 17,520, or 35,040 rows (no header), where values represent mean consumption power at the grid connection point. If the data in the file is for a leap year, please remove 1 day of data to match 8,760, 17,520, or 35,040 rows. The first value in the file corresponds to the beginning of the year, while the last value corresponds to the end of the year. After selecting a file, a message is displayed indicating whether the data import was successful or if errors were detected.
Check imported data [button]	Opens a pop-up window with an interactive chart showing the imported fixed electricity consumption data.

Additional GUI elements

GUI element	Description
Delete consumer [button]	Click if you want to remove this consumer from your fixed electricity consumption system. All data will be lost.
Add new consumer [button]	Click if you want to add a new electricity consumer to the overall fixed electricity consumption.
Fixed electricity consumption profile [button]	Opens a pop-up window displaying the fixed electricity consumption profile chart.

4.2.8.2 Optimization output

This component does not introduce any decision variables in the optimization model.

4.2.8.3 Interface options

The Fixed electricity consumption component provides the following interface options:

• Generate profile: Select consumer types from the database and specify their installed power and annual energy consumption to automatically generate a consumption profile.
• Import data: Import an existing consumption profile from a CSV file with 8,760 (hourly), 17,520 (30-minute), or 35,040 (15-minute) rows.
• Multiple consumers: Add multiple consumers to create a combined consumption profile representing all existing electricity loads at the location.
• Data verification: Use the Check imported data button to visually verify the consumption profiles.

4.2.8.4 Related components

• Electrical grid connection, as the fixed electricity consumption determines the minimum grid connection capacity required.

4.2.8.5 Troubleshooting

Common issues and solutions:

• Issue 1: CSV file import fails with row count error. Ensure your file has exactly 8,760, 17,520, or 35,040 rows with no header. If using leap year data, remove one day (24, 48, or 96 rows depending on resolution).

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4.2.9 Electrolyser

The electrolyser is the key component in hydrogen production. It uses electricity to split water molecules into hydrogen and oxygen, while producing heat due to inefficiencies in the conversion process. Therefore, it has 2 inputs (electricity and water) and 3 outputs:

• Hydrogen (H\(_2\)) – the main output of the electrolyser.
• Oxygen (O\(_2\)) – a byproduct of electrolysis that can be utilized or released into the atmosphere.
• Heat – thermal energy resulting from conversion losses. The tool distinguishes between low-temperature (LT) and high-temperature (HT) heat. An electrolyser may produce either of these, both, or none, depending on the selected configuration.

The user can specify multiple electrolysers, each with its own set of parameters. An electrolyser is added by clicking on the Add new electrolyser button.

By right-clicking on an electrolyser node, a pop-up menu appears with the following options:

• Rename electrolyser – change the name of the electrolyser.
• Delete electrolyser – removes the electrolyser from the overall setup.

This section also includes parameters of auxiliary equipment required for proper electrolyser operation:

• Hydrogen compressor: compresses hydrogen from the electrolyser outlet to the hydrogen storage tank using electricity. Its size is determined by the hydrogen mass flow rate, while its power consumption depends on the inlet pressure (electrolyser outlet) and outlet pressure (nominal hydrogen tank pressure).
• Hydrogen storage tank: stores hydrogen between production and consumption or sale. The tank must be sized to store at least one full day of hydrogen sales.

4.2.9.1 Input parameters

Basic parameters – Electrolyser

Parameter	Description
Electrolyser type [dropdown menu]	An electrolyser from the tool catalog. Once selected, all required parameters are automatically populated according to the chosen type. Any parameter can be modified afterward.
Electrical efficiency [%]	Efficiency of converting electrical energy into hydrogen on a higher heating value (HHV) basis. A value of 100% corresponds to the thermodynamic minimum energy requirement: - 285.8 kJ/mole - 39.41 kWh/kg - 3.54 kWh/Sm3 - 3.36 kWh/Nm3 Sm3 = Standard cubic meter means temperature of 0 °C and pressure of 1.01325 bar (standard DIN 1343). Nm3 = Normal cubic meter means temperature of 15 °C and pressure of 1.01325 bar (standard ISO 2533). This parameter is tied to Power consumption (by mass) and Power consumption (by volume).
Power consumption (by mass) [kWh/kg]	Electrical energy required to produce 1 kg of hydrogen. The minimum value is 39.41 kWh/kg, corresponding to 100% efficiency (HHV limit). This parameter is tied to Electrical efficiency and Power consumption (by volume).
Power consumption (by volume) [kWh/Nm3]	Electrical energy required to produce 1 Nm3 of hydrogen. Nm3 (normal cubic meter) denotes hydrogen at 15 °C and 1.01325 bar (≈11.128 Nm³/kg). The minimum value is 3.36 kWh/Nm3, corresponding to 100% efficiency. This parameter is tied to Electrical efficiency and Power consumption (by mass).
Investment price [€/kW]	Specific investment cost per unit of input electrical power. It includes all required equipment, materials, and labor (design, installation, commissioning, etc.) until full operation.
Electrolyser already exists? [checkbox]	Indicates whether an electrolyser is already installed at the site.
Existing electrolyser size [kW]	Nominal electrical power of the existing electrolyser. Visible only if Electrolyser already exists? is enabled. The parameters above apply to both the existing unit and any optimized expansion.

Advanced parameters – Electrolyser

Parameter	Description
Recoverable high temperature heat? [checkbox]	Indicates whether heat from the electrolyser cooling circuit can be recovered for high-temperature heating applications.
Heating efficiency (high temperature) [%]	The Electrical efficiency determines hydrogen production per unit of electricity, while the remaining share represents total heat losses. Heating efficiency defines the fraction of this recoverable heat available at high temperature. The sum of high- and low-temperature heating efficiencies must not exceed 100%. This parameter is tied to Usable heat output.
Usable heat output (high temperature) [kWh/kg]	The amount of usable heat (at high temperature) produced by the electrolyser for every 1 kg of produced hydrogen. This parameter is calculated as: Power consumption (by mass) \(\times\) (100% - Electrical efficiency) \(\times\) Heating efficiency (high temperature)
Operating temperature (high temperature) [°C]	Temperature at which the high-temperature heat is released from the electrolyser at nominal conditions, i.e. nominal power.
Recoverable low temperature heat? [checkbox]	Indicates whether heat from the electrolyser cooling circuit can be recovered for low-temperature heating applications.
Heating efficiency (low temperature) [%]	The Electrical efficiency determines hydrogen production per unit of electricity, while the remaining share represents total heat losses. Heating efficiency defines the fraction of this recoverable heat available at low temperature. The sum of high- and low-temperature heating efficiencies must not exceed 100%. This parameter is tied to Usable heat output.
Usable heat output (low temperature) [kWh/kg]	The amount of usable heat (at low temperature) produced by the electrolyser for every 1 kg of produced hydrogen. This parameter is calculated as: Power consumption (by mass) \(\times\) (100% - Electrical efficiency) \(\times\) Heating efficiency (low temperature)
Operating temperature (low temperature) [°C]	Temperature at which the low-temperature heat is released from the electrolyser at nominal conditions, i.e. nominal power.
Hydrogen outlet pressure [bar]	Gauge pressure of hydrogen at the electrolyser outlet under nominal conditions, i.e. at nominal power, expressed as difference from the atmospheric pressure (sometimes denoted with “barg”).
Water consumption [l/kg]	Water required for producing 1 kg of hydrogen. The theoretical minimum is approximately 9 kg (≈9 l) of water per kg of hydrogen.
Minimum electrolyser size [kW]	Lower limit on the size (installed power in [kW]) of the electrolyser. If greater than zero, Maximal payoff period and Maximum investment in Financial parameters must be disabled.
Maximum electrolyser size [kW]	Upper limit on the size (installed power in [kW]) of the electrolyser.
Maintenance price [€/kW]	Estimated annual operation and maintenance (O&M) price per installed power. O&M does not include degradation of the system.
Replacement price [€/kW]	Future specific investment cost applied when the electrolyser reaches end of life. The subsidy does not apply to replacement costs.
Lifetime [years]	Number of years after which the whole electrolyser must be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

Advanced parameters – Hydrogen compressor

Parameter	Description
Hydrogen compressor already exists [checkbox]	Indicates whether a hydrogen compressor is already installed at the site.
Existing compressor size [kg/h]	Nominal mass flow of the existing hydrogen compressor. Visible only if Hydrogen compressor already exists is enabled. The parameters below apply to both the existing unit and any optimized expansion.
Hydrogen compressor unit [dropdown menu]	A hydrogen compressor unit from the tool catalogue. Once selected, all required parameters are automatically populated according to the chosen type. Any parameter can be modified afterward.
Efficiency [%]	The tool first calculates the theoretical mechanical power required to reach the desired discharge pressure using the adiabatic compression model for ideal gases, based on the electrolyser outlet pressure and the hydrogen storage tank pressure. The compressor efficiency is then applied to determine the required electrical power consumption. When entering Efficiency, Power consumption is updated as well. Efficiencies greater than 100% are allowed in order to include isothermal compressors.
Power consumption [kWh/kg]	Electrical energy required to compress 1 kg of hydrogen from the electrolyser outlet pressure to the hydrogen storage tank pressure. It is calculated using the adiabatic compression model for ideal gases and includes the effect of Efficiency. When entering Power consumption, Efficiency is updated as well.
Minimum inlet pressure [bar]	Minimum allowable hydrogen pressure at the compressor inlet. This ensures proper lubrication and cooling (especially for oil-lubricated compressors). This parameter is used only to validate compatibility between the electrolyser and the hydrogen compressor.
Maximum discharge pressure [bar]	Maximum allowable compressor discharge pressure. Exceeding this limit may lead to system overpressurization and potential mechanical failure. This parameter is used only to validate compatibility between the hydrogen compressor and the storage tank.
Investment price [€/(kg/h)]	Specific investment cost per unit of mass flow. It includes the compressor itself, additional equipment (e.g. metering devices), installation, commissioning, and all other necessities until full operation.
Maintenance price [€/(kg/h)]	Estimated annual operation and maintenance (O&M) price per mass flow. O&M does not include degradation of the system.
Replacement price [€/(kg/h)]	Future specific investment cost applied when the compressor reaches end of life. The subsidy does not apply to replacement costs.
Lifetime [years]	Number of years after which the whole compressor unit must be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

Advanced parameters – Hydrogen storage tank

Parameter	Description
Hydrogen tank already exists? [checkbox]	Indicates whether a hydrogen storage tank is already installed at the site.
Existing storage tank size [kg]	Nominal hydrogen mass that can be stored in the existing tank at rated pressure. Visible only if Hydrogen tank already exists? is enabled. The parameters below apply to both the existing unit and any optimized expansion.
Hydrogen storage tank type [dropdown menu]	A hydrogen storage tank from the tool catalogue. Once selected, all required parameters are automatically populated according to the chosen type. Any parameter can be modified afterward.
Rated pressure [bar]	Maximum allowable operating pressure of the storage tank.
Minimum capacity [kg]	Lower limit on the size (mass capacity) of the tank. If this value is greater than zero, Maximal payoff period and Maximum investment in Financial parameters must be disabled.
Maximum capacity [kg]	Upper limit on the size (mass capacity) of the tank.
Investment price [€/kg]	Specific investment cost per unit of storage capacity which includes the storage tank itself, additional equipment (e.g. metering devices), installation and commissioning, and all other necessities until full operation.
Maintenance price [€/kg]	Estimated annual operation and maintenance (O&M) price per unit of storage capacity. O&M does not include degradation of the system.
Replacement price [€/kg]	Future specific investment cost applied when the tank reaches end of life. The subsidy does not apply to replacement costs.
Lifetime [years]	Number of years after which the whole storage tank unit must be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

4.2.9.2 Optimization output

Electrolyser

Variable	Description
Installed capacity [kW]	Optimized installed electrical power for each electrolyser and in total.
Power consumption [kW]	Electrical power consumption of each electrolyser in every time step, optimized by the model. Based on the power consumption, the following time series are derived: - Hydrogen production [kg/h] - Oxygen production [kg/h] - Low-temperature heat generation [kW] - High-temperature heat generation [kW] - Water consumption [kg/h]
Investment cost [€]	Investment costs for each electrolyser and in total.
Maintenance cost [€]	Annual operation and maintenance costs for each electrolyser and in total.
Degradation cost [€]	Annual cost associated with system degradation over its lifetime, reported for each electrolyser and in total.

Hydrogen compressor

Variable	Description
Installed capacity [kg/h]	Optimized installed mass flow capacity of the compressor.
Power consumption [kW]	Electrical power consumption of the compressor in each time step, optimized by the model.
Investment cost [€]	Total investment cost of the hydrogen compressor.
Maintenance cost [€]	Annual operation and maintenance costs.
Degradation cost [€]	Annual cost accounting for system degradation over its lifetime.

Hydrogen storage tank

Variable	Description
Installed capacity [kg]	Optimized installed hydrogen mass capacity.
State of charge (SoC) [kg]	Amount of hydrogen stored in the tank at each time step, reported separately for green and non-green hydrogen.
Investment cost [€]	Total investment cost of the hydrogen tank.
Maintenance cost [€]	Annual operation and maintenance costs.
Degradation cost [€]	Annual cost accounting for system degradation over its lifetime.

4.2.9.3 Interface options

Parameters of electrolysers can be predefined by selecting one of the available types from the database. Any parameter can still be manually modified after selection. By default, the first type in the list is used. The same is valid for hydrogen compressor and hydrogen storage tank.

4.2.9.4 Related Components

• Water supply – defines water supply used by the electrolysers
• H2 sales – hydrogen sales, where another hydrogen compressor is defined
• O2 sales – oxygen sales, where oxgen compressor and oxygen storage tank are defined
• Waste heat – waste heat utilization, where heat consumption is defined

4.2.9.5 Troubleshooting

• No electrolyser defined: At least one electrolyser must be defined in the tool. Otherwise, the optimization will return an error.

• Deleting electrolyser: If an electrolyser is removed, all associated data are deleted as well. Once an electrolyser is deleted, it cannot be restored.

• Efficiency and power consumption do not match: When reviewing a product datasheet, the manufacturer may provide both the efficiency and the specific power consumption of the electrolyser. If these values do not match those in the tool, the efficiency may be reported with respect to the lower heating value (LHV) instead of HHV, or it may refer only to the electrolyser stack while excluding auxiliary equipment (e.g. power electronics).

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4.2.10 Water supply

Water is a feedstock for hydrogen production via electrolysis. The primary source is the water grid, while rainwater and a body of water can serve as additional renewable sources. All water used must be demineralized before entering the electrolyser. This section describes the parameters for the following components:

• Water grid connection: the primary source of water. It is assumed that it has no limit on usage. It is used if any hydrogen is being produced.

• Rain collection: a secondary water source limited by the local rainfall and the collection area. If enabled, it requires a water pump and a water tank. Monthly precipitation data is obtained from Open-Meteo API through internet.

• Body of water: a secondary water source such as a river, lake, stream, or estuary. Daily availability is limited. If enabled, it requires a water pump.

• Demineralizer: prepares water for the electrolyser by removing minerals and impurities. It is used for all water sources.

• Water pump: pumps water from the water tank and from a body of water. Its electricity consumption comprises overcoming the height difference and any (ultra-)fine filtration. It is used if at least one of Rain collection and Body of water is enabled.

• Water tank: stores collected rainwater. It is used only when Rain collection is enabled.

4.2.10.1 Input parameters

Water grid connection parameters

Parameter	Description
Show predefined values for the country [dropdown menu]	The country is automatically selected according to the site location, but it can be changed manually. Available countries are those that participated in HyEfRe project: Austria, Croatia, Czechia, Germany, Hungary, Italy, Poland, and Slovenia. If the selected location is in another country, the value of this parameter remains empty. By selecting one of the countries, all other parameters are populated. Any parameter can be modified afterward.
Water price [€/m3]	The price of water from the water grid, including all the fees and taxes.
Existing water connection point? [checkbox]	Whether the grid connection already exists at the location or not.
Existing water connection capacity [m3/h]	The size of the existing grid connection in terms of water mass flow. The parameter is visible only if Existing water connection point? is enabled.
Capacity price for water grid connection [€/(m3/h)]	It represents the price for building and installation of the connection depending only on the capacity, i.e. size. It can be determined from existing projects: cost of the connection divided with the capacity of the connection.
Unit price for water grid connection [€/(m3/h km)]	It represents the price for building and installation of the connection depending on the capacity and Distance to the nearest connection point. This parameter is used only for greenfield investments – it is visible only when Existing water connection point? is disabled. It can be determined from existing projects: cost of the connection divided with the capacity and distance to the nearest connection point.
Distance to the nearest connection point [km]	A connection point represents a piece of infrastructure to which the renewable energy hub must be connected to. This parameter is used only for greenfield investments – it is visible only when Existing water connection point? is disabled. It is used to calculate the total price of the grid connection: Unit price * Distance + Capacity price

Rain collection parameters

Parameter	Description
Available area [m2]	Area that is available for rain collection. For example, if rain can be collected from a roof, the available area is the area of the roof.
Expected rainfall in Month [mm]	The depth of precipitation that occurs over a unit area, i.e. measure of rainfall amount. There is Expected rainfall for every month of the year. The values for each month are automatically populated based on the selected location, but can be modified afterward. Source of rainfall data is Open-Meteo and it is based on the entered Location.
Existing rain collection area [m2]	Rainfall catchment area that is already present at the site.
Minimum rain collection area [m2]	Lower limit on the size of the rainfall catchment area. If this value is greater than zero, Maximal payoff period and Maximum investment in Financial parameters must be disabled.
Investment price [€/m2]	Specific investment cost per unit of area. It includes all required equipment, materials, and labor until full operation.
Maintenance price [€/m2]	Estimated annual operation and maintenance (O&M) price per installed area. O&M does not include degradation of the system.
Replacement price [€/m2]	Future specific investment cost applied when the rain collection system reaches end of life. The subsidy does not apply to replacement costs.
Lifetime [years]	Number of years after which the rain collection system must be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

Body of water parameters

Parameter	Description
Price of extracted water [€/m3]	Price of water extracted from the body of water, including all the fees and taxes.
Maximum amount of water for extraction (daily) [m3]	Maximum amount of water for extraction permitted by, e.g. local authorities. Same value applies for every day of the year.
Investment price [€/(m3/h)]	Specific investment cost of the water extraction system, per unit of water flow. It includes all required equipment, materials, and labor until full operation.
Maintenance price [€/(m3/h)]	Estimated annual operation and maintenance (O&M) price of the water extraction system, per unit of water flow. O&M does not include degradation of the system.
Replacement price [€/(m3/h)]	Future specific investment cost applied when the water extraction system reaches end of life. The subsidy does not apply to replacement costs.
Lifetime [years]	Number of years after which the water extraction system must be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

Demineralizer parameters

Parameter	Description
Demineralizer already exists? [checkbox]	Indicates whether a demineralizer is already installed at the site.
Existing demineralizer size [m3/h]	Nominal output water flow of the existing demineralizer. Visible only if Demineralizer already exists? is enabled. The parameters below apply to both the existing unit and any optimized expansion.
Demineralizer type [dropdown menu]	A demineralizer from the tool catalog. Once selected, all required parameters are automatically populated according to the chosen type. Any parameter can be modified afterward.
Power consumption [kWh/m3]	Amount of electrical energy required to produce 1 m3 of demineralized water.
Water losses [%]	Percentage of water that is lost at the demineralizer due to its way of operation.
Minimum demineralizer size [m3/h]	Lower limit on the size (installed capacity in [m3/h]) of the demineralizer. If greater than zero, Maximal payoff period and Maximum investment in Financial parameters must be disabled.
Maximum demineralizer size [m3/h]	Upper limit on the size (installed capacity in [m3/h]) of the demineralizer.
Investment price [€/(m3/h)]	Specific investment cost of the demineralizer system, per unit of water flow. It includes all required equipment, materials, and labor until full operation.
Maintenance price [€/(m3/h)]	Estimated annual operation and maintenance (O&M) price of the demineralizer system, per unit of water flow. O&M does not include degradation of the system.
Replacement price [€/(m3/h)]	Future specific investment cost applied when the demineralizer system reaches end of life. The subsidy does not apply to replacement costs.
Lifetime [years]	Number of years after which the demineralizer system must be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

Water pump parameters

Parameter	Description
Water pump already exists? [checkbox]	Indicates whether a water pump unit is already installed at the site.
Existing water pump size [kW]	Nominal electrical power of the existing water pump unit. Visible only if Water pump already exists? is enabled. The parameters below apply to both the existing unit and any optimized expansion.
Water pump type [dropdown menu]	A water pump unit from the tool catalog. Once selected, all required parameters are automatically populated according to the chosen type. Any parameter can be modified afterward.
Water pump power consumption [kWh/m3]	Specific power consumption for pumping water. The power is used for overcoming the height difference and (ultra-)fine filtration.
Minimum water pump size [kW]	Lower limit on the size (installed power) of the water pump unit. If greater than zero, Maximal payoff period and Maximum investment in Financial parameters must be disabled.
Maximum water pump size [kW]	Upper limit on the size (installed power) of the water pump unit.
Investment price [€/kW]	Specific investment cost of the water pump unit, per unit of electrical power. It includes all required equipment, materials, and labor until full operation.
Maintenance price [€/kW]	Estimated annual operation and maintenance (O&M) price of the water pump unit, per unit of electrical power. O&M does not include degradation of the system.
Replacement price [€/kW]	Future specific investment cost applied when the water pump unit system reaches end of life. The subsidy does not apply to replacement costs.
Lifetime [years]	Number of years after which the water pump unit must be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

Water tank parameters

Parameter	Description
Water tank already exists? [checkbox]	Indicates whether a water tank is already installed at the site.
Existing water tank size [m3]	Capacity of the existing water tank. Visible only if Water tank already exists? is enabled. The parameters below apply to both the existing unit and any optimized expansion.
Water tank type [dropdown menu]	A water tank from the tool catalog. Once selected, all required parameters are automatically populated according to the chosen type. Any parameter can be modified afterward.
Minimum water tank size [m3]	Lower limit on the size (available capacity) of the water tank. If greater than zero, Maximal payoff period and Maximum investment in Financial parameters must be disabled.
Maximum water tank size [m3]	Upper limit on the size (available capacity) of the water tank.
Investment price [€/m3]	Specific investment cost of the water tank, per unit of storage capacity. It includes all required equipment, materials, and labor until full operation.
Maintenance price [€/m3]	Estimated annual operation and maintenance (O&M) price of the water tank, per unit of storage capacity. O&M does not include degradation of the system.
Replacement price [€/m3]	Future specific investment cost applied when the water tank reaches end of life. The subsidy does not apply to replacement costs.
Lifetime [years]	Number of years after which the water tank must be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

4.2.10.2 Optimization output

Variable	Description
Installed capacities	Optimized installed sizes: - Capacity of the water grid connection [m3/h] - Rain collection area [m2] - Capacity of the water extraction system for the body of water [m3/h] - Capacity of the demineralizer [m3/h] - Water pump installed power [kW] - Capacity of the water tank [m3]
Water flows	Profiles of water sources as flows in every time step, optimized by the model: - From the water grid connection [m3/h] - From the rain collection system [m3/h] - From the body of water [m3/h]
Power consumptions	Electrical power consumption of water preparation components in each time step, optimized by the model: - Power consumption of the demineralizer [kW] - Power consumption of the water pump [kW]
Tank state of charge (SoC)	Amount of water stored in the tank at each time step optimized by the model [m3].
Investment costs [€]	Total investment cost of each component: water grid connection, rain collection system, water extraction system, demineralizer, water pump, and water tank.
Maintenance cost [€]	Annual operation and maintenance cost of each component: water grid connection, rain collection system, water extraction system, demineralizer, water pump, and water tank.
Degradation cost [€]	Annual cost accounting for system degradation over its lifetime, of each component: water grid connection, rain collection system, water extraction system, demineralizer, water pump, and water tank.

4.2.10.3 Interface options

Water supply components are visible depending on the system configuration:

• Water grid connection: It is always visible, because it is the primary water source of any electrolyser.
• Rain collection system: It is visible if checkbox Collect rain? is enabled.
• Body of water: It is visible if checkbox Use a body of water? is enabled.
• Demineralizer: It is the main water processing component, so it is always visible.
• Water pump: It is visible if Rain collection system or Body of water are enabled.
• Water tank: It is visible only if Rain collection system is enabled.

Parameters of all water supply components can be predefined by selecting one of the available types from the database. Any parameter can still be manually modified after selection. By default, the first type in the list is used.

4.2.10.4 Related Components

• Electrolyser – water supply is necessary for the electrolysis.
• Location – monthly rainfall is dependent on the geographic location.

4.2.10.5 Troubleshooting

Common issues and solutions:

• Monthly rainfall is not updated with location change: Check your internet connection. The Open-Meteo service may be temporarily unavailable.

• Coordinates not set: Open-Meteo data generation requires location coordinates. Ensure the location is properly set in the Location component.

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4.2.11 H2 sales

The Hydrogen sales component represents the interface for selling hydrogen to different customers and the gas grid. Hydrogen can be sold to different potential customers, each with different parameters. The customers are said to be “potential” because the model determines the optimal amounts to be sold, and the customers’ demands are limits for the sales.

Every customer can demand purely green hydrogen. The tool then takes into account energy sources and makes sure that hydrogen produced is 100% green. Because hydrogen is usually transported at a pressure higher than for stationary application, additional hydrogen compressor is needed. However, when injecting hydrogen into the gas grid, the compressor is not needed because the pressure of gas grids is lower. A predefined compressor is already entered in the tool. However, parameters of the gas grid connection and prices for gas injection are left to the user to enter.

The component consists of 3 main sections:

• Customer management: Add and manage multiple hydrogen customers with individual demands.
• Gas grid injection: Parameters for selling hydrogen by injecting it into the gas grid.
• Hydrogen compressor: Technical and financial parameters for the compressor used for hydrogen sales to customers (not needed for gas grid injection).

4.2.11.1 Input parameters

Customer parameters

Each customer has the following configurable parameters:

Parameter	Description
Add new customer [button]	Button to add a new hydrogen customer. Each customer has individual demand parameters and can be configured separately.
Allow only green hydrogen? [checkbox]	Whether the hydrogen sold to this customer must be 100% green or not. If checked, the tool takes into account energy sources and makes sure that hydrogen sold to this customer is 100% green.
Demand frequency [dropdown menu]	How often the customer requests hydrogen. Choose between daily, weekly, monthly, or yearly.
Demand mass [kg]	Maximum amount of hydrogen for the frequency defined above.
Price for hydrogen sold [€/kg]	Price that the renewable energy hub would realize, after tax.
Required pressure [bar]	Pressure of hydrogen that is required for the customer.

Gas grid injection – Gas grid connection

Parameter	Description
Hydrogen allowed in the gas grid? [checkbox]	Whether or not you allow the optimization to sell hydrogen by injecting it into the gas grid. If enabled, the parameters below become visible.
Gas grid connection exists? [checkbox]	Whether or not there is an existing gas grid connection at the site. The connection must be intended for gas injection.
Existing connection capacity [kWh/h]	The capacity of the existing gas grid connection for injection, in kWh/h (kW). The connection is assumed to allow hydrogen injection.
Distance to the nearest connection [km]	When there is no existing gas grid connection at the site, a new one must be made. Also, a new pipeline must be put from the existing gas grid to the site. The total investment cost of the new gas grid connection depends on this distance.
Unit price of grid connection [€/kW/km]	Unit price for the installation of pipeline for the new grid connection, per unit of hydrogen flow (power), per unit of distance. It includes all necessary equipment, material, labor, administration, and financing costs. Since the maintenance of the connection is the responsibility of the grid operator, there are no operating and maintenance (O&M), and replacement costs.
Capacity price of grid connection [€/kW]	Capacity price for the installation of the new gas grid connection, per unit of hydrogen flow (power). It includes all necessary equipment, material, labor, administration, and financing costs. Since the maintenance of the connection is the responsibility of the grid operator, there are no operating and maintenance (O&M), and replacement costs.
Maximum hydrogen flow allowed [kg/h]	Maximum flow of hydrogen that is allowed to be injected into the gas grid.
Pressure of the gas grid [bar]	Pressure at which the gas grid operates.

Gas grid injection – Hydrogen prices

Parameter	Description
Allow only green hydrogen? [checkbox]	Whether the injected hydrogen must be 100% green or not. If checked, the tool takes into account energy sources and makes sure that hydrogen injected is 100% green.
Pricing frequency [dropdown menu]	Dynamics of pricing. It is possible to choose between: i) constant price throughout the year; ii) winter and summer prices; or iii) monthly prices. By selecting the frequency, corresponding prices are shown.
Start of winter period [dropdown menu]	The first month of winter period.
Start of summer period [dropdown menu]	The first month of summer period.

Gas grid injection – Green H2 prices

Parameter	Description
Price of green hydrogen - constant [€/MWh]	Price for injecting green hydrogen. This price is constant throughout the year.
Price of green hydrogen - winter [€/MWh]	Price for injecting green hydrogen during winter period.
Price of green hydrogen - summer [€/MWh]	Price for injecting green hydrogen during summer period.
Price of green hydrogen - [Month] [€/MWh]	Price for injecting green hydrogen during a specific month. Shown when Pricing frequency is set to monthly prices.

Gas grid injection – Non-green H2 prices

Parameter	Description
Price of non-green hydrogen - constant [€/MWh]	Price for injecting non-green hydrogen. This price is constant throughout the year.
Price of non-green hydrogen - winter [€/MWh]	Price for injecting non-green hydrogen during winter period.
Price of non-green hydrogen - summer [€/MWh]	Price for injecting non-green hydrogen during summer period.
Price of non-green hydrogen - [Month] [€/MWh]	Price for injecting non-green hydrogen during a specific month. Shown when Pricing frequency is set to monthly prices.
Grid fee for injection [€/MWh]	Grid fee that is paid to the grid operator. It is simply deducted from the hydrogen price.

Hydrogen compressor for H2 sales (advanced)

This section contains parameters for the hydrogen compressor used when selling hydrogen to customers (not needed for gas grid injection).

Parameter	Description
Hydrogen compressor unit [dropdown menu]	Choose a hydrogen compressor from the application’s database and its parameters will be filled automatically. Only suitable compressors will be available. A suitable compressor can: i) handle hydrogen pressure of the electrolyser at the input, ii) provide at least the pressure of the storage tank at the output. Afterwards you can change any of its parameters.
Hydrogen compressor already exists? [checkbox]	Whether or not there is an existing hydrogen compressor at the site.
Existing compressor size [kW/(kg/h)]	Size of the existing hydrogen compressor.
Efficiency [%]	Amount of power to produce adequate pressure level at the discharge of the compressor is calculated by the model, but no compressor is perfect so the model includes efficiency of the compressor to get the required electrical power consumption for compression. When entering Efficiency, Power consumption will be updated.
Power consumption [kW/(kg/h)]	Amount of electrical power needed for compression of hydrogen with mass flow of 1 kg/h. This value will be calculated when entering Efficiency. Alternatively, you can enter Power consumption and Efficiency will be calculated. The unit of flow rate is [kg/h], but it can be easily converted into normal volumetric flow rate. For reference, 1 kg/h = 11.207 Nm3/h of hydrogen.
Minimum inlet pressure [bar]	Minimum inlet pressure required for proper compressor operation. Below this threshold, the compressor may be damaged or underperform.
Maximum inlet pressure [bar]	Maximum inlet pressure the compressor can handle safely. Exceeding this can cause damage or failure.
Minimum discharge pressure [bar]	Minimum discharge pressure required to meet downstream demand. Falling below this may cause equipment malfunction.
Maximum discharge pressure [bar]	Maximum discharge pressure the compressor can generate safely. Exceeding this may cause system failure.
Investment price [€/(kg/h)]	Investment price per unit of gas flow which includes the compressor itself, additional equipment (e.g. metering devices), installation, commissioning, financing, and all other necessities until full operation. The unit of flow rate is [kg/h], but it can be easily converted into normal volumetric flow rate. For reference, 1 kg/h ≈ 11.207 Nm³/h of hydrogen.
Operation and maintenance price [€/(kg/h)]	Estimated annual operation and maintenance (O&M) price per unit of gas flow. O&M includes (but does not limit to) inspections, regular services, administration costs, overhauls, and replacing broken components. O&M does not include degradation of the compressor. The unit of flow rate is [kg/h], but it can be easily converted into normal volumetric flow rate. For reference, 1 kg/h = 11.207 Nm3/h of hydrogen.
Replacement price [€/(kg/h)]	Replacement price per unit of gas flow includes all necessary elements, materials, and labour from dismantling the old compressor until the full operation of the new compressor. The unit of flow rate is [kg/h], but it can be easily converted into normal volumetric flow rate. For reference, 1 kg/h = 11.207 Nm3/h of hydrogen.
Lifetime [years]	Number of years after which the tank needs to be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement cost.

4.2.11.2 Interface options

The Hydrogen sales component provides several interface options:

• Adding customers: Click the Add new customer button to create a new customer.
• Managing customers: Right-click on a customer ID to access options to rename or delete customers.
• Predefined compressor: Select a hydrogen compressor from the dropdown menu in the compressor section to automatically populate technical and financial parameters.
• Pricing strategies: Choose between constant, winter/summer, or monthly pricing for hydrogen injected into the gas grid.

4.2.11.3 Optimization output

After running the optimization, the tool calculates the optimal technical and economic values for hydrogen sales.

Variable	Description
Hydrogen sold to customers	For each customer, the optimization determines the optimal amount of hydrogen sold, at each time step. Results include: - Hydrogen sales profile [kg/h] - Revenue from hydrogen sales [€]
Hydrogen injected to grid	The optimization determines the optimal amount of hydrogen injected into the gas grid, at each time step. Results include: - Hydrogen injection profile [kg/h] - Revenue from grid injection [€]
Compressor operation	If a compressor is used for customer sales, the optimization determines the compressor’s operating profile, at each time step: - Compressor power consumption [kW]
Gas grid connection investment	If a new gas grid connection is needed, the optimization determines: - Required connection capacity [kW] - Investment cost [€]

4.2.11.4 Related components

• Electrolyser, as hydrogen is produced by the electrolyser and sold through this component. Also, the hydrogen storage tank is defined with the electrolyser.

4.2.11.5 Troubleshooting

Common issues and solutions:

• No customers configured: Ensure at least one customer or the gas grid connection is added with valid parameters before running optimization.
• Compressor not suitable: When selecting a predefined compressor, ensure it can handle the required pressure levels for your customers.
• Green hydrogen requirement: When Allow only green hydrogen? is enabled, ensure sufficient renewable energy sources are configured in the system.

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4.2.12 O2 sales

The Oxygen sales component enables the renewable energy hub to generate revenue by selling oxygen produced as a by-product of water electrolysis. Oxygen can be sold to different potential customers, and each of them has different parameters. The customers are said to be “potential” because the model determines the optimal amounts to be sold, and the customers’ demands are limits for the sales.

The component consists of 3 main sections:

• Customer management: Add and manage multiple oxygen customers with individual demands.
• Oxygen storage tank: Optional storage infrastructure for oxygen.
• Oxygen compressor: Optional compression equipment to fill the storage tank.

4.2.12.1 Input parameters

Customer parameters

Each customer represents a potential oxygen buyer with specific demand requirements. You can add multiple customers to model different sales opportunities. For each customer, you can define the demand frequency, amount, price, and required delivery pressure.

Parameter	Description
Add new customer [button]	Click the Add new customer button to create a new oxygen customer. A popup window will appear asking for the customer’s name. After entering a unique name, the customer entry is created with default values. You can then configure the customer’s demand parameters.
Customer tree node [tree node]	Each customer appears as a tree node in the interface. Right-click on a customer name to access options for renaming or deleting the customer. All demand parameters for that specific customer are configured within this tree node.
Demand frequency [dropdown menu]	Determines how the maximum oxygen sales amount is applied over time. Options include: - Daily: Maximum amount can be sold each day - Weekly: Maximum amount can be sold each week - Monthly: Maximum amount can be sold each month - Yearly: Maximum amount represents total annual sales limit
Demand mass [kg]	Mass of oxygen demanded by the customer. If you enter the demand in volume, the mass will be calculated automatically. It also works vice versa, if you enter the demand in mass the volume will be calculated automatically. For reference, 1 kg of oxygen has volume of 700.44 l at STP.
Price [€/kg]	Price that a customer would pay for oxygen.
Rated pressure [bar]	Pressure of oxygen that is required for the customer.

Oxygen storage tank parameters

The oxygen storage tank section allows you to configure an optional oxygen storage tank. This tank stores oxygen produced by the electrolyser, enabling flexible sales patterns and buffer capacity. This section is advanced and hidden by default in a collapsible tree node.

Parameter	Description
Oxygen storage tank type [dropdown menu]	Choose an oxygen storage tank from the application’s database and its parameters will be filled automatically. Afterwards you can change any of its parameters, and save this changes for future use.
Oxygen tank already exists? [checkbox]	Enable this checkbox if there is existing oxygen storage infrastructure at the location. When enabled, the Existing oxygen storage tank parameter becomes visible.
Existing oxygen storage tank [kg]	If there is existing oxygen storage, input the size of existing storage in kg of oxygen that can be stored. This parameter is visible only if Oxygen tank already exists? is enabled.
Rated pressure [bar]	The maximum pressure allowed in the storage tank.
Minimum capacity [kg]	Lower limit of the oxygen tank size. If this value is greater than zero, Maximal payoff period and Maximum investment parameters are disabled.
Maximum capacity [kg]	Upper limit of the oxygen tank size. The tank’s size is considered unlimited if no value is entered.
Investment price [€/kg]	Investment price per unit of storage capacity which includes the storage tank itself, additional equipment (e.g. metering devices), installation, commissioning, financing, and all other necessities until full operation.
Operation and maintenance price [€/kg]	Estimated annual operation and maintenance (O&M) price per unit of storage capacity. O&M does not include degradation of the tank.
Replacement price [€/kg]	Replacement price per unit of storage capacity that includes all necessary elements, materials, and labour from dismantling the old tank until the full operation of the new tank.
Lifetime [years]	Number of years after which the tank needs to be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement cost.

Oxygen compressor parameters

The oxygen compressor section allows you to configure compression equipment that pressurizes oxygen before storing it in the tank. This section is advanced and hidden by default in a collapsible tree node.

Parameter	Description
Oxygen compressor unit [dropdown menu]	Choose a oxygen compressor from the application’s database and its parameters will be filled automatically. Only suitable compressors will be available. A suitable compressor can: - handle oxygen pressure of the electrolyser at the input, - provide at least the pressure of the storage tank at the output. Afterwards you can change any of its parameters, and save this changes for future use.
Oxygen compressor already exists? [checkbox]	Enable this checkbox if there is existing oxygen compression equipment at the location. When enabled, the Existing compressor size parameter becomes visible.
Existing compressor size [kg/h]	Size of the existing oxygen compressor. This parameter is visible only if Oxygen compressor already exists? is enabled.
Efficiency [%]	Amount of power to produce adequate pressure level at the discharge of the compressor is calculated by the model, but no compressor is perfect so the model includes efficiency of the compressor to get the required electrical power consumption for compression. When entering Efficiency, Power consumption will be updated.
Power consumption [kW/(kg/h)]	Amount of electrical power needed for compression of oxygen with mass flow of 1 kg/h. This value will be calculated when entering Efficiency. Alternatively, you can enter Power consumption and Efficiency will be calculated. The unit of flow rate is [kg/h], but it can be easily converted into normal volumetric flow rate. For reference, 1 kg/h ≈ 0.7 Nm³/h of oxygen.
Minimum inlet pressure [bar]	Most compressors require a minimum inlet pressure to operate efficiently. This minimum pressure ensures that the compressor can maintain proper lubrication and cooling, especially for oil-lubricated compressors. If the inlet pressure drops below this limit, the compressor may not function correctly, leading to potential damage or reduced performance.
Maximum inlet pressure [bar]	Compressors also have a maximum inlet pressure limit, beyond which they may be at risk of damage or malfunction. Exceeding this limit can strain the compressor components, leading to potential leaks, overheating, or even catastrophic failure. Therefore, it’s crucial to operate the compressor within its specified inlet pressure range to ensure safe and efficient operation.
Minimum discharge pressure [bar]	In some cases, compressors may also have a minimum discharge pressure limit. This limit ensures that there is sufficient pressure in the system to meet the required downstream demand or maintain proper operation of connected equipment. Falling below this limit may result in inadequate performance or malfunction of downstream devices, especially in applications where a minimum pressure is necessary for proper function.
Maximum discharge pressure [bar]	Compressors have a maximum discharge pressure limit, which represents the highest pressure that the compressor can safely generate. Exceeding this limit can lead to overpressurization of the system, potentially causing leaks, ruptures, or other catastrophic failures. Manufacturers specify this limit based on the design and materials of the compressor components, as well as safety standards and regulations.
Investment price [€/(kg/h)]	Investment price per unit of gas flow which includes the compressor itself, additional equipment (e.g. metering devices), installation, commissioning, financing, and all other necessities until full operation. The unit of flow rate is [kg/h], but it can be easily converted into normal volumetric flow rate. For reference, 1 kg/h ≈ 0.7 Nm³/h of oxygen.
Operation and maintenance price [€/(kg/h)]	Estimated annual operation and maintenance (O&M) price per unit of gas flow. O&M includes (but does not limit to) inspections, regular services, administration costs, overhauls, and replacing broken components. O&M does not include degradation of the compressor. The unit of flow rate is [kg/h], but it can be easily converted into normal volumetric flow rate. For reference, 1 kg/h ≈ 0.7 Nm³/h of oxygen.
Replacement price [€/(kg/h)]	Replacement price per unit of gas flow includes all necessary elements, materials, and labour from dismantling the old compressor until the full operation of the new compressor. The unit of flow rate is [kg/h], but it can be easily converted into normal volumetric flow rate. For reference, 1 kg/h ≈ 0.7 Nm³/h of oxygen.
Lifetime [years]	Number of years after which the compressor needs to be replaced.
Subsidy [%]	Percentage that is deductable from the investment cost. Does not apply to the replacement cost.

4.2.12.2 Interface options

The Oxygen sales component provides several interface options:

• Adding customers: Click the Add new customer button to create a new oxygen customer.
• Managing customers: Right-click on a customer name to access options to rename or delete customers.
• Predefined storage tank: Select an oxygen storage tank from the dropdown menu to automatically populate technical and financial parameters.
• Predefined compressor: Select an oxygen compressor from the dropdown menu to automatically populate technical and financial parameters.

4.2.12.3 Optimization output

After running the optimization, the tool calculates the optimal technical and economic values for the defined scenario. This subsection shows what variables are tied to the Oxygen sales component and are shown in Results.

Variable	Description
Oxygen sales revenue	The optimization determines the optimal amount of oxygen to sell to each customer based on their demand limits and the product price. Results include: - Oxygen sales profile as mass flow rates for each time step [kg/h] - Total oxygen sold over the simulation period [kg] - Revenue from oxygen sales [€]
Oxygen storage tank	If the oxygen storage tank is enabled, the optimization determines the optimal tank size and operation: - Optimal tank capacity [kg] - Storage level profile over time [kg] - Investment cost for new tank or use of existing capacity [€]
Oxygen compressor	If the oxygen compressor is enabled, the optimization determines the optimal compressor size and power consumption: - Optimal compressor size [kg/h] - Compressor power consumption profile [kW] - Investment cost for new compressor or use of existing capacity [€] - Operation and maintenance costs over the simulation period [€]

4.2.12.4 Related components

• Electrolyser, as oxygen is a by-product of hydrogen production through water electrolysis.

4.2.12.5 Troubleshooting

Common issues and solutions:

• At least one customer must be defined: No oxygen customers have been added to the component. The solution: Click the Add new customer button to create at least one oxygen customer.

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4.2.13 Fuel cell stack

The fuel cell stack is a component that produces electricity and heat from hydrogen. Normally, fuel cell refers to a single electrochemical cell, while fuel cell stack refers to a series of individual fuel cells connected together with all other necessary elements to make a functional electricity generation unit used in real applications.

It is considered a combined heat and power (CHP) technology by the EU in Directive 2012/27/EU. It combines hydrogen and oxygen molecules into water to produce electricity while producing heat due to inefficiencies in the conversion process. The hydrogen is supplied from the hydrogen storage tank while the oxygen comes from air. Therefore, it has a single input (hydrogen) and 3 outputs:

• Electricity – the main output of the fuel cell stack. It can be considered green or non-green depending on the type of hydrogen used.
• Heat – thermal energy resulting from conversion losses. The tool distinguishes between low-temperature (LT) and high-temperature (HT) heat. A fuel cell stack may produce either of these, both, or none, depending on the selected configuration.
• Water – in the form of steam. It can be extracted during electricity production, saved in the water tank and reused later.

The user can specify multiple fuel cell stacks in order to find the most suitable for the investment, each with its own set of parameters. Optimization will determine the optimal size of each stack as nominal electrical power. A fuel cell stack is added by clicking on Add new fuel cell stack button.

By right-clicking on a fuel cell stack node, a pop-up menu appears with the following options:

• Rename fuel cell stack – change the name of the fuel cell stack.
• Delete fuel cell stack – removes the fuel cell stack from the overall setup.

4.2.13.1 Input parameters

Basic parameters

Parameter	Description
Fuel cell stack type [dropdown menu]	A fuel cell stack from the tool catalog. Once selected, all required parameters are automatically populated according to the chosen type. Any parameter can be modified afterward.
Electrical efficiency [%]	The electrical efficiency of the fuel cell stack represents the percentage of chemical energy from hydrogen that is converted to electrical energy from higher heating value (HHV) perspective. Efficiency expressed for lower heating value (LHV) is 18.2% higher. This parameter is tied to Electrical energy production, where efficiency of 100% equals to: - 285.8 kJ/mol - 39.41 kWh/kg - 3.54 kWh/Sm3 - 3.36 kWh/Nm3 Sm3 = Standard cubic meter means temperature of 0 °C and pressure of 1.01325 bar (standard DIN 1343). Nm3 = Normal cubic meter means temperature of 15 °C and pressure of 1.01325 bar (standard ISO 2533).
Electrical energy production [kWh/kg]	Amount of electrical energy produced by the fuel cell stack from 1 kg of hydrogen. Theoretical maximum for energy production is 39.41 kWh/kg, corresponding to electrical efficiency of 100% (HHV limit). This parameter is tied to Electrical efficiency.
Investment price [€/kW]	Specific investment cost per unit of output electrical power. It includes all required equipment, materials, and labor (design, installation, commissioning, etc.) until full operation.
Fuel cell stack already exists? [checkbox]	Indicates whether a fuel cell stack is already installed at the site.
Existing fuel cell stack size [kW]	Nominal electrical power of the existing fuel cell stack. Visible only if Fuel cell stack already exists? is enabled. The parameters above apply to both the existing unit and any optimized expansion.

Advanced parameters

Parameter	Description
Recoverable high temperature heat? [checkbox]	Indicates whether heat from the fuel cell stack cooling circuit can be recovered for high-temperature heating applications.
Heating efficiency (high temperature) [%]	The Electrical efficiency determines hydrogen consumption per unit of electrical energy, while the remaining share represents total heat losses. Heating efficiency defines the fraction of this recoverable heat available at high temperature. The sum of high- and low-temperature heating efficiencies must not exceed 100%. This parameter is tied to Usable heat output.
Usable heat output (high temperature) [kWh/kg]	The amount of usable heat (at high temperature) produced by the fuel cell stack for every 1 kg of consumed hydrogen. This parameter is calculated as: 39.41 kWh/kg \(\times\) (100% - Electrical efficiency) \(\times\) Heating efficiency (high temperature)
Operating temperature (high temperature) [°C]	Temperature at which the high-temperature heat is released from the fuel cell stack at nominal conditions, i.e. nominal power.
Recoverable low temperature heat? [checkbox]	Indicates whether heat from the fuel cell stack cooling circuit can be recovered for low-temperature heating applications.
Heating efficiency (low temperature) [%]	The Electrical efficiency determines hydrogen consumption per unit of electrical energy, while the remaining share represents total heat losses. Heating efficiency defines the fraction of this recoverable heat available at low temperature. The sum of low- and high-temperature heating efficiencies must not exceed 100%. This parameter is tied to Usable heat output.
Usable heat output (low temperature) [kWh/kg]	The amount of usable heat (at low temperature) produced by the fuel cell stack for every 1 kg of consumed hydrogen. This parameter is calculated as: 39.41 kWh/kg \(\times\) (100% - Electrical efficiency) \(\times\) Heating efficiency (low temperature)
Operating temperature (low temperature) [°C]	Temperature at which the low-temperature heat is released from the fuel cell stack at nominal conditions, i.e. nominal power.
Water production [l/MWh]	It represents amount of usable water produced as a byproduct of electricity generation, since some water is lost as vapour. The value is expressed as liters of water for each MWh of electrical energy generated. Equivalent value is for the parameter in ml/kWh. The parameter is capped to the theoretical maximum. The theoretical maximum is determined as: 9 / (39.41 kWh/kg * Electrical efficiency)
Minimum stack size [kW]	Lower limit on the size (installed power in [kW]) of the fuel cell stack. If greater than zero, Maximal payoff period and Maximum investment in Financial parameters must be disabled.
Maximum stack size [kW]	Upper limit on the size (installed power in [kW]) of the fuel cell stack.
Maintenance price [€/kW]	Estimated annual operation and maintenance (O&M) price per installed power. O&M does not include degradation of the system.
Replacement price [€/kW]	Future specific investment cost applied when the fuel cell stack reaches end of life. The subsidy does not apply to replacement costs.
Lifetime [years]	Number of years after which the whole fuel cell stack must be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

NoteWater extraction

Although there is parameter Water production that determines how much water can be extracted from the fuel cell stack for each 1 kg of hydrogen used, it is not used in the background calculation. All the water produced by the fuel cell stack is considered to be released as steam into the atmosphere.

Water extraction would introduce computational complexity while not contributing significantly to the result. Future versions of the tool might include the water extraction.

4.2.13.2 Optimization output

Variable	Description
Installed capacity [kW]	Optimized installed electrical power for each fuel cell stack and in total.
Power production [kW]	Electrical power production of each fuel cell stack in every time step, optimized by the model. Based on the power production, the following time series are derived: - Hydrogen consumption [kg/h] - Low-temperature heat generation [kW] - High-temperature heat generation [kW]
Investment cost [€]	Investment costs for each fuel cell stack and in total.
Maintenance cost [€]	Annual operation and maintenance costs for each fuel cell stack and in total.
Degradation cost [€]	Annual cost associated with system degradation over its lifetime, reported for each fuel cell stack and in total.

4.2.13.3 Interface options

Parameters of fuel cell stacks can be predefined by selecting one of the available types from the database. Any parameter can still be manually modified after selection. By default, the first type in the list is used.

4.2.13.4 Related Components

• Electrolyser – defines hydrogen storage tank, among other components
• Waste heat – waste heat utilization, where heat consumption is defined

4.2.13.5 Troubleshooting

• No fuel cell stack defined: At least one fuel cell stack must be defined in the tool. Otherwise, the optimization will return an error.

• Deleting fuel cell stack: If a fuel cell stack is removed, all associated data are deleted as well. Once a fuel cell stack is deleted, it cannot be restored.

• Efficiency and power consumption do not match: When reviewing a product datasheet, the manufacturer may provide both the efficiency and the energy production of the fuel cell stack. If these values do not match those in the tool, the efficiency may be reported with respect to the lower heating value (LHV) instead of HHV, or it may refer only to the fuel cells and not the whole fuel cell stack as a system.

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4.2.14 Waste heat

The heat generated from conversion losses of the electrolysers and/or the fuel cell stacks, i.e. from their cooling systems. This heat can be supplied to a local consumer within the renewable energy hub (e.g., a building, a greenhouse, a drying facility, etc.) and/or exported to a district heating (DH) network.

In the case of local heat consumption, any excess heat that cannot be absorbed by the consumer is considered wasted. If there is not enough heat produced by electrolysers and fuel cell stacks, additional heat must be purchased from the current heating source at its regular price. Therefore, the waste heat is effectively lowering current spending on heating requirements.

When heat is sold to a DH network, the model assumes no export limit by default. However, a limit can be imposed if the DH network cannot accept large amounts of heat.

The temperature level of both the local consumption and DH connection is assumed to be the same.

For more flexible heat delivery, the system includes a thermal energy storage (TES) unit.

If low-temperature heat must be upgraded to supply a high-temperature demand, a heat pump is required, which operates using electricity.

Heat from the electrolyser(s) and fuel cell stack(s) is delivered through low-temperature and high-temperature heat exchangers. These represent the complete heating subsystem, including pipes, valves, pumps, and control equipment.

Heat flows are automatically balanced by the optimization model between local consumption, TES, and DH export.

4.2.14.1 Input parameters

Local consumption

The local heat demand can be provided as a generic profile from the tool catalogue and annual energy consumption, or it can be imported from a file. Each way of providing the demand data has its own tab.

Generate data tab

Parameter	Description
Building type [dropdown menu]	A type of building for which heating demand exists. The tool has a generic profile for each of the provided building types.
Annual heat consumption [MWh]	Amount of heat consumed annually. The profile defined with Building type is scaled to achieve this value.

Import data tab

Parameter	Description
File with the consumption profile [text field]	Defines the name of the CSV file containing the heat demand time series. It is not possible to write in this field – it is automatically populated after clicking on button Browse….
Browse [button]	By clicking Browse, the user selects a CSV file from the local system. File format requirements: - File format: .csv - Single column - No header row Allowed number of rows: - 8,760 (hourly resolution) - 17,520 (30-minute resolution) - 35,040 (15-minute resolution) Each row must contain a numerical value representing the heat consumption in kW. The first value in the file corresponds to the beginning of the year (January 1st, 00:00), and the last value corresponds to the end of the year (December 31st, 23:00 for hourly resolution). If the dataset originates from a leap year (8,784 hourly values), one day of data must be removed to match one of the supported row counts. After selecting a file, a message is displayed indicating whether the data import was successful or if errors were detected.

Common parameters

Parameter	Description
Check consumption data [button]	Opens a pop-up window displaying a chart of the heat consumption profile. The chart is dynamic, meaning it can be zoomed in or out and moved around. This allows the user to visually verify data continuity, seasonal trends, extreme values, and possible data inconsistencies. The chart is for verification purposes only and does not modify the data. This button is applicable to both tabs (generic data and custom data).
Current heating price [€/MWh]	The current price of heat paid by the local consumer.
Temperature level [dropdown menu]	The temperature level required for the local consumer – it could be either low- or high-temperature. It matches the temperature level of the DH network, if enabled. By changing this value, the temperature level of the DH changes to the same value, and vice versa.

District heating

Parameter	Description
DH demand has limit? [checkbox]	Indicates whether the DH network has an export limit or the renewable energy hub can supply unlimited heat. If there is a limit, it should be imported as a profile. There is no option to generate the data.
File with the demand profile [textbox]	Defines the name of the CSV file containing the DH demand limit time series. It is not possible to write in this field – it is automatically populated after clicking on button Browse….
Browse [button]	By clicking Browse, the user selects a CSV file from the local system. File format requirements: - File format: .csv - Single column - No header row Allowed number of rows: - 365 (daily resolution) - 8,760 (hourly resolution) - 17,520 (30-minute resolution) - 35,040 (15-minute resolution) Each row must contain a numerical value representing the heat demand limit as mean powers in kW. The first value in the file corresponds to the beginning of the year (January 1st, 00:00), and the last value corresponds to the end of the year (December 31st, 23:00 for hourly resolution). If the dataset originates from a leap year (8,784 hourly values), one day of data must be removed to match one of the supported row counts. After selecting a file, a message is displayed indicating whether the data import was successful or if errors were detected.
Check demand data [button]	Opens a pop-up window displaying a chart of the heat demand profile. The chart is dynamic, meaning it can be zoomed in or out and moved around. This allows the user to visually verify data continuity, seasonal trends, extreme values, and possible data inconsistencies. The chart is for verification purposes only and does not modify the data.
DH connection already exists? [checkbox]	Indicates whether the connection to the DH network already exists or not.
Size of the existing connection [kW]	Nominal heating power of the existing connection to the DH network. It is visible only if DH connection already exists? is activated.
Temperature level [dropdown menu]	The temperature level required for the DH network – it could be either low- or high-temperature. It matches the temperature level of the Local consumption, if enabled. By changing this value, the temperature level of the Local consumption changes to the same value, and vice versa.
Price for provided heat [€/MWh]	The price that the renewable energy hub earns from selling heat to the DH network, after taxes.
Investment price [€/kW]	The price of the investment into the DH connection per unit of power. It is assumed that the DH provider takes care of the connection and provides necessary maintenance. Therefore, the DH connection does not have maintenance nor replacement price.
Subsidy [%]	Percentage that is deductible from the investment cost.

Heat exchangers (advanced)

The tool assumes there are two heat exchangers: one for each temperature level. It does not represent only the heat exchanger itself, but rather a heating (sub)system that consists of pipes, valves, pumps, etc. In the table below there are parameters listed for a single heat exchanger, but it applies to both of them.

Parameter	Description
Heat transfer efficiency [%]	Total heat transfer efficiency of the heat exchanger.
Heat exchanger already exists? [checkbox]	Indicates whether the heat exchanger already exists at the site or not.
Existing heat exchanger power [kW]	The nominal power of the existing heat exchanger. It is visible only if Heat exchanger already exists? is enabled.
Investment price [€/kW]	The price of the investment into the heat exchanger per unit of power. It includes the exchanger itself, all necessary material and auxiliary equipment (pipes, valves, pumps, etc.), and labour until the full operation.
Maintenance price [€/kW]	Estimated annual operation and maintenance (O&M) price per installed power. O&M does not include degradation of the system.
Replacement price [€/kW]	Same as investment price, but after the lifetime of the system, i.e. the future investment price. The main difference from the investment price is that the subsidy does not apply to the replacement price.
Lifetime [years]	Number of years after which the heat exchanger needs to be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

Thermal energy storage (advanced)

Parameter	Description
Storage efficiency [%/day]	Effectiveness of a system to store and reuse heat, minimizing energy loss and maximizing beneficial output, expressed as percentage of heat retained during 24 hours (100% - self-discharge percentage).
Storage already exists? [checkbox]	Indicates whether a thermal energy storage already exists at the site or not.
Existing storage capacity [kWh]	The capacity of the existing thermal energy storage. It is visible only if Storage already exists? is enabled.
Investment price [€/kWh]	The price of the investment into the thermal energy storage per unit of energy. It includes the storage tank itself, all necessary material and auxiliary equipment (pipes, valves, pumps, etc.), and labour until the full operation.
Maintenance price [€/kWh]	Estimated annual operation and maintenance (O&M) price per installed capacity. O&M does not include degradation of the system.
Replacement price [€/kWh]	Same as investment price, but after the lifetime of the system, i.e. the future investment price. The main difference from the investment price is that the subsidy does not apply to the replacement price.
Lifetime [years]	Number of years after which the thermal energy storage needs to be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

Heat pump (advanced)

The heat pump is visible only when the sources (electrolysers or fuel cell stacks) provide low-temperature heat while the demand (Local consumption or DH network) requires high-temperature heat.

Parameter	Description
Heat pump COP [-]	Coefficient of performance of the heat pump. It represents a ratio of thermal power to electrical power required.
Heat pump already exists? [checkbox]	Indicates whether a heat pump already exists at the site or not.
Existing heat pump power [kW]	The nominal thermal power of the existing heat pump. It is visible only if Heat pump already exists? is enabled.
Investment price [€/kW]	The price of the investment into the heat pump per unit of thermal power output. It includes the heat pump itself, all necessary material, auxiliary equipment, and labour until the full operation.
Maintenance price [€/kW]	Estimated annual operation and maintenance (O&M) price per installed power. O&M does not include degradation of the system.
Replacement price [€/kW]	Same as investment price, but after the lifetime of the system, i.e. the future investment price. The main difference from the investment price is that the subsidy does not apply to the replacement price.
Lifetime [years]	Number of years after which the heat pump needs to be replaced.
Subsidy [%]	Percentage that is deductible from the investment cost. Does not apply to the replacement price.

4.2.14.2 Optimization output

The optimization provides detailed results describing how recovered heat is utilized, stored, exported, or wasted within the renewable energy hub. All time-series outputs are reported with the same temporal resolution as the input profiles.

Variable	Description
Local heat utilization	- Locally consumed heat – profile in [kW]: Amount of recovered heat supplied to the local consumer at each timestep. This represents useful heat demand covered by waste heat from electrolysers and/or fuel cell stacks. - Heat from current source – profile in [kW]: Heat supplied by the existing (conventional) heating source when recovered heat is insufficient to meet local demand. This value is non-zero only when waste heat and thermal storage cannot fully satisfy the local consumption. - Savings by recovering waste heat in [€]: Annual cost savings achieved by replacing heat from the current heating source with recovered waste heat. The savings are calculated using the specified current heating price.
District heating (DH) export	- Heat exported to DH network – profile in [kW]: Heat delivered from the renewable energy hub to the DH network at each timestep. Export respects any user-defined DH limit. - Revenue from DH export in [€]: Annual revenue generated by selling heat to the DH network, calculated using the specified DH selling price.
Heat losses	Amount of usable heat that could not be utilized locally, stored in the TES, or exported to the DH network. This typically occurs when: - local demand is fully satisfied, - TES is full, and - DH export is limited or disabled.
Additional profiles	- TES state of charge (SoC) – profile in [kWh]: Thermal energy stored in the TES at each timestep, expressed relative to the storage capacity. The profile reflects charging, discharging, and standing losses according to the specified storage efficiency. - Heat pump electricity consumption – profile in [kW]: Electrical energy consumed by the heat pump at each timestep when temperature upgrading is required.
Economic results	The optimization reports investment and operational costs associated with heat recovery infrastructure: - DH connection: investment cost - Heat exchanger: investment, maintenance, and degradation cost - Thermal energy storage: investment, maintenance, and degradation cost - Heat pump: investment, maintenance, and degradation cost

4.2.14.3 Interface options

The Waste heat section allows the user to configure how recovered heat from electrolysers and fuel cell stacks is utilized, upgraded, stored, or exported. The user can select either Local consumption or District heating, or both, for waste heat utilization.

• Local consumption: The profile of consumption can be either generated from the generic data in the tool background, or imported from a CSV file.

• District heating: If the exported heat should be limited, the profile of limits must be imported from a CSV file.

• Heat pump: It is visible only if the temperature level of local consumption and/or DH is set to high-temperature.

4.2.14.4 Related components

• Electrolyser – a possible source of heat.
• Fuel cell stack – a possible source of heat.

4.2.14.5 Troubleshooting

Common issues and solutions:

• No heat utilization selected: If neither Local consumption nor District heating is enabled, the application will display an error message when attempting to run the optimization.

• No heat sources defined: The application will display an error message if none of the configured electrolysers or fuel cell stacks have recoverable waste heat.

4.2.15 Financial parameters

The Financial parameters component defines the economic constraints and incentives that apply to the entire hydrogen infrastructure project. These global financial settings affect the optimization of all components in the system.

This component is always present in the system and does not require any component selection checkbox. It contains settings for investment constraints, subsidies, and project lifetime.

4.2.15.1 Input parameters

Investment constraints

The investment constraints section allows you to set limits on the project’s payback period and total investment amount. These constraints help guide the optimization towards economically viable solutions.

Parameter	Description
Limit the payoff period? [checkbox]	If enabled, the optimization will constrain the payback period to be within the specified maximum. If a lower bound on the size of any component is set to > 0, then this should be automatically turned off to ensure the feasibility of the optimization problem.
Maximum payback period [years]	The longest acceptable timeframe (in years) for the project’s cumulative savings to offset the initial investment. This parameter is only visible if Limit the payoff period? is enabled.
Limit the investment amount? [checkbox]	If enabled, the optimization will constrain the total investment to be within the specified maximum. If a lower bound on the size of any component is set to > 0, then this should be automatically turned off to ensure the feasibility of the LP solution.
Maximum investment [€]	The highest total amount (in €) you’re willing to invest in the project. This parameter is only visible if Limit the investment amount? is enabled.

Investment incentives

The investment incentives section allows you to define subsidies that can reduce the effective cost of the project. These subsidies are applied to component investments during the optimization.

Parameter	Description
Apply subsidy to all components? [checkbox]	If checked, the subsidy will be applied to the cost of all microgrid components (e.g., electrolyzer, heat exchanger). If unchecked, you can specify which components receive the subsidy individually.
Investment subsidy [%]	The percentage of the total project cost covered by government or other financial incentives. This parameter is only visible if Apply subsidy to all components? is enabled.

Project lifetime

The project lifetime settings define the planning horizon for the optimization. This affects the calculation of annualized costs and the payback period analysis.

Parameter	Description
Design lifetime infinite [checkbox]	Check this box if you want your system to work indefinitely. When enabled, the Design lifetime parameter is hidden.
Design lifetime [years]	Lifetime of the whole system. This parameter determines the number of years used for calculating annualized costs and the payback period. This parameter is hidden if Design lifetime infinite is enabled.

4.2.15.2 Interface options

The Financial parameters component provides the following interface options:

• Payoff period constraint: Enable or disable the payback period constraint based on your investment criteria.
• Investment limit: Set a maximum investment amount to keep the project within budget.
• Subsidy configuration: Apply subsidies uniformly across all components or configure them individually per component.
• Lifetime settings: Choose between a finite project lifetime or an infinite planning horizon.

4.2.15.3 Troubleshooting

Common issues and solutions:

• Minimum component size set: If size of any component is constraint in a way that a minimum size is set, you should unselect Limit the payoff period and Limit the investment amount.

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4.2.16 Simulation parameters

Simulation parameters control the simulation period, time resolution and solver settings used in the mathematical model. The simulation parameters are always present and must be configured for each scenario.

4.2.16.1 Input parameters

Time settings

Parameter	Description
Simulation start date [date picker]	Starting day of the simulation period. If the simulation period is shorter than a year, all profiles (demands, consumptions, prices, etc.) are repeated until the whole year is fulfilled. The maximum duration is 365 days.
Simulation end date [date picker]	The last day of the simulation period. If the simulation period is shorter than a year, all profiles (demands, consumptions, prices, etc.) are repeated until the whole year is fulfilled. The maximum duration is 365 days.

Sampling settings

Parameter	Description
Sampling time - electrical part [h] (dropdown)	The sampling time for the purely electrical components of the hub: electrical grid connection, LREP, PV system, Wind farm, BESS, and electrical consumption. This sampling time must be less than or equal to the sampling time for hydrogen and heat. Common values are 1 hour (default), 2 hours, or 4 hours. With lower sampling time comes greater accuracy, but the price is greater computational complexity.
Sampling time - hydrogen and heat [h] (dropdown)	The sampling time for H2 and heat components of the hub: water supply, electrolyser, fuel cell, waste heat. This sampling time must be greater than or equal to the sampling time for electrical part. Common values are 1 hour, 2 hours, 4 hours, or 24 hours. H2 and O2 sales have a fixed sampling time of 24 hours. With lower sampling time comes greater accuracy, but the price is greater computational complexity.

Optimization settings

Parameter	Description
Solver optimality tolerance [-]	Both primal and dual feasibility tolerance. A lower value means more precise optimization but may require longer computation time. Default value is 1.0.
Optimization timeout [min]	The maximum time within which the optimization can be performed. If an optimal solution can be found within the solver optimality tolerance before the timeout is reached, the Results screen will be shown. Otherwise, a timeout error message will be displayed. Default value is 60 minutes.

4.2.16.2 Understanding time sampling

The sampling time determines the time resolution of the optimization model. There is a trade-off between accuracy and computational complexity:

• Hourly sampling (1 hour): Provides the highest accuracy for modeling daily fluctuations in electricity prices, renewable generation, and demand. This is the default and recommended setting for most analyses.

• 2-4 hour sampling: Reduces computational time but may miss some short-term dynamics. Suitable for preliminary analyses or when investigating seasonal patterns.

• Daily sampling (24 hours): Very fast but may not capture important intra-day effects. Typically used only for hydrogen part components which are modeled with daily resolution.

The electrical sampling time should always be less than or equal to the hydrogen/heat sampling time. The tool will automatically enforce this constraint.

4.2.16.3 Simulation period

The simulation period defines the time horizon for the optimization:

• Full year (default): January 1 to December 31. All hourly profiles are used directly.

• Partial year: Any period up to 365 days. If the period is shorter than a year, the profiles are repeated to fill the year. For example, if you simulate January to March, the model will repeat Q1 data for the remaining months.

The default simulation period is one full year (365 days).

4.2.16.4 Troubleshooting

• Simulation duration too long: If the simulation period exceeds 365 days, an error message will be displayed. Reduce the simulation duration to a maximum of one (non-leap) year.

• Optimization timeout: If the optimization does not complete within the specified timeout, consider:

  • Increasing the optimization timeout
  • Increasing the sampling time (e.g., from 1 hour to 2 hours)
  • Reducing the simulation period
  • Simplifying the system configuration by removing some components

• Sampling time mismatch: If the electrical sampling time is greater than the hydrogen sampling time, the tool will automatically adjust the hydrogen sampling time to match.

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4.3 Run optimization

After configuring all system components and their parameters, click Run optimization to generate the results. Once clicked, the tool performs the following sequence of operations:

1. Project save prompt

: The tool first asks whether you want to save the project before starting the optimization. You can choose to: - save the project,
- continue without saving, or
- cancel the optimization.

Saving the project is recommended in case an error occurs and the application closes unexpectedly.

2. Data validation

: The tool validates all parameters and their combinations to ensure they are within allowed ranges. If an invalid value is detected, a pop-up window titled Input validation failed appears. The message: - identifies the component where the issue occurs, and
- explains the reason for the failure.

Only the first detected issue is shown. After resolving it, run the optimization again to reveal any remaining issues.

3. Data processing

: The tool prepares all required inputs for the optimization, including: - obtaining profiles from online sources (PVGIS, renewables.ninja, Open-Meteo),
- scaling profiles according to user-defined values,
- generating and converting additional parameters (e.g., unit adjustments).

During this phase, additional validation is performed on the processed data.  
If validation fails here, the cause is usually:
- an incompatible combination of parameters, or  
- a temporary internet connectivity issue.

4. Problem generation

: After successful data preparation, the tool formulates the optimization problem and passes it to the solver.

5. Solving the problem

: The optimization problem is solved using the open-source HiGHS solver. When the solver finishes, one of the following status messages is displayed: - Successful optimization – the optimal solution was found.
- Time limit reached – a feasible but suboptimal solution was obtained.
- Unexpected error – the solver failed to complete.

6. Results post-processing

: After a successful run, the tool processes the results for presentation. A new window (Results) is created under the scenario tree node and automatically opened in the main workspace.

Waiting

During the entire procedure, a message Working, please wait… is displayed together with a loading indicator. While optimization is running:

• the user interface is temporarily disabled,
  
• no interaction is possible, and
  
• the process cannot be stopped from within the application.

Stopping the optimization is planned for future releases. Currently, it can only be terminated via the system task manager.

Saving the data

Results are not saved automatically after optimization. Make sure to save the project manually to preserve the results.