Electrolyzer System
The Electrolyzer System employed by DER-VET is modeled as a technology that consumes electricity to produce hydrogen.
Hydrogen Schedule
To define how to control the amount of hydrogen production, the user may select up to 3 modes. These are explained below under Hydrogen Schedule.
Efficiency
Efficiency can be handled in two ways: as a fixed value across all times, or as a post-optimization calculation using the actual amount of hydrogen produced from a variable efficiency. When incl_variable_efficiency is ON, a calculated variable efficiency will replace the constant scalar efficiency, but only in post-optimization. Two new columns of data will appear in the Time series Output Results CSV: 'Efficiency Actual (kg/kWh)' and 'Hydrogen Production Actual (kg)'. The new values of Hydrogen Production Actual are then used in performance and financial results. The reason for this treatment is that with variable efficiency ON, using it will create a nonlinear constraint and will break our optimization approach. Instead, we must handle it post-optimization. Note that the calculation of LCOH (Levelized Cost of Hydrogen), which appears in the payback.csv output file, will also use the new values of Hydrogen Production Actual.
Degradation
When the boolean parameter incl_degradation is ON, both calendar degradation and cycle degradation will be considered. Calendar degradation is set with the yearly_degrade parameter while cycle degradation is calculated using a cycle_life_filename input file. Degradation due to cycling for an Electrolyzer System is handled similarly to how Battery cycling degradation. The notable differences are listed below. For an Electrolyzer System:
- we do not consider user inputs for state_of_health or cycle_life_table_eol_condition, but instead treat these as zero.
- the end-of-life is when the SOH goes to zero.
- we use power fluctuation (as a percentage of rated_power), and not energy.
Note that DER-VET disallows having both Electrolyzer System sizing and degradation active in the same case.
Inputs
Rated Power
| Tag | Key | Description |
| ElectrolyzerSystem | rated_power | This input sets the power capacity of the electrolyzer system in kW.
Set this to 0 to have DER-VET optimally size this parameter. |
Minimum Power
| Tag | Key | Description |
| ElectrolyzerSystem | min_power | The minimum power an electrolyzer system can produce in kW. |
Hydrogen Schedule
| Tag | Key | Description |
| ElectrolyzerSystem | hydrogen_schedule_mode | Defines how to control hydrogen production:
0=no control, 1=apply a fixed schedule according to an input time series of 'ElectrolyzerSystem Schedule (kW)', 2=use hydrogen_production_quota parameter to set the quantity of hydrogen (kg) that must be produced in each optimization window. |
Hydrogen Production Quota
| Tag | Key | Description |
| ElectrolyzerSystem | hydrogen_production_quota | The quantity of hydrogen (in kg) that must be produced in each optimization window. The parameter only becomes active when hydrogen_schedule_mode is set to 2. |
Efficiency
| Tag | Key | Description |
| ElectrolyzerSystem | efficiency | ElectrolyzerSystem efficiency in kg of hydrogen per kWh of energy. |
Variable Efficiency ON/OFF
| Tag | Key | Description |
| ElectrolyzerSystem | incl_variable_efficiency | T or F (boolean) to calculate (as a post-optimization step) the actual amount of hydrogen produced from the actual efficiency, according to an input variable efficiency 'turndown' curve. |
Variable Efficiency Curve Filename
| Tag | Key | Description |
| ElectrolyzerSystem | variable_efficiency_filename | This input points to a file containing the turndown curve describing the variable efficiency. The file must have two columns with a header of 'Efficiency (kg/kWh),Fractional Power (%)'. Fractional Power represents percentage of full power and values must be between 0 and 1. |
Hydrogen Unit Value
| Tag | Key | Description |
| ElectrolyzerSystem | hydrogen_unit_value | The value of Hydrogen in $ per kg. |
Calendar Degradation
| Tag | Key | Description |
| ElectrolyzerSystem | yearly_degrade | Percent degradation per year. This calendar degradation combines with cycling degradation to get total degradation. |
Degradation ON/OFF
| Tag | Key | Description |
| ElectrolyzerSystem | incl_degradation | T or F (boolean) to include degradation (both calendar degradation and cycle degradation) |
Degradation Curve Filename
| Tag | Key | Description |
| ElectrolyzerSystem | cycle_life_filename | This input points to a file containing the degradation curve of the electrolyzer system. The file must have two columns with a header of 'Power Fluctuation (%),Cycle Life Value (cycles)'. For our rainflow model, defines the buckets and the number of cycles per bucket the ElectrolyzerSystem can withstand before requiring replacement. |