Flexible electrolyzer operations #1487
Description
Concerning flexible operations for electrolyzers, we have data for:
- Minimum stable level of operation (see figure below, and 80% for SOEC (https://www.sciencedirect.com/science/article/pii/S0306261922005190?utm
https://cdn.catf.us/wp-content/uploads/2023/11/15092028/solid-oxide-electrolysis-report.pdf ) - Minimum partial load without efficiency loss (and efficiency loss related to the passage from this condition to minimum stable level of operation) (see figure below)
- Ramp-up time: in the order of seconds/milliseconds, thus NEGLIGIBLE
- Ramp up- and down rate: 20% of the nominal load per second (https://ris.utwente.nl/ws/files/249961465/1_s2.0_S036031992034725X_main.pdf ), again NEGLIGIBLE
- Startup and shutdown time: 30-60 minutes for Alkaline (https://ris.utwente.nl/ws/files/249961465/1_s2.0_S036031992034725X_main.pdf), 10 minutes for PEM (https://cdn.catf.us/wp-content/uploads/2023/11/15092028/solid-oxide-electrolysis-report.pdf ), 10 seconds for SOEC (https://cdn.catf.us/wp-content/uploads/2023/11/15092028/solid-oxide-electrolysis-report.pdf )
The simplest thing, that can be done already in #1227 , is to force electrolyzers to operate only in conditions >= minimum stable level of operation → p_min_pu = 0.6 (Alkaline & PEM) / 0.8 (SOEC)
More complex alternatives to this may be:
- Ignore efficiency loss range → p_min_pu = 0.4 (Alkaline) / 0.25 (PEM) and efficiency = nominal efficiency
- Implement piece-wise function to represent efficiency drop from minimum stable level of operation to minimum partial load without efficiency loss. In this case p_min_pu would be 40% for alkaline and 25% for PEM with efficiency = 0.01 * nominal efficiency at this step up to efficiency = nominal efficiency when reaching 60% of p_nom
3 Model Alkaline and PEM electrolyzers as parallel links with 1) reduced efficiency in the range 0.4 / 0.25 <= p_min_pu < 0.6 and 2) nominal efficiency for p_min_pu >= 0.6
To consider startup and shutdown time:
- Considering the most conservative value (60 minutes) to get to stable operation without efficiency loss → ramp_limit_start_up = 0.0 (Alkaline) (i.e. no hydrogen can be produced in the first hourly time step after startup as it takes 60 minutes) / ramp_limit_start_up = 0.9 (PEM) (i.e. startup takes 10 minutes) + committable=True
I think we have no option to represent restart from standby mode, so we would be considering always the most conservative option.
In the case of Alkaline electrolyzers case though, possible conflicts may arise in the first time step when p_min_pu = 0.6 but ramp_limit_start_up = 0.0.
What do you think @ekatef @davide-f @hazemakhalek @yerbol-akhmetov @GbotemiB ?