What C-rate 0.5C and 0.25C mean
C-rate is the ratio of power to capacity. 0.5C means discharge in 2 hours, 0.25C in 4 hours, 0.125C in 8 hours. The lower the C-rate, the lower the thermal stress on cells and the slower the degradation.
2 h — daily arbitrage, peak shaving, capacity market
The 2-hour variant maximizes revenue per invested zloty wherever payment is tied to power: capacity market, capacity charges, regulation. PCS cost is spread over less capacity, so cost per kWh is higher but cost per kW is lower.
4 h — shifting PV production and ancillary services
In a solar farm, the overproduction window lasts 4–6 hours, so 0.25C absorbs the entire surplus. Longer discharge duration also means lower cost per kWh and less degradation.
| Application | Discharge duration | C-rate |
|---|---|---|
| Capacity market | 2 h | 0.5C |
| Peak shaving at an industrial plant | 2 h | 0.5C |
| FCR regulation | 1 h | 1C |
| Solar farm — production shifting | 4 h | 0.25C |
| Utility-scale project | 4–8 h | 0.25–0.125C |
Impact on price per kWh
At the same power rating, moving from 2 h to 4 h raises CAPEX by 55–70%, but lowers unit capacity cost by 15–25%, since the PCS, transformer, and site works don't change.