Key application · PV + BESS
Energy storage for solar farms — BESS from 1 MWh to 1000 MWh
Short answer
For a PV farm, the recommended ratio is 2 MWh of capacity per 1 MW of installed power, in a 4-hour configuration (0.25C). The storage system absorbs the surplus from the 11:00–15:00 window and releases it during the evening peak, at the same connection point.
- No more selling during negative-price hours
- Full use of the existing grid connection capacity
- Retrofit of an existing farm without a new connection
Problem
A PV farm earns the least exactly when it produces the most
The solar production profile coincides with the hours of lowest market prices. The result is negative prices, curtailment and a capture price well below the average exchange price.
11:00–15:00
window in which most negative prices occur
5–12%
of annual production lost to curtailment
15–30%
gap between capture price and average exchange price
Negative prices in the 11:00–15:00 hours
When nationwide PV generation exceeds demand, the day-ahead market price drops below zero. An installation without storage then has two options: sell below zero or curtail production.
Curtailment — how much energy is lost each year
Generation-reduction orders and self-curtailment today take away 5–12% of a typical farm's annual volume. A 4-hour storage system captures most of that energy.
Capture price versus average exchange price
The capture price is the average price weighted by the actual production profile. For PV it is 15–30% lower than the average exchange price, because production is concentrated in the lowest-price hours. Storage shifts volume to higher-price hours and raises the capture price.
Sizing
Matching capacity to farm power
| PV farm power | BESS power | Capacity | C-rate | 20 ft containers |
|---|---|---|---|---|
| 1 MW | 0.5 MW | 2 MWh | 0.25C | 1 |
| 2 MW | 1 MW | 4 MWh | 0.25C | 1 |
| 5 MW | 2.5 MW | 10 MWh | 0.25C | 2 |
| 10 MW | 5 MW | 20 MWh | 0.25C | 4 |
| 20 MW | 10 MW | 40 MWh | 0.25C | 6–8 |
| 50 MW | 25 MW | 100 MWh | 0.25C | 16–20 |
Retrofitting an existing farm
Do the grid connection terms need to change
Yes — the installation becomes hybrid. If the power fed into the grid does not increase, the procedure comes down to amending the connection terms and the agreement, without building a new connection. Realistic timeframe: 90–150 days.
What about the PPA and the energy offtaker
Energy discharged from storage must be metered separately from energy covered by a PPA or a support scheme. In practice this means an additional metering configuration and an amendment to the sale agreement.
Space on the farm site
For 10 MWh, 150–300 m² is enough, including a service road and fire zone, usually near the existing transformer station.
Cost and payback period
| System | CAPEX | Simple payback |
|---|---|---|
| 1 MW farm + 2 MWh | PLN 1.9–2.6 million | 6–9 years |
| 5 MW farm + 10 MWh | PLN 8.8–12.0 million | 5–8 years |
| 20 MW farm + 40 MWh | PLN 32–44 million | 5–7 years |
Scope of our delivery
- Profitability analysis based on the farm's production data
- Design, configuration selection and documentation for the connection-terms amendment
- Liquid-cooled 20 ft containers, PCS, transformers, MV switchgear
- EMS optimised for capture price and the balancing market
- Commissioning, testing and O&M service with an LTSA
Lead magnet
Free profitability analysis for your farm
Give us four parameters — within 48 h we'll prepare a capacity recommendation, an estimate of captured energy and a CAPEX range.
FAQ
Request a quote — pricing in 48 h
Send us the project scale in MWh, the site location and the available grid capacity. We reply with a configuration, CAPEX range and delivery schedule.