8 kW solar system: when a bigger size makes sense
Eight kilowatts suits homes using 6,000 kWh a year or more. Check how much of that output you would actually use.
Yearly saving on your bills
PLN 4,642
8,400 kWh produced · 28 % used on site
| Used directly and from the battery | 2,368 kWh |
| Exported to the grid | 6,032 kWh |
| Deposit (×1.23) | PLN 2,053 |
| Deposit spent on energy | PLN 1,976 |
| Overpayment refunded | PLN 78 |
| Bill before / after | PLN 6,123 / PLN 1,558 |
| Pays back in 10 years up to | PLN 46,424 |
Hourly model of an average day in each month; surplus priced at the last 12 months of RCEm (PSE) plus the gain from negative RCE counted as zero. An estimate, not an offer; fixed charges excluded.
An 8 kWp system means about 18 or 19 panels and 35–40 m² of roof, and in Warsaw about 8,400 kWh a year according to PVGIS. That size makes sense mainly where use is high: at 6,000 kWh a year the house uses about 30 % of output on the spot and saves about PLN 4,754 a year. At 4,000 kWh of use the same system saves PLN 3,840, and PLN 346 of deposit is forfeited after 12 months. That is the main lesson of net-billing: a bigger system mostly increases sales to the grid at the wholesale price, and in 2026 that price was often negative at midday. A negative RCE counts as zero for a prosumer, but surplus in those hours earns nothing. Eight kilowatts therefore pays off for homes that use power in daytime: with a heat pump for hot water, air conditioning or a car charged at home.
Checked by Radif Partners · Editorial policy · Method
8 kWp at different levels of use, RCE and RCEm
A prosumer who began exporting before 1 July 2024 is settled at RCEm unless they filed a statement switching to RCE. Newer prosumers are settled at RCE. The table shows both, plus a variant with a 10 kWh battery.
| Use | Saving, RCE | Saving, RCEm | RCE and 10 kWh battery | Deposit forfeited |
|---|---|---|---|---|
| 4,000 kWh | PLN 3,840 | PLN 3,635 | PLN 4,567 | PLN 346 |
| 6,000 kWh | PLN 4,754 | PLN 4,652 | PLN 6,335 | PLN 0 |
| 8,000 kWh | PLN 5,279 | PLN 5,187 | PLN 7,061 | PLN 0 |
| 10,000 kWh | PLN 5,758 | PLN 5,675 | PLN 7,451 | PLN 0 |
With a large system, the gap between RCE and RCEm widens, because more energy reaches the grid in hours with a negative price. April 2026 had 98 such hours and May 62. Details and price history are on the RCE and RCEm page.
A heat pump and 8 kWp
A heat pump raises use, but mostly in winter. In summer it only heats water, so the summer surplus stays almost the same. For a house with a heat pump, it is better to compare the size with the real spread of use on the heat pump and solar page than to divide the yearly total by the yield per kilowatt.