4 kW solar system for low electricity use
Four kilowatts is a sensible size when the bill shows 2,000 to 3,500 kWh a year. Check the result for your municipality.
Yearly saving on your bills
PLN 2,321
4,200 kWh produced · 28 % used on site
| Used directly and from the battery | 1,184 kWh |
| Exported to the grid | 3,016 kWh |
| Deposit (×1.23) | PLN 1,027 |
| Deposit spent on energy | PLN 988 |
| Overpayment refunded | PLN 39 |
| Bill before / after | PLN 3,061 / PLN 779 |
| Pays back in 10 years up to | PLN 23,212 |
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.
A small 4 kWp solar system means nine or ten panels and 18–20 m² of roof. In Warsaw PVGIS gives it about 4,200 kWh a year, and across Poland between 3,700 and 4,456 kWh. For a home using 2,800 kWh a year that is almost the whole bill, but under net-billing timing matters, not the total. With use spread evenly over the day the home consumes about 28 % of output on site, and the saving is about PLN 2,321 a year. The strength of a small system is that the deposit is almost entirely put to use: it is spent on energy drawn in the evening and in winter instead of being forfeited. The system pays back within 10 years at a price of up to PLN 23,212. This is an estimate for Warsaw; the calculator works it out for your municipality.
Checked by Radif Partners · Editorial policy · Method
How much of 4 kWp stays in the house
The table shows the share of output used straight away under three patterns: house empty in the daytime, use spread evenly over the day, and someone at home all day. The saving in the last column is for the middle pattern.
| Use | Empty by day | Even over the day | Someone at home | Saving |
|---|---|---|---|---|
| 2,000 kWh | 16 % | 21 % | 26 % | PLN 1,920 |
| 2,800 kWh | 22 % | 28 % | 35 % | PLN 2,321 |
| 3,500 kWh | 26 % | 34 % | 43 % | PLN 2,512 |
The gap between the first and third columns is larger than the gap between the weakest and the best municipality in Poland. That is why, for a small system, shifting laundry, dishwashing and water heating to 10:00–15:00 does more than adding panels. The prosumer deposit page explains the settlement in detail.
Small systems and fixed costs
Some installation costs do not depend on size: design, notification, protection devices, the crew’s travel and an inverter of the smallest size on offer. The price per kilowatt of a small system is therefore usually higher than for a large one, even though the total is lower. When comparing quotes, look at the total and the payback the calculator shows.