How many kWp do I need in 2026? Every size compared
For 4,000 kWh of consumption in Hanover, a 4 kWp system covers annual demand on paper, but among sizes up to 15 kWp the highest net gain after 20 years comes from 10 kWp.
Checked by Radif Partners · Editorial policy · How we calculate
Most economic size
10 kWp
€6,953 net gain after 20 years, self-use 16 %
| kWp | kWh | Self | Autarky | Payback |
|---|---|---|---|---|
| 3 | 3,010 | 38 % | 28 % | 11.8 |
| 4 | 4,013 | 31 % | 31 % | 12.1 |
| 5 | 5,016 | 27 % | 33 % | 12.5 |
| 6 | 6,019 | 23 % | 35 % | 12.9 |
| 8 | 8,026 | 19 % | 37 % | 13.6 |
| 10 | 10,032 | 16 % | 39 % | 14.2 |
| 12 | 12,039 | 13 % | 40 % | 14.9 |
| 15 | 15,048 | 11 % | 42 % | 15.7 |
| 20 | 20,064 | 8 % | 42 % | 17.0 |
Step-by-step calculation
- Cost per size: €2,000 fixed (scaffold, meter, registration) plus €1,500 per kWp; you enter both, we do not know your quote.
- Each size runs through the same simulation: south roof at 30°, surplus feed-in, 60% limit without smart meter, current period rate.
- The highest net gain after 20 years comes from 10 kWp; 4 kWp cover the annual consumption on paper.
Estimate based on average weather 2005 to 2023 (PVGIS) and metered household loads. A single year can differ by a few per cent. How we calculate
The question of how many kWp a house needs has two answers, and the sizing calculator shows both. The first is coverage: at what capacity does the roof produce as much as the household uses in a year? In Hanover, with 4,000 kWh, that is 4 kWp, delivering 4,013 kWh. The second is economics: because scaffolding, the meter cabinet and registration cost almost the same whether four or twelve panels go up, the price per kWp falls with size. Each extra kilowatt-hour is mostly exported, but it still earns the feed-in tariff (Einspeisevergütung). With €2,000 of fixed costs and €1,500 per kWp, a 10 kWp system achieves the largest net gain after 20 years in this example, €6,953, even though the household uses only 16 % of its power itself. The smallest system has the shortest payback, the mid-sized one the highest profit.
What the sizing calculator puts side by side
The calculator runs every size from 3 to 20 kWp through the same annual simulation: south roof at 30°, yield from PVGIS for your postcode, consumption from the quarter-hour profiles of HTW Berlin, surplus feed-in at the current period's rate from the Federal Network Agency. Without a smart meter, new systems are capped at 60 % of rated output (section 9(2) EEG), which hits large systems harder at midday. Costs are a fixed amount plus a price per kWp; you enter both yourself.
The Hanover example
| Size | Output | Self-use | Self-sufficiency | Payback | Net gain |
|---|---|---|---|---|---|
| 3 kWp | 3,010 kWh | 38 % | 28 % | 11.8 yrs | €4,543 |
| 4 kWp | 4,013 kWh | 31 % | 31 % | 12.1 yrs | €5,211 |
| 5 kWp | 5,016 kWh | 27 % | 33 % | 12.5 yrs | €5,679 |
| 6 kWp | 6,019 kWh | 23 % | 35 % | 12.9 yrs | €6,051 |
| 8 kWp | 8,026 kWh | 19 % | 37 % | 13.6 yrs | €6,579 |
| 10 kWp | 10,032 kWh | 16 % | 39 % | 14.2 yrs | €6,953 |
| 12 kWp | 12,039 kWh | 13 % | 40 % | 14.9 yrs | €6,858 |
| 15 kWp | 15,048 kWh | 11 % | 42 % | 15.7 yrs | €6,692 |
Self-sufficiency grows slowly: from 4 to 10 kWp it only rises from 31 % to 39 %, because the household needs grid power at night and in winter anyway. The net gain, by contrast, rises up to 10 kWp; beyond that, at these costs, the lower rate above 10 kWp and the 60 per cent cap outweigh it.
When a smaller system is the right choice
If you want to tie up less capital, or have a complicated roof where each extra panel gets expensive, the size with the shortest payback is the better pick. The same applies if your quote per kWp is well above the assumption: the optimum then moves down, as the calculator shows at once. What a system costs per kWp is covered in the guide to solar PV cost.
Limits that matter with size
Income from systems up to 30 kWp per dwelling, at most 100 kWp per taxpayer, is exempt from income tax (section 3 no. 72 Income Tax Act). Above 10 kWp the tariff falls for the additional share of capacity; the blended rate is worked out on the feed-in tariff page. The yield for your location at other tilts is shown under PV yield by postcode.