6 kWp solar system in France: which households does it pay for?
A 6 kWp system only makes sense if the house uses a lot during the day. Here is the calculated threshold, and what electric heating or an electric car changes.
A 6 kWp system produces about 6,790 kWh a year in Paris and 9,339 in Marseille, roof at 30° due south, according to PVGIS data. That is double a 3 kWp system, but not double the gain: for a 4,500 kWh household only 28 % of that output is used on site, the rest goes to the grid at 1.1 c€/kWh, and payback on an estimated installed price of €10,000 exceeds twenty years. 6 kWp becomes worthwhile when daytime usage keeps up: in Paris it beats the 20-year result of 3 kWp from about 11,000 kWh a year, and a 12,000 kWh household pays it back in 12.3 years. Such households usually have a heat pump, a pool, a hot-water tank timed for daytime or a car charged at home. The price, surplus sales and the standing-charge surcharge are in the calculation; any future rise in electricity prices is not.
How many years until your panels pay for themselves?
Pays for itself in
> 20 years
| Output per year | 6,790 kWh |
| Gain in year 1 | €417 |
| Installed price (estimate) | €10,000 |
| Net over 20 years | -€1,429 |
Département median, roof at 30° due south, surplus sold at 1.1 c€/kWh.
Checked by Radif Partners · Editorial policy · Method and sources
3 or 6 kWp: head to head by usage
Here we compare the 20-year net gain, price paid deducted, of both sizes for the same Paris household. While usage stays modest, the 6 kWp surplus does not pay for its extra cost.
| Usage (Paris) | 20-year net, 3 kWp | 20-year net, 6 kWp | 6 kWp payback |
|---|---|---|---|
| 4,500 kWh | +€665 | -€1,429 | over 20 years |
| 8,000 kWh | +€3,570 | +€2,603 | 15.9 years |
| 10,000 kWh | +€4,803 | +€4,510 | 13.8 years |
| 12,000 kWh | +€5,690 | +€6,308 | 12.3 years |
| 15,000 kWh | +€6,599 | +€8,691 | 10.7 years |
The tipping point is around 11,000 kWh a year in Paris. Below it, 3 kWp keeps the lead; above it, the extra output finds a use in the house and 6 kWp wins. What counts is usage during sunny hours, not the yearly total alone.
Electric heating: a false friend
A household heated by electricity uses a lot, but mainly in winter, when panels produce least. At the same 12,000 kWh, a 6 kWp system pays back in 12.7 years with a heating profile against 12.3 years without. A heat pump that also makes hot water or cools in summer makes better use of the output.
Up to what price does a battery pay off?
Pays off if it costs less than
€3,952
| Extra used on site | 1,058 kWh/yr |
| Extra gain per year | €200 |
| Self-consumption without / with | 47 % → 78 % |
Hour-by-hour calculation (Paris, PVGIS 2023 and Enedis profile), over 20 years, 95% efficiency on charge and discharge.
Surplus and its limits
The purchase contract pays 1.1 c€/kWh for surplus, indexed by 2 % a year, up to 1,600 hours at full power, i.e. 9,600 kWh a year for 6 kWp (tariff rules). A house’s surplus almost never reaches that cap. Above 3 kWp, sales income is no longer tax-exempt.
If you are unsure
Start from your actual usage, shown on your bills or customer account. The calculator gives the best-value size and also shows 3 kWp and 9 kWp: choosing 6 kWp to “anticipate” future usage only pays if that usage arrives soon.