9 kWp solar system: the upper limit for a French house
The largest size that keeps reduced VAT and the small-system rules. It only pays back for very heavy users: the calculation city by city.
Nine kilowatts-peak mark the boundary of residential solar in France: it is the maximum size for VAT at 5.5 %, under conditions, and also the size up to which selling all output has been closed since the order of 26 March 2025, leaving surplus sales only. A 9 kWp system produces about 10,185 kWh a year in Paris and 14,008 in Marseille, roof at 30° due south, according to PVGIS, for an estimated installed price of €15,000 based on recent quotes. For an 8,000 kWh household, only 32 % of that output is used on site and it does not pay back within twenty years in Paris. It only beats 6 kWp from about 22,500 kWh a year, which means a large house with a heat pump, a pool and daytime car charging, or a business run from home.
How many years until your panels pay for themselves?
Pays for itself in
> 20 years
| Output per year | 10,185 kWh |
| Gain in year 1 | €481 |
| Installed price (estimate) | €15,000 |
| Net over 20 years | -€4,996 |
Département median, roof at 30° due south, surplus sold at 1.1 c€/kWh.
Checked by Radif Partners · Editorial policy · Method and sources
Years to pay back 9 kWp, by city and usage
| Usage | Lille | Paris | Lyon | Marseille |
|---|---|---|---|---|
| 8,000 kWh | > 20 years | > 20 years | 19.5 yrs | 17.5 yrs |
| 12,000 kWh | 16.5 yrs | 15.8 yrs | 15.0 yrs | 13.3 yrs |
| 16,000 kWh | 13.8 yrs | 13.2 yrs | 12.4 yrs | 10.7 yrs |
| 20,000 kWh | 12.1 yrs | 11.5 yrs | 10.7 yrs | 9.2 yrs |
| 25,000 kWh | 10.7 yrs | 10.1 yrs | 9.3 yrs | 7.8 yrs |
At 8,000 kWh a year, 9 kWp pays back within twenty years only in Lyon and Marseille, and only just; in Lille and Paris it takes around 12,000 kWh. The reason is simple: the house cannot use what nine kilowatts-peak produce during sunny hours, and each exported kWh earns only 1.1 c€.
6 or 9 kWp?
In Paris, 9 kWp beats the 20-year result of 6 kWp from about 22,500 kWh a year. The price per watt-peak falls with size, but not enough to offset surplus paid so little. A smaller, well-used system is better than a large one that exports.
A battery on 9 kWp?
A 9 kWp system has a large surplus, which makes a battery more useful than elsewhere. For a 16,000 kWh Paris household, a 10 kWh usable battery adds 2,249 kWh used on site a year and €425 of gain; to pay for itself over twenty years it should cost no more than €8,398 installed. Compare that ceiling with real quotes on the battery page.
Does your system qualify for 5.5% VAT?
Reduced 5.5% rate
Possible
| VAT at 5.5% | €303 |
| Price incl. 5.5% VAT | €5,803 |
| Conditions | 9 kWp max, ≤ 530 kgCO2/kWp |
Heavy-metal limits and an energy-management system are also required (order of 8 September 2025): the installer certifies it.
What changes above 9 kWp
Reduced VAT stops at 9 kWp. The surplus tariff set by the order of 1 June 2026 covers systems up to 100 kWp on buildings, but the draft submitted to the CRE also planned to close total sales from 9 to 100 kWp. Those systems call for different reasoning, closer to a producer’s, which this site does not cover.