Solar panels in Brittany
The calculator opens on Rennes. Brittany is said to be too cloudy for solar: the PVGIS figures clearly qualify that idea.
Brittany produces a median of 1,144 kWh per kWp a year, against 1,185 for the national median, by our calculation on the European Commission’s PVGIS data. The gap, around 3 %, is far smaller than the region’s rainy reputation suggests. Above all, it hides a clear contrast between inland areas and the southern coast. Morbihan leads with 1,190 kWh, level with the French average, and the Morbihan islands exceed 1,250 kWh. Conversely, Côtes-d'Armor stops at 1,115, and the Monts d’Arrée are the least productive part of the region. Rennes produces 1,158 kWh per kWp, more than Paris (1,140). For a household using 4,500 kWh a year with 3 kWp, payback is 18.1 years in Rennes and 18.3 years in Brest. Solar therefore remains worthwhile, provided it is sized on daytime usage.
Pays for itself in · 3 kWp in Rennes
18.1 years
Net result over 20 years: +€625
| Output per year | 3,454 kWh |
| Used on site (46 %) | 1,590 kWh |
| Bill saving, year 1 | €318 |
| Surplus sold (1,864 kWh) | €21 |
| Standing-charge surcharge (export) | −€12 |
| Gain in year 1 | €327 |
| Share of your bill covered | 35 % |
| Price used (estimate) | €6,000 |
| Best-value size (estimated prices) | 2 kWc |
Month-by-month output in Rennes (3 kWp)
December: 127 kWh; July: 401 kWh. PVGIS average 2005-2023.
Checked by Radif Partners · Editorial policy · Method and sources
The four départements
| Département | Median kWh/kWp | Communes: from… to… | 3 kWp pays back in |
|---|---|---|---|
| Morbihan (56) | 1,190 | 1,109 – 1,282 | 18.0 years |
| Ille-et-Vilaine (35) | 1,155 | 1,128 – 1,204 | 18.2 years |
| Finistère (29) | 1,120 | 1,050 – 1,252 | 18.4 years |
| Côtes-d'Armor (22) | 1,115 | 1,059 – 1,155 | 18.4 years |
Output ranges from 1,050 to 1,282 kWh per kWp from one commune to the next. The top of the range is all along the southern coast, from Penmarch to Belle-Île; the bottom in the inland Argoat, around the Monts d’Arrée and central Côtes-d’Armor. In Quimper, output is 1,147 kWh per kWp, and payback 18.2 years for 3 kWp.
What a cloudier sky changes
Summer output remains strong but winter output is low, so the share used on site depends heavily on daytime usage. For an 8,000 kWh household in Rennes, the best 20-year size is 3.5 kWp; in Brest, 3.5 kWp. The mini-calculator below opens on the Morbihan, where 3 kWp pays back in 18.0 years at the département median.
How many years until your panels pay for themselves?
Pays for itself in
18.0 years
| Output per year | 3,550 kWh |
| Gain in year 1 | €330 |
| Installed price (estimate) | €6,000 |
| Net over 20 years | +€689 |
Département median, roof at 30° due south, surplus sold at 1.1 c€/kWh.
Before signing
Have the fitting priced on your actual roof covering, slate or tile, and ask for the wind-resistance calculation. Then check the twenty-year return for your usage, and the self-consumed share you can expect.