Solar Battery Payback Calculator (France): Storage ROI

Is a home solar battery worth it? Calculating the real gain

A battery's gain = extra self-consumed kWh × (grid price − surplus feed-in tariff). With 6 kWp, 10 kWh of storage, the French regulated tariff of August 2026 and the 1.1 c€/kWh feed-in rate, the tool finds about €511 in year one and a 10-year payback on €5,800.

What the tool isolates

The simulator only values the battery's contribution, not that of the panels. It compares two cases:

• Without battery: output = kWp × 1,150 kWh, 35% of which is self-consumed.
• With battery: stored energy is added, capped at capacity × 300 cycles × 90% round-trip efficiency and at 45% of output; total self-consumption cannot exceed 85% of household use.
• Annual gain = extra kWh × grid price − extra kWh × feed-in tariff (the surplus no longer sold).
• The grid price rises each year by the inflation rate you enter; the feed-in tariff stays flat.

Example with the default values

6 kWp produce 6,900 kWh; 2,415 kWh are used without a battery. The 10 kWh battery adds min(2,700; 3,105) = 2,700 kWh, giving 5,115 kWh self-consumed (74.1%). At €0.2003/kWh and a €0.011/kWh feed-in rate, year-one gain is 2,700 × (0.2003 − 0.011) ≈ €511. With 3.5% annual inflation, the €5,800 is recovered in year 10. Under the former €0.13/kWh feed-in rate the price gap was smaller and payback took 17 years.

Battery payback in Germany (EEG)

The “Tariff framework” selector applies the German benchmarks; it is preselected on the German-language page.

• Surplus feed-in tariff (Einspeisevergütung, Teileinspeisung) by commissioning date, as published by the Bundesnetzagentur: 7.70 ct/kWh up to 10 kWp, 6.66 ct/kWh from 10 to 40 kWp and 5.44 ct/kWh from 40 to 100 kWp for systems commissioned from 01/08 to 31/12/2026 (7.78, 6.73 and 5.50 from 01/02 to 31/07/2026). It falls by 1% every six months, stays fixed for 20 years and is applied pro rata across the bands above 10 kWp (§ 23c EEG). No rate has been published for 2027 yet.
• Electricity price: €0.37/kWh, the 2026 household average in the BDEW-Strompreisanalyse of August 2026 (3,500 kWh a year, standing charge included pro rata).
• 0% VAT since 2023 on the battery and its installation when the system is 30 kWp or less on or near a home (§ 12(3) UStG).
• Solarspitzengesetz (25/02/2025): new systems below 100 kW export at most 60% of their capacity until a smart meter and control box are fitted (§ 9(2) EEG), and periods with negative prices are no longer paid from the year after the smart meter is installed (§ 51 EEG). A battery reduces these losses; the tool does not count them.

Example: 6 kWp, 10 kWh and €5,800, commissioned in October 2026. The 2,700 kWh shifted earn 2,700 × (0.37 − 0.077) = €791 in year one. Payback time = 5,800 ÷ 791 = 7.3 years; with a 3.5% yearly price rise, the battery has paid for itself in year 7.

Limits

• The 35% no-battery rate and 300 cycles a year are averages; a household at home during the day self-consumes more without storage.
• Payback is searched over 20 years, while a lithium battery usually lasts 10 to 15 years; its replacement is not counted. If there is no payback within 20 years, the tool shows "more than 20 years".
• Indicative estimate; it does not replace an installer's study.

For the profitability of the whole PV system, use the solar panel payback simulator.

Sources and dates: default grid price = French Tarif Bleu, Base option 3-6 kVA on 01/08/2026, 13.61 c€/kWh excl. tax (CRE deliberation 2026-147 of 15/07/2026, annex B) plus the €30.85/MWh excise duty in force since 01/02/2026 (BOFiP, BOI-RES-EAT-000240) and 20% VAT, i.e. €0.2003/kWh incl. tax; surplus bought at 1.1 c€/kWh excl. VAT, indexed by 2% a year, for grid connection requests filed since 05/06/2026 (French order of 1 June 2026 amending the S21 tariff order, art. 8). German figures: Bundesnetzagentur, EEG rates and BDEW-Strompreisanalyse, August 2026, checked on 22/10/2026. French figures checked on 14/10/2026.

Frequently Asked Questions

Is a home solar battery worth it in 2026?

In France, surplus from new installations has only been bought at 1.1 c€/kWh since 5 June 2026, so each stored kWh is worth close to the grid price, about €0.20/kWh. For 6 kWp and 10 kWh, the tool finds about €511 a year and a 10-year payback on €5,800.

How much does a battery raise self-consumption?

The tool starts from 35% self-consumption without a battery. With 10 kWh of storage on 6 kWp it rises to 74.1% of output, capped at 85% of household consumption.

Why does the feed-in tariff matter?

Every stored kWh is a kWh you no longer sell. The net gain is the gap between the grid price and the feed-in tariff: 0.2003 − 0.011 = €0.189 per kWh with the default values.

What battery capacity should I choose?

Past a certain size the battery no longer fills up: the tool caps stored energy at 45% of output and 300 cycles a year. For 6 kWp, capacity above roughly 11.5 kWh adds nothing in this model.

How long does a solar battery take to pay back in Germany?

With the tool's German framework (6 kWp, 10 kWh, €5,800, commissioned in October 2026, EEG feed-in at 7.70 ct/kWh and the BDEW average price of €0.37/kWh), the battery saves €791 in year one. Simple payback is 5,800 ÷ 791 = 7.3 years; with a 3.5% yearly price rise it has paid for itself in year 7.

What EEG feed-in tariff applies to a German system in 2026?

For surplus export, the Bundesnetzagentur publishes 7.78 ct/kWh up to 10 kWp and 6.73 ct/kWh from 10 to 40 kWp for systems commissioned from 1 February to 31 July 2026, then 7.70 and 6.66 ct/kWh from 1 August to 31 December 2026. The rate stays fixed for 20 years; above 10 kWp it is applied pro rata across the bands.

Which electricity price should I use for Germany?

The tool uses €0.37/kWh, the 2026 household average from BDEW (August 2026). Your contract's price per kWh, without the standing charge, is more accurate, because that is all the battery saves. At €0.32/kWh the saving drops to €656 a year and simple payback rises to 8.8 years.

Which 2025 German rules change the case for a battery?

Since 2023, the battery and its installation carry 0% VAT for systems of 30 kWp or less on a home (§ 12(3) UStG). Under the Solarspitzengesetz, in force since 25 February 2025, new systems below 100 kW export at most 60% of their capacity without a smart meter and control box, and are no longer paid during negative prices from the year after the smart meter is fitted. A battery avoids part of these losses, which the tool does not count.

Is this tool really free?

Yes, all tools on Kristools are 100% free and accessible without registration.

Is my data protected?

Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.