Solar panels with a battery: the price not to exceed
A battery stores midday surplus for the evening. What it earns, calculated hour by hour, and the price above which it costs more than it brings in.
A home battery charges with the power your panels produce in excess during the day and releases it in the evening, when they stop producing. Every kWh shifted this way saves you a purchase at your kWh price, but also means you no longer sell it: since 5 June 2026, with exports earning only 1.1 c€, nearly all of the avoided kWh price becomes gain. Our hour-by-hour simulation over a full year, using Enedis load profiles and 95 % efficiency on both charge and discharge, shows that a 5 kWh battery lets a Paris household using 4,500 kWh with 3 kWp of panels consume 1,058 kWh more a year, a gain of €200. Over twenty years it only pays off if it costs less than €3,952. With 6 kWp, which leaves more surplus to store, that ceiling rises to €5,017. Compare this ceiling with the quote: it tells you whether the battery is justified.
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.
Checked by Radif Partners · Editorial policy · Method and sources
Break-even price by household usage
No public body publishes an average price for home batteries, and prices vary widely with the chemistry and the inverter. Rather than invent one, we calculate the amount above which the battery does not pay back over twenty years: the sum, over twenty years, of the extra kWh it lets you use, valued at your kWh price, minus the export income lost.
| Household usage | 2.5 kWh | 5 kWh | 10 kWh |
|---|---|---|---|
| 3,000 kWh/yr | €2,543 | €3,794 | €4,174 |
| 4,500 kWh/yr | €2,373 | €3,952 | €4,786 |
| 8,000 kWh/yr | €1,573 | €2,714 | €3,347 |
| Household usage | 2.5 kWh | 5 kWh | 10 kWh |
|---|---|---|---|
| 3,000 kWh/yr | €2,844 | €4,314 | €5,016 |
| 4,500 kWh/yr | €2,763 | €5,017 | €6,468 |
| 8,000 kWh/yr | €2,536 | €4,843 | €7,967 |
The more power the household uses in the evening, the more usefully the battery fills and empties. The larger the system, the more surplus there is to store. But beyond a few kWh, each extra kWh of capacity is useful on fewer and fewer days of the year.
How much of your output will you use yourself?
Self-consumption rate
46 %
| Used on site | 1,620 kWh |
| Exported to the grid | 1,909 kWh |
| Share of the bill covered | 36 % |
| Saving in year 1 | €324 |
Median French output (1,185 kWh/kWp), roof at 30° due south, hour-by-hour calculation.
What a 5 kWh battery changes in Paris
For 3 kWp and a household using 4,500 kWh in Paris, the share of output used on site rises from 47 % to 78 %, and the share of the bill covered from 36 % to 59 %. The year-1 gain grows by €200. It is real, but the battery’s price decides: compare it with the ceiling in the table.
How the calculation works
For every hour of 2023, a reference city’s PVGIS output is compared with a typical household’s consumption (profiles published by Enedis). When output exceeds consumption, the excess charges the battery up to its capacity; when it falls short, the battery discharges, with 95 % efficiency each way. The battery is assumed to charge or discharge half its capacity in an hour. The result counts neither cell ageing nor a possible replacement along the way.
To go further, the self-consumption page explains other ways to use more of your output, often cheaper than a battery, and the calculator accepts any capacity.
A battery does not always protect against power cuts
For safety, a grid-connected system shuts down when the grid goes down, battery included, so as not to send power onto a line under repair. Only systems with a backup function and a dedicated circuit keep a few appliances running. If that is what you want, ask for it explicitly on the quote: it is different equipment, at a different price.