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Which solar battery capacity should you choose? The answer by profile
5, 10 or 15 kWh? The question may sound technical, but it isn't: the right battery capacity depends on one thing alone — what your home consumes between your evening return and sunrise. Here is the method to find out in five minutes using a bill, along with typical profiles and the two costly mistakes to avoid.
The principle in one sentence
The battery is a reservoir: it fills with the day's surplus and empties to cover your evening and nighttime consumption. The right size is therefore the size of your night, not the size of your roof or your budget. If it is too small, it is full at 2 p.m. and the rest of your solar energy is sent to the grid for 1 cent per kWh. If it is too large, you have paid for storage capacity that is never filled. In both cases, efficiency is lost — and this can be avoided.
The 5-minute method: estimate your “night”
Take your annual consumption in kWh (shown on your bill) and divide it by 365: this gives you your average daily consumption. For a typical household, half to two-thirds of this consumption takes place between 5 p.m. and 8 a.m. — the period the battery needs to cover. Two examples:
A household using 4,500 kWh/year consumes around 12 kWh per day, including 6 to 8 kWh in the evening and at night: a 5 kWh battery covers most of it. A household using 9,000 kWh/year consumes around 25 kWh/day, including 13 to 16 kWh in the evening: this is where 10 kWh comes in, or even 15 kWh if an electric vehicle is added. If you already have solar panels, your monitoring app provides these figures precisely — check how much energy you import from the grid between 6 p.m. and midnight.
Quick reference: usable capacity ≈ your consumption between sunset and sunrise. There is no need to cover 100% of the night — aiming for 80% almost always delivers the best investment-to-savings ratio.
The 5 typical profiles
| Your profile | Typical annual consumption | Recommended capacity | What this changes |
|---|---|---|---|
| Couple, away during the day, apartment or small house | 3,000 – 5,000 kWh | 5 kWh | Evening covered: cooking, TV, internet box, dishwasher running at night |
| Family, main home, daily household appliances | 5,000 – 8,000 kWh | 10 kWh | Evening + night + early morning: the most common profile |
| Family + working from home (present during the day) | 6,000 – 9,000 kWh | 5 to 10 kWh | Being present during the day already means plenty of natural self-consumption: the battery can remain modest |
| Large house, electric heating or hot water | 9,000 – 13,000 kWh | 10 to 15 kWh | A large evening load to cover, with strong storage profitability |
| House + electric vehicle charged in the evening | 10,000 kWh and more | 15 kWh | The car absorbs the evening storage: the reasonable upper limit is fully justified |
You will notice the upper limit: we recommend staying at 15 kWh or less — beyond this, regulations require modifications that increase the budget without a proportional benefit for a household, and our configurations comply with this threshold by default. One reassuring detail: the “working from home” profile shows that bigger is not always better — being present during the day does part of the battery's work for free.
The two classic mistakes (and how to avoid them)
Mistake no. 1: sizing based on production rather than consumption. “I have 6 kWp, so I need a large battery” — no. If your evening consumption is only 6 kWh, a 15 kWh battery will rarely fill beyond half its capacity. Production determines the filling speed, not the usable size of the reservoir.
Mistake no. 2: buying the size you might need in five years. An electric vehicle planned “one day”, a heat pump “maybe”: oversizing today for hypothetical uses means tying up thousands of euros in equipment that produces nothing. There is an elegant solution: choose a modular system — our batteries can be expanded by stacking modules, without replacing anything. Buy what you need today and add a module when the car arrives. This is also the answer if you are hesitating between two sizes: choose the smaller one; the option remains open.
What this changes in euros: a typical example
Let's return to the family household with 6 kWp in the south (the detailed case in our solar profitability guide). Without a battery, 45% of its production is self-consumed; with a properly sized 10 kWh battery, 75%. The difference: around €460 in additional savings per year. A 15 kWh battery for the same household would provide only €30 to €60 more per year — for an additional investment of €1,500 to €2,500. This example sums up the entire logic of this guide: proper sizing delivers better returns than simply choosing a larger system.
Your bill already tells you which battery you need
An expert reviews your actual consumption, calculates your “night” and tells you the right capacity — even if it is the smallest option, or none at all. Free, with no commitment.
Choose my time slot → Or call our experts directly: 04 49 42 00 98Frequently asked questions
Which battery is suitable for a family of 4?
Most often 10 kWh: this capacity covers the evening, night and early morning for a family household using around 6,000–8,000 kWh/year. However, two families of 4 may have very different evening consumption — your bill is a better guide than the size of your household.
Is one 10 kWh battery better than two 5 kWh batteries?
With equal capacity, the main question is scalability: a modular system (with stackable modules) lets you start at 5 and increase to 10 or 15 without discarding anything. This is the architecture we favour — the details of the different formats are in our complete battery guide.
Is a 5 kWh battery too small to be useful?
Not at all: for a moderate household that is away during the day, 5 kWh captures most of the surplus and covers the evening — it is often the best euro invested in the entire installation. “Too small” only exists in relation to your consumption, not in absolute terms.
Can I expand my battery later?
With a modular system, yes: modules can be added without replacing the existing equipment. This is the deciding argument when you are hesitating between two sizes, or when an electric vehicle is being considered but is not certain — start with the right size and expand when the time comes.
Why not exceed 15 kWh?
Beyond this threshold, French regulations require specific installation modifications that significantly increase the budget, for only a marginal benefit in residential use. Our configurations remain below this limit by default — there is nothing for you to check.
Consumption breakdowns and savings are approximate figures for a typical household in mainland France (based on EDF Tarif Bleu for the first half of 2026, €0.1940/kWh incl. VAT; surplus €0.011/kWh). Your actual profile may differ from these averages — that is precisely the purpose of the free assessment. Article updated in July 2026.
