Solar Batteries: Is It Worth Storing Energy for Use at Night?

Have you noticed that your solar panels produce the most energy precisely when you’re away from home or in the middle of the afternoon, when no one is cooking or turning on the air conditioner? That’s where solar batteries come in: they store that excess energy so you can use it at night, instead of “giving it away” to the grid for very little money. But is the extra investment worth it? Let’s look at some real numbers.

What a Solar Battery Actually Does

A battery-less photovoltaic system only saves you money while the sun is shining and you’re consuming electricity at the same time. Otherwise, the surplus goes into the power grid, typically paid at a price well below what you pay when you buy energy back at night. Solar batteries solve exactly this mismatch: they store what’s left over during the day for you to use hours later, without relying on the sun or the grid.

In practice, this changes your “self-consumption” (the portion of your solar production that you consume yourself) and your “autonomy” (the portion of your total consumption that no longer comes from the grid). Without a battery, a home or business can typically self-consume 30% to 40% of the energy it produces. With a properly sized battery, this figure often rises to 70% or more, because you no longer lose the surplus generated in the afternoon.

It’s also worth noting that a solar battery doesn’t replace the panels—it complements them. If your solar production is already low (few panels, a partially shaded roof, or an unfavorable orientation), the battery has less surplus to store, and it takes longer to see a return on investment. Ideally, you should size both together, based on your actual consumption profile.

How it works in practice, step by step

1. During the day: the panels produce more than you consume. The surplus charges the battery instead of feeding into the grid.
2. In the late afternoon and at night: when consumption rises (dinner, lighting, appliances) and the sun is no longer producing power, the battery discharges to power the home.
3. If the battery is full: only then does the extra surplus flow into the grid, just as it did before the battery was installed.
4. In the event of a grid outage: systems with a backup function (such as the Sigenergy SigenStor) automatically switch to the battery, keeping essential loads powered.
5. Whenever you need to charge your electric car: some “all-in-one” (5-in-1) inverters already integrate battery management with the charger, optimizing when to use stored solar energy or grid power.

What battery size to choose

1. Look at your actual nighttime consumption: add up what you use after sunset. Dinner, lighting, TV, laundry and dishwasher, and charging your car. That’s the amount the battery needs to cover.
2. Don’t overdo the capacity: a battery larger than your daily surplus of solar energy will never fully charge, and you’ll be paying for capacity you don’t use.
3. Think in terms of modules, not a fixed size: most current systems (such as the Sigenergy SigenStor) are modular. You start with one module and add more later if your consumption increases.
4. Check the inverter’s compatibility: if you already have panels installed, the inverter may not support a battery directly, requiring a hybrid inverter or an additional system.

How much does it cost, and what’s the return?

The cost of a battery depends mainly on its capacity (kWh) and the brand/technology. As a market benchmark for 2026, a lithium battery module of about 9 to 10 kWh costs, around €3,000 plus VAT for the equipment alone, plus installation, an electrical panel, and a compatible inverter (in “all-in-one” systems, the inverter is already configured for the battery).

The payback period for a system with a battery is usually longer than for a system with just panels, but the calculation must include the additional savings from self-consumption, not just the investment. Equipment such as the Sigenergy inverter typically comes with a 10-year warranty, and the lithium battery retains a significant portion of its capacity after a decade of daily use, so the investment is designed to last. See the real-world example below to see how this translates into concrete numbers.

With or without a battery: what changes

Is it worth it for you? Support options to consider

A subsidy from the Environmental Fund for self-consumption has been announced—though the details are still to be finalized—and is expected to cover storage as well; we’ve already written about the subsidies planned for fall 2026. If you don’t yet have a photovoltaic system, it makes the most sense to design the project with a battery in mind right from the start (even if you install it later), so you won’t have to redo the electrical panel and inverter later on. If you already have panels, your existing inverter may or may not be compatible. It’s worth conducting a technical study before making a decision.

Conclusion

A solar battery isn’t required to save money with solar power, but it’s what separates “saving well” from “saving as much as possible.” If you use a lot of power at night (dinner, shower, charging your car), if your area experiences occasional power outages, or if you simply want to rely as little as possible on the grid, the investment tends to pay for itself within a few years, as shown in the example above.