A 3000W solar panel generates electricity during the day, often when no one is home to consume it. Without storage, a significant portion of this production goes to the grid.
With the announced decrease in the feed-in tariff for surplus energy (a draft decree examined in April 2026 plans to reduce it from 4 c€/kWh to 1.1 c€/kWh), storing energy in a battery becomes much more profitable than before. The question remains which one to choose, and especially what capacity to aim for.
Falling feed-in tariff: why solar batteries are changing status in 2026
Until recently, selling surplus energy back to the grid was profitable enough that many homeowners could do without a battery. That calculation no longer holds.
The same draft decree also plans to eliminate the self-consumption bonus and stop purchasing surplus during hours of negative spot prices. In other words, selling surplus solar energy no longer even covers the administrative costs of the contract. Storing energy for self-consumption in the evening or at night becomes the only economically logical option.
This does not mean one should rush to buy the largest battery on the market. The PPE3 (multi-year energy programming) directs households towards a self-consumption approach with controllable and scalable storage. The idea is to install the panels, optimize usage, and then add a battery later if the need arises. Knowing which battery to choose for a 3000W solar panel first requires understanding what you actually consume in the evening and at night.
Storage capacity in kWh: the calculation that avoids oversizing
You get home from work at 7 PM, turn on the oven, the washing machine, and the lights. This is when the battery takes over from the panels. The question is not “what is the largest possible battery?”, but “how many kWh do I consume between sunset and the next morning?”.
To find out, check your electricity bills or your Linky meter. Note your average nighttime consumption. For a 3 kWc installation, a storage capacity between 5 and 10 kWh covers the majority of residential uses. Below that, the battery discharges too quickly. Above that, you pay for a capacity that remains unused for a large part of the year.
Depth of discharge: the figure that no one reads
You buy a battery rated at 10 kWh capacity. Can you use all 10 kWh? Not necessarily. The depth of discharge (DoD) indicates the percentage of energy that is actually usable without damaging the battery.
A lithium iron phosphate (LFP) battery generally allows for a very high depth of discharge, whereas a lead battery should not go below half of its capacity for fear of reducing its lifespan. The usable capacity matters more than the nominal capacity displayed.
Lithium LFP vs lead: comparison for a 3 kWc installation
There are plenty of competitors listing all existing technologies. Let’s focus on the two options that are truly relevant for residential use paired with 3000W of panels.
| Criterion | Lithium iron phosphate (LFP) | Lead (gel or AGM) |
|---|---|---|
| Lifetime | Several thousand cycles | Several hundred cycles |
| Depth of discharge | Very high | Limited (about half) |
| Weight | Light | Very heavy |
| Maintenance | None | Regular monitoring |
| Initial price | Higher | More accessible |
| Cost per cycle | Low | High (frequent replacement) |
Lead remains tempting due to its low purchase price. In practice, a LFP battery is cheaper over the total lifespan because it lasts much longer and tolerates repeated deep discharges without degrading.
Lead still has its appeal in a specific case: occasional use, such as an isolated site used a few weeks a year. For a house occupied year-round with 3 kWc panels, lithium LFP is the clear choice.
Install the battery now or prepare for future addition
Should you buy the battery at the same time as the panels? Not necessarily. Experts recommend in 2026 a gradual approach: first install the panels, observe actual production and consumption habits for a few months, then size the battery with informed knowledge.
This strategy avoids two common mistakes:
- Oversizing the battery based on theoretical production estimates, while roof orientation or shading reduces actual yield
- Buying technology that evolves quickly, while storage prices are regularly decreasing and new models appear every year
- Losing your feed-in tariff contract (OA), which does not happen if the power and operating mode remain unchanged when adding the battery
Subsequently adding a battery does not jeopardize an existing OA contract, as long as the power of the installation is not modified. A rarely mentioned point that reassures those who hesitate.
Smart control before physical storage
Even before investing in a battery, some professionals recommend maximizing self-consumption through control. Programming the water heater, washing machine, or electric vehicle charging during midday, when solar production is at its peak, allows for absorbing a significant portion of the surplus without any additional equipment.
Once this control is in place, the battery only stores the residual surplus. The result: a smaller battery is sufficient, and the investment becomes profitable more quickly.
Choosing a battery for a 3000W solar panel ultimately comes down to three concrete decisions: measure your actual nighttime consumption, opt for lithium LFP unless in a specific case, and not rush if the control of devices has not yet been implemented. The decrease in the feed-in tariff makes storage relevant, but well-sized storage is always more profitable than oversized storage.