Does a home battery lower your capacity tariff?

Yes, a home battery lowers your capacity tariff when it is set up for it. It needs enough power to cover the gap above your limit and a reserve that is there on a cold evening. It also needs control that watches the whole house, heat pump and charger included. A battery that only stores solar power for later does part of the job by chance. In an all-electric house, chance is not enough.

You did what everyone recommended. Heat pump, induction hob, maybe an electric car on the drive. Then the capacity tariff arrived and it felt like a trap. "First push everyone to do everything electric, and then come with the capacity tariff," one Flemish owner wrote (translated). Another spent thirty days spreading every appliance by the book. Then one quarter-hour with the dryer, the washing machine, the pasta on the hob and the heat pump starting at once. "And you pay for all 30 days, not for that quarter-hour" (translated).

The obvious fix is a home battery. It is half right. Most home batteries are chosen in kWh, for the solar panels, while the capacity tariff is counted in kW. A battery that gives 2.5 kW cannot hide a 9 kW evening. And on a grey January day there is little sun to fill it. Then the heat pump, the oven and the car all ask for power after dark.

A site in Hamme shows the other approach. Nobody is there during the day and most power is used in the evening. A three-phase battery with back-up of 9 kVA and 30.8 kWh stores the daytime sun for those evening hours, the electric car included.

How does the capacity tariff work in an all-electric house?

In Flanders you pay part of the grid costs on your highest quarter-hour of each month, averaged over the last twelve months. Everyone pays at least 2.5 kW, and only what you take from the grid counts.

The digital meter measures your average power over every 15 minutes. The highest quarter-hour of the month is your monthly peak. The Flemish regulator (Vlaamse Nutsregulator) puts the 2026 average at about 53.39 euro per kW per year, excluding VAT. The exact rate differs per grid operator. The average household peak in Flanders is 4.24 kW. According to Fluvius, about 4 in 5 customers are above the 2.5 kW minimum.

An all-electric house lives above that average. Fluvius names electric cars and large heat generators such as heat pumps as the heaviest loads. Dryers, dishwashers, washing machines, hobs and ovens come second. The time of day does not matter: a peak at three in the morning costs the same as one at six in the evening. Solar power you inject does not count.

Fluvius also points out the other side. Households with an electric car or a heat pump can pay less in grid costs than under the old system, if they spread their use. How the same rules work for a company is in our guide to calculating the capacity tariff.

When does a home battery actually lower your peak?

When the battery delivers power at the moment the house asks for more than your limit. The Flemish government gives a simple example: a 2.5 kW battery covers part of a 4.6 kW demand, and the grid sees only 2.1 kW.

An independent practical test by Energent (2024) followed 19 home batteries in Ghent and data from 518 more. With a 2.5 kW battery, a reserve of about 0.5 kWh was usually enough to lower the peak by at least 1 to 2.5 kW. The same study found that a battery on self-use already flattens many peaks. But for the capacity tariff it is enough that self-use fails once in a month. That is why the researchers still advise targeted peak control.

On a Victron system this is part of ESS. With an energy meter at the grid connection, you set import and export current limits for the complete system (Venus OS v3.30 and later). Victron names heat pumps and EV chargers explicitly: they count even when they are not on the battery output. When the house goes over the limit, the battery assists; when the battery is low, charging from the grid is held under the same limit.

Why does a battery sized for solar often miss the winter peak?

Because in winter the heat pump runs most while the solar panels give least. The battery that was full every summer evening can be empty by five in the afternoon in January.

One owner wrote that his 3.5 kWp installation gives him 1 to 2 kWh a day in winter. That barely covers the fridge and the router, let alone a heat pump. So the evening peak lands on the grid: heating, cooking and often the car, all after dark. Those winter months are part of your twelve-month average. Three winter months without a working battery can undo a summer of flat peaks.

The fix is not a bigger battery for its own sake. It is a reserve that the system protects, topped up at a quiet hour when needed. Victron ESS can charge from the grid in up to five scheduled windows, and stops at the state of charge you set. With a peak limit active, that charging itself stays under the limit. How far a battery carries the heat pump through a winter day is covered in heat pump and home battery.

How do you set up a home battery for the capacity tariff?

Measure first, then set a limit, a reserve and the order of the heavy loads. The battery is one tool; the heat pump and the charger must play along.

Fluvius gives the same advice for heavy loads: choose devices that can be controlled, so they adjust to the rest of the house. For business sites, the same technique is explained in peak shaving with a battery.

How much does a lower peak save, honestly?

Each kW off your twelve-month average saves about 53 euro a year in Flanders (2026 average, excl. VAT). The saving grows with the size of the step you remove.

Take an all-electric house whose monthly peaks average 9 kW. Brought back to 5 kW, that is 4 kW less, or about 214 euro a year excl. VAT. It is real money, earned every year. But it will not justify a large battery on its own.

The Energent test came to the same conclusion for small batteries of 5 to 15 kWh with 2.5 kW of power. Reserving part of the battery for peaks cost about as much self-use as it saved on the capacity tariff. In their words, the capacity tariff is currently too low for peak control to add much.

What real back-up needs, from a few circuits to the whole house, is in home battery with backup power. For three-phase houses, read three-phase home battery for full back-up.

Is it different in Wallonia and Brussels?

Yes. In 2026 a standard household in Wallonia or Brussels does not pay on a measured monthly peak. A battery then works through the time of use, not the peak.

In Wallonia the IMPACT tariff splits the day into bands, with the peak band from 17:00 to 22:00. A battery that stores the midday sun and delivers it in the evening fits that logic. In Brussels, Brugel plans a capacity tariff per kVA of power made available from 1 January 2028, set in the smart meter. That is a draft decision of 25 March 2026, so details may still change. The same regional rules for companies are in grid tariffs in Wallonia and Brussels.

Does a bigger battery or a plug-in battery help more?

For the peak, power counts more than storage. Extra kWh only help when the peak lasts long or the battery must last a whole winter evening.

The Flemish government notes that plug-in batteries usually have less storage and less power than fixed home batteries. What else a plug-in cannot do is in plug-in battery or installed home battery.

How do we set up a home battery for peaks and back-up?

We measure before we choose, and we set the peak limit, the reserve and the back-up together. Our team has three certified battery specialists, and we connect almost all types of solar inverter to a home battery.

In Kontich the customer has an electric car and plenty of solar panels. With the digital meter, the surplus no longer ran the meter backwards, so the battery keeps as much solar power as possible in the house.

1. Step 1: We look at your consumption, your monthly peaks and your plans: heat pump, car, pool or sauna.
2. Step 2: We choose the inverter power and storage, and agree on a peak limit, a reserve and the back-up circuits.
3. Step 3: We install and set the system, with a meter that sees the heat pump and the charger too.
4. Step 4: You follow production, consumption and the battery in the free VRM app and portal, and we adjust the limit when your house changes.