The capacity tariff explained: what your peak power costs and how a battery flattens it
Since 1 January 2023 part of your grid costs in Flanders is charged on the highest quarter-hour power you draw each month, not only on the kilowatt hours you use. That is the capaciteitstarief, or capacity tariff, and it applies to every home with a digital meter. The average household sits around 3.5 to 4 kW; an electric car charger or a heat pump can double that if nothing manages it. This article explains how the peak is measured, what it costs and what actually lowers it.
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What the capacity tariff is
Your electricity bill in Belgium has three parts: the energy itself from your supplier, taxes and levies, and the grid costs paid to the distribution grid operator, which in Flanders is Fluvius. Grid costs used to be charged purely per kWh. Since 2023 the Flemish regulator VREG splits them: a smaller part stays per kWh and a larger part is charged per kilowatt of peak capacity.
The reasoning is that the grid has to be sized for the moment everyone draws the most power at once, not for the average. Someone who spreads consumption over the day loads the grid less than someone who runs the oven, the dryer and a 7.4 kW car charger at 18:00, even if both use the same number of kilowatt hours. Fluvius describes it as a different way of sharing the same costs rather than an extra tariff; for an average household it is roughly 7 percent of the total bill.
How your peak is measured
The digital meter records your average power draw over every quarter of an hour. The highest of those quarter-hour averages in a calendar month is your monthly peak, the maandpiek. Your capacity tariff is then based on the average of your last twelve monthly peaks, so a single bad evening does not wreck a whole year, but it does stay in the average for twelve months.
Two details matter. First, it is a quarter-hour average, not an instantaneous value. A kettle at 2 kW for three minutes adds only about 0.4 kW to that quarter. A car charger at 7.4 kW for the full fifteen minutes adds the full 7.4 kW. Second, Fluvius applies a minimum monthly peak of 2.5 kW to every digital meter. Even a flat that never exceeds 1.5 kW is billed as if it peaked at 2.5 kW; Fluvius calls it a kind of subscription cost for being connected.
If you still have an analogue meter, peaks cannot be measured. You pay a fixed capacity contribution equal to the 2.5 kW minimum and a higher price per kWh instead. Households on the social tariff do not pay the capacity tariff at all.
What a kilowatt costs
The price per kW per year is set by the regulator per grid area and changes yearly. For the Fluvius areas in the province of Antwerp it has been in the region of 40 to 50 euro per kW per year including VAT; the current figure is published on the VREG dashboard and on your supplier's tariff card. The examples below use 45 euro.
A household with an average monthly peak of 4 kW pays about 180 euro a year in capacity costs. A household that charges an electric car at full power every evening and averages 8 kW pays about 360 euro. The difference, 180 euro a year, is the same electricity in both cases; only the timing differs. Shave the peak from 8 kW to 5 kW and you save 135 euro a year without using one kWh less.
What pushes your peak up
A few appliances dominate. Most of the rest of the house, lighting, television, fridge, laptop, together rarely exceeds 1 kW.
- Electric car charger: 7.4 kW on a single-phase connection, 11 kW on three-phase
- Heat pump or air conditioning in heating mode: 1 to 3 kW, more during defrost cycles in winter
- Electric hob with several zones on: 3 to 5 kW
- Oven, dryer, washing machine heating element: 2 to 3 kW each
- Instant electric water heater or electric boiler: 2 to 6 kW
How a battery flattens the peak
A home battery with peak shaving watches your grid draw and discharges whenever you exceed a threshold you set, say 4 kW. If the oven and the dryer together pull 5.5 kW for twenty minutes, the battery supplies 1.5 kW of that and the meter sees 4 kW. On a 5 kW inverter it can cover roughly one appliance's worth of peak on top of the evening load; it cannot absorb an 11 kW charger on its own.
That is why the combination matters. A home battery handles the household peaks, and a smart EV charger with dynamic load management lowers its charging power when the house is busy and charges at full speed after midnight. A car that needs 30 kWh for the next day charges in a little over four hours at 7.4 kW; spreading it over eight hours at 3.7 kW gets the same result with half the peak. Most chargers can also follow your solar surplus during the day, which keeps both the peak and the energy cost down.
You can check your own peaks in Mijn Fluvius under your consumption data, per month and per quarter hour. Look at the hour when your three or four highest peaks occurred: that is usually one appliance, and it is usually movable. Roakus-E uses those same quarter-hour values to size a battery or to set the limits on a charger, so the saving is calculated on your data rather than estimated.
Frequently asked questions
Does the capacity tariff apply if I do not have solar panels?
Yes. It applies to every household and small business on the Flemish grid regardless of production. It is a way of charging grid costs, not a rule about solar power.
Does the day and night tariff still exist?
Not in the grid costs: Fluvius charges the same per kWh and per kW at any hour. Suppliers may still offer day and night or dynamic prices for the energy part, so charging at night can still be cheaper on that part of the bill.
Can I see my peak before the bill arrives?
Yes. Log in to Mijn Fluvius and open your consumption data. The monthly peak and the quarter-hour values are shown with a delay of about a day.