The capacity tariff is one of the most misunderstood-and often most costly-parts of a Belgian SME electricity bill. Unlike the energy component, which tracks how much you consume (kWh), the capacity tariff charges you for how much power you draw at once (kW). In Belgium, that charge is driven by your highest 15-minute average demand in the billing period. One short spike can set your charge for the entire month. This guide explains how it works, how it differs by region, and how to reduce avoidable costs.
What is the capacity tariff in Belgium?
The capacity tariff (capactarief, tarif de capacité) is a component of your electricity bill that reflects the cost of maintaining grid capacity for your peak power demand. Your distribution system operator (DSO)-Fluvius in Flanders, ORES or Resa in Wallonia, Sibelga in Brussels-measures your power draw every 15 minutes. The highest average kW in any single 15-minute interval during the month becomes your monthly peak. That peak is multiplied by a €/kW rate to determine your capacity charge.
The logic is simple: the grid must be sized to handle your maximum draw. If you occasionally spike to 100 kW, the grid infrastructure must support that. The capacity tariff passes that cost to you.
How 15-minute peaks work
Digital meters record your power draw in 15-minute intervals. Each interval produces an average kW value. At the end of the month, your DSO takes the highest of those values-that is your monthly peak. It does not matter if that peak lasted one interval or many; one spike is enough to set the charge.
This is why "we didn't use more energy" does not explain a higher bill. Your total kWh can stay the same while your peak rises. Several heavy loads starting in the same 15-minute window-HVAC, compressors, process lines, EV charging-can create a new peak. For more detail on what drives peaks, see our guide on capacity tariff monthly peak rules. capacity tariff monthly peak rules.
Regional differences: Fluvius, ORES, Sibelga, Resa
The logic of the capacity tariff (15-minute peak) is consistent across Belgium. The DSOs differ in tariff structure, rates, and invoice labels.
Fluvius (Flanders)
Covers Flanders. Publishes its own tariff and portal (mijn.fluvius.be) for interval data. Look for terms like capactarief or piek on the invoice.
ORES / Resa (Wallonia)
Cover Wallonia. Each has its own tariff structure and portal. Invoice labels may differ from Fluvius.
Sibelga (Brussels)
Covers Brussels. Same 15-minute peak logic; different tariff rates and invoice layout.
If you have sites in multiple regions, keep a short note per DSO: where to find the peak on the invoice, how to request the 15-minute curve, and whom to contact for meter issues. For a deeper look at Fluvius specifically, read our Fluvius capacity tariff guide. Fluvius capacity tariff guide.
How the capacity line appears on your invoice
Capacity and distribution charges are usually in a separate section or table. Look for terms like "capactarief", "piek", "puissance souscrite", "distribution", or "netbeheer". The capacity component is often expressed as a €/kW or €/kVA rate applied to your measured peak. If your peak goes up by 10 kW, the extra cost is that delta times the tariff.
If the stated peak seems wrong-far above what your site could physically draw-check the billing period and EAN first. Then request the 15-minute interval curve from your DSO and use it as evidence in a dispute. Our electricity bill audit checklist helps you verify capacity and other line items systematically. electricity bill audit checklist.
How to reduce capacity tariff costs
The main lever is reducing peak concentration. Stagger heavy loads so they do not overlap in the same 15-minute window. Map your top startup windows (first hour, post-break, end-of-day) where equipment overlaps. Define a simple stagger rule: no more than two major loads in the same 15-minute window unless operationally required. Use 10–20 minute offsets for flexible systems like EV charging, ventilation, and hot water.
For a step-by-step playbook, see our guide on how to reduce peak demand charges. For real-world examples of how peaks translate to costs, read our capacity tariff examples for SMEs. how to reduce peak demand charges. capacity tariff examples for SMEs.
Indexation and contract terms
Capacity tariff rates can change with indexation. If your contract is variable, the €/kW rate may be adjusted periodically. Our electricity contract indexation guide explains how to validate indexation logic on supplier invoices. electricity contract indexation guide.
Tools and next steps
Use our free capacity tariff calculator to estimate your annual and monthly capacity-related costs by region, peak kW, and billing period. Combine that with operational controls and regular invoice checks to keep capacity costs under control. capacity tariff calculator.
Key takeaway
The capacity tariff charges you for your highest 15-minute peak, not total consumption. One spike can set your charge for the month. Stagger heavy loads, verify peaks on invoices, and use the calculator to estimate costs. Combine operational controls with regular invoice checks to keep capacity costs under control.