What is peak shaving, and when does a battery pay off?

A peak shaving battery flattens your consumption peaks. As soon as your offtake from the grid rises above a set limit, the battery supplies the difference. The quarter-hour peak your grid operator measures comes out lower, and in Flanders you pay less capacity tariff. The battery power (kW) follows from how much you want to shave off, the capacity (kWh) from how long and how often those peaks last. Whether it pays off depends on your tariff group: on medium voltage the amounts per kW are larger and the access power also counts. On a small low-voltage connection, peak shaving rarely pays off as the only use. How we size and control this for businesses is on our page about commercial battery systems for peak shaving.

You probably know the situation. A supplier offers a battery "for peak shaving", with a payback that looks good on paper. Your invoice shows a monthly peak, but not which quarter-hour set it. The risk is not the battery. It is sizing it on a guess: too small and it is empty before the real peak, too big and it never earns its cost. This article shows how to check both before you sign.

Why does every quarter-hour count in peak shaving?

Peak shaving means you cap the highest power demand of your installation. In Flanders that matters because of the capacity tariff: you pay per kW of your highest quarter-hour peak per month (Vlaamse Nutsregulator).

The word "quarter-hour" is the key. Fluvius does not charge on instantaneous power, but on the average over 15 minutes (Fluvius). A motor drawing a starting current for 20 seconds barely counts. An oven running at full power for half an hour while the compressors run does. If you want to lower your peak power, you aim at the quarter-hour average, not at every short power spike.

In Wallonia the logic differs. With peak metering, ORES bases two thirds of its capacity term on the eleventh highest quarter-hour of the month (ORES). A battery there has to hold the peak down on more than ten quarter-hours a month, not just on one. On standard low voltage up to 56 kVA there is no capacity term at all, so peak shaving saves nothing on the network tariff there (ORES tariffs 2026).

The amounts per kW and the formulas for low and medium voltage are worked out in our article on calculating the capacity tariff for businesses. The system side is on our commercial battery page.

How does a peak shaving battery system work?

A system has four parts that have to work together:

• An energy meter at the grid connection that measures offtake continuously.
• An inverter/charger that delivers power from the battery or charges it.
• The battery with BMS (battery management system), which protects the cells and reports the state of charge.
• The control (EMS, energy management system), which decides when the battery steps in and when it recharges.

Victron added peak shaving to its ESS control in Venus OS v3.30, for systems with an energy meter. According to Victron, the system watches the current at the meter. When offtake rises above the set limit, the battery steps in. The system also limits battery charging if charging would exceed the limit. The function works with the MultiPlus, Quattro, MultiPlus-II and EasySolar inverter/chargers and needs a recent ESS Assistant, set up by a trained installer.

Two technical points follow. The limit is set as a current (amps), not in kW, while the grid operator charges on a quarter-hour average in kW. Converting your target into a current limit therefore takes knowledge of your profile. And a battery that recharges at full power right after the peak can cause a new peak itself. Recharging has to stay under the limit, preferably with solar power or in the quiet moments of your own profile.

What do the EMS and energy management software do?

Two batteries with identical cells can give completely different results. The difference is in the control:

• Target limit: set too low and the battery is empty before the real peak arrives; too high and you save nothing.
• Reserve: which part of the capacity stays available for peaks, and which part may be used for solar self-consumption? In the Victron ESS settings you set, among other things, a minimum state of charge.
• Recharge strategy: when, and at what power, does the battery charge back?
• Interplay with other loads: charge points, heat pumps or boilers you can limit reduce what the battery has to deliver.

An EMS set-up in a Victron system has two layers. Control happens locally: the GX device with ESS drives the inverters based on the meter. The energy management software above it is for follow-up. We monitor systems through the VRM monitoring platform, where you see consumption per phase, live battery capacity and reports per minute, hour or day (our monitoring). That way you see whether the settings still fit when your profile changes. Do you need one before you buy a battery? Read what an energy management system does for a business.

How do you size a peak shaving battery in kW and kWh?

Size on measured quarter-hour data, never on a rule of thumb. The starting point is a year of quarter-hour values from your grid operator (in Flanders Mijn Fluvius) or your own measurement. Then:

• Choose a realistic target. Look at the spread of your quarter-hour values. Often only a few quarter-hours per month lie far above the rest.
• Power (kW): highest peak minus target, plus a margin for metering inaccuracy and growth.
• Energy (kWh): add up the energy above the target for each peak event. Take the heaviest event, not the average.
• Repetition: if there are several peak events per day, check whether the battery can recharge in between without crossing the limit itself.
• Usable capacity: the control keeps part of the battery in reserve. Size on usable capacity, not on nominal capacity.

What does a peak shaving battery deliver on medium voltage?

This example is illustrative. It uses the 2026 rates of Fluvius Imewo for the 1 to 26 kV grid from the tariff list of the Vlaamse Nutsregulator, in Flanders. The monthly peak costs 54.23 euro per kW per year there, the access power 36.11 euro per kVA per year, both excluding VAT.

Situation. A food company runs a base load of around 400 kW. A few times a week ovens, cooling and a line start-up coincide, and the quarter-hour peak climbs to 520 kW. The access power is set at 540 kVA to avoid excess charges.

Goal. Cap offtake at 430 kW and lower the access power to 450 kVA. Note: access power can only be lowered if the last choice or raise was at least 12 months ago. For simplicity we assume a power factor close to 1, so kW and kVA run roughly equal.

Sizing.

• Power: 520 minus 430 = 90 kW; with margin, an inverter capacity of about 100 kW.
• Energy: the heaviest peak event lasts one hour, on average 60 kW above the limit. That is 60 kWh. With reserve and margin you arrive at roughly 100 kWh of usable capacity.
• Recharging: between peak events offtake is around 400 kW, so there is about 30 kW of room under the limit to recharge.

Effect on the network tariffs (per year, excl. VAT).

That is the saving as long as the battery actually catches the peak every month. One missed quarter-hour costs straight away. On medium voltage an excess over the access power is charged for 12 months, at a rate 50% above the access-power rate (Fluvius). So the reliability of the control weighs more here than a few extra kWh.

When does peak shaving not pay off?

Honest numbers up front prevent a bad investment:

• A small low-voltage connection. In Flanders you save between about 49 and 57 euro per kW of average monthly peak per year in 2026, excluding VAT, depending on your network operator. Shaving off a few kW then brings only a limited amount. In Wallonia, on standard low voltage up to 56 kVA, there is no capacity term to save on.
• Broad, long peaks. If your offtake stays high for hours, you need many kWh for little kW gain. Load shifting or control usually makes more sense.
• Peaks you can avoid for free. Charge points controlled to a target power, or machines that do not have to start together, cost nothing. Fluvius itself stresses that heavy loads such as charge points and heat pumps should be controllable.
• A profile that changes fast. With expansion plans, size on the future profile.

When does a peak shaving battery become the right choice?

The numbers change when the battery has more than one job:

• Solar self-consumption: charging with surplus during the day, discharging later.
• Dynamic energy contract: the same battery charges when the market price is low. Victron has Dynamic ESS for this, which plans charge cycles on day-ahead prices. According to the manual, it works with the import and export limits from the ESS menu, so cheap charging does not become a new peak. We work out that combination in a dynamic energy contract with a battery.
• Backup power: a system designed to run off-grid takes over the critical loads during a power cut. That is the difference between a real energy system and a storage box. The video about a Victron backup system for an airport control tower shows an example.
• Grid congestion: when the grid operator cannot give you a heavier connection, a battery that catches peaks is often the faster answer. For businesses that want to go further, there are semi off-grid systems.