Can a Battery Reduce Your kVA Capacity Charge?

Most businesses looking at battery storage focus on unit rates. The charge that often makes the case, though, is the one that has nothing to do with how much electricity you use: the standing charge for the capacity you have reserved, billed in kVA whether you draw it or not. Power in kW and energy in kWh answer different questions when you size a battery against a peak, as kW vs kWh explains.

Here is how agreed capacity works, when a battery can realistically reduce it, and why giving capacity back deserves more thought than it usually gets.

What agreed capacity actually is

A half-hourly metered site holds an agreed (or authorised) supply capacity with its distribution network operator, expressed in kVA. It is a reservation: the network has to be able to deliver that much power to you at any moment, so you pay a standing charge for it every day of the year.

Two consequences follow. First, capacity you hold and never use is pure cost. Second, capacity you exceed usually attracts excess capacity charges, and repeated excesses can prompt the network to require a formal increase.

The distinction from unit charges matters. Move a kWh from an expensive hour to a cheap one and you save the price difference. Remove the need for 100 kVA of reserved capacity and you save a standing charge every day, whether or not the site was busy.

Why kVA, not kW

Capacity is reserved in kVA — apparent power — rather than kW, because the network has to carry the current your site draws, including the reactive component. Sites with lots of motors, older lighting or poorly corrected power factor draw more kVA for the same useful kW.

That has a practical implication before you buy anything: if your power factor is poor, correction equipment may cut your kVA demand more cheaply than storage. A proposal that never mentions power factor has skipped a cheaper answer.

When a battery can reduce agreed capacity

A battery lowers measured demand by discharging through the site’s peaks. If it does that reliably, the site’s maximum demand falls, and a lower agreed capacity may become viable. Three conditions have to hold.

The peak must be predictable. Peaks driven by a shift pattern or a despatch run are easy to cover. Peaks driven by a process that fires without warning are harder, and sizing must allow for the worst case rather than the typical one.

The battery must cover the whole peak, not the start of it. Power alone is not enough: the system needs the stored energy to hold the reduction for as long as the peak lasts. Our guide to reading your half-hourly data sets out how to measure both.

There must be headroom for failure. A battery under maintenance, or one that has spent its charge on a backup reserve, is not shaving anything that day. If your capacity has been cut to the bone, one outage becomes an excess capacity charge.

The risk nobody mentions: getting it back

Reducing agreed capacity is not a tariff switch. It is a change to your connection agreement, and capacity you release may not be available later — particularly on a constrained network where others are queuing for it. A business that gives up 200 kVA and then wins a contract needing new plant can find itself applying for capacity it used to hold, with a network study and possible reinforcement attached.

So treat it as two separate decisions. Take the peak-shaving saving first, which is yours regardless. Then, once the reduction has proved itself over enough months to cover your seasonal worst case, consider whether to reduce the reservation — weighing your growth plans, and what a G99 connection or capacity increase would involve if you needed it back.

How it stacks with everything else

Capacity savings rarely justify a battery alone. They sit alongside the red-band savings explained in our DUoS charges guide, load shifting and, on suitable sites, grid-services income. What makes the capacity element valuable is its predictability: it does not depend on a market, only on your own demand shape and a battery that performs when it is needed.

For sites where a single afternoon peak sets the capacity for the whole year — common across manufacturing and distribution — that can be the difference between a marginal case and a clear one. Our guide to commercial battery storage in Nottinghamshire works through it for East Midlands manufacturers, where one daily production peak typically sets both the red-band exposure and the capacity charge.

Send your postcode and rough annual spend and the feasibility summary will show what your peak is costing you in both, and what a battery sized to your load would change.

Independent guidance published by SEO Dons Ltd. We are not an installer, an energy supplier or a manufacturer.