Using battery storage to beat a grid-connection constraint

The problem: your meter is full but your business is growing

A growing number of UK sites hit the same wall. The electrical demand of the business has crept up to the limit of the agreed import capacity on the meter, and now there is a project on the table that needs more power: a bank of EV chargers for the fleet, a new production line, a heat pump, an extra shift, or a compressor that draws hard on start-up. The half-hourly data shows the site already brushing its ceiling at the daily peak, and the obvious answer from the Distribution Network Operator (DNO) is a connection upgrade.

That upgrade is rarely cheap. Reinforcing a connection can mean a new transformer, fresh cabling back to the substation, and in some cases works on the wider network. Quotes commonly run into five and six figures, and the lead time can stretch to a year or more. For many businesses the cost and the wait are enough to shelve the project entirely.

A behind-the-meter battery offers a different route. Rather than buying a bigger pipe, you store energy on site and use it to cover the peaks. The connection stays the same size; the battery does the heavy lifting at the moments that would otherwise breach it.

How a battery raises your usable demand without raising your connection

Your agreed import capacity is the maximum power, in kVA, that you are contracted to draw from the grid at any instant. It is a power limit, not an energy limit. A battery sits on your side of the meter and discharges to meet load locally, so the grid only ever sees the difference between what the site is using and what the battery is supplying.

In practice that means the site can run at a demand higher than its import capacity for the duration the battery can sustain. A 250 kW / 500 kWh system is a two-hour battery: it can deliver 250 kW for two hours before it needs recharging. If your peak demand spike is shorter than that window, the battery shaves the top off the curve and the grid never sees a breach.

The discipline here is matching the battery’s power and energy to the shape of your peaks, not just their height. A battery is sized by power (kW) and by energy (kWh) separately. A short, sharp morning peak needs power; a long afternoon plateau needs energy. Start from your own half-hourly meter data: the peak-shaving calculator on this site applies the published charge bands to it. This is the same engineering that underpins peak-shaving, where the battery cuts red-band DUoS charges, available-capacity (kVA) charges, and peak unit rates of 25-45p/kWh by flattening the demand profile.

A worked picture

Say a site has 300 kVA of import capacity and runs comfortably at 220 kW for most of the day, but a new 60 kW EV charger bank would push the afternoon peak to roughly 340 kW for about an hour and a half. That breaches the connection. A battery rated to deliver the surplus over that window discharges to cover the gap, the metered draw stays under 300 kW, and the chargers go in. No reinforcement, no new transformer, no twelve-month wait.

What this unlocks

The constraint is usually the thing standing between a site and a specific investment. Removing it tends to unlock more than one project.

• EV charging. Fleet depots and customer car parks are the most common trigger. A battery lets you energise EV charging without an upgrade, and it can charge overnight on cheap power ready for the daytime demand.
• New plant and process load. An extra machine, a larger oven, a second compressor, or an additional shift can be supported off the battery during peaks rather than requiring a heavier connection.
• Electrification of heat. Replacing gas with heat pumps adds electrical demand precisely when many sites are already near their limit.

In every case the battery is not just defending the connection. It is also stacking the value streams that make commercial storage worth its cost: arbitrage, peak-shaving, solar self-consumption uplift, resilience, and grid-flexibility revenue. The grid-constraint saving is one stream among several, which is what keeps the economics honest.

The grid-connection mechanics: G99, export limitation and ANM

A commercial battery is a connected generating asset, so it needs DNO sign-off. Most systems go through a G99 application; only the very smallest qualify for the lighter G98 route. The G99 process can take a long time depending on the network area and the available headroom, so it is the first thing to submit, not the last. Our G99 application page explains the steps.

Two outcomes are worth understanding because they shape the design:

• Export limitation. Where the local network has little spare capacity to accept export, the DNO may permit the battery to connect on the condition that it does not export beyond a set limit, sometimes zero. For a behind-the-meter battery whose job is to cover your own peaks, that is usually no obstacle at all. The value is in displacing import, not selling power back. The system is configured to charge from the grid or from on-site solar and to discharge only into your own load.
• Active Network Management (ANM). On constrained parts of the network the DNO may offer a managed connection under ANM, where the asset’s output can be curtailed dynamically in response to network conditions. This can deliver a connection far faster and more cheaply than a firm reinforcement, with the trade-off that availability is not guaranteed at all times. For a peak-shaving battery this is often an acceptable compromise; for a site relying on the battery for backup power and resilience, the design has to account for any curtailment.

The system is designed to the IET Code of Practice for Electrical Energy Storage Systems and built to BS EN/IEC 62933 and IEC 62619, with fire, thermal, detection and separation design considered from the outset, CDM 2015 applied to the works, and your insurer engaged before energisation. None of this is optional, and it is where a properly accredited installer earns its place.

Honest limits

A battery is not a licence to ignore your connection. If your demand is high for many hours at a stretch rather than peaking briefly, the energy you would need to store becomes large and expensive, and at some point a connection upgrade is genuinely the cheaper answer. The battery works best where the problem is the height and shortness of the peaks, not a sustained, all-day step-change in baseload.

There are also cases where the constraint is on export rather than import, which is a different problem. If you are pairing storage with a large solar array and want to export surplus, an export-limited connection may cap what you can sell, and solar battery storage is then about raising the share of your own generation used on site rather than chasing export revenue.

We will say so if the numbers do not stack up. There is no point installing a battery to dodge a reinforcement if the reinforcement is the right engineering and financial decision.

What it costs and where to start

Commercial battery storage runs from roughly £200-450 per kWh at commercial scale, falling to £140-240 per kWh for larger containerised systems, with whole-project costs from around £45,000 for a 100-150 kWh system up to £450,000 and beyond at 1 MWh. The full cost is recoverable against profits through the Annual Investment Allowance, and the 20% VAT is recoverable in full by any VAT-registered business. The detail is on our cost page.

The honest way to know whether a battery beats your constraint is to test it against your real load. Sizing starts from twelve months of half-hourly meter data: match the battery to the shape of your peaks, check that it keeps you inside your import capacity through the new load, and compare that with the cost of a connection upgrade. The peak shaving calculator applies the published network charge bands to your own figures. There is no charge and no obligation. Send us your details and we reply by email.

Related reading

• constrained connections across Oxfordshire
• Northamptonshire distribution sites
• retrofitting storage to existing solar

The operator that quotes for any reinforcement is the one for your licence area. If you are not sure which that is, here is how to find your DNO from your MPAN.