Spare grid capacity on your site: how to find it, and what it's worth

Plenty of industrial, logistics and storage sites hold a grid connection bigger than they now use. With new UK connections taking years, that unused capacity has real value. This guide shows how to measure it and what you need to check before anyone else uses it.

1. Find your agreed capacity

Your Maximum Import Capacity (MIC) is the amount agreed between you and your network operator, measured in kVA^[1]. It's written into your connection agreement, and may also appear in your electricity supply contract as authorised supply capacity (ASC)^[1]. Many suppliers show it on the invoice too, sometimes as a capacity charge^[2].

MIC is a contractual entitlement. It isn't the rating on your transformer's nameplate, which may be higher or lower.

2. Measure your real peak

Ask your supplier or meter operator for at least 12 months of half-hourly data. Networks measure demand against MIC in kVA, every half hour^[3]. Use kVA rather than kWh: reactive power counts towards capacity, and the charging rules calculate it from both active and reactive energy in each half hour^[4].

3. Work out the headroom

Subtract your highest half-hourly demand from your MIC. For example, a 2,000 kVA MIC with a 400 kVA peak leaves 1,600 kVA. That's a screening figure, not a promise. Before relying on it, allow for:

• winter or seasonal peaks the data might not show yet;
• growth you're planning on your own site;
• the new equipment's own loads, such as cooling and power losses, not just its headline rating;
• whether your cables, switchgear, transformer and protection can carry the extra load. An engineer has to confirm this.

For scale: a Hexi pod needs about 930 kVA of spare import for four GPU racks, 1.5 MVA for seven and 1.7 MVA for eight (Hexi engine estimates, including cooling and a 40°C heatwave).

4. Know what it already costs you

You pay for your MIC whether you use it or not. Under SSEN's 2026/27 charges, chargeable import capacity is simply the MIC, priced per kVA per day^[5]. On its HV site-specific tariff, 10.06p per kVA per day, a 1,000 kVA MIC costs about £3,018 a month in capacity charges alone, before energy and other charges^[5]. Your own network area and supplier contract set your actual rate.

Going over your MIC is expensive in a different way. Under London Power Networks' rules, the exceeded amount is charged for the whole billing period, not just the half hour it happened in^[4]. Poor power factor can add a separate reactive charge, triggered when reactive energy goes above 33% of active energy^[4].

5. Think before you give it back

You can ask to reduce your MIC to cut the charge. UK Power Networks issues a new connection agreement, allows one change in any 12 months, and applies it from the following month^[6]. But it warns that the original capacity may not be available again without reinforcement and charges^[4]. If there's any chance you'll use it, or let someone else use it, keep it.

6. Check the rules before anyone else uses it

This is where most of the work is. In Great Britain, supplying or distributing electricity needs a licence or an exemption^[7]. Class exemptions apply automatically if you meet their conditions, without an application, but it's your job to check you qualify^[7]. There are separate exemptions for reselling electricity you buy from a licensed supplier and for private distribution to non-domestic users^[8], and private network operators still have safety and supplier-access duties^[9].

Contracts matter as much as law. Your connection agreement and supply contract still apply, and network operators ask to be told in advance about increased load or equipment that could affect voltage^[1]. A lease alone doesn't transfer your MIC, so take legal and engineering advice on the structure.

Documents to gather

• Your connection offer and connection agreement, with the MIC.
• Recent electricity bills and your MPAN.
• 12 months or more of half-hourly active and reactive demand data.
• Transformer nameplate, test certificates and the latest maintenance records.
• Single-line diagram and drawings of the incoming supply and switchgear.

This is our recommended pack, not a national list, but it's what any engineer will ask for first.

Myths worth clearing up

"The network map shows capacity, so we have it." Headroom maps describe the wider network, and UK Power Networks warns that unused capacity may already be committed to customers^[10]. Your agreement and your meter data are what count.

"Unused capacity will be taken away." The 2023 Connections Action Plan considered asking customers to return unused capacity^[11], and Ofgem is still developing demand reforms such as phased and flexible connections^[12]. As of October 2026 there's no national rule removing existing sites' MIC, but it's a live policy area.

How Hexi works with site owners

A Hexi pod is a factory-built AI compute facility that sits on a prepared base next to an existing supply. The company that owns the GPUs pays for the pod, and you lease the plot and the capacity. If you think your site has spare import, tell us about it or run a free site check.