Your agreed supply capacity is the maximum demand your electricity connection is set up for, measured in kVA. To see how much room you have, convert your busiest half hours from kW to kVA (divide by the power factor) and compare them with the agreed capacity. The gap is your headroom for new equipment such as heat pumps and EV chargers.
What agreed supply capacity is
Larger electricity supplies have an agreed capacity, sometimes called authorised or available capacity. It's set in the connection agreement and usually shown on the bill in kVA. You normally pay a daily charge for it whether you use it or not. If you go over it you may face extra charges, and the network operator may ask you to increase it.
kW and kVA
Meters measure energy in kWh. Half-hourly data gives the average power in each half hour, in kW. Capacity is set in kVA, which also includes reactive power: power drawn by equipment such as motors that doesn't do useful work. The two are linked by the power factor:
Working out headroom
- Find your busiest half hours over at least a year, so winter peaks are included.
- Convert them to kVA using your power factor.
- Keep a safety margin, for example 10%, below the agreed capacity.
- Your headroom is the largest constant extra load you could add without going over that margin in any half hour.
Half-hourly readings are averages, so they smooth out very short spikes. Treat this as an early check, and confirm with your network operator before relying on it.
Heat pumps and EV charging
A heat pump uses much less electricity than the heat it produces. With a coefficient of performance (COP) of 3, a heat pump producing 150 kW of heat draws about 50 kW of electricity. It works hardest in winter, which is usually when a building's peaks are highest, so the two add together. EV charging is different: if it happens overnight, it falls when most sites are quietest. The analyser lets you test a new load at a chosen time of day and season against your actual half-hourly peaks.
Solar panels and your connection
Solar can reduce the electricity you draw from the grid during the day, but any output you don't use is exported through the same connection. The UK Solar Calculator has a guide to planning and grid connections, and the analyser's Capacity tab estimates how much of a system's output your site would use itself. See sizing solar from half-hourly data.
Questions people ask
Where do I find my agreed supply capacity?
On your electricity bill or connection agreement, in kVA. Your supplier can confirm it.
What power factor should I use?
If you don't know it, 0.95 is a reasonable starting assumption. It's probably lower if your bill shows reactive power charges.
Is half-hourly data enough to plan a new connection?
It's a good first check, but half-hour averages hide very short peaks. For a significant new load, speak to your network operator before committing.
