How many solar panels do I need?

The usual way this question gets answered is by bedroom count, which is a proxy for consumption used by people who do not have your bill. You do have your bill.

So start there: annual kWh, from a bill or a smart meter. Everything else follows from it, your location and which way the roof faces.

One warning before the numbers, because it is the thing this calculator is most likely to be misread on. A system that generates as much as you use in a year does not cover your bill. Generation is daytime and summer-weighted; consumption is evening and winter-weighted. Without storage, self-consumption for a typical household runs at 14% to 23%, and the rest is exported at a fraction of what you pay to buy it back.

How this works

Generation comes from our own PVGIS modelling at 20% system losses, for 25 UK reference locations, five pitches and five orientations — the same dataset behind generation by region and our other calculators.

Cost comes from the Department for Energy Security and Net Zero’s Solar photovoltaic (PV) cost data, which is derived from the MCS Installation Database. It is a national median for the relevant size band, not a quote.

Panel count rounds up to whole panels, because you cannot buy two thirds of one.

What we could not establish

Your roof’s usable area. The calculator tells you how much you need; only a survey tells you how much you have, once edge clearances, vents, windows and shading are taken off.

Your self-consumption. The warnings quote MCS’s archetypes, which are averages for groups of similar households.

Whether your inverter will be sized to the array. A larger array behind a smaller inverter is a legitimate design — see the 3.5 kW page.

This is information, not advice

A sizing figure from a web page is a starting point for a conversation with an installer who has stood on your roof, not a substitute for one.