How Many Panels Do I Need

Most UK homes with an annual electricity use of around 3,700 kWh are well-served by a 10–12 panel, 4kWp system. But the right number for your property depends on how much you consume, when you consume it, and how much usable roof space you have.

Start with your energy bill

Your annual electricity consumption in kWh is the starting point. The UK average is around 3,700 kWh per year. If you have an EV or are planning to get one, add roughly 2,000–3,000 kWh for typical annual driving. Electric heating or a heat pump raises the figure further.

Rule of thumb for sizing

A 1kWp system generates roughly 850–950 kWh per year in the UK (south-facing, no shading). So a 4kWp system produces around 3,400–4,200 kWh — broadly matching average household use. Each modern monocrystalline panel is typically 400–430W, so 4kWp is 10–11 panels.

Roof space limits

A single 420W panel is roughly 1.7m × 1.1m. Ten panels need approximately 19 square metres of usable, unobstructed roof. If your roof is smaller or partially blocked by rooflights, chimneys, or skylights, a smaller system that fits cleanly is better than cramming panels around obstructions.

When bigger is not always better

If you work away most of the week and cannot add battery storage, a very large system generates more than you can use and more than you can export at high rates. A system well-matched to your actual consumption pattern typically outperforms an oversized one on long-term return.