One of the most common questions we get from homeowners considering solar is: how many panels do I actually need? The answer depends on a few factors — your roof, how much electricity you use, and what you’re hoping to achieve.
Here’s a practical guide to working it out.
Start with your electricity usage
The starting point is your annual electricity consumption, measured in kilowatt-hours (kWh). You’ll find this on your energy bill or through your smart meter. The average UK home uses around 3,500kWh per year, though this varies significantly depending on the size of the property, number of occupants, and whether you have an EV or electric heating.
As a general rule, you want a solar system that can generate roughly what you consume. In Bristol, a well-positioned 1kWp of solar panels generates approximately 850–950kWh per year. So a 4kWp system would produce around 3,400–3,800kWh — a reasonable match for an average household.
Common system sizes and who they suit
3kWp (around 7–8 panels): A good fit for a smaller property, flat occupancy, or a home with limited roof space. Typical annual generation around 2,700kWh.
4kWp (around 9–10 panels): The most common size for an average three-bedroom home. Covers a good proportion of typical household consumption. Annual generation roughly 3,400–3,800kWh.
6kWp (around 14–15 panels): Suited to larger homes, households with higher consumption, or anyone adding an EV charger. Annual generation roughly 5,000–5,600kWh. With an EV, the extra generation goes directly into charging the car rather than being exported.
8kWp+: For large properties, high consumption households, or those looking to maximise generation — particularly if combining solar with a heat pump or a large EV. Requires adequate roof space and it’s worth checking whether your supply is sufficient to handle a larger system.
Roof orientation matters more than size
A south-facing roof at a pitch of around 30–40 degrees is the ideal. East/west split installations — where panels go on both sides of the roof — are a good alternative and can actually spread generation more evenly across the day, which is useful if you’re home during morning and evening rather than midday.
North-facing roofs aren’t viable for solar in the UK. Significant shading from trees, chimneys, or neighbouring buildings reduces output considerably and is worth assessing carefully before committing to a system size.
Should you add a battery?
If you’re out during the day when your panels are generating, a significant proportion of that generation will be exported to the grid rather than used in your home. The Smart Export Guarantee pays for that exported power, but at a lower rate than you’d pay to buy electricity. A battery stores that surplus for use in the evening, which considerably improves how much of your own generation you actually consume.
As a rough guide: without a battery, most households self-consume around 30–40% of what their panels generate. With a battery, that typically rises to 70–90%. The difference in bill saving is significant.
Don’t oversize just for the sake of it
Bigger isn’t always better. If you install more capacity than you can use or store, the excess goes to the grid at the SEG rate — currently 3–15p per kWh depending on your tariff. That’s a return, but it’s lower than the value of electricity you’d use yourself. The sweet spot is a system sized to match your consumption, with a battery to capture what you’d otherwise export.
If you’re planning to add an EV charger or electric heating in the future, it’s worth factoring that increased demand into the sizing conversation now rather than finding you’ve undersized the system.
Getting the right answer for your home
The figures above are a guide — the right system size for your home depends on your specific roof, usage, and what you want to achieve. We carry out free surveys across Bristol and South Gloucestershire and will give you a clear recommendation with honest numbers rather than a pitch for the largest system we can fit. Get in touch to arrange a survey.
