How Many Solar Panels Do I Actually Need?
Part 3 of our “Ask GLANtech” series, where we answer the questions, our customers ask us most. Once customers know roughly what solar costs, the next question is almost always: “okay, but how many panels do I actually need?” It’s a great question to ask before you get a quote, because it helps you sense-check whatever number an installer gives you.
The Short Answer
Most UK homes need somewhere between 6 and 14 panels — but the right number for your home depends on your actual electricity usage, not your house size.
The Quick-Reference Table
Home type Typical annual usage Panels typically needed
1–2 bed flat ~1,500–1,800 kWh 4 – 8 panels
3-bed semi (most common UK home) ~2,700–3,100 kWh 8 – 12 panels
4–5 bed detached ~4,100+ kWh 12 – 16 panels
These figures assume modern 350–450W panels. Bedroom count is a useful starting point, but it’s a rough proxy, your actual electricity bill is the more reliable number.
The Simple Calculation (No Maths Degree Required)
1. Find your annual electricity usage in kWh — not pounds spent, since prices change but usage doesn’t. It’s on your bill or smart meter, usually labelled “annual consumption.”
2. Check the panel wattage you’re considering — commonly 400W, 450W, or 480W for residential installs.
3. Divide your annual usage by the panel’s expected annual output. In the UK, a 450W panel typically produces around 380–400 kWh a year, accounting for our (frequently grey) weather.
Worked example: a home using 3,600 kWh a year, with 400W panels producing roughly 380 kWh each → 3,600 ÷ 380 ≈ 9–10 panels, rounded up.
Your installer will refine this using satellite roof data and shading analysis, but this gets you within a panel or two of the real number, useful for sanity-checking any quote you receive.
What Actually Changes the Number
· Roof orientation. South-facing roofs perform best; east/west-facing typically lose around 10% output; north-facing roofs are rarely worthwhile.
· Roof pitch. Around 30–40° is close to ideal for most of the UK.
· Shading. Trees, chimneys, and neighbouring buildings can meaningfully cut output, even partial shade on one panel can drag down a whole string, depending on your inverter setup. · Panel wattage. Higher-wattage panels (see our monocrystalline vs polycrystalline comparison) mean fewer panels for the same output, useful if roof space is tight.
· Future plans. Thinking about an EV or heat pump in the next 5–10 years? Factor that in now. An EV typically adds around 2,000 kWh a year to your usage, and a heat pump can add 3,000+ kWh, both push your ideal panel count up meaningfully. · A battery. Adding battery storage doesn’t change how many panels you need to generate power, but it changes how much of what you generate you get to use.
Don't Just Maximise the Roof
It’s tempting to think “more panels = better,” but oversizing a system beyond your usage and export capability doesn’t always pay for itself, you’ll simply export more at a lower rate rather than using power directly. The right-sized system for your actual consumption (with maybe a little headroom for future EV or heat pump plans) is usually the smartest financial choice, not the biggest one that fits.
GLANtech's Honest Take
We’d rather size your system to your real usage than your roof’s maximum capacity. During your free survey, we’ll pull your actual consumption data, check your roof’s orientation and shading with satellite tools, and give you a number, and a quote — that’s built around your home, not a national average.
