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Solar System Size Calculator — the UK

Convert your monthly electricity bill in the UK into the kW of solar, panel count and roof area you need.

What size solar system does your bill justify in the UK? Enter the average monthly bill and your tariff; the tool back-calculates consumption, applies the local solar yield (2.9 kWh/m²/day average irradiance) and returns the array size, number of panels and roof area. British systems live on diffuse light — oversizing the array relative to the inverter and accepting a flatter tilt captures more of the grey-sky energy; SEG export rates vary 4–15p.

6.3 kW
Recommended system size
12
Panels needed
31 m²
Roof area
Monthly consumption556 kWh
Site yield2.6 kWh/kWp/day (UK — South England)
Annual production6,003 kWh

556 kWh/month × 90% target ÷ (2.6 kWh/kWp/day × 30.4) = 6.3 kW. Round up to the nearest panel string your inverter supports.

Sources: Global Solar Atlas GHI — UK — South England; NREL PVWatts loss model (PR ≈ 0.79 fixed rooftop)

Indicative estimates only, not financial or investment advice. Tariffs, subsidies and net-metering rules change — verify with your DISCOM, utility or installer before committing.

Use the free Solar System Size Calculator — the UK online — Convert your monthly electricity bill in the UK into the kW of solar, panel count and roof area you need. Runs instantly in your browser: no signup, no upload, mobile-friendly.

About Solar System Size Calculator — the UK

What size solar system does your bill justify in the UK? Enter the average monthly bill and your tariff; the tool back-calculates consumption, applies the local solar yield (2.9 kWh/m²/day average irradiance) and returns the array size, number of panels and roof area. British systems live on diffuse light — oversizing the array relative to the inverter and accepting a flatter tilt captures more of the grey-sky energy; SEG export rates vary 4–15p.

How to use Solar System Size Calculator — the UK

  1. 1Enter your average monthly bill and the per-unit tariff from it.
  2. 2Pick your bill-offset target (100% = offset everything the rules allow).
  3. 3Read the recommended kW, panel count at your chosen wattage, and the roof area required.

Why use Solar System Size Calculator — the UK?

  • ✓Works backwards from the bill — the number you actually know
  • ✓Region-correct yield baked in, so the same bill gives different (correct) sizes in different cities
  • ✓Returns panel count and roof-area needs alongside the kW figure
  • ✓Offset target slider handles net-metering caps and partial-offset strategies

Frequently asked questions

How many solar panels do I need for my monthly bill?+

Divide the bill by the tariff to get monthly kWh, then divide by your region's per-kW monthly yield (≈110–135 kWh/kW in sunny India). A ₹4,000 bill at ₹8/unit (500 kWh) typically needs 3.5–4.5 kW — seven to nine 550 W panels. This calculator does exactly that math with local values.

How much roof area does a solar system need?+

Modern 540–580 W panels occupy ~2.6 m² each; with walkways and spacing, budget 80–100 sq ft (7.5–9.5 m²) per kW for flat roofs. A typical 3 kW home system needs roughly 250–300 sq ft of shade-free area.

Should I size for 100% of my bill?+

Usually 80–95%. Net-metering rules may cap capacity at your sanctioned load, slabs mean your last units are the cheapest to leave on the grid in some states, and consumption varies seasonally. Oversizing into low-value exports rarely pays — check your state's settlement rules.

What if my consumption grows after installing?+

Solar scales: leave inverter headroom (DC/AC ratio up to 1.3) or wall space for a second string. EV purchases and new ACs typically add 100–400 kWh/month — if those are planned within two years, size for them now; module additions later cost more per watt than doing it once.

Embed Solar System Size Calculator — the UK on your website

Want Solar System Size Calculator — the UKon your own site? Paste this snippet into any HTML page — it's free, with no API key or sign-up. The tool loads in an iframe and keeps working exactly as it does here.

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