Rooftop Solar Calculator — the UK
Estimate yearly kWh and bill savings from a rooftop solar system in the UK using local irradiance (2.9 kWh/m²/day) and tariffs.
How much will a rooftop solar system actually generate in the UK? 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. This estimator starts from the long-term local irradiance (2.9 kWh/m²/day) and a realistic loss stack, then prices the energy at the local tariff (£0.27/kWh, editable) — adjust tilt and soiling to match your roof.
With your numbers: 5 kW × 2.9 kWh/m²/day × 365 × 1.10 (plane-of-array) × 82% PR = 4,750 kWh/year. First-year figure — subtract ~0.5%/yr panel degradation for later years.
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 Rooftop Solar Calculator — the UK online — Estimate yearly kWh and bill savings from a rooftop solar system in the UK using local irradiance (2.9 kWh/m²/day) and tariffs. Runs instantly in your browser: no signup, no upload, mobile-friendly.
About Rooftop Solar Calculator — the UK
How much will a rooftop solar system actually generate in the UK? 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. This estimator starts from the long-term local irradiance (2.9 kWh/m²/day) and a realistic loss stack, then prices the energy at the local tariff (£0.27/kWh, editable) — adjust tilt and soiling to match your roof.
How to use Rooftop Solar Calculator — the UK
- 1Enter your system size in kW (or keep the segment-typical default).
- 2Fine-tune irradiance, tilt and soiling to match your site — the help text gives local reference values.
- 3Read annual kWh, specific yield, PR and the monthly split; set your tariff to price the energy.
Why use Rooftop Solar Calculator — the UK?
- ✓Region-true defaults: long-term irradiance, optimal tilt and local tariff are pre-loaded, not guessed
- ✓PVWatts-style physics — plane-of-array gain, full loss stack and performance ratio shown transparently
- ✓Month-by-month generation table exposes the seasonal shape, not just an annual headline
- ✓Everything computes instantly in your browser — no signup, no quote-form ambush
Frequently asked questions
How accurate is the Rooftop Solar Calculator — the UK?+
It uses the same physics as NREL's PVWatts: irradiance × plane-of-array factor × performance ratio. With honest inputs, expect results within ±10% of a professional simulation — good enough for sizing and payback decisions. For bankable projects, follow up with site-measured data and a full TMY simulation.
What is specific yield and what's a good value?+
Specific yield is annual kWh produced per kW of panels. It removes system size from the comparison: 1,400–1,700 kWh/kWp is typical across sunny India, 950–1,100 in Germany or the UK. If a quote promises far above the regional norm, question the assumptions.
Why is my real output lower than the calculator says?+
The usual suspects in order: more shading than assumed, dust (soiling can cost 5–15% where cleaning is irregular), inverter undersizing/clipping, and higher cell temperatures than the default loss stack assumes. Compare measured monthly output against the table here to localize the gap.
Does panel direction matter as much as size?+
Orientation typically moves output 5–25%. Equator-facing at near-latitude tilt is ideal; east/west roofs lose roughly 10–20% but spread generation across the day, which can be worth more under time-of-use tariffs or self-consumption rules.
Embed Rooftop Solar Calculator — the UK on your website
Want Rooftop Solar 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.
<iframe src="https://tooljolt.com/tools/rooftop-solar-calculator-uk" width="100%" height="640" style="border:1px solid #e5e7eb;border-radius:12px;max-width:680px" title="Rooftop Solar Calculator — the UK — ToolJolt" loading="lazy"></iframe>Related tools
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