Indicative result
- System size
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- Panels (≈440 W)
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- Annual generation
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- Indicative system cost
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- Estimated annual saving
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- Simple payback
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- Saving over 25 years
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Indicative only — based on ~950 kWh/kWp/yr, ~7.5 m²/kW, 26p/kWh grid, 6p/kWh export, and self-consumption by barn type. Excludes 100% AIA tax relief (which shortens payback further for working barns) and any re-roof. A real proposal comes from your meter data and a survey.
Get a real, no-obligation quoteHow the barn solar calculator works
This calculator turns two simple inputs — your usable roof area and barn type — into an honest first estimate. Here is exactly what it assumes, so you can sanity-check the numbers:
- System size from roof area at about 7.5 m² per kW (the realistic figure once you allow for walkways, edge set-backs and roof lights), capped at the area you enter.
- Panel count at roughly 2.27 modern ~440 W modules per kW.
- Generation at a conservative 950 kWh per kW per year for a UK barn roof — southern, unshaded roofs do better; northern or shaded ones a little less.
- Self-consumption by barn type: a 24/7 poultry or pig unit uses ~85% on site; a dairy or livestock barn ~80%; a grain store ~45%; a general steel portal shed ~50%; a low-load field barn or stable ~35%.
- Savings at 26p/kWh for electricity you use on site and 6p/kWh exported under the Smart Export Guarantee.
- Cost on a sliding £/kW scale that falls with size — see the full barn solar cost guide.
One thing the calculator deliberately leaves out: 100% Annual Investment Allowance. For a working-barn business that writes the system off against tax in year one — typically a further ~25% effective discount — so your real payback is usually shorter than shown. It also assumes a sound roof; if yours is asbestos cement a re-roof comes first. For the honest, building-specific numbers, request a free feasibility study.
Barn solar calculator — questions
How accurate is the barn solar calculator?
It gives an honest, conservative indication — it uses real UK figures (around 7–8 m² of roof per kW, ~950 kWh generated per kWp per year, and self-consumption rates by barn type). It is not a quote: a real proposal comes from your half-hourly meter data, a roof and structural survey, and a DNO check. Treat the result as a starting point, not a promise.
How many solar panels fit on my barn roof?
As a rule of thumb, around 7–8 m² of clear roof per kW, and roughly 2.2–2.3 modern (≈440 W) panels per kW. So a 600 m² portal-barn roof takes roughly an 80 kW system of about 180 panels. The calculator does this maths for you from your roof area.
Why does barn type change the payback?
Because it changes self-consumption — the share of your generation you use on site rather than export. A poultry or dairy barn with a 24/7 load uses 80–90% on site (fast payback); a grain store or low-load field barn exports more (slower payback, more reliant on the Smart Export Guarantee). The calculator adjusts for this.