Do the sums first
Commercial solar savings calculator
Put your own building through the numbers — no contact details asked, because it is a planning tool, not a lead trap.
Do the sums first
What could commercial solar do for your building?
Move the sliders and watch the arithmetic. It's an illustration, not a quote — the real numbers come from a survey of your roof and your half-hourly consumption.
Set up your site
Pick a size, then tune it to your building.
Quick-pick a system
Size it by
10 kWp500 kWp
10,0001,000,000 kWh
20%95%
10p40p
0p15p
Estimated annual benefit
£0
bill offset + export income
Indicative payback
0–0 yrs
a range, refined by a real quote
Bill offset
£0
solar used on-site, per year
Export income
£0
surplus sold to the grid, per year
covered by the roof
Your 25-year outlook
cumulative position, after the system pays for itself
Break-even in —
Mid-point of the £700–£1,100/kWp band · flat prices · no degradation
Every assumption behind these numbers
- Generation: 850 kWh per year for each kWp installed. That comes from running the European Commission's PVGIS model for Durham — around 937 kWh/kWp on an ideally pitched south-facing roof, 841 on the shallow-pitched sheet roof most of our clients actually own, 770 facing east or west — and taking a mid-band planning figure rather than the best case.
- Roof area → system size: 6 m² per kWp for a pitched sheet roof, allowing for access routes and rooflights. Ballasted flat roofs fit less per square metre — typically 8–10 m² per kWp — so treat the area mode as the pitched-roof answer.
- On-site use is capped by your daytime consumption. Solar generates in daylight, so the model never lets the roof "cover" evening or night load — that's what the daytime-use slider controls. Battery storage changes this conversation; ask us.
- Import rate defaults to 17p per kWh — the cautious end of what manufacturing businesses averaged through 2025 — and export defaults to a deliberately conservative 5p per kWh, as at July 2026. Both are yours to set: your bill and your export offer beat our averages.
- The payback range uses the 2026 planning band of £700–£1,100 per kWp installed for commercial rooftop systems. It is a band, not a price: your itemised quote replaces it.
- Flat prices, first-year output. No energy-price-rise assumptions, no panel-degradation curve, no tax effects — each would flatter the result, and we would rather the surprises ran in your favour.
This is an illustration, not a quote or a promise. Real numbers depend on your roof, shading, consumption profile and tariff — that's what the free survey is for.
What it asks, and what it gives back
Four inputs: roof area in square metres (or a system size in kWp), annual consumption in kWh from your bill, your daytime-use share, and any export rate you have been offered. From those it estimates the array your roof carries, its annual generation this far north, the grid purchasing it displaces, what the surplus earns — and, dividing installed cost by that first-year benefit, a payback range rather than a single flattering number.
Every assumption, disclosed
Calculators disagree because their hidden assumptions disagree, so ours are in the open — the full list sits beside the results above. The headline: generation uses 850 kWh per year for each kWp installed, from running the European Commission's PVGIS model for Durham — around 937 kWh/kWp on an ideally pitched south-facing roof, 841 on the shallow-pitched sheet roof most of our clients actually own, 770 facing east or west — and taking a mid-band planning figure rather than the best case. Roof area converts at 6 m² per kWp for a pitched sheet roof; the import price defaults to 17p per kWh — the cautious end of what manufacturing businesses averaged through 2025 — and export to a deliberately conservative 5p, as at July 2026. Your bill and your export offer beat our averages, which is exactly why both fields are editable. The installed-cost band is £700–£1,100 per kWp, the 2026 planning band for commercial rooftops — which is why payback shows as a range, not a point.
What it deliberately leaves out
No panel degradation, no assumed electricity-price rises, no tax effects — each would flatter the result, and we would rather the surprises ran in your favour. In practice the Annual Investment Allowance can shorten real-world payback meaningfully; that upside is explained on the solar page and belongs in a conversation with your accountant, not buried in a widget. Batteries are not modelled either — storage changes the daytime-share arithmetic and deserves its own page rather than a fudge factor. And there are no funding products in the maths, because we do not sell any.
Two questions about the numbers
Why are your figures lower than other calculators?
Because the constants are local and disclosed. A national-average yield of 900–1,000 kWh/kWp flatters a North East sheet roof; our 850 comes from modelling Durham specifically, at the pitch these roofs actually have. A calculator that will not show you its assumptions is a brochure with sliders.
Our building runs mostly at night — is it worth modelling?
Model it honestly: set the daytime share low and watch what happens — the calculator will not hide it. A night-heavy site is usually a weak case for solar alone and a candidate for battery storage — or for spending the capital elsewhere, and we will say so if the numbers do.
The output is indicative, not a quote. It knows nothing about your roof structure, shading, metering or grid connection — the survey exists because those change the answer. When the modelled numbers look worth pursuing, the next step uses your actual building.
Turn the estimate into a real number
Send us the building, the bill and the roof type and we will model your site from its own consumption data — itemised, in writing, no obligation. Call 07720 802405 or use the form.
Get your free, no-obligation quote
Commercial solar, battery, EV or any electrical work — no pressure.