Commercial solar calculator.
For business systems from 50 kWp. Draw your roof, add your electricity use and see your system size, savings, cost and payback in seconds.
Solar calculator
How we work it out
- Size. About 0.15 kWp for each m² of roof, leaving room for edges and access. We size the system to your roof or your use, whichever is smaller.
- Power. 1,000 kWh a year per kWp on a south-facing roof, 900 on east and west or flat roofs. That's typical for the South West. Further north it's a little lower.
- Saving. Solar you use yourself saves your unit price (25p per kWh unless you enter yours). Spare power is exported at about 5p. How much you use yourself depends on what kind of site it is and how your use compares with what the panels make.
- Cost. Based on recent commercial quotes, around £860 per kWp ex VAT, shown as a range. The calculator covers 50 to 500 kWp. Over 500 kWp, we give a bespoke quote.
- Payback and 25 years. Energy prices rising 3% a year, panels wearing 0.4% a year, and running costs of £8 per kWp a year.
No tax relief, grants or finance are included. See commercial solar payback, grants and tax relief and solar with no upfront cost.
Solar calculator questions
How accurate is the solar calculator?
It gives a fair first idea, not a quote. Real figures depend on your roof structure, shading, the grid connection and how you use power through the day. Send us your details and we will work it out properly for your site.
Where does the price come from?
From recent commercial quotes, around £860 per kWp ex VAT for a system of about 150 kWp, shown as a range. The calculator prices systems from 50 to 500 kWp. Larger systems get a bespoke quote. Roof repairs and network upgrades can add to it.
Can I get solar with no upfront cost?
Often, yes. With a solar PPA, a funder pays for the system and you buy the power it makes at an agreed price, usually below what you pay now. We can price both options for your site.
Do I need planning permission for solar on my business roof?
Many business roofs in England are permitted development. Systems over 50kW usually need prior approval from the local planning authority first. We check this for you.