Solar savings calculator
See how much you could save with solar panels and how long it could take to cover the installation cost.
- Choose your home type, bedrooms and number of people first.
- Use figures from your electricity bill and quote where you have them. You can start with the example figures if you’re still exploring.
- Change a figure to see how it affects the estimate.
Your numbers
Choose your home type, bedrooms and household size first. Then adjust the figures using your quote and electricity bill. Electricity prices are in pence per unit (kWh).
Medium-use home. Choose your roof direction and slope, then use your postcode for a local estimate. Run the check again if you change either roof setting.
The starting figures are an example. Your own bill and written quote will give you a more useful estimate.
What the starting numbers mean
- 9 panels at 450 W: a total rated power of 4.05 kWp. Ask an installer how many panels suit your roof.
- £7,000 installed price: an example installation cost. Replace it with the full price from your quote.
- 850 kWh per kWp: an example of yearly output for each kWp of panels. Divide your quoted annual output by the system size to compare this figure. The postcode tool can provide a local estimate.
- 2,700 kWh household use: a starting estimate based on Ofgem household figures. Use the annual total on your bill if you have it.
- 45% used at home, 25p to buy electricity, 12p for exports, £100 upkeep and a 0.5% yearly fall in output: example figures to help you start. Change them to suit your home and tariffs.
The postcode check sends your postcode to Postcodes.io to find your location, then sends the location to PVGIS for a solar estimate. The calculator stores the solar result rather than your postcode.
Your estimate
The payback number uses the first year’s savings and payments after upkeep. The chart also allows for the yearly fall in panel output, so its break-even year may be later. Allow separately for finance, extra roof work and replacement parts; future electricity prices may change.
Make the estimate useful for your home
Try a lower export rate or a smaller share of solar electricity used at home. If the result changes a lot, ask the installer to explain those figures in your quote.
If you change the roof direction or slope after using the postcode lookup, run the lookup again. Your installer should still assess the roof and any nearby shade.
How are the savings calculated?
The calculator adds the electricity-bill savings to payments for spare electricity sent to the grid, then subtracts your yearly upkeep budget.
The “years to cover the cost” figure uses the first year’s total. The chart also allows for the yearly fall in panel output, so it may show the cost being covered later.
For example, the starting settings use nine 450 W panels, a £7,000 installation cost and estimated output of about 3,443 kWh a year. With 45% used at home, electricity at 25p per unit, export payments at 12p and £100 for upkeep, the yearly total is about £514. At that first-year rate, covering £7,000 would take about 13.6 years.
You can change all these figures. They are an example, not a quote for your home.
What else should you allow for?
These are estimates. The calculator keeps electricity prices unchanged and does not separately calculate loan repayments, roof repairs, battery charging or future replacement bills. Include those costs in your decision where they apply.
For help checking your quote, read how to compare savings estimates or use the quote worksheet.
Sources and further reading
Get a tailored quote
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An installer can check your roof and give you a price. Keep your calculator figures to compare with the quote.
Free to request, with no obligation to accept a quote.