How to compare solar savings estimates

Two solar quotes can predict different savings even when they offer similar panels. Put the main figures side by side so you can see what explains the difference.

Start with the same equipment and work

Check that both prices include the same system size, scaffolding and electrical work. If one includes a battery and the other does not, ask for the battery to be priced separately.

Compare panel and inverter models, warranties and aftercare as well as the total.

Check how much electricity each system should make

Look for the estimated annual output in kWh and the system size in kWp. kWh measures electricity; kWp describes the combined rated power of the panels.

For similar systems on the same roof, ask the installer to explain any large difference. Find out how the estimate allows for roof direction, shade and equipment losses.

Check how much you are expected to use

Electricity you use at home saves you buying it from the grid. Spare electricity sent to the grid earns the export rate, which may be lower.

Ask how the installer estimated your daytime use. The savings should reflect your household, including whether people are usually at home.

Compare the prices used in the calculation

• The price you pay for electricity from the grid.
• The payment for spare electricity sent to the grid.
• Whether either figure is expected to rise.
• How long any special tariff lasts and what happens afterwards.

Use the same prices when comparing quotes so a generous tariff assumption does not make one system look better than it is.

Allow for costs over time

Ask whether the estimate includes upkeep, loan interest and possible inverter or battery replacements. Check the number of years covered and whether a battery is expected to be replaced during that time.

Try a less optimistic estimate

In the calculator, try a lower export rate, less solar electricity used at home or a higher upkeep budget. See how much the result changes.

The calculator does not separately model loan repayments, battery charging or replacement bills. Ask the installer to show those costs in a fuller comparison if they apply to you.

Keep the figures together

Use one column per quote in the comparison worksheet. Leave missing figures blank and ask the installer to provide them.

A clearer explanation and complete written offer are more useful than a headline savings figure on its own.