Is it better to use your solar power or sell it to the grid?

01 / 03

Using power on site avoids an import

When solar supplies an appliance as it runs, the property buys less from its electricity supplier. Value that unit at the import price applying then, not a general annual average if you have a time-of-use tariff. Daytime occupancy, an EV charging schedule or a working-from-home pattern can make self-use higher than a standard household assumption. Do not assume a planned heat pump or EV already exists in today's figures.

02 / 03

A battery trades one value for another

Storing a spare solar unit may avoid an evening import, but not all of the unit comes back out: charging and discharging cause losses. It also means giving up the export payment that would otherwise have been earned, and the battery itself must be paid for. Compare the extra annual evening units actually delivered by each proposed battery size, not just the advertised capacity.

03 / 03

Export has a separate, changeable price

Ofgem's Smart Export Guarantee provides a route for eligible generators to be paid, but suppliers set their own rates and terms. A quote should state the tariff used, how many units are forecast to be exported, meter and eligibility assumptions, and whether the rate is fixed or variable. Test a lower export payment and a changed import tariff to see how sensitive the payback is. Never multiply total solar generation by both prices.

When is your solar power worth more to you?

Put a normal summer weekday beside a winter weekday. On each, note the hours when someone is home, the large loads that run and how much solar the proposed roof is expected to produce. If the house is empty at midday, a quote assuming nearly all generation will be used directly needs an explanation. If a business operates through daylight, its self-use may be much higher.

A simple quote comparison should show four separate figures: expected generation, direct use, battery-displaced imports and export. It should then multiply each flow by the appropriate tariff, with battery losses and cost shown separately. If one installer cannot show the split, you cannot fairly compare its payback with a more conservative quote.

Lifestyle changes can help, but don't exaggerate them. Running a dishwasher or charging an EV in daylight may move existing use; buying extra appliances to 'use the solar' does not create a saving. Ask FLO to test the current routine first, then clearly labelled future scenarios.