Solar Payback Calculator

Divide the installed cost by the annual benefit, where the benefit is import you avoid plus income from export. Degradation means the benefit falls slightly each year, so walking the years gives a longer and more honest figure than dividing once.

Because electricity you use is worth the import price and electricity you export is worth much less — often half or a third. Raising self-consumption from 30% to 60% can improve the return more than adding panels.

Shift laundry, dishwashing, water heating and car charging into daylight hours. Timers on appliances cost nothing and are the highest-return change available. A battery raises it further and has to earn its own payback.

Commonly quoted at 0.3% to 0.5% a year, with most manufacturers warranting around 80% to 85% of rated output at 25 years. It is a slow decline rather than a cliff.

It depends on the price gap between import and export and on how much you currently export. Run the payback on the battery separately from the panels — bundling them hides a battery that does not pay for itself.

It depends heavily on latitude, orientation and shading — roughly 750 to 1,100 kWh per kW in northern Europe and 1,300 to 1,700 in sunnier regions. An installer's site-specific estimate beats any national average.

Yes, at reduced output — diffuse light still generates. Panels are also more efficient in cool conditions, which is why a bright cold day can outperform a hot one.

South-facing at around 30 to 40 degrees in the northern hemisphere. East-west split arrays generate less in total but spread it across the day, which can raise self-consumption and sometimes the financial return.

Panels are commonly warranted for 25 years at 80 to 85% of rated output and often keep working beyond it. The inverter is the component most likely to need replacing, typically at 10 to 15 years.

Evidence suggests a modest positive effect where the system is owned outright. Leased systems or ones with a debt attached can complicate a sale, which is worth knowing before signing a financing arrangement.

Very little — occasional cleaning where rainfall does not do it, and an inverter check. Output monitoring is the useful maintenance, since a failed string can go unnoticed for months otherwise.

Enter the net cost after any grant, since that is what you actually pay. Export tariffs vary enormously by scheme and are often the difference between a good and a poor return.