The four numbers that decide it
One: system cost. A typical 4kW installation runs to about £8,400 fitted, with installation zero-rated for VAT until 31 March 2027. Two: generation, roughly 850 to 1,000 kWh per kilowatt per year on a sensible roof, so around 3,400 to 4,000 kWh from that system. Three: how much of it you use directly, typically 35% to 50% without a battery. Four: your import and export rates, because used generation saves the import price while exported generation earns the export rate.
Worked through at typical rates, a 4kW system in an average household offsets several hundred pounds a year between avoided import and export income. That puts payback for many homes in the ten-to-fourteen-year range without a battery, against panels warrantied for 25 years and inverters for 10 to 12.
What shortens the payback, and what stretches it
Shorteners: high daytime usage, working from home, an EV charging from the surplus, a strong export tariff, and simply using more electricity overall, because every kWh of self-use saves the full import rate. Rising electricity prices shorten it further, which is the quiet reason solar keeps getting more attractive without the kit changing.
Stretchers: heavy shading, a north-only roof, low usage with everyone out all day and no battery, and paying over the odds for the installation in the first place. The last one is the only stretcher entirely in your control, which is the case for comparing quotes properly rather than taking the first figure.
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Two factors sit outside the payback sum. Homes with solar tend to hold a modest value premium, and an EPC improvement can help with mortgage products tied to efficiency. And the risk side is genuinely small: panels have no moving parts, maintenance is minimal, and the single likely mid-life cost is an inverter replacement around year ten to twelve, covered in solar maintenance and lifespan.
The honest summary: on a decent roof with average usage, solar in 2026 is a sound buy that gets better the more of the output you can use. Sizing it to your usage is what makes the sum work, and comparing quotes from up to three MCS-certified installers is how you find the price that keeps the payback short.
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