UK solar installations hit 200,000 in 2025, the highest annual figure since the Feed-in Tariff era. The average 4 kW system now costs £5,000–£6,500, and with electricity at 24.5p/kWh, the payback period has fallen below 12 years for most households.
Yet the market is flooded with panels promising 450W, 500W, even 600W from a single module. As The Independent reports in its latest expert comparison, the headline wattage alone tells you almost nothing about real-world performance on a British roof. The article tests panels under UK light conditions, diffuse, cloudy, low winter sun, which is where most lab ratings fall apart.
What efficiency actually means for your roof
Efficiency is the percentage of sunlight converted to electricity. A 22% panel produces 22 watts per 100 watts of light hitting it. For a typical 3-bed semi with 30 m² of south-facing roof, the difference between 19% and 23% panels is roughly 400 kWh a year, £98 at current rates.
The catch is that higher efficiency costs more. SunPower Maxeon 6 panels (24.1% efficiency) cost about £1.20 per watt, while JA Solar 400W panels (21.2% efficiency) run at £0.85 per watt. The premium panel adds £1,400 to a 4 kW system but yields only £98 extra per year, a 14-year payback on the premium alone. For most UK homes, the mid-range 21–22% panels from REC, Longi, or Trina are the sweet spot.
But if your roof is small, shaded, or north-facing, the premium panel may be the only way to hit your generation target. Energy Saving Trust recommends modelling both options with your roof’s exact orientation before buying.
Who qualifies, and who doesn’t
The Smart Export Guarantee (SEG) pays you for electricity you send to the grid. Rates vary by supplier: Octopus Outgoing Fixed pays 15p/kWh, while others pay as low as 3p. The typical UK household exports about 50% of its solar generation, so at 15p/kWh that’s roughly £180 a year from a 4 kW system.
But SEG is not the Feed-in Tariff. You don’t get paid for every kWh you generate, only for what you export. That makes self-consumption the real driver of returns. A battery (typically £1,500–£2,500 for 5 kWh) can double your self-consumption from 30% to 60%, cutting your payback by 3–4 years.
Ofgem confirmed in December 2025 that SEG rates will remain uncapped until at least 2027, but suppliers can change them with 30 days’ notice. The government’s Clean Heat Market Mechanism does not apply to solar panels, so no direct subsidy exists, only the 0% VAT rate on installations until 2027.
What it costs a typical 3-bed semi
A 4 kW system with 10 panels (400W each) and a 5 kWh battery costs £8,000–£10,000 installed. Without battery: £5,000–£6,500. Annual generation: 3,400–4,200 kWh depending on location and orientation. South-facing roof in the South East: 4,200 kWh. North-facing in Glasgow: 2,800 kWh.
Payback without battery: 11–13 years. Payback with battery: 9–11 years. The battery adds £2,000 but cuts grid imports by 1,200 kWh/year, £300 saved at 25p/kWh. The numbers assume you use 60% of what you generate. If you work from home, that figure rises to 80%.
EPC impact: solar panels add 5–10 points to the EPC score, typically moving a D-rated home to C or a C-rated home to B. That matters from 2028, when the government’s proposed minimum EPC C for rental properties takes effect. Landlords installing solar now are front-running a compliance deadline.
The one number that matters more than wattage
Temperature coefficient, how much output drops as panels heat up. UK panels can hit 65°C on a summer roof. A panel with a coefficient of -0.35%/°C loses 14% output at that temperature. A panel at -0.25%/°C loses 10%. The difference: 150 kWh a year on a 4 kW system, about £36.
Premium panels like SunPower and REC have coefficients of -0.24% to -0.26%. Budget panels often hit -0.40%. In a heatwave summer (which the UK now gets every 2–3 years), the gap widens. The Independent’s comparison ranks temperature coefficient as the second most important spec after efficiency. It’s a detail most online calculators ignore.
Households on standard variable tariffs can apply for solar quotes through the Energy Saving Trust’s find-a-trade service from any day. The 0% VAT rate runs until 31 March 2027. Panels installed before that date lock in the saving. After that, VAT returns to 20%, adding £1,000–£1,300 to a typical system.
Frequently Asked Questions
Yes, but generation drops by 30–40% compared to south-facing. A 4 kW system on a north-facing roof in Manchester produces about 2,500 kWh/year instead of 3,800. It still pays back in 14–16 years, but a battery becomes essential to capture what little you generate.
Not for most homes, they are permitted development under the Town and Country Planning Act. Exceptions: listed buildings, conservation areas, and flats. For those, you need prior approval from the local planning authority, which takes 8–12 weeks.
