The mercury hit 38°C in parts of southern England last week, the third heatwave in as many summers. For homeowners without air conditioning, that meant sleepless nights and a scramble for fans that do little more than shuffle hot air. But for the 1.3 million UK households with solar panels, the story was different: their systems generated enough electricity to run a medium-sized air conditioning unit for about five hours a day, entirely free of charge.
That calculation comes from CleanTechnica, which analysed generation data during the recent heatwave. As reported by CleanTechnica, a typical 4kW solar array in London produced 16–18 kWh on the hottest days, more than enough to cover a 2.5 kW portable air con unit running for five hours (12.5 kWh), with surplus left for fridges, lights, and phone charging. The catch is that most UK homes still lack both solar panels and air conditioning. Only 5% of households have either, according to the Energy Saving Trust. But as heatwaves become more frequent, that equation is shifting.
Who qualifies, and who doesn’t
Solar panels alone won’t cool your home. You need an air conditioning system, typically a split-unit or portable model, rated at 2–3 kW. A portable unit costs £300–£600; a split-system installation runs £1,500–£3,000. The solar panels themselves cost £5,000–£8,000 for a 4 kW system, including installation. That is a £6,500–£11,000 upfront outlay. But the payback is real. Ofgem’s Smart Export Guarantee pays you for excess electricity you send to the grid, currently around 5–15p per kWh, or up to £150 a year for a typical system. On a heatwave day, the solar-generated cooling costs nothing beyond the original capital. Compare that to running air con from the grid at 30p per kWh: five hours of cooling would cost £3.75 a day. Over a two-week heatwave, that is £52.50 saved, and the panels keep saving year-round.
Yet not every home is suitable. South-facing roofs with minimal shading are ideal. East-west arrays work but produce less peak power. Renters and flat-dwellers are largely locked out unless their landlord installs panels. The government’s Boiler Upgrade Scheme does not cover solar panels (that is for heat pumps only), but the Smart Export Guarantee is open to anyone with a certified installation. Local councils also offer small grants in some areas, check your postcode on gov.uk.
What it costs a typical 3-bed semi
Consider a 1930s semi-detached in Milton Keynes with a 4 kW solar array and a 2.5 kW split-unit air con in the living room. On a 30°C day, the panels generate 17 kWh. The air con runs from 1pm to 6pm, peak sun hours, using 12.5 kWh. The remaining 4.5 kWh powers the fridge, TV, and router. The homeowner’s electricity bill for that day: zero for cooling, and a small credit from the Smart Export Guarantee for any surplus. Over a year, the panels generate about 3,500 kWh. The household uses 2,800 kWh of that directly, saving £840 at current prices. The air con adds perhaps 150 kWh of summer daytime use, displacing grid electricity that would have cost £45. The total annual saving: £885. Payback on a £6,500 system: 7.3 years, faster if energy prices rise.
But there is a catch. The EPC impact is modest if you already have good insulation. Solar panels add up to 2 points on the EPC rating (typically from D to C, or C to B). Air conditioning, if efficient, can add another point. But the real gain is resilience: you can stay cool without worrying about the price cap, which Ofgem raised by £63 in October to £1,928 for typical dual-fuel households. That is the third increase in 18 months.
What this misses, and what to do next
The CleanTechnica analysis assumes perfect conditions: south-facing, unshaded, with a battery to store midday surplus. Without a battery, you lose the 4.5 kWh of excess, about 30p worth. A 5 kWh battery adds £2,000–£3,000 to the system cost but lets you run the air con in the evening too. That pushes payback to 10–12 years. For households that cannot afford the upfront cost, the government’s Great British Insulation Scheme offers free or subsidised insulation, which reduces cooling needs in the first place. The Energy Company Obligation (ECO4) provides grants for low-income households to install solar panels, up to £5,000 in some cases.
The bottom line: if you own your home and have a south-facing roof, solar panels can pay for themselves in under 8 years while keeping you cool during heatwaves. The technology exists, the grants are available, and the maths works. Check your EPC rating on gov.uk, get three quotes from MCS-certified installers, and apply for the Smart Export Guarantee. The next heatwave is not optional, your cooling strategy should be.
Frequently Asked Questions
Yes, if you run the air con during peak sun hours (typically 10am–4pm). A 4 kW solar system generates enough power to run a 2.5 kW unit for 5–6 hours. Without a battery, you cannot store excess for evening use, but you can still save significantly on daytime cooling costs.
Solar panels alone can improve your EPC by up to 2 bands (e.g., D to C). Adding air conditioning with a high Seasonal Energy Efficiency Ratio (SEER) can add another point. However, the biggest EPC gains come from insulation and draught-proofing first.
