38.1C at Kew.
Solar carried the afternoon.
13 August was the hottest day of 2026. 38.1C at Kew Gardens, the fifth hottest day ever recorded in the UK. Forty weather stations passed 36C. It was the fifth heatwave of the summer. Rooftops did more of the work than most people realise.
🌡️ The heat
2026 has now had four days at or above 36C, more than any year on record, and two days of 38C, matching 2022.
Heat is bad news for the grid. Gas plants lose output, cables carry less, French nuclear turns down because rivers get too warm, and everyone turns the fans on.
☀️ What solar did
Across 26 heatwave days this summer, household solar saved an estimated £86.7m on bills according to Carbon Brief. That is panels on roofs, not fields.
On a hot day the sun is strongest exactly when the fans, fridges and offices are working hardest. That is the one time solar and demand line up.
The problem arrives at 7pm. Still 30C. Panels fading. Everyone home. That hour is where the expensive electricity lives.
🏠 What to do on the next one
Run the washing, the dishwasher and the car charger between 11am and 3pm. Free electricity if you have panels, cheap electricity if you do not.
Pre cool the house in the afternoon and let it drift in the evening. A fridge does not need to work harder at 7pm than at 2pm if you leave it shut.
A battery does all of this for you. So does a grid that pays you to shift, if you are connected to one.
The hottest day of the year was also one of the best solar days of the year. Most households exported the midday surplus for pennies and bought the evening back at full price. Same roof, wrong timing.