Solar broke 16GW for the first time.
It cooled the country for free.
During this week's heatwave, British solar generation went past 16 gigawatts. That has never happened before. It covered the entire surge in cooling demand without a single extra gas plant being asked to help, and then it shoved wholesale prices below zero for good measure.
🌡️ The heat brought its own cure
There is a neat symmetry to a solar-heavy grid in a heatwave. The thing making everyone reach for a fan is the same thing powering the fan.
Cooling demand climbed all week. Normally that means gas plants firing up to cover the extra, at a price, with the emissions to match.
This time the solar fleet simply absorbed it. The extra demand was met, in full, by the sun that caused it. No additional gas required.
📉 And then it overshot
Having covered the cooling demand, solar kept going, because the sun does not stop when it has done enough.
Output overwhelmed what the country could use, and wholesale prices went negative again. In the middle of a heatwave. While people worried about their bills.
The most expensive week of the summer for households contained some of the cheapest electricity of the year. Both things were true at once, and only one of them made the news.
🧊 The catch arrives at 8pm
This is the bit that undoes it. Solar collapses in the early evening, fast, and the heat does not.
It is still 28 degrees at 8pm. The fans are still on. The sun has gone. Gas has to cover the whole thing, at peak prices, and by Thursday the grid was in real trouble. We will get to that.
A house that pre-cooled itself at 2pm, on free electricity, coasts through the evening. A house that starts cooling at 8pm pays the worst price of the day for the same comfort.
Britain set a solar record, met a heatwave without touching a gas plant, and then gave the surplus away for less than nothing. It was the best day the grid has ever had and the average household experienced it as a slightly higher bill.