Five weeks ago I wrote about the evening Britain's grid ran out of margin — the forty-eight minutes on 23 June when frequency sat below 49.8 Hz, bottoming out at 49.657 just after eight, while NESO halted exports to the Netherlands and phoned Paris. I watched most of it unfold from the sofa, which is the correct place to watch a grid event from. What I keep coming back to, though, is what was happening in my garage. Twenty kilowatt-hours of battery — fully charged since dawn, the most flexible asset I own — sat through the grid's worst evening in years doing absolutely nothing. NESO files the whole week under "a complex operational challenge", which is control-room for we'd rather not do that again.
My battery sat it out because it is frequency-blind, and so is nearly every battery and EV charger in the country. It can see the clock and it can see the price. It cannot see the one signal that says, second by second, whether the grid is struggling — even though the inverter it lives behi…