I think the mysterious "Misc" electricity which sometimes appears at dawn and then dusk in the UK is likewise BESS†. The raw data doesn't seem to have labels for BESS, a lot of it was oriented around how electricity works twenty five years ago, there's an 850MW power plant here, and one there and one there, and we measure those. So it can cope with a wind farm - say 500MW or 1GW coming ashore somewhere, but not really with the idea that there's 10GW of solar just scattered all over the place on a bright summer's day and the batteries might similarly be too much?

† My thinking is: Dawn because in a few hours the solar comes online, you can refill those batteries at whatever price that is, so sell what you have now for the dawn price, and Dusk because the solar is mostly gone but people are running ovens and so on to make food in the evening, so you can sell into that market. But I might be seeing what I expect not reality.