What are the black dots around the map when you zoom in? For instance South-East Wales / Bristol, I see a few black dots that look like they cover shaded areas or something. They also show up at the sites for wind farms, possibly they're the turbines themselves?

Yup, that's exactly it! When you zoom in you get to see the wind farms and wind turbines using data from the amazing Open Infrastructure Map [0]. I also show the cables for the offshore wind farms.

[0] https://openinframap.org/