Is it me or the size of the circles is proprtional to the installed capacity instead of the generated capacity (i.e. a 1200MW nuclear plant is as big as a 1200MW wind turbine, which seems not right to me)

I don't think they're directly proportional, seems to be some sort of tailing off - Seagreen 1 (1075) and Torness (1200MW) seem to be a very similar size to Neart Na Gaoithe (450MW). (This could just appear similar because area of circles isn't a great way to visualise data though.)

If so there is a very generous floor. Solar would probably not be visible if it was install capacity.