At a level I studied physics, maths, chemistry and French.
For what I do, maths and physics were the this I needed most. There are jobs in solar power where chemistry would be a big help.
At university, I took physics with French. The physics was the useful thing for my career but the French was fun (especially because I got to spend a year living in the Alps)
Well, I don’t actually work with solar power! However, I took A-Levels in Physics, Biology, Chemistry and an AS in Maths. I use all these subjects every day in my job, because my field of research is really interdisciplinary.