If you check out the wiki article then you can see that you are absolutely correct. You can get a system like this working on a mountainside as long as it face

If you check out the wiki article then you can see that you are absolutely correct. You can get a system like this working on a mountainside as long as it faces the sun. I think there are some engineering tradeoffs that have to be considered and also environmental concerns. I think it's a lot easier to find a desert with minimal ecosystem compared to a mountainside