When we had our pool solar installed a few years ago, they installed it after the existing filter and SWG, like this...
I've since learned that the SWG should be after the filter and the solar.
I may replace my SWG soon and putting it anywhere other than were it is now will be a challenge because of how tight all of the piping is. I'm curious why the SWG should be the last item. Does it decrease the life of the cell or make it less efficient if placed before the solar?