If you don't want to move it, lots of plants and selective shading - fully or partially covering the back when too much sunlight does seem likely to cause problems - may prevent algae issues.
Nothing's better than daylight for plants - but results will vary according to circumstance, and years of trouble-free daylight may suddenly alter, or vice versa.
I have a Walstad directly in front of a window, and I simply plan to pull the curtain over that window, if I get direct sunlight which I think is too strong or it seems that the tank's possibly in danger of becoming too warm.
But if you don't have any live plants, you may want to consider earning extra money with the algae farm likely to result.
Edit - thanks for pointing that out, Jonty, that's hilarious - although the poor begger certainly did get a very late reply...