It's all about the algae lots of sunlight can encourage its growth but if you keep on top if it it'll be fine I wouldn't worry one of my tanks is opposite a window and I've never had a problem although I am in England and have pretty much forgotten what sunlight looks like lol
In addition to direct sunlight encouraging algae growth, if the sun is strong enough, it can raise the water temperature in the tank, which will lead to temperature fluxuations once the sun is no longer beating on the tank.
My only experience with green water was in a betta tank placed near a window. It never received direct sunlight, yet it had some serious algae problems. A nearby betta tank also tended to develop algae even without running artificial lights more than a few minutes per day over an extended period. I'm not sure what factors determine whether a tank near a window will have problems, but I'd bet that latitude has a lot to do with it. I'm considerably closer to the equator than either Magoo or Psalm18.2.
Thanks everyone, I don't have such a big algae problem and I try to keep it clean. Sunlight hit is just for a few minutes max an hour and its early in the morning when sun is not that strong I don't think it makes a differences n the water.