Direct sun from a south facing window (given that you are in the northern hemisphere, of course) can get really hot, and so much light demands CO2. You could put a sheer curtain in the window and reduce the light some, and this may keep the tank cooler.
Will there be good light in the winter? Some of my tanks get winter light because the sun is lower, and reaches under the eaves. In the summer the eaves keep the sun away in the middle of the day, but morning and evening sun comes in.
My plants thrive in natural light, but without CO2 yes, algae will also have a field day.