My idea is simple.
Since one side of the apartment is much hotter when the sun is shining. Especially in winter time. I thought I could even out the temperature distribution a bit by blowing air on the hot window from the inside of the apartment.
With a USB fan this is done with very little electric energy. Just 2.5 watts. It could be run on solar battery charger panel.
Be sure to turn it of when the temperature of the window is cooler than room temperature.
My hot window was at the glass balcony. For larger buildings I think something could be built inspired by this idea. Fan aided natural heating.
Hot side. This is where you can use a USB fan on the window.
Cold side. The idea is to distribute some heat from the warm side to the cold side using fans.