Solar collector or window? Window
The same as on the collector the sun shines on the window. But who cared for that till now? Almost nobody!
Can a cheap window bring more energy than an expensive collector? Yes it can!
Where do more of sun rays fall in winter on? On the window!
Can we use a regulation of solar profits for saving of energy? Yes we can!
How to manage this? See the presentation above.
Energy calculator will tell you how much energy can you get from the window.