Solar Window Heaters

Heating Your Home From Your Windows

Does anyone know of a solar window heater design that would work by being attached to the inside of the window? I've seen solar air heater designs that work by being placed on the outside of the home but if we could use existing windows as the glazing we could reduce the cost of the item.

The goals for the solar heater would be as follows.

1.Cheap
2.Efficient
3.Easy to remove and operate.
4.High percentage of recycled materials.