I've been looking for a good solution for something like this for a while. This product claims to reflect heat without severely limiting visible light. The idea is to reflect the heat from a house back into the house in the winter and then turn the panels around to reflect the summer heat back out of the house.

A see through Insulating Panel mounted to the inside of windows, doors or skylights. The panel is manufactured of a metalized, coated, polyethylene sheet laminated to a sheet of carbon graphite PVC that is then perforated and laminated to a sheet of clear polyester.

The IN'FLECTOR insulating panel is reversible, so the reflective surface can face outward during the seasons when solar gain is a problem, and the carbon PVC surface can face outward during cold seasons to reflect heat back into the building and collect convective sunlight for conversion to radiant heat. The panel is held in place with magnets which form a virtually air tight seal and inhibits infiltration, conduction and convection while providing additional dead air space for insulation.