A solar collector is designed for use in the window opening of a house and also serves to retain the window function for the occupants of the house. The collector has a rectangular frame having an inner pane of glass, an outer pane or panes and a plurality of rotatable louvers mounted in the frame between the inner and outer panes. The louvers have a reflective material on one side and a dark or solar absorbing surface on the other, thereby allowing the proper side to be rotated into position depending on the season. A heated chamber is provided within the louvers so that the working fluid may flow directly through the louvers and allow the heat transfer to occur therein.