Covalent Solar Idea
MIT spin out, covalent solar have a great product that can turn sheets of glass into solar collectors. A special dye on the surface captures light within a glass sheet. The light travels through the glass untill it reaches the edges and can be fed into long thin photovoltaic cells built into a frame. This allows a large area of sun light to be focused on a much smaller area of photovoltaics (which are expensive).
The improvement idea is simple, to reduce the area of photovoltaics further, mirror all but 1 edge of the glass sheet.