I guess I was on a painting kick when I came up with this and the previous idea, so bear with me. Imagine having paint that would act like a solar panel and actually convert light to power. You could literally capture ambient light in a house and pump the power back into the household grid. Sure there would be a significant loss, but just capturing a little would have a serious impact.
Take this a step further and paint the outside of your house with the same paint and imagine every surface of your house generating electricity.