Less obvious than solar panels are photovoltaic roof shingles. The shingles are indistinguishable from normal roof shingles. By performing double duty, they make the cost of solar cells competitive over the life of the shingles, according to the National Renewable Energy Lab, an Energy Department arm. The shingles produce about 5 watts per square foot based on the average sun hours per day. Thermal storage is integrated into the design of the house.
Windows are costly because they have to be custom-made, in many cases.
In some designs, passive solar heat can be stored in the walls, called Trombe walls. Another popular solar product is the pool heater, of which there are 300,000 in use nationally.