Perfecting the solar shingle

The technology exists for creating an aesthetically pleasing solar shingle

Asphalt shingles with their desirable aesthetics and proven performance have been the steep-slope roofing material of choice in the U.S. for more than half a century. According to "Residential Roofing 2010: A Market Focused Update," published by Principia Partners, Exton, Pa., more than 80 percent of sales in the U.S. residential roofing market are asphalt shingles or bitumen-based roofing materials.

Shingles typically are constructed by coating a reinforcement layer with molten bitumen and covering the surface with roofing granules to protect the bitumen from harmful ultraviolet (UV) radiation while providing desirable colors.

Roofing granules usually are made from naturally occurring mineral particles that are translucent to UV radiation. However, roofing granules typically have high absorption of solar heat, so shingles tend to have low solar reflectance. As a result, asphalt shingles can reach relatively high surface temperatures during hot summer days.

Recently, there has been high demand for roofing materials that can reflect more solar heat, reducing the energy need for indoor cooling loads. This particularly is true in Sun Belt states and regions where energy costs are relatively high. Furthermore, there has been a growing trend in building codes by local building officials to mandate cool roof systems not only because of their energy benefits but also because of potential benefits to cut greenhouse gases for global warming reduction.