Solar shingles, also called photovoltaic shingles, are solar cells designed to look like conventional asphalt shingles. There are several varieties of solar shingles, including shingle-sized solid panels that take the place of a number of conventional shingles in a strip, semi-rigid designs containing several silicon solar cells that are sized more like conventional shingles, and newer systems using various thin film solar cell technologies that match conventional shingles both in size and flexibility. Solar shingles are manufactured by several companies.
Commercial solar shingles were first available in 2005. In a 2009 interview with Reuters, a spokesperson for the Dow Chemical Company estimated that their entry into the solar shingle market would generate $5 billion in revenue by 2015 and $10 billion by 2020. The first location the Dow solar shingles became available was in Colorado, in October 2011.
Solar shingles are photovoltaic cells, capturing sunlight and transforming it into electricity. Most solar shingles are 12 by 86 inches (300 by 2,200 mm) and can be stapled directly to the roofing cloth. When applied they have a 5 by 86 inches (130 by 2,200 mm) strip of exposed surface. Different models of shingles have different mounting requirements. Some can be applied directly onto roofing felt intermixed with regular asphalt shingles while others may need special installation.
Solar shingled roofs have a deep, dark, purplish-blue color, and therefore look similar to other roofs in most situations. Home-owners may be drawn to solar shingles because of their aesthetic value, allowing the homeowner to utilize solar power without large panels on their roofs.
All photovoltaic power is produced in the form of direct current (DC). Homes use alternating current (AC). Therefore part of the cost of installation of solar shingles is the price of an inverter to make the conversion.
Energy storage 
The most inexpensive way to install solar shingles is to use the grid as a backup source of electricity. Backup storage, in the form of batteries, is expensive, adds complexity to the installation, and is uneconomic in any large scale. Battery backup units require an array of additional hardware. This includes batteries, battery enclosures, battery charge controllers, and separate sub panels for critical load circuits. However, grid power is only useful as a backup system if it is available when solar power is not.
Older solar shingle designs were more expensive to install than traditional PV panels, but new, more efficient designs such as thin-film copper indium gallium selenide (CuInxGa(1-x)Se2) cells can be installed in 10 hours, compared with the 22 to 30 hours required for the installation of traditional panels. The lower cost of installation dramatically reduces the cost of solar power implementation.
Three companies that make solar shingles are Uni-Solar (which filed for bankruptcy in 2012), Dow, and CertainTeed. Dow solar shingles as of February 2013 are available in California, Colorado, Connecticut, Michigan, New York, Texas, and will soon be available in Louisiana, Maryland, Massachusetts, North Carolina, and Washington D.C.