What customers may not know is that there's a dirtier side.

While solar is a far less polluting energy source than coal or natural gas, many panel makers are nevertheless grappling with a hazardous waste problem. Fueled partly by billions in government incentives, the industry is creating millions of solar panels each year and, in the process, millions of pounds of polluted sludge and contaminated water.

To dispose of the material, the companies must transport it by truck or rail far from their own plants to waste facilities hundreds and, in some cases, thousands of miles away.