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Homeowners on the hunt for sparkling solar panels are lured by ads filled with images of pristine landscapes and bright sunshine, and words about the technology’s benefits for the environment — and the wallet.

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.

The fossil fuels used to transport that waste, experts say, is not typically considered in calculating solar’s carbon footprint, giving scientists and consumers who use the measurement to gauge a product’s impact on global warming the impression that solar is cleaner than it is.