While much of the waste produced is considered toxic, there was no evidence it has harmed human health.
The vast majority of solar companies that generated hazardous waste in California have not been cited for waste-related pollution violations, although three had minor violations on file.
In many cases, a toxic sludge is created when metals and other toxins are removed from water used in the manufacturing process. If a company doesn't have its own treatment equipment, then it will send contaminated water to be stored at an approved dump.
According to scientists who conduct so-called "life cycle analysis" for solar, the transport of waste is not currently being factored into the carbon footprint score, which measures the amount of greenhouse gases produced when making a product.
Life cycle analysts add up all the global warming pollution that goes into making a certain product — from the mining needed for components to the exhaust from diesel trucks used to transport waste and materials. Not factoring the hazardous waste transport into solar's carbon footprint is an obvious oversight, analysts said.
"The greenhouse gas emissions associated with transporting this waste is not insignificant," Mulvaney said.
Mulvaney noted that shipping, for example, 6.2 million pounds of waste by heavy-duty tractor-trailer from Fremont, Calif., in the San Francisco Bay area, to a site 1,800 miles away could add 5 percent to a particular product's carbon footprint.
Such scores are important because they provide transparency to government and consumers into just how environmentally sustainable specific products are and lay out a choice between one company's technology and another's.
The roughly 20-year life of a solar panel still makes it some of the cleanest energy technology currently available. Producing solar is still significantly cleaner than fossil fuels. Energy derived from natural gas and coal-fired power plants, for example, creates more than 10 times more hazardous waste than the same energy created by a solar panel, according to Mulvaney.
The U.S. solar industry said it is reporting its waste, and sending it to approved storage facilities — thus keeping it out of the nation's air and water. A coal-fired power plant, in contrast, sends mercury, cadmium and other toxins directly into the air, which pollutes water and land around the facility.
"Having this stuff go to ... hazardous waste sites, that's what you want to have happen," said Adam Browning, executive director of the Vote Solar Initiative, a solar advocacy group.
Environmental advocates say the solar industry needs greater transparency, which is getting more complicated as manufacturing moves from the U.S. and Europe to less regulated places such as China and Malaysia.
The Silicon Valley Toxics Coalition, a watchdog group created in 1982 in response to severe environmental problems associated with the valley's electronics industry, is now trying to keep the solar industry from making similar mistakes through a voluntary waste reporting "scorecard." So far, only 14 of 114 companies contacted have replied. Those 14 were larger firms that comprised 51-percent of the solar market share.
"We find the overall industry response rate to our request for environmental information to be pretty dismal for an industry that is considered 'green,'" the group's executive director, Sheila Davis, said in an email.
While there are no specific industry standards, Smirnow, head of the solar industry association, is spearheading a voluntary program of environmental responsibility. So far, only seven of the group's nearly 81 manufacturers have signed the pledge.
"We want (our program) to be more demanding, but this is a young industry and right now manufacturing companies are focused on survival," he said.
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