There is a downside to China having become the largest producer and consumer of solar energy (J. A. Mathews and H. Tan Nature 508, 319; 2014). The rapidly expanding manufacture of solar photovoltaic products is risking serious environmental pollution.

According to Greenpeace and the Chinese Renewable Energy Industries Association, some two-thirds of the country's solar-manufacturing firms are failing to meet national standards for environmental protection and energy consumption. The production of polysilicon and silicon wafers for solar panels creates dangerous by-products, in particular silicon tetrachloride and hydrofluoric acid, which are being discharged into the environment after inadequate waste treatment (see; in Chinese).

For example, in 2011, fluoride concentrations in the Mujiaqiao River near a solar-panel factory in Haining City, eastern China, were more than ten times higher than permitted, killing fish and raising concerns about human health.

Another source of pollution is the careless disposal of used solar-panel equipment, which includes battery waste containing lead, cadmium, antimony and sulphuric acid (see H. Wang and J. Nima Qinghai Soc. Sci. 5, 58–60; 2007).

Improved waste treatment, environmental monitoring and education are essential to avoid the undesirable impacts of these otherwise valuable technological advances.