The Story of Cadmium Telluride (another video)
With the above understanding of why cadmium telluride (CdTe) panels are desirable, we must address the concerns raised by Stop-Solar voices. First, they raise the concern of CdTe vaporizing if the panels burn. What they do not tell you is that common pasture fires are not hot enough to vaporize CdTe; flame temperatures in roof fires are in the 800-900 C range, and, in confined below ground spaces, in the 900-1000 C range. The melting point of CdTe is 1041 C, and evaporation starts at 1050 C. The melting point of CdS is 1750 C. Read this full report from the National Photovoltaic Environmental Health and Safety Assistance Center at Brookhaven National Laboratory.
One recent study of a 2,000-acre installation in a desert stated “Residents raised questions about the panels’ vulnerability to a desert wildfire. ‘The amount of fuel that’s available,’ Sinha said of the 2,000-acre site that will be replanted with native grasses when construction of the ground-mounted arrays is complete, ‘is pretty minimal,’ so ‘the maximum temperature would be 800 to 1,000 degrees Celsius for ten to twenty seconds.’
At those temperatures, Sinha said, the CdTe would remain stable. In tests at up to 1,100 degrees Celsius, he added, the CdTe migrated into the heat-softened glass and was encapsulated. Only 0.4 percent of it would be released.”
Another article makes these points and provides references to support them.
- Solar panels are not at all fragile; they are made mostly of aluminum and shatter-resistant glass. They can withstand golf ball-sized hail. Similar to a car window, if they crack, they do not usually shatter.
- Solar panels contain only materials in “solid-state” form, just like the electronic components in laptops and smartphones. They do not contain liquids that can “leak.”
- The amount of “chemicals” in solar panels is miniscule. For example, a typical solar panel has about half the amount of lead (used as solder) as a single shotgun shell, and a single battery used in a car or farm equipment has more lead than 700 solar panels.[2] An Ohio manufacturer uses a semi-conducting layer of cadmium telluride in its solar panels that is only 3% of the thickness of a human hair.
- Several of the chemicals used in solar panels that the website claims are toxic to humans are not. For example, cadmium telluride (CdTe), which presents no safety issues at solar facilities, is not the same as the element cadmium (Cd), which may be toxic. According to Virginia Tech, “[t]o draw a simple analogy, the properties of water (H2O) are not similar to those of hydrogen gas (H2) just because the two species both contain hydrogen. Just as it is improper to assume water can burn because hydrogen burns, it is invalid to treat CdTe as if it were as toxic as Cd.”
- Rain or moisture at operating solar facilities is not a concern. In order to ensure their functioning over decades and satisfy warranties, solar panels’ semi-conducting layer is protected from moisture by encapsulation within an airtight envelope. As reported by Virginia Tech, “[w]hen photovoltaic modules break in the field, they remain intact. Encapsulation of the module components is achieved through use of a glass-laminate-glass design . . . [whose] bond strength is on the order of ~50 kg/cm2 making it very difficult to separate the front and back of the module. For example, in a landfill experiment, photovoltaic modules were crushed with six passes by a landfill compactor with a compact load of 50 tons, and the crushed module pieces maintained the front-back encapsulation.”
When considering pollution from solar we must remember that our most likely alternative is a coal-powered electric generation with its fly ash and air quality issues.
Everyone agrees that recycling solar panels at their end of life is critical. Although First Solar (the major CdTe panel producer) guarantees their Ohio-produced panels for 25 years, they have already established a system for recycling CdTe panels.
Here is a link to a more complete article on thin-film CdTe Photovoltaics.
In conclusion American made cadmium telluride panels have many reasons to be considered. We should not allow Stop-Solar folks to black ball them with fear-mongering.