Cadmium Telluride (CdTe) PV Panels

This subsection examines the components of a cadmium telluride (CdTe) PV panel. Research demonstrates that they pose negligible toxicity risk to public health and safety while significantly reducing the public’s exposure to cadmium by reducing coal emissions. As of mid-2016, a few hundred MWs of cadmium telluride (CdTe) panels, all manufactured by the U.S. company First Solar, have been installed in North Carolina.

Questions about the potential health and environmental impacts from the use of this PV technology are related to the concern that these panels contain cadmium, a toxic heavy metal. However, scientific studies have shown that cadmium telluride differs from cadmium due to its high chemical and thermal stability. 18 Research has shown that the tiny amount of cadmium in these panels does not pose a health or safety risk. 19 Further, there are very compelling reasons to welcome its adoption due to reductions in unhealthy pollution associated with burning coal. Every GWh of electricity generated by burning coal produces about 4 grams of cadmium air emissions. 20 Even though North Carolina produces a significant fraction of our electricity from coal, electricity from solar offsets much more natural gas than coal due to natural gas plants being able to adjust their rate of production more easily and quickly. If solar electricity offsets 90% natural gas and 10% coal, each 5-megawatt (5 MWAC, which is generally 7 MWDC) CdTe solar facility in North Carolina keeps about 157 grams, or about a third of a pound, of cadmium out of our environment. 21 , 22

Cadmium is toxic, but all the approximately 7 grams of cadmium in one CdTe panel is in the form of a chemical compound cadmium telluride, 23 which has 1/100th the toxicity of free cadmium. 24 Cadmium telluride is a very stable compound that is non-volatile and non-soluble in water. Even in the case of a fire, research shows that less than 0.1% of the cadmium is released when a CdTe panel is exposed to fire. The fire melts the glass and encapsulates over 99.9% of the cadmium in the molten glass. 25

It is important to understand the source of the cadmium used to manufacture CdTe PV panels. The cadmium is a byproduct of zinc and lead refining. The element is collected from emissions and waste streams during the production of these metals and combined with tellurium to create the CdTe used in PV panels. If the cadmium were not collected for use in the PV panels or other products, it would otherwise either be stockpiled for future use, cemented and buried, or disposed of. 26 Nearly all the cadmium in old or broken panels can be recycled which can eventually serve as the primary source of cadmium for new PV panels. 27

Similar to silicon-based PV panels, CdTe panels are constructed of a tempered glass front, one instead of two clear plastic encapsulation layers, and a rear heat strengthened glass backing (together >98% by weight). The final product is built to withstand exposure to the elements without significant damage for over 25 years. While not representative of damage that may occur in the field or even at a landfill, laboratory evidence has illustrated that when panels are ground into a fine powder, very acidic water is able to leach portions of the cadmium and tellurium, 28 similar to the process used to recycle CdTe panels. Like many silicon-based panels, CdTe panels are reported (as far back ask 1998 29) to pass the EPA’s Toxic Characteristic Leaching Procedure (TCLP) test, which tests the potential for crushed panels in a landfill to leach hazardous substances into groundwater. 30 Passing this test means that they are classified as non-hazardous waste and can be deposited in landfills. 31 , 32 For more information about PV panel end-of-life, see the Panel Disposal section.

There is also concern of environmental impact resulting from potential catastrophic events involving CdTe PV panels. An analysis of worst-case scenarios for environmental impact from CdTe PV panels, including earthquakes, fires, and floods, was conducted by the University of Tokyo in 2013. After reviewing the extensive international body of research on CdTe PV technology, their report concluded, “Even in the worst-case scenarios, it is unlikely that the Cd concentrations in air and sea water will exceed the environmental regulation values.” 33 In a worst-case scenario of damaged panels abandoned on the ground, insignificant amounts of cadmium will leach from the panels. This is because this scenario is much less conducive (larger module pieces, less acidity) to leaching than the conditions of the EPA’s TCLP test used to simulate landfill conditions, which CdTe panels pass. 34

First Solar, a U.S. company, and the only significant supplier of CdTe panels, has a robust panel take-back and recycling program that has been operating commercially since 2005. 35 The company states that it is “committed to providing a commercially attractive recycling solution for photovoltaic (PV) power plant and module owners to help them meet their module (end of life) EOL obligation simply, cost-effectively and responsibly.” First Solar global recycling services to their customers to collect and recycle panels once they reach the end of productive life whether due to age or damage. These recycling service agreements are structured to be financially attractive to both First Solar and the solar panel owner. For First Solar, the contract provides the company with an affordable source of raw materials needed for new panels and presumably a diminished risk of undesired release of Cd. The contract also benefits the solar panel owner by allowing them to avoid tipping fees at a waste disposal site. The legal contract helps provide peace of mind by ensuring compliance by both parties when considering the continuing trend of rising disposal costs and increasing regulatory requirements.

References
  1. ^ Bonnet, D. and P. Meyers. 1998. Cadmium-telluride—Material for thin film solar cells. J. Mater. Res., Vol. 13, No. 10, pp. 2740-2753
  2. ^ V. Fthenakis, K. Zweibel. CdTe PV: Real and Perceived EHS Risks . National Center ofr Photovoltaics and Solar Program Review Meeting, March 24-26, 2003. www.nrel.gov/docs/fy03osti/33561.pdf. Accessed May 2017
  3. ^ International Energy Agency Photovoltaic Power Systems Programme. Life Cycle Inventories and Life Cycle Assessments of Photovoltaic Systems . March 2015. Accessed August 2016. http://iea-pvps.org/index.php?id=315
  4. ^ Data not available on fraction of various generation sources offset by solar generation in NC, but this is believed to be a reasonable rough estimate. The SunShot report entitled The Environmental and Public Health Benefits of Achieving High Penetrations of Solar Energy in the United States analysis contributes significant (% not provided) offsetting of coal-fired generation by solar PV energy in the southeast.
  5. ^ 7 MW * 1.5 GWh/MW * 25 years * 0.93 degradation factor * (0.1 *4.65 grams/GWh + 0.9*0.2 grams/GWh)
  6. ^ Vasilis Fthenakis. CdTe PV: Facts and Handy Comparisons. January 2003. Accessed March 2017. https://www.bnl.gov/pv/files/pdf/art_165.pdf
  7. ^ Kaczmar, S., Evaluating the Read-Across Approach on CdTe Toxicity for CdTe Photovoltaics , SETAC North America 32nd Annual Meeting, Boston, MA, November 2011. Available at: ftp://ftp.co.imperial.ca.us/icpds/eir/campo-verde-solar/final/evaluatin…, Accessed May 2017
  8. ^ V. M. Fthenakis et al, Emissions and Encapsulation of Cadmium in CdTe PV Modules During Fires Renewable Progress in Photovoltaics: Research and Application: Res. Appl. 2005; 13:1–11, Accessed March 2017, www.bnl.gov/pv/files/pdf/abs_179.pdf
  9. ^ Fthenakis V.M., Life Cycle Impact Analysis of Cadmium in CdTe Photovoltaic Production , Renewable and Sustainable Energy Reviews, 8, 303-334, 2004. www.clca.columbia.edu/papers/Life_Cycle_Impact_Analysis_Cadmium_CdTe_Ph…, Accessed May 2017
  10. ^ International Renewable Energy Agency. Stephanie Weckend, Andreas Wade, Garvin Heath. End of Life Management: Solar Photovoltaic Panels . June 2016. Accessed November 2016.
  11. ^ International Journal of Advanced Applied Physics Research. Renate Zapf-Gottwick1, et al. Leaching Hazardous Substances out of Photovoltaic Modules . January 2015. Accessed January 2016. www.cosmosscholars.com/phms/index.php/ijaapr/article/download/485/298
  12. ^ Cunningham D., Discussion about TCLP protocols, Photovoltaics and the Environment Workshop, July 23-24, 1998, Brookhaven National Laboratory, BNL-52557
  13. ^ Parikhit Sinha, et al. Evaluation of Potential Health and Environmental Impacts from End-Of-Life Disposal of Photovoltaics, Photovoltaics, 2014. Accessed May 2016
  14. ^ Practical Handbook of Photovoltaics: Fundamentals and Applications. T. Markvart and L. Castaner. Chapter VII-2: Overview of Potential Hazards . December 2003. Accessed August 2016. https://www.bnl.gov/pv/files/pdf/art_170.pdf
  15. ^ Norwegian Geotechnical Institute. Environmental Risks Regarding the Use and End-of-Life Disposal of CdTe PV Modules . April 2010. Accessed August 2016. https://www.dtsc.ca.gov/LawsRegsPolicies/upload/Norwegian-Geotechnical-…
  16. ^ First Solar. Dr. Yasunari Matsuno. December 2013. August 2016. Environmental Risk Assessment of CdTe PV Systems to be considered under Catastrophic Events in Japan . http://www.firstsolar.com/-/media/Documents/Sustainability/Peer-Reviews…
  17. ^ First Solar. Parikhit Sinha, Andreas Wade. Assessment of Leaching Tests for Evaluating Potential Environmental Impacts of PV Module Field Breakage . 2015 IEEE
  18. ^ See p. 22 of First Solar, Sustainability Report. Available at: www.firstsolar.com/-/media/First-Solar/Sustainability-Documents/03801_F…, Accessed May 2017
NC State Credit