CIGS Solar Cells: Is there sufficient gallium?
CIGS (copper, indium, gallium, selenium) solar cells are much in the news because they promise good efficiency on relatively simple substrates (including flexible plastic) using simple manufacturing methods such as ink solutions and low temperature processing, unlike CVD films. Indium (In), gallium (Ga), selenium (Se) are relatively rare elements in the earth's crust, which leads to the question: Is there enough material available for identified applications?
The elements of the -IGS part of CIGS are produced from the mining and extraction operations associated with copper, aluminum, and coal, among others. Some recent price volatility indicates that demand can exceed current supply, but that does not really address the longer term requirements. Ga is essential to the expanding light-emitting-diode (LED) industry, and Ga has become an element of interest for the also expanding thin-film solar cell or photovoltaic (PV) industry. The following considers one possible quantity requirement for Ga CIGS PV applications.
Currently, approximately 80 metric tons (mT) of Ga are processed annually, including re-processing. Using some simple approximations (10-4 cm film thickness, ~20% Ga in the film, 1.2g Ga/m2, 1600W for 10 hours for 16kWh per household, 160W solar radiance with 15% conversion efficiency), a single household would require approximately 67m2 of CIGS solar cell area or ~80g of Ga. Thus, CIGS PV panels for 15 million households (or equivalent) would require ~1200mT of Ga. At the current rate of 80mT/year, all the Ga processing for approximately 15 years would be required to provide Ga for CIGS solar cells to power 15 million households or about 15% of the households in the U.S.A.
The 15 year number indicates that there may be sufficient Ga production; however, other considerations are important and unknown, such as the Ga quantity requirements for other applications, the actual efficiencies of manufacturing and solar conversion, the actual adoption rate of CIGS solar cells (or the Ga equivalent) in PV applications, and the ability to significantly increase Ga production.
It is highly likely that demand for Ga (and related elements) will increase in the near future, and that demand could exceed supply. Longer term, recycling will be important.
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