Material considerations for terawatt level deployment of photovoltaics

The stabilization of future CO, atmospheric concentrations to levels that might prevent anthropogenic alterations of the world climate calls for tens of terawatts of carbon free renewable energy resources. The combined energy production potential of all known non-solar carbon-free renewable resources seems insufficient to meet these targets. Consequently, over the next decades solar energy, and in particular photovoltaics, is expected to fill the gap. In this work several mature photovoltaic technologies, ranging from silicon to thin films, and solar concentrator systems are analyzed. The estimates of the energy production limits are established for each technology, based on available global material reserves. It is shown that many existing technologies, albeit playing an important in the present sub-gigawatt energy production levels, are affected by severe material shortages, that would prevent their scale-up to the terawatt range. This is the case for thin film solar cells technologies based on CdTe and CIGS where the showstopper is the scarcity of tellurium and indium respectively. Despite the abundance of silicon, crystalline Si-based solar cells will hardly reach the terawatt range as additional scale-up of the technology will be impeded by the global reserves of silver, commonly used as electrode material. As for amorphous silicon and dye sensitized thin film technologies, avoiding the use of indium tin oxide transparent conductor films appears as a must for exceeding the few tenth of terawatt barrier. For existing III-V concentrator cells, operating under moderate concentration (<200X), terawatt year level may be afforded by circumventing the use of Ge substrates and by minimizing the use of In and An in the cell fabrication process. In conclusion the study summarizes current material challenges for terawatt level deployment of the existing solar cells, and for each technology, identifies improvements and innovations needed for further scale-up. (C) 2007 Elsevier Ltd. All rights reserved.