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Life-cycle assessment (LCA) is utilized to analyze SolFocus Inc. concentrator solar systems. A hybrid LCA methodology is explained that combines process and input-output LCA techniques. The use of the greenhouse gas return on investment metric for solar technologies is discussed as a complement to energy metrics. Finally, preliminary results of a hybrid LCA for the SolFocus concentrator technology are presented. It is found that transportation and electricity consumption play a significant role in energy consumption and greenhouse gas emissions.

A supply-chain decision tool is outlined that will assess the life-cycle greenhouse gases and energy demand of solar energy technology using a hybrid LCA structure. Energy and greenhouse gas metrics appropriate for the climate change mitigation goals of solar energy are discussed. Applying this methodology to SolFocus Inc. concentrator systems, preliminary results indicate that the energy payback time of SolFocus Panels can vary from 0.6 to 5 years depending on manufacturing locations. The greenhouse gas payback time, a new metric for energy technologies, varies from 1.1 to 64 years depending on the same factors indicating that greenhouse gas metrics are more sensitive to installation and supply chain decisions than energy metrics.

The greenhouse gas return on investment (GROI) metric is introduced as a compliment to the energy return on investment (EROI). Unlike EROI, GROI accounts for the life cycle energy mix, the efficiency, circularity, and supply chain of energy distribution, and the energy offset by a new energy installation. The average greenhouse gas emissions of labor and electricity are calculated for multiple countries to be used in GROI calculations. GROI is applied to a case study of SolFocus Inc. solar panels, and the potential extension of GROI methodology to a modified EROI and to decision making beyond energy is discussed.

Aiming at understanding the structural integrity of two representative concentrating photovoltaic (CPV) module configurations, finite element thermal stress analysis is carried out in this investigation. This study covers the nominal and extreme operating conditions, including system startup and shutdown. While the first CPV module is bonded by epoxytype material, the bonding material for the second CPV module is lead-free solder. The analysis of the first module confirms that this CPV module can endure the thermal stress under steady-state operation. However, residual stress analysis shows that the epoxy homing together the PV cell/aluminum nitride and aluminum nitride/heat sink pairs will likely break, first at some sporadic spots, and then in a good part of the bond causing the failure of the CPV module, as the cell temperature drops from 100[degrees]C to 0[degrees]C. Nonlinear viscoplastic analysis using the temperature profile of CPV cell fatigue test ongoing at United Technologies Research Center (UTRC) is performed to evaluate the structure strength and subsequently predict the life of the second CPV module. The result reveals that the maximum characteristic stresses of the PV cell components and heat sink are below the strength allowable for the corresponding materials under both the steady-state and overnight idle conditions. Critical locations on the solder that are potentially susceptible to structural failure after a few thousand thermal cycles due to the excessive shear stress are identified. A rough estimation of the module life is provided and compared with the fatigue test. This investigation provides firsthand understanding of the structural integrity of CPV modules and is thus beneficial for the solar energy community. [DOI: 10.1115/1.2840572] Keywords: concentrating photovoltaic cell (CPV), thermal stress, fatigue test, viscoplastic, life prediction, reliability

This article is a response to an article titled "One-Month Teacher Training Courses: Time for a Change?" that appeared in a previous issue of this journal (v57 n1 Jan 2003). The article questioned the concept of short, entry-level certification courses in English language teaching. (Author/VWL)