Energy pay-back time: methodological caveats and future scenarios

Energy pay-back time (EPBT) has almost universally been adopted as the indicator of choice to express the energy performance of photovoltaics (PV). In this paper, an in-depth review of the methodology and all underlying assumptions and conventions is presented. A prospective analysis of the potential evolution of the EPBT of PV over the next four decades is then performed, assuming optimistic grid penetration figures and taking into account expected technological improvements. Results show that combining the two opposing effects of a reduction in cumulative energy demand for PV manufacturing and an increase in grid efficiency will likely result in severely limited reductions, or even possible increases, in the EPBT of PV. This is entirely due to how EPBT is operationally defined, and it has nothing to do with the actual energy performance of PV in the future. Copyright (c) 2012 John Wiley & Sons, Ltd.