Energy Return on Energy Invested (ERoEI) for photovoltaic solar systems in regions of moderate insolation: A comprehensive response

A recent paper by Ferroni and Hopkirk (2016) asserts that the ERoEI (also referred to as EROI) of photovoltaic (PV) systems is so low that they actually act as net energy sinks, rather than delivering energy to society. Such claim, if accurate, would call into question many energy investment decisions. In the same paper, a comparison is also drawn between PV and nuclear electricity. We have carefully analysed this paper, and found methodological inconsistencies and calculation errors that, in combination, render its conclusions not scientifically sound. Ferroni and Hopkirk adopt ‘extended’ boundaries for their analysis of PV without acknowledging that such choice of boundaries makes their results incompatible with those for all other technologies that have been analysed using more conventional boundaries, including nuclear energy with which the authors engage in multiple inconsistent comparisons. In addition, they use out-dated information, make invalid assumptions on PV specifications and other key parameters, and conduct calculation errors, including double counting. We herein provide revised EROI calculations for PV electricity in Switzerland, adopting both conventional and ‘extended’ system boundaries, to contrast with their results, which points to an order-of-magnitude underestimate of the EROI of PV in Switzerland by Ferroni and Hopkirk.