An Exploration of Divergence in EPBT and EROI for Solar Photovoltaics

Abstract

Solar photovoltaics (PV) is widely regarded as one of the most promising renewable energy technologies. Net energy analysis (NEA) is a tool to evaluate the energetic performance of all energy supply technologies, including solar PV. Results across studies can appear to diverge sharply, which leads to contestation of NEA's relevance to energy transition feasibility assessment and contributes to ongoing uncertainty in relation to the critical issue of the sustainability of PV. This study explores how PV NEA approaches differ, including in relation to goal definitions, methodologies and boundaries of analysis. It focuses on two principal NEA metrics, energy return on investment (EROI) and energy payback time (EPBT). Here we show that most of the apparent divergence between studies is accounted for by six factors-life-cycle assessment methodology, age of the primary data, PV cell technology, the treatment of intermittency, equivalence of investment and output energy forms, and assumptions about real-world performance. The apparent divergence in findings between studies can often be traced back to different goal definitions. This study reviews the differing approaches and makes the case that NEA is important for assessing the role of PV in future energy systems, but that findings in the form of EROI or EPBT must be considered with specific reference to the details of the particular study context, and the research questions that it seeks to address. NEA findings in a particular context cannot definitively support general statements about EROI or EPBT of PV electricity in all contexts.

A Biophysical Perspective of IPCC Integrated Energy Modelling

“…ISO [78] (Section 6.4.5) and ISO [79] (Section 5.2.3) require that stages, unit processes or inputs are followed until they 'lack significance' within the given scope. This can be problematic when LCAs are applied to energy transition exercises since a high level of 'completeness' is often assumed by modellers applying LCA data [21]. Environmentally-extended input-output analysis (EEIOA) connects energy flows to monetary flows using national input-output (I/O) tables and ensures systematic completeness.…”

“…In the case of solar photovoltaics for instance, the choice of goal definition, methodology and boundaries can alter the EROI by an order of magnitude [21]. Since the LCA literature has tended to converge towards a standard suite of guidelines, study results emphasise differences between studies, rather than a high level of completeness.…”

“…For example, the cost of oil and gas production has been shown to be inversely related to EROI [18,19], but the market price is overlaid with cycles and subject to many factors [20]. On the other hand, the price of solar photovoltaics may be a poor proxy for its energetic evaluation [21]. Nuclear power is subject to economic, regulatory and social constraints (e.g., von Hippel et al [22]), rather than underlying biophysical constraints, depending on factors such as reactor type, ore grade and enrichment method [23].…”

“…Ideally, EROI should provide a means to supplement conventional economic and environmental analysis and inform and shape energy transition analysis. However, a lack of methodological consistency has led to contestation of NEA's relevance to the broader and IAM scenario literature [21].…”

Trends in Scientific Literature on Energy Return Ratio of Renewable Energy Sources for Supporting Policymakers

“…For this reason, this type of analysis is specifically applicable to energy producing industries. NEA's goal is to calculate whether the energy output supplied by a production system, surpasses the energy input required to build, operate and maintain the infrastructure (Palmer and Floyd 2017). Moreover, it is necessary to take into account the quantity of energy to extract the energy resources and convert them, etc.…”