The flourishing of most modern societies has largely been made possible through the exploitation of vast reserves of fossil energy; furthermore, as societies evolve, they often come to rely more and more heavily on electricity as a ubiquitous and versatile energy carrier. Conventional oil and gas reserves are being depleted at an increasingly fast rate, though, and there is increasing interest in ‘alternative’ energy sources such as ‘renewable’ electricity generation technologies, and photovoltaics (PV) in particular.
The Energy Return On energy Investment (EROI) metric was introduced to assess “how much energy is gained from an energy production process compared to how much energy is required to extract/grow/produce a new unit of the energy in question”. The EROI of PV has often been reported as too low for PV to be a viable alternative to fossil fuels. However, in a recent scientific publication, the authors have now reviewed the methodology, discussed methodological variations and presented updated EROI values for a range of modern PV systems, in comparison to conventional fossil-fuel based electricity life-cycles. Their results show that, when calculated in terms of equivalent primary energy, the EROI of modern PV technologies is in the range 19-38, similar to that of oil (10-30) and approaching that of coal (40-80). That means that, depending on the location and the specific technology, PV systems return 19 to 38 times more energy than the energy they use.
Energy Payback time (EPBT) of PV systems have been reduced from about 40 to 0.5 years from 1970 to 2010, thus today’s PVs return far more energy than that embodied in the life cycle of a solar system. In other words, PV systems need less than one year to generate the same amount of energy (in terms of primary energy equivalence) that was used to produce the system itself.
PV is not a base-load technology, though, and deploying it on a large scale, beyond approximately 20% of grid penetration, may require building an extensive (and potentially costly) energy storage infrastructure. Also, PV, like all other renewable technologies, must still be supported by an initial investment of primary energy, which is, as of today, of fossil origin. It is therefore argued that available monetary and energy resources should be funnelled in the right direction without delay, lest not enough high-EROI fossil fuels are left to support demand during times of gradual shift to renewable resources.
Raugei, M., Fullana-i-Palmer, P., Fthenakis, V. (2012) The energy return on energy investment (EROI) of photovoltaics: Methodology and comparisons with fossil fuel life cycles. Energy Policy 45: 576–582.DOI:10.1016/j.enpol.2012.03.008
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