In this post, Marco Raugei makes a fundamental point about an often raised question: if we have to use fossil fuels to manufacture renewable plants, doesn’t it mean that renewables are useless? Raugei’s answer is a resounding "no". In fact, the EROEI of fossil fuels acts as a multiplier for the final EROEI of the whole process. It turns out that if we invest the energy of fossil fuels to build renewable plants we get an overall EROEI around 20 for a process that leads to photovoltaic plants and an even better one for wind plants. So, if we want to invest in our future, that’s the way to go, until we gradually arrive to completely replace fossil fuels! (image above from "The Energy Collective")

The EROI and promise of PV (and other renewables). Trying to avoid unnecessary inconsistency and confusion, and to keep an open mind and a balanced viewpoint.

The energy return on energy investment (acronym: EROI or EROEI) provides a numerical quantification of the benefit that the user gets out of the exploitation of an energy source, in terms of “how much energy is gained from an energy production process compared to how much of that energy (or its equivalent from some other source) is required to extract, grow, etc., a new unit of the energy in question” [1].

As straightforward as this definition may sound, when dealing with the diverse range of existing energy sources and technologies, the devil is in the details.

It goes without saying that, in order to ensure comparability, it would be wise to at least approach all EROI studies of different energy technologies by applying a strictly consistent methodology, including the all-important aspect of system boundaries (i.e. what should be included and what not). Otherwise, a reported lower extended-boundary EROI for any given new energy technology may (artfully or artlessly) be taken out of context by readers who have their own axe to grind (or who are just too eager to oversimplify), and then used to incorrectly single out that particular technology as a worse performer vis-à-vis more conventional ones (typically, fossil fuel-fired electricity production).
An instance of such a potentially tricky situation has recently arisen with the publication of a book on the EROI of the photovoltaic (PV) sector in Spain [2].

One aspect of the controversy is rooted in the fact that the interdependence of PV and fossil fuels is not ‘symmetrical’ – no-one in their right mind could claim otherwise – and hence the EROI of PV is affected by the EROI of the fossil fuels (oil, coal, and gas) that underpin it. Additionally, fossil fuel technologies are much more ‘mature’, and much of the necessary infrastructure for their operation (rigs, pipelines, roads, etc.) was developed long ago and has largely been amortized already. As a result, it may well be that extending the boundaries of the EROI analysis for fossil fuel-based technologies may end up making a smaller difference vs. doing the same for newer technologies such as PV.

Yet, it seems that this argument is too often brought up to imply that, since PV development and deployment is currently (largely) underpinned by fossil energy, and hence PV is not (yet) a fully independent and truly 100% renewable energy technology, then "why bother" in the first place?
Actually, this kind of critique is aimed at countering the incurable technological optimists’ view that "there is nothing to worry about: we can continue unabated in our reckless business-as-usual overconsumption of energy (and resources) because soon PV (and other renewables) will seamlessly step in and take the baton from dirty fossil fuels, and all will be well".

Such through-rose-tinted-glasses optimism is most likely wrong-headed and should probably be tamed. But it is also worth looking at the issue from another angle. Let us assume that the average EROI of the current mix of fossil fuels (which still represent our main sources of primary energy, globally) is some value X > 1. And let us also agree that we (as a society) need a large and ever-growing share of our energy budget in the form of electricity (to power our computers, telecommunications, trains, home appliances, etc).

Broadly speaking, we therefore have two options:

1) keep using all the oil (and other fossil fuels) directly as FEEDSTOCK fuel in conventional power plants. In so doing, we would get out roughly 1/3 of the INPUT energy as electricity (electricity production efficiency in conventional power plants being ~0.33). This would be the "quick and dirty" option, that maximizes the short-term (almost instantaneous, in fact) "bang for the buck".

2) Use the same amount of available oil (and other fossil fuels) as (direct and indirect) INPUT for the production of PV plants.

Building and deploying a modern crystalline silicon PV system requires approximately 3 GJ of primary energy per m2 (note that this value takes into account the conversion to electricity at ~0.33 efficiency prior to use in the PV manufacturing operations which are carried out using electric power). When installed in southern Europe (irradiation = 1,700 kWh/(m2*yr)), such system, operating at an average efficiency of 13% (reference) * 80% (performance ratio) = 10%, will produce approximately 5 MWh (= 18 GJ) of electricity per m2 over its 30-year lifetime [3,4]. What this means is that the c-Si PV system would provide an output of electricity roughly equal to 18/3 = 6 times its primary energy input, which corresponds about 6/0.33 = 18 times the amount of electricity that we would have obtained, had we burnt the fuel(s) as FEEDSTOCK in conventional power plants (option 1 above), instead of using them as INPUT for the PV plant.

Of course, we cannot afford to switch to option 2 tout-court overnight, for a number of technical as well as systemic reasons [5]. First and foremost, we simply would not be left with enough energy output in the short term to sustain and power our complex society. But an almost 20x improvement in the efficiency with which we use our limited and dwindling endowment of fossil fuels must be worth at least some consideration.

A planned long-term investment might be advisable, for instance, aimed at bringing about a gradual transition. The latter is in fact what many have been advocating, often only to be met with rather negative ‘gloom and doom’ reactions by others on a number of prominent discussion forums. It seems as if, in the minds of the latter, the desire to show that ‘the emperor has no clothes’ (i.e. that PV and other renewables are not yet, and might never be in full, a real, completely independent and high-EROI alternative to fossil fuels) overrides all other considerations, and prevents them from realizing/admitting that, after all, it may still be reasonable and recommendable to try and push this slow transition forward.

To conclude, I would like to dispel all doubts and clearly state that I do agree with the aforementioned ‘pessimists’ that if we (as a society) do not come to grips with the notion that there is no such thing as infinite growth on a finite planet [6,7], and re-align our goals and ‘development’ strategies accordingly, then all the technological fixes in the world stand little to no chance of being enough to avert an ominous crash. But, why write off PV (and other renewables) and deny their value as useful tools to (hopefully) help us out on a safe slide along the slopes of a "prosperous way down" [8]?


1. Murphy D.J., Hall C.A.S., 2010. Year in review – EROI or energy return on (energy) invested. Ann. N.Y. Acad. Sci. 1185:102-118
3. Fthenakis V.M., Held M., Kim H.C., Raugei M., 2009. Update of Energy Payback Times and Environmental Impacts of Photovoltaics. 24th European Photovoltaic Solar Energy Conference and Exhibition; Hamburg, Germany
4. Fthenakis V.M., Kim H.C., 2011. Photovoltaics: Life-cycle analyses. Solar Energy 85(8): 1609-1628
5. Smil V., 2010. Energy Transitions: History, Requirements, Prospects. Praeger, ISBN-13: 978-0313381775
6. Meadows, D H., Meadows D.L., Randers J., Behrens W., 1972. Limits to Growth. Signet, ISBN-13: 978-0451057679
7. Bardi U., 2011. The Limits to Growth Revisited. Springer, ISBN-13: 978-1441994158
8. Odum, H.T., Odum E.C., 2001. A Prosperous Way Down. Colorado University Press, ISBN-13: 978-0870819087