The cheetah in the figure knows very well that it cannot spend more energy in chasing the impala than the impala can provide once eaten (in other words, the cheetah needs an energy return on the investment (EROEI)
>1). Carnivores make no calculations about that question, they only know that, if they want to survive, they have to run. And this is our destiny, too. If we want to survive, we need energy and we need to move away from fossil fuels before depletion or climate change (or both) destroy us. But, unlike lions and cheetahs, we tend to discuss a lot on the subject and, sometimes, to get it wrong. This is the problem with the recent movie "Planet of the Humans" and its wrong evaluation of renewable energy (image by Nick Farnhill, creative commons license)
Years ago, when I discovered the concept of "EROEI" (or EROI), energy return for energy invested, I was both delighted and elated. "Here is," I thought, "an objective way to evaluate and compare the efficiency of energy technologies. No more shaky financial calculations, no more ideology, no more politics, only facts. And everyone has to agree on the facts." And the beauty of the concept was that if the EROEI is smaller than one for a certain technology, then it is an energy sink, not an energy production system.
I was wrong more than I could have imagined. From when the idea of EROEI was first proposed, in the 1980s by Charles Hall, the concept was stretched, squashed, squeezed, twisted, and shaken until it became a useless mongrel. Ideology took over from physics and EROEI became a support for preconceived ideas rather than an evaluation tool.
I should have known better, but I hadn't realized how difficult it is for most people, including opinion leaders, to think in terms of data. One of the problems with EROEI is that many people just can't understand it, but the main one is that it is not easy to quantify its value. You can say, "this apple is red" just by looking at it, but not "this plant has an EROEI of 12.5." That is unless you perform a complex calculation based on the rules of LCA (life cycle analysis). Impossible if you are not trained in this specific field of work.
In practice, it is not difficult to find people with sufficient knowledge of the rules to be able to bend them in such a way to obtain the results they (or their sponsors) want. The result is a jungle: for every conceivable energy technology, you can find a range of values of the EROEIs so large that you can pick one according to what you like (2+2=5).
But it is not so much a question of cheating, it is just that science and politics talk two different languages. If you are a scientist, you reason in terms of data and models. If you are like most people, you reason in narrative terms. And narrative, as we all know, is all about a conflict between bad guys and good guys. So, that's the way people tend to evaluate the EROEI issue: they judge the messenger rather than the message. And they tend to like messengers who bring them messages they like. It is called "selective exposure" or "confirmation bias."
That's the reason for the success of a movie such as "Planet of the Humans." It is a clever movie because it passes a simple message that resonates with many people in the environmentalist movement: "big capital bad." That may even be true: there are plenty of scams embedded in concepts such as "green growth." But, in the movie, the real target is not big, bad capitalism, but renewable energy. It is presented as being unable to support itself because it has EROEI<1 or that, at least, the value of the EROEI is too small to support a complex civilization.
Then, most environmentalists know nearly nothing about the most elementary technologies of communication and many of them reacted by criticizing the many factual errors of the movie. But they didn't realize that most people are unable to evaluate the details of the takedown of the movie that many experts engaged in. And the result was a remarkable success for the movie and for its sponsors.
In any case, you can't change the way people think, not in a short time at least. So, my personal opinion is that it is useless to engage in infinite discussions about the EROEI of renewables or of other technology. And it is especially useless to discuss at length about a bad movie such as "Planet of the Humans." The human mind is such that it can demonstrate just about anything on the basis of apparently logical arguments. You probably know the story of how in 1903 the American physicist Simon Newcomb "demonstrated" on the basis of physics that human-made machines couldn't fly -- that was just five years before the first flight of the Wright brothers.
I am sure that with a little work it would be possible to "demonstrate" on the basis of physical principles that cheetahs cannot catch impalas. But cheetahs don't need theories telling them that they cannot feed on impalas. They run and they catch their prey. So, we can demonstrate that renewables work by installing renewable energy plants, as many as possible. And show that they work -- they do produce energy. And the more plants we install, the better the world will be for us and for those who'll come after us. It will help climate to stabilize, too.
On this matter, below you may read a post that I wrote three years ago. See also a post I published in 2016: But what's the REAL energy return of photovoltaic energy?
Why EROEI matters: the role of net energy in the survival of civilization
Published on Cassandra's Legacy, March 13,, 2017 (slightly modified in this version of May 15, 2020)
The image above was shown by Charlie Hall in a recent presentation that he gave in Princeton. It seems logical that the more net energy is available for a civilization, the more that civilization can do. Say, build cathedrals, create art, explore space, and more. But what's needed, exactly, for a civilization to exist? Maybe very high values of the EROEI (energy return on energy invested) are not necessary.
A lively debate is ongoing on what should be the minimum energy return for energy invested (EROEI) in order to sustain a civilization. Clearly, one always wants the best returns for one's investments. And, of course, investing in something that provides a return smaller than the investment is a bad idea. So, a civilization grows and prospers on the net energy it receives, that is the energy produced minus the energy required to sustain production. The question is whether the transition from fossil fuels to renewables could provide enough energy to keep civilization alive in a form not too different from the present one.
It is often said that the prosperity of our society is the result of the high EROEI of crude oil as it was in the mid 20th century. Values as high as 100 are often cited, but these are probably widely off the mark. The data reported in a 2014 study by Dave Murphy indicate that the average EROEI of crude oil worldwide could have been around 35 in the past, declining to around 20 at present. Dale et al. estimate (2011) that the average EROEI of crude oil could have been, at most, around 45 in the 1960s Data for the US production indicate an EROEI around 20 in the 1950s; down to about 10 today.
We see that the EROEI of oil is not easy to estimate but we can say at least two things: 1) our civilization was built on an energy source with an EROEI around 30-40. 2) the EROEI of oil has been going down, owing to the depletion of the most profitable (high EROEI) wells. Today, we may be producing crude oil at EROEIs between 10 and 20 on the average, and the net energy yield keeps going down.
Let's move to renewables. Here, the debate often becomes dominated by emotional or political factors that seem to bring people to try to disparage renewables as much as possible. Some evidently wrong assessments claim EROEIs smaller than one for the most promising renewable technology, photovoltaics (PV). In other cases, the game consists of enlarging the boundaries of the calculation, adding costs not directly related to the exploitation of the resource. That's why we should compare what's comparable; that is, use the same rules for evaluating the EROEI of fossil fuels and of renewable energy. If we do that, we find that, for instance, photovoltaics has an EROEI around 10. Wind energy does better than that, with an average EROEI around 20. Not bad, but not as large as crude oil in the good old days.
Now, for the mother of all questions: on the basis of these data, can renewables replace the increasing energy-expensive oil and sustain civilization? Here, we venture into a difficult field: what do we mean exactly as a "civilization"? What kind of civilization? Could it build cathedrals? Would it include driving SUVs? How about plane trips to Hawaii?
Here, some people are very pessimistic and not just about SUVs and plane trips. On the basis of the fact that the EROEI of renewables is smaller than that of crude oil, considering also the expense of the infrastructure needed to adapt our society to the kind of energy produced by renewables, they conclude that "renewables cannot sustain a civilization that can sustain renewables." (a little like Groucho Marx's joke, "I wouldn't want to belong to a club that accepts people like me as members.").
Maybe, but I beg to differ. Let me explain with an example. Suppose, just for the sake of argument, that the energy source that powers society has an EROEI equal to 2. You would think that this is an abysmally low value and that it couldn't support anything more than a society of mountain shepherds, or not even that. But think about what an EROEI of 2 implies: for each energy-producing plant in operation there must be a second one of the same size that only produces the energy that will be used to replace both plants after that they have gone through their lifetime. And the energy produced by the first plant is net energy fully available to society for all the needed uses, including cathedrals if needed. Now, consider a power source that has an EROEI= infinity; then you don't need the second plant or, if you have it, you can make twice as many cathedrals. In the end, the difference between two and infinity in terms of the investments necessary to maintain the energy-producing system is only a factor of two.
It is like that: the EROEI is a strongly non-linear measurement. You can see that in the well-known diagram below (here in a simplified version, some people trace a vertical line in the graph indicating the "minimum EROEI needed for civilization", which I think is unjustified)):
You see that oil, wind, coal, and solar are all in the same range. As long as the EROEI is higher than about 5-10, the energy return is reasonably good, at most you have to re-invest 10%-20% of the production to keep the system going. It is only when the EROEI becomes smaller than ca. 2 that things become awkward. So, it doesn't seem to be so difficult to support a complex civilization with the technologies we have. Maybe trips to Hawaii and SUVs wouldn't be included in a PV-based society, but about art, science, health care, and the like, well, what's the problem?
Actually, there is a problem. It has to do with growth. Let me go back to the example I made before, that of a hypothetical energy technology that has an EROEI = 2. If this energy return is calculated over a lifetime of 25 years, it means that the best that can be done in terms of growth is to double the number of plants over 25 years, a yearly growth rate of less than 3%. And that in the hypothesis that all the energy produced by the plants would go to make more plants which, of course, makes no sense. If we assume that, say, 10% of the energy produced is invested in new plants then, with EROEI=2, growth can be at most of the order of 0.3%. Even with an EROEI =10, we can't reasonably expect renewables to push their own growth at rates higher than 1%-2%(*). Things were different in the good old days, up to about 1970, when, with an EROEI around 40, crude oil production grew at a yearly rate of 7%. It seemed normal, at that time, but it was the result of very special conditions.
Our society is fixated on growth and people seem to be unable to conceive that it could be otherwise. But it is clear that renewables, with the present values of the EROEI, cannot support a fast-growing society. But is that a bad thing? I wouldn't say so. We have grown enough with crude oil, actually way too much. Slowing down, and even going back a little, can only improve the situation.
(*) The present problem is not to keep the unsustainable growth rates that society is accustomed to. It is how to grow renewable energy fast enough to replace fossil fuels before depletion or climate change (or both) destroy us. This is a difficult but not impossible task. The current fraction of energy produced by wind and solar combined is less than 2% of the final consumption (see p. 28 of the REN21 report), so we need a yearly growth of more than 10% to replace fossils by 2050. Right now, both solar and wind are growing at more than a 20% yearly rate, but this high rate is obtained using energy from fossil fuels. The calculations indicate that it is possible to keep these growth rates while gradually phasing out fossil fuels by 2050, as described in a 2016 paper by Sgouridis, Bardi, and Csala
