And yet it moves. Why the EROI of renewables may be higher than that of fossils

 

Eppur si move; (yet it moves). Galileo is said to have pronounced these words after having been condemned for supporting the heliocentric model of the solar system. New ideas take time to be accepted, and often the resistance against them is tenacious. This is especially true when the new ideas change an existing paradigm. It was the case for the heliocentric model; it may be the case for renewable energy technologies. So far, they have been considered little more than toys for greens, but now we face a radical change of paradigm: they may be able to do better, -- even much better -- than fossil fuels. That's far from certain, of course, but it is what's emerging from the data and the calculations. And if it will turn out to be true, our future will be completely different from what we thought it would be.   

The idea that renewable energy can provide a better energy return (EROI) than fossils is often met with not just skepticism; as it would be normal for a still unproven hypothesis. It is seen as absurd, impossible, unbelievable, outworldly, and worse. If you mention it in the discussion on social media, you risk being insulted, berated, accused of nefarious intentions, and your mental sanity questioned. It happened to me with the comments on my previous post. 

It is understandable that radical changes in paradigms upset people, making them worried and even angry. It happened with the heliocentric view of the Solar System at the time of Galileo, and if it turns out that renewable energy is a technology superior to fossil fuels, then it is an even larger change of paradigm. You know how deeply fossil fuels changed the world. Renewables may have similar effects, although in different ways. 

Now, please don't make me say that the higher EROI of renewables is an established truth. It is not. But from the data we have, I suspect that it might be. In any case, it is surely an idea well worth exploring. For a long-term view, you can see a paper of mine. Here, I'll try to discuss some available evidence that favors this possibility. 

The central point of this discussion is a paper by Murphy et al., who re-examined the available data about the EROI of energy sources, making sure that the evaluations were carried out in comparable conditions. That is, ensuring that the yield was compared at the "point of use" (POU) rather than at the "well mouth," which would give an unfair advantage to fossil fuels. Renewables directly produce usable energy, unlike fossil fuels which, after being extracted, need to be processed into fuels and turned into useful energy in inefficient thermal engines. 

The data presented by Murphy et al. indicate that the EROI of photovoltaics may be about five times larger than that of crude oil. Of course, all data and their interpretation are affected by uncertainties. So, let me propose some additional evidence that goes in the same direction. 

One obvious consequence of a high EROI for a technology is that you expect it to grow fast. It is the same mechanism of compound interest that generates exponential growth in the yield of a financial investment. This growth is proportional to the return on investment (ROI), the financial equivalent of EROI. Ultimately, in our economic system, energy is worth money, and a technology that has a good energy yield also has a good ROI, so we expect it to grow fast. (*)

On this point, there is no doubt that renewable energies are growing fast; very fast, especially for photovoltaic energy. Here are the current growth curves for photovoltaic energy (from "Our World in Data")

PV energy production is growing at an approximately exponential rate of about 25% yearly, leading to doubling every three years. Actually, the rate has been closer to 35% during the past few years, with a doubling time as low as two years. PV grows faster than any other modern renewable technology; the whole sector is growing at 16% yearly. 

But how fast does PV energy need to grow to prove that it has a higher EROI than fossils? At the very least, it should grow faster, and it does. Let's take a look at the data for global oil production:

During the heyday of the age of oil, in the 1950s and 1960s, production was doubling every 8-10 years, corresponding to a growth rate of 7%-8% yearly. Much slower than PV is doing nowadays. 

We can carry out the same evaluation for other energy technologies. In the 1970s, nuclear energy had a doubling time of a little more than 2 years. Meaning a growth of 25% per year. For coal, during the late 19th century, production doubled in no less than 20 years. Finally, biomass for power production never grew at high rates nor produced amounts of energy comparable to those of renewables. 

Overall, these data indicate a qualitative proportionality of the growth rate of a technology with its EROI. The fastest growth rate is observed for PV, in agreement with the proposals by Murphy et al. for an EROI around 20 on the average. Nuclear also fits this interpretation with a high EROI reported by Murphy et al, but for a plant lifetime larger than that of PV. The POU EROI of oil is reported by Murphy as around 5; and that fits with the slower growth rate. Note that the EROI at the well mouth may have been high in the 1960s -- over 30; but the POU EROI may have been similar to the current one. About the slow growth of biomass power production, it fits with the data indicating a low EROI. Regarding coal, the proportionality seems to be lost, since coal may have had a large EROI. But the data for more than a hundred years ago can't be compared with those of our times. 

In the end, I think the main evidence for the high efficiency of renewable energy is this graph that comes from recent Bloomberg data, (Figure by R. Craig)

You see how, for the same investment, renewable energy is growing fast (16% for the average, 35% for PV), whereas fossil fuel production is growing very slowly, if at all. 

These data strongly support the idea that renewables, and PV in particular, have a larger, actually much larger EROI than fossil fuels. That seems to be true for the present situation, but the question is for how long the growth of renewables can maintain this high EROI and continue growing. At some point, the curve will necessarily start flattening out, as it has already happened for oil and nuclear. The limits of the availability of solar energy are far away, but mineral resource bottlenecks are possible and even probable. These bottlenecks would have the effect of increasing the energy costs of new plant, and cause their EROI to plummet. Also, political factors are not to be discounted. Nuclear energy was rapidly growing in the 1960s, and you might have thought that it would soon replace fossil fuels. Indeed, people were speaking about the upcoming "nuclear age." But the technology was killed mainly by political and strategic factors. Today, if governments want to kill renewable energy, they can do that (and may be preparing to do exactly that). 

How long does the curve need to continue growing? Right now, wind and solar produce about 3500 TWh per year, a little more than 2% of the world's primary energy (about 160,000 TWh/year ). Actually, we don't need to ramp up production to such a level. Taking into account the losses in turning fossil fuels into energy and the various inefficiencies of the current infrastructure, Jacobson estimates that we need no more than half of that to match the current demand. Even with 50,000 TWh, our civilization would survive, although rather battered. Yet, it is a steep climb that we face, from about 5% to 100%. (For a more quantitative estimate, see this paper of mine with Sgouridis and Csala). Can we make it? It is a fighting challenge, but it is not impossible. At the current growth rates, renewables could reach 100% of what we need in one or two decades.  

The future, as usual, is obscure. But we have one of those opportunities that happen once in a lifetime (the lifetime of a civilization!).  

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(*) No energy technology can start its growth by pulling its own strings. In the beginning, it needs the support of energy from an already established technology (it is what we called "the sower's paradigm"). Coal grew on wood and human energy, oil grew on coal, and, at present, renewables are growing using the energy produced by oil and gas. The capability of a technology to grow on itself appears only when it has reached a significant fraction of the total production; it depends on the EROI -- and only technologies with a good EROI can reach this stage. Surely, the EROI of renewables is more than sufficient for them to support themselves.