Is the Energy Return of Renewables Really Higher than that of Fossil Fuels? A Rebuttal to Art Berman's Criticism

 

The "net energy cliff," a popular graphic often used to demonstrate that renewables will never be able to support an industrial society. It is mostly wrong or at least obsolete. The EROI of crude oil never was so high as shown here, and the idea that there is a "minimum EROI needed" to support modern society is debatable, to say the least.

It is a very good thing that Art Berman, a well-known expert in oil and fossil fuel matters, has intervened in the EROI debate on renewables with a recent post. It means that the EROI is becoming the focus of the debate, as it should be. The most recent data indicate that the EROI of renewables significantly surpasses that of oil when examined at the "point of use" rather than at the "well mouth." And, of course, as users of energy, the point of use it is what we are interested in.

First of all, a note: nowadays, the debate on the energy transition is almost purely political. As such, it is based on slogans, and we know that slogans are not based on data or facts. So, it is a pleasure to see that Art Berman, a well-known expert in matters related to oil and fossil fuels, engages in a fact-based debate. That allows me to respond with a different interpretation, still remaining within the boundaries of what a debate should be; with the discussants respecting each other. 

This said, let me go to Berman's criticism which is specifically directed to a recent paper by Murphy et al., where the authors make the point that the EROI of renewables is now significantly larger than that of fossil fuels when a correct comparison is made. 

The problem, here, is that social media are flashing with messages that say that Murphy's paper is "wrong" or that it contains "mathematical errors." It is not true, but when everybody keeps repeating the same thing, it becomes true. It has already happened with the 1972 study, "The Limits to Growth," which was said so often to contain "wrong predictions" that it became common knowledge that it did. Except that it didn't. But that's the way the memesphere works. 

I think that the element that has generated the idea of "errors" in Murphy's paper is described here by Berman.

  

This statement from that paper was a huge red flag for me.

“Even if crude oil were measured to have an EROI of 1000 or more at the point of extraction, the corresponding EROI at the point of use, using global average data for the energy “cost” of the process chain, would still only be a maximum of 8.7.”

This means that the supply-chain energy costs for refining and product distribution create a permanent penalty that prevents oil from reaching an EROI of more than 8.7. It furthermore implies that refining must be a marginally profitable business at best which it is not.

At first sight, the statement by Murphy et al., looks strange, even unreasonable. But it is not so. It is a correct interpretation of how the concept of EROI works. 

The EROI is the ratio of the energy produced to the energy spent to make a certain energy production system work. It is something deeply embedded in the concept of "biophysical economics." It derives from the idea that the human economy works in the same way as an ecosystem. Not just because they have the same term "eco" (from the Greek oikos) in the name, but because they are both "dissipation structures," in the sense described by Prigogine long ago. A dissipation structure turns energy into waste or, if you prefer, does its job of increasing the entropy of the universe. (see some references at the bottom of this post).

So, the EROI is analogous to the economic return on investments. In mathematical terms, it is the same as the "effective reproduction rate" in biology, and also to the "reproduction number" (Rt) that was so fashionable during the pandemic, when people struggled to "flatten the curve." In EROI terms, they were striving to reduce the EROI of virus replication. The opposite of what we are trying to do with energy sources!

Unfortunately, as they say, "the devil is in the details," and the discussion on EROI is affected by misunderstandings and by the unavoidable uncertainty involved in evaluating complicated systems such as the oil industry. The paper by Murphy et al. that Berman discusses is aimed at clarifying a fundamental problem: "energy" is a well-defined physical quantity, but we are not interested in energy as such, but in energy potentials. A concept that defines how much useful work can be obtained from energy. The energy potential is a mix of the two fundamental concepts of energy and entropy. We are interested in, basically, how much entropy we can create using what we call an "energy source" (sun, oil, wind, whatever). 

And here is the point of the discussion: you can measure the energy embedded in a barrel of oil and compare it to the energy embedded in a lithium battery. But the battery will dissipate that energy in the form of electric power at more than 90% efficiency. To obtain the same amount of work from the oil contained in the barrel, you have to go through a series of steps, including transporting, processing, refining, more transporting, and finally burning it inside a thermal engine that, typically, has an efficiency of about 30%. Not all energies are created equal!

That's the key point of the reasoning in Murphy's paper. They note, correctly, that the EROI of crude oil is often measured at the "mine mouth" or "well mouth." That is, it does not include the energy lost in the various steps needed to turn the oil into useful energy. They use the term EROI(POU) (point of use) to indicate the correct way of estimating the EROI of crude oil when it is a question of comparing it with that of solar or wind energy, which directly produce useful electric energy. 

In this procedure, it is perfectly reasonable that the EROI of oil at the "mine mouth" or "well mouth" has no importance in determining the EROI at the point of use (POU). It is because a multi-stage EROI chain works like a metal chain: it is as strong as its weakest link. In the ratio of "Energy Out" to "Energy In," the first term is the energy produced by the last step of the chain, instead, the "Energy in" is the energy lost (and hence in need to be replaced) at each step. We could write that:

EROI = Eout/(Ein(1) + Ein(2) + Ein(3) +.....).

And you see that if, say, Ein(2) (refining) is much larger than Ein(1) (extraction), then reducing Ein(1) (increasing the EROI of extraction) will have no significant effect on the overall EROI. Note that in this view, all energy inputs are treated as the same. They may not be in terms of monetary costs, but it is another matter. 

Having established that Murphy et al.'s proposal that oil's EROI is no more than 8.7 is not a mistake but a correct interpretation of the definition of EROI, we need to examine whether it is a likely interpretation of the current situation. Berman criticizes it on the basis of several observations; for instance, that it would mean that refining would be at best an unprofitable business, which is not. 

I trust Art completely if he says that refining is profitable. But we don't have a precise correspondence between profitability and EROI. Besides, if we think of an EROI of 8.7 in financial terms, you would be very happy the return on your investment is more than 8 times the capital invested! The problem, here, is that the EROI is a ratio of two energy flows, but it says nothing about how large these flows are. If they are very small, of course, it matters little how large the EROI is. Here, Berman makes a correct point when he notes that, 

"Society does not function and survive on the per-unit net energy to society but on the full-system net energy delivered to society. This is like saying that I can solve my personal financial problems by delivering newspapers because the per-unit returns are so high. The net income from the paper route is so small, however, that it wouldn’t even help with the monthly escrow payment on my mortgage."

Equivalently, we could say that engaging in a career as a beggar requires a very small initial investment, and hence it has a high ROI, but it is not a good way to make a living. Nevertheless, while this is true in financial terms, in terms of energy production it is a restatement of what I called the "Godzilla Egg" fallacy: a small egg does not mean that the adult creature will be small. Obviously, renewables will not solve any problem as long as the energy they provide to society is small -- no matter how low the cost. But, of course, renewables can grow

Their potential of renewables in terms of solar energy available is enormous, even though we may run into other kinds of limitations in terms of mineral resources. But, at present, these limits are not preventing renewables from growing fast, and their good EROI indicates that the materials used can be effectively recycled using the energy that renewables themselves produce. Some European economies already produce half or more of their electric power from renewable sources, for instance, Germany. So, it is possible to move onward and create a sustainable energy infrastructure that will last for a long time and that will sustain a resilient human civilization, not anymore depending on the vagaries of the depletion of mineral energy resources.   

There are many more points that could be discussed in relation to Berman's post, mainly about the idea that the low EROI of fossil fuels cannot be so low as some studies indicate because it would be insufficient to sustain a complex industrial civilization such as ours. That would require a long discussion. Let me just say, here, that the "minimum EROI needed" for civilization is, at best, a debatable concept and that the value of "5-7" should be understood as highly uncertain, to say the least. 

I think these are the main elements of the story. If you want to know more about the concept of EROI as an essential element of biophysical economics, I suggest two recent papers that I published together with my coworkers Perissi and Lavacchi

The Role of Energy Return on Energy Invested (EROEI) in Complex Adaptive Systems, by Ilaria Perissi, Alessandro Lavacchi, and Ugo Bardi), Energies, 2021

Peaking Dynamics of the Production Cycle of a Nonrenewable Resource, by Ilaria Perissi, Alessandro Lavacchi, and Ugo Bardi, Sustainability 2023

Electricity: the universal energy currency

 

By Harald Desing

Energy is conserved. Counter to common language, energy can neither be "produced" nor "consumed", but only transformed. However, there are more and less useful forms of energy: electricity, for example, is extremely versatile and can be transformed into any other form of energy with close to 100% efficiency. In contrast, low temperature heat cannot do much work anymore; it is the energy "waste" with no work potential. The work potential is called exergy: electricity has 100% exergy content, whereas heat at the same temperature than the surroundings has 0%. Society is driven by useful work provided through different energy resources. So, different energy forms should be compared with the useful work they are able to do.

Commonly, this is not the case. Energy statistics, such as the IEA or from national statistic offices, do compare apples with oranges: "Primary" energy is accounted on different levels: calorific energy content of fuels (that is the heat potential that can be generated by burning the fuel) alongside with solar electricity and geothermal heat at different temperature levels. All of them have different work potentials, and they are later used as different forms of energy: heat for buildings and industry, electricity, or motion for mobility.

When we defossilize the energy system, most of the fossil energy applications, which are not yet electricity, have to be replaced by renewable electricity. For example, instead of internal combustion engines in cars and trucks, we need battery electric vehicles and electric trains; gas boilers can be replaced by heat pumps powered by electricity; and high temperature heat for industry with either direct electric heating (such as an electric arc furnace) or hydrogen produced with renewable electricity (such for hydrogen-reduced steel). Low temperature heat could also be provided by solar thermal collectors, with a similar efficiency than converting to solar electricity first and to heat with heat pumps later. High temperature heat could be provided by concentrated solar systems, however, this is currently not very practical for most applications in industry. In particular cases, it may make sense to provide heat directly from solar, biomass or geothermal. However generally, electricity is the universal and versatile intermediary form of energy for all sectors.

We do not have to replace "primary" fossil energy, but only the useful work they provide to society. Fictively converting all primary energy to electric energy equivalents using state-of-the-art conversion technologies, provides a more reasonable estimate for what really needs to be replaced. It reduces the energy supply to society from almost 19 terawatt (TW) in 2019—as counted by IEA as "primary" energy—to 7.3TW.  Renewable energies already provide 15% of this, so "only" 6.3TW needs to be replaced during the energy transition with renewable electricity.

Sometimes, this reduction is labeled "gigantic efficiency improvements" when switching to RE systems, but actually it is merely counting energies on the basis of usefulness to society. The efficiency of the subsequent energy services remain the same. The efficiency of the energy provisioning system, in contrast, could be measured by tracing energy conversions all the way back to their origin. For most energy forms, this is our sun. Hydropower is nothing but converted sunlight: sunshine on oceans evaporates water, forms clouds and generates winds that carry vapor over land where it falls as rain. The height difference of the runoff back to the oceans is what can be used as hydropower. This description makes it clear already that from the original solar energy, only a tiny fraction can be converted to hydroelectricity. The same applies to wind and biomass. All of them are much less efficient than direct solar energy conversion. Fossil fuels are also nothing but (ancient) sunlight. They had been slowly built over many million years by buried biomass; now we burn them at a rate more than ten thousand times faster than they were built. The solar energy that created coal, oil and gas deposits is again much more than solar energy stored in recent biomass, reducing the conversion efficiency from sunlight to useful work even further. Nuclear, geothermal and tidal energies do not originate from our sun. They originate from exploding stars and need to be traced back all the way to the big bang. The energy from our sun can be traced back to the big bang too, which would be truly primary energy: all the useful work at our disposal originates from there.

Due to all the additional conversion steps for other energy forms, direct solar energy conversion is the most efficient way to provide useful work to society. And electric energy is the embodiment of useful work (100% exergy), which is why it is ideal for comparisons and modelling substitutions among different energy provisioning systems.