Sunday, September 14, 2008

The net energy cliff

Charles Hall, the father of the energy return on investment (EROI) concept, once told me that our current society would probably not be able to function if the EROI for the entire society slipped below five.

What does that mean? First, a quick review. It takes energy to get energy. EROI is a measurement of how efficient a process, an enterprise or a society is in obtaining energy. EROI is usually expressed in a ratio, say, 20 to 1. That would mean that the process being studied produced 20 units of energy for every one unit expended. As it turns out, that's about what conventional crude oil returns.

Hall estimates that the United States is currently running on an EROI of just under 40 to 1. This looks like a fairly substantial margin of safety over the 5 to 1 that might lead to societal breakdown. But worrisome developments in the oil, natural gas and coal fields may send us rushing toward that figure.

A post earlier this year on The Oil Drum suggests that the EROI for natural gas in North America is dropping like a stone. This is, in part, reflected in the price of natural gas which is up fourfold in this decade. It is also reflected in the number of wells and the number of total feet drilled just to maintain production. We are having to drill faster and deeper just to stay even. The recent uptick in U. S. supplies may represent a small flattening of the EROI decline, but those supplies are the product of furious drilling and huge exploration expenditures.

The tar sands, presumed to be the great energy savior for North America, have long been a low EROI source of oil. Estimates range from 1 to 1 to about 7 to 1. Work by Charles Hall and his students posted on The Oil Drum gives a tentative estimate of 5.2 to 1 based on admittedly incomplete data.

Coal has a very high return when used to generate electricity, around 80 to 1. But evidence now suggests that in the United States at least, not only has the energy content per ton of coal declined by more than 30 percent since 1955, but the total energy content of coal mined in the country is now falling despite rising coal tonnage.

But what about nuclear? Hall and his students once again attempted to calculate the EROI. Others have made claims of 1.86 to 1 to 93 to 1. The very high estimates appear to leave out many steps in the nuclear fuel and construction cycle. Some contend that the EROI of nuclear is favorable enough--perhaps 11 to 1--to argue for expansion of nuclear power. But, if one takes into account all the energy that will be expended over time storing nuclear waste and guarding the waste and the mothballed nuclear plants in the future, the EROI could drop below 1. Essentially, we get the benefit now, and future generations get both the security and energy expenditures.

On its current trajectory, nuclear power may not even maintain its share of world energy production. It would certainly be useful to know what the true EROI of nuclear power is in order to assess its importance to our energy future.

Solar power has promise as shown in this chart compiled by Hall and his students. But, the estimated EROI ranges are so wide that it would be difficult to promise that solar photovoltaic could consistently provide returns above 5 to 1.

This chart provides an estimate of above 70 to 1 for wind power in one location. EROI in this case, of course, depends heavily on whether the wind generators are located in ultra-windy Denmark or not-so-windy Japan. The main problem with wind and solar, however, is that they are intermittent; the energy produced is difficult to store for use during nighttime or low-wind conditions.

Finally, hydroelectric has a very high EROI. While there is still room for some expansion of hydro power in the developing world, most of the good sites have already been taken in North America and Europe.

And, this brings us to the idea of the net energy cliff. If our energy transition away from fossil fuels does not result in their replacement by high EROI sources of energy with the necessary versatility and storage characteristics, or if such replacements are possible, but delayed too long, then we may be facing a net energy cliff.



It may seem that the difference between an EROI of 40 to 1 and one of, say, 30 to 1 would be comparable to a move from 20 to 1 to 10 to 1. But the mathematics say otherwise. In a society that has an EROI of 40 (which is approximately what the United States is thought to have) about 2.5 percent of the economy is devoted to gathering energy for the other 97.5 percent. If an economy has an EROI of 30 to 1, then the portion of the economy involved in gathering energy rises to about 3.3 percent. This is a significant jump, but probably manageable. However, an EROI that drops from 20 to 1 to 10 to 1 results in the doubling of the part of the economy devoted to securing energy from 5 percent to 10 percent. A further drop to an EROI of 5 to 1, puts 20 percent of the economy within the general classification of energy gathering. This is the net energy cliff.

A drop to an EROI of 5 in today's American economy would mean that the energy sector of society would have to grow eightfold. If the drop came quickly, it would be very difficult to adapt. If the EROI were to drop to, say, 3, this would imply that potentially every third person would be involved in gathering energy in some fashion. Such a society would have little resemblence to the one we now inhabit.

The net energy cliff shows us how important EROI is when considering energy alternatives. Even very large resources such as the tar sands and oil shale become problematic when one considers their EROI.

There appear to be two ways forward then. One is to hope for breakthroughs which increase the energy returns of alternative energy sources. A second is to rework our infrastructure and our way of living so that our society can better withstand a significant overall decline in EROI should it develop.

7 comments:

Clifford J. Wirth, Ph.D. said...

The collapse will come even before Charles Hall calculates.

All energy sources depend on oil for their mining, manufacture, transportation and maintenance; this includes nuclear power, hydroelectric power, coal, natural gas, and wind/solar

Soon oil will be so expensive that state governments will not be able to both subsidize residential heating (to keep people from freezing to death) and pay for the personnel and diesel for highway maintenance. State revenues will plummet in the coming recession, and revenues from state gasoline taxes (for highway maintenance) will evaporate. The northern states use incredible amounts of diesel and funds for personnel in snow plowing alone.

We are facing the collapse of the highways that depend on diesel trucks for maintenance of bridges, cleaning culverts to avoid road washouts, snow plowing, roadbed and surface repair. When the highways fail, so will the power grid, as highways carry the parts, transformers, steel for pylons, and high tension cables, all from far away. With the highways out, there will be no food coming in from "outside," and without the power grid virtually nothing works, including home heating, pumping of gasoline and diesel, airports, communications, and automated systems. Cliff Wirth http://survivingpeakoil.blogspot.com/

Rice Farmer said...

I believe Mr. Wirth is correct. People do not understand the magnitude of the problem. In fact, we just heard recently that the US highway construction trust fund is nearly broke and desperately needs a cash infusion.

http://ricefarmer.blogspot.com/2008/09/fuel-taxes-and-road-maintenance-again.html

Do a search for news stories on road maintenance, and you can easily find articles about how cash-strapped local governments are already leaving some needed road maintenance undone. The US power grid is already in need of much upgrading and maintenance. Power outages and shortages are frequent occurrences in many countries. Fossil fuels are needed to manufacture, deploy, and maintain the infrastructure for renewables, and even if we deployed a huge infrastructure for renewables in the "crash program" advocated by many, it would not be capable of propping up what fossil fuels have built. Underlying this problem is a huge pitfall: the belief that real-time solar energy is comparable to stored solar energy.

http://ricefarmer.blogspot.com/2008/09/fossil-fuels-vs-real-time-energy.html

Since at this stage we are already beginning to see the problems listed by Mr. Wirth, the situation has deteriorated more than is realized.

Anonymous said...

This debate should have taken 30 years ago. We won't get another 30.
Major disruptions will occur. Further dependence on oil (foreign, offshore, or ANWR is foolish). Any thing short of commitment to 50%
alternatives by 2025 will be too little, too late. If we can build dams to tame rivers, we should do the same for wind/solar.

Iconoclast421 said...

I think humanity has collectively "chosen" to go with option #2, the reworking of our infrastructure and our way of living to be more fuel efficient. This appears to be coming in the form of a major economic catastrophe.

I dont understand how anyone with a PhD could look at all the deflationary forces at work and conclude that oil is going to be too expensive.

Oil wont be expensive once 20 million SUV-driving energy-hogging yuppies lose their jobs. We could be looking at the greatest oil surplus in all of human history. It is up to the peak oil community to make sure that this surplus gets used in a rational way. If not, then the next economic expansion will put us right back to where we are now.

You are going to destroy all your credibility if you keep framing oil in terms of dollar amounts. The price of oil is determined by monetary policy, not on how much is coming out of the ground or its EROI.

Most importantly, in all of human history I see no evidence that humans are capable of managing a downsloping resource bell curve by any means other than a dieoff. So there will be a dieoff. Humanity will not change. The population will simply be reduced until business as usual can continue.

Henry Warwick said...

I posted my opinion on this to europe.theoildrum.com a while ago.

Basically, IIRC, it used to be 80% of a country was farming, while the rest did other things, and that was in a solar economy. food production is the most essential form of energy production, therefore, when we reach 80% farmers in the workforce, we know we're back with the 18th century.

from my view EROEI is a red herring. The real measure is in labour, and what labour is doing. When more people are involved with food and energy, and then finally food, you know EXACTLY where your EROEI is - in the terlit.

My post to oildrum follows:

Actually I would argue the first point is covered by the second point and shows the pointlessness of EROEI arguments. How?

All the energy we use is the energy we use. Yes, a tautology, but one with meaning. If ALL energy production systems (oil, nuke, etc.) disappeared and we had to make due with a pre-industrial energy diet, we would experience a lot of misery, but we would have to use all the energy we use - it would just be a tiny fraction of what we use today. Energy production is a social practice, and arrives from a social circumstance. Sure: you could run a nuke plant without Moe's, or the QuikEmart, or the comic book shop, but: that's the whole point of the power station - to permit the existence of Moe's (so power station workers like Homer can go have a pint of suds), or the QuickEmart (so Apu can provide slushies to Bart), and the comic book shop (so a fat geek has somewhere to go 8 hours a day).

Moe's is critical to the operation of the plant, as it is a social focal point for Homer, and without Homer the whole thing would go critical and melt down and kill everyone. OK, maybe Homer is disposable, but you get my point. The powerstation provides the power so the society can function, and the society functions so people will work at soul deadening jobs like the powerstation.

Imagine if our society had NO use for petroleum. If we chased the bison herds for a living and scratched some plants out of the soil. Would we use petroleum? No. What would EROEI matter? nothing at all. People either starve or not. Energy production is a product of social practice and cannot be separated out from society, as society itself is an energetic and entropic process, of which energy production is part and parcel.

Hence, EROEI is ALWAYS 1:1. Forever. The question, in my opinion, is one that devolves on labour. The common wisdom is that 2% of society in our petroleum based system makes the food for themselves and the other 98% of the society, who are thusly freed up from food production to engage themselves in such eminently worthwhile professions like croupier, online porn actress, advanced debt instrument designer, public relations account assistant, fingernail artist, market speculator, gangster, right wing think tank administrative assistant, cold call telephone sales associate, closet organisation assistant, dog walker, and whatever the job title it is of the guy who stands in the middle of the street holding the sign that says "slow - construction" when the street is clearly ripped apart an covered with orange cones.

There is a much more accurate way to determine the energy content of a society: how many people are engaged in subsistence agriculture, or food production in general? When the number of farm workers expands and the nail salons disappear, then you know your energy production systems are not generating the quantities it once did. When the gangsters are put to work digging ditches because the backhoe went idle, then you know things are getting slim.

You don't need elaborate abstract calculations of input and output - you just need to keep an eye on how many people it takes to feed society. That ratio will tell you how you're doing. If the EROEI is really high, then it will supply energy for something other than itself and more of the Fine Careers I listed above can be supported. If the EROEI blows chunks, then we will see more people growing food, as the quantity of energy left over from Energy PRoduction will necessarily be reduced and reduce the number of people working in such fields of endeavour.

Pretty straight-forward from my perspective.

Rice Farmer said...

Oil wont be expensive once 20 million SUV-driving energy-hogging yuppies lose their jobs.

And here's another pitfall. Those 20 million yuppies -- and a lot of other unemployed billions -- won't be buying any petroleum products, either. Let's say that demand destruction brings the price of oil down substantially, and that by some miracle it revives the economy. A revived economy means a consuming economy, and oil will get expensive again in response to increased demand. And renewables aren't going to save industrial civilization because it was not designed to run on such low-density energy. Meanwhile, the countless unemployed and hungry people are going to create more social unrest than the world has ever seen.

Anonymous said...

"Coal has a very high return when used to generate electricity, around 80 to 1"

This is not true. Turbines convert thermal energy of coal into electricity at as much as a 40 % rate, so EROIel would be of about 32. This is obviously unimportant for coal as a net energy source, but reveals the as unnecessary as undesirable tendency within energy-crisis-think-tank to hype the power of fossil fuels and prejudiciously scorn ALL renewables for their supposedly unviable EROI. In strict EROI terms, PV electricity is perfectly comparable to coal. It's true that solving its intermittence will reduce such EROI, but it's true as well that coal's EROI of 80 is referred to minemouth and doesn't take into account the energy spents of transportation and power plant building.
I'm not denying that the party will come to an ugly and abrupt end, but financial chaos and individual and political inertia and not thermodynamics will be the wet blanket...
Regards from the free falling Spain,
LCR