The Azimuth Project wiki has been up and running for exactly one month!
We’ve built up a nice bunch of articles sketching some of the biggest environmental problems we face today — and some ideas for dealing with them. I invite you to look these over and improve them! It’s very easy to do.
I also invite you to join us at the Azimuth Forum, where we are deciding the fate of humanity (or something like that). We need your help!
In the weeks to come I want to tell you what we’ve learned so far. I especially want to talk about various plans of action that people have formulated to tackle global warming. Even sitting here in the comfort of this cozy blog, you can help us compare and criticize these plans.
But I also want to tell you about some interesting concepts. And the first is EROEI, or “Energy Return On Energy Invested”. The Azimuth Project entry on this concept was largely written by David Tweed. Three cheers for David Tweed!
It also had help from Eric Forgy, Graham Jones and David Pollard, and a major contribution from Anonymous Coward. I’ll shorten it and amp it up for the purposes of this blog. I know you’re here to be entertained.
You’ve probably heard the saying “it takes money to make money”. Similarly, it takes energy to make energy. More precisely, it takes useful energy to make useful energy.
Energy Returned On Energy Invested or EROEI captures this idea: it’s simply the ratio of “useful energy acquired” to “useful energy expended”. Note that money does not enter into this concept. The difficult and often heated debate arises when we try to decide which inputs and outputs count as “useful”.
There are other names for this concept and closely related concepts. “Energy profit ratio”, “surplus energy”, “energy gain”, and “EROI”, and EROEI all describe virtually the same idea: how much energy we receive per energy put in. See:
• Nate Hagen, A Net Energy Parable: Why is ERoEI Important?, The Oil Drum, 2006.
The concept of “energy yield ratio” is also very similar, but tends to be used in slightly different ways. See the Azimuth Project article for more.
The definition of EROEI for a process of “extracting energy”
is the useful acquired energy divided by the useful energy expended. The “useful” tag denotes energy which is usable by human beings now. For example: a supernova wastes a lot of energy in the process of making uranium and blasting it out into space. But that was done long before we came along, so it makes no sense to include it in the EROEI inputs.
In practice, people include inputs and outputs that aren’t strictly “energies”, but rather “substances from which energy can be extracted”. For example: one could look at the EROEI of growing trees for fuel, where the wood produced is counted as an output according to the energy extractable by burning.
In general, having a high EROEI value counts as “good”. Indeed, when the EROEI drops below 1 more energy is being used in the extraction process than is being output at the end! But because it only considers energy issues (and not resource scarcity, scalability, pollution, etc.), EROEI should only be one input into our process of deciding on technologies and actions.
When it comes to computing EROEI, the hard part is deciding which inputs and outputs should be included in the ratio — particularly since this involves considering which other competing processes are genuinely viable.
Another complication is that while various forms of energy can generally be converted to each other, this will incur losses due to conversion inefficiencies. So, you can’t look at two schemes with the same useful energy inputs that produce different kinds of energy — e.g., electricity and heat — and declare the one with the higher EROEI as more suitable.
To see some of the difficulties in calculating an EROEI, let’s imagine growing a crop of grass and then fermenting it to produce a liquid fuel. The most obvious inputs and outputs are:
1. The liquid fuel itself. This is unarguably useful output “energy”.
2. There may be excess heat produced by the fermentation process. Whether this is useful is debatable since the energy is of high entropy and produced at plants located away from energy consumers.
3. The remaining biomass may be suitable for burning. Again the usefulness is debatable, since the biomass may be better used for fertilising the fields used to grow the crop. Even if this isn’t the case, the biomass may require yet more energy to collect into a dry, burnable state.
1. Sunlight. Except for exceptional circumstances, there is no other use for sunlight falling on fields so this does not count as a useful input.
2. Artificial fertilizer. This requires energy to produce and could be used for growing food or other crops, so it definitely counts as a useful energy input.
3. Energy used by motorized vehicles, both during farming and transportation to the biomass plant. For the same reasons as fertilizer, this counts as a useful energy input.
4. Mechanical energy used to extract liquid fuel after fermentation and clear waste products from the apparatus. Again a useful energy input.
Thus one computation of EROEI would count outputs 1 and inputs 2, 3 and 4.
However, suppose that the grass crop is genuinely being grown for other reasons — e.g., as part of a crop rotation scheme — and the plant is sufficiently small that the excess heat can be used fully by the plant for staff heating. Then you could argue that the EROEI should count outputs 1 and 2 and count inputs 3 and 4. So, to determine the EROEI you need to decide which alternative uses are genuinely viable.
Note also that this EROEI calculation is purely about energy! It does not reflect issues such as whether the land usage is sustainable, possible soil depletion/erosion, scarcity of mineral inputs for artificial fertilizer, etc.
Okay, but enough of these nuances and caveats. Important as they are, I know what you really want: a list of different forms of energy and their EROEI’s!
Natural gas: 10:1
Oil (Ghawar supergiant field): 100:1
Oil (global average): 19:1
Tar sands: 5.2:1 to 5.8:1
Oil shale: 1.5:1 to 4:1
Hydro: 11:1 to 267:1
Tides: ~ 6:1
Geothermal power: 2:1 to 13:1
Solar photovoltaic power: 3.75:1 to 10:1
Solar thermal: 1.6:1
Nuclear power: 1.1:1 to 15:1
Biodiesel: 1.9:1 to 9:1
Ethanol: 0.5:1 to 8:1
This list comes from:
• Richard Heinberg, Searching for a Miracle: ‘Net Energy’ Limits & the Fate of Industrial Society.
You can read this report for more details on how he computed these numbers. If you’re like me, you’ll take a perverse interest in forms of energy production with the lowest EROEIs. For example, what idiot would make ethanol in a way that yields only half as much useful energy as it takes to make the stuff?
The US government, that’s who: the powerful corn lobby has been getting subsidies for some highly inefficient forms of biofuel! But things vary a lot from place to place: corn grows better in the heart of the corn belt (like Iowa) than near the edges (like Texas). So, the production of a bushel of corn in Iowa costs 43 megajoules of energy on average, while in Texas it costs 71 megajoules.
Similar, ethanol from sugar cane in Brazil has an EROEI of 8:1 to 10:1, but when made from Louisiana sugar cane in the United States, the EROEI is closer to 1:1.
“Solar thermal” also comes out looking bad in the table above, with an EROEI of just 1.6:1. But what’s “solar thermal”? Heinberg has a section on “active” or “concentrating” solar thermal power, where you focus sunlight to heat a liquid to drive a turbine. He also has one on “passive” solar, where you heat your house, or water, by sun falling on it. But he doesn’t give EROEI’s in either of these sections — unlike the sections on other forms of energy. So I can’t see where this figure of 1.6 is coming from.
Anyway, there’s a lot to think about here. Each one of the numbers listed above could serve as the starting-point for a fascinating discussion! Let’s start…