EROEI Energy Return on Energy Expended

I’ve been looking for a beginner’s guide to EROEI, and lifted this. It’s from a post on The Oil Drum, by one of it’s stalwart contributors ‘Gail the Actuary’. I’m sure she won’t mind this excerpt being reproduced here:

What is “Energy Returned on Energy Invested” or “EROEI”?

This is a concept that a person runs into frequently, if one reads any of the more advanced articles about peak oil on the internet. Analysis based on EROEI helps to explain why many scientists are discouraged about the newer energy prospects – both alternatives like ethanol and “unconventional” oil like oil sands.

EROEI is a measure of how much energy an investor gets out, compared to how much energy the investor puts in. Some of the energy invested is not in fuel directly, but in things that are made using fuel, like oil rigs and refining equipment.

In the early days of oil, much of the oil extracted came from highly pressurized wells, so little effort was required to get the oil out. At that time, the typical EROEI was about 100. As those wells became depleted, more and more effort was required to get the oil out. A typical EROEI for oil is now about 15, considering additional costs like repressurization of wells and drilling in underwater locations.

One problem that we are running into with “unconventional oil” and alternatives is that it takes a huge amount of effort (in terms of energy expended) to get the energy out. EROEI is in the low single digits for oil sands, and is barely above 1 for ethanol from corn. Oil in very deep sea locations is also expected to have a low energy return (assuming it can be extracted at all), because of all the very fancy equipment required.

If we had a huge amount of other energy from a readily available source that we could use for producing oil and oil alternatives, such as natural gas or coal, a low EROEI would not necessarily be a big issue. But it is now becoming clear that natural gas is in nearly as short supply as oil, at least in North America. And coal has a lot of issues as well — it is implicated in climate change, is mixed with toxic pollutants, is not as easy to transport, and is not in as unlimited supply as most believe.

When we have energy sources with a low EROEI, we are using a lot of fuel to get oil or oil alternative. The energy we have left to do everything else we do — build roads, build shopping malls, produce food — is less. I once heard an estimate that it takes an average EROEI of 6 to have enough energy left over to fuel today’s society. If new energy sources all have EROEIs of 3 or less, we are likely to

• Need a large share of workers to work in energy-related occupations

• Have less energy left over for other uses

• Experience a significant fall in our standard of living


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