This link has been bookmarked by 3 people . It was first bookmarked on 15 Sep 2008, by Kallu Kalakar.
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08 Feb 10
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15 Sep 08
Energy NetCharles 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. -
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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.
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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.
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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.
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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.
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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.
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