How Much Energy Does It Take to Get Our Energy?
If you look closely, not all energy sources are created equal in terms of the amount of net energy they produce.
By John Gulland
December 2010/January 2011
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These bars represent the estimated maximum energy return on investment of both renewables and fossil fuels. Oil's ratio has declined over time with the increased difficulty of bringing it to consumers.
SOURCE: CHARLES A. S. HALL AND JOHN W. DAY JR./AMERICAN SCIENTIST, GRAPH: MATTHEW T. STALLBAUMER
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The future of our finite supply of fossil fuels is uncertain at best, and development of new energy options continues to gain speed. It’s likely we’ll use a combination of renewable energies and fossil fuels for the forseeable future.
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If you listen to some representatives of the alternative energy industry, you’d think every renewable fuel source out there is the No. 1 candidate to meet the world’s future energy needs — the most qualified to replace oil, coal and natural gas. So, which type of renewable energy will provide us with the highest net gain in energy?
Energy return on energy invested is more commonly stated as energy return on investment (EROI). The term was coined by Charles Hall, professor of environmental science and forestry at the State University of New York (SUNY), and is presented as a ratio of energy produced to the energy consumed during production. An energy source that yields positive net energy has an EROI ratio of more than 1:1. Anything less than that constitutes an energy sink, or net loss.
Focusing on the Future
It takes energy to find, extract, refine and transport energy commodities. The energy cost of energy wasn’t a topic worthy of study throughout most of the era of fossil fuels because coal, oil and natural gas were so accessible and easy to deliver that their EROI ratios were very high.
However, no longer can an oil company drill a hole on easily accessible, vacant land and get a gusher. Although new discoveries are announced regularly, most are small and many are difficult and increasingly expensive to extract. Consider the deep water oil wells in the Gulf of Mexico, the frozen shorelines of the Arctic Ocean, the tar sands in Alberta, Canada, or the shale oil deposits in Wyoming as examples. Oil’s EROI remains high compared with most renewables, but it’s continually declining. (Note the changing EROI values of oil in 1930, 1970, 2000 and 2005 shown in red in the graph above.) And, because the production and consumption of energy always has environmental impacts, the more energy that must be invested to produce usable energy, the greater the environmental cost of that source.
A cautionary example is the recent situation with corn ethanol. According to research from Hall and SUNY graduate student David Murphy, corn ethanol’s EROI is just barely positive on average at 1.1:1. This is the root of much of the controversy surrounding ethanol: Critics rightly wonder if it’s worthwhile to put so many resources into an energy source that yields such a small rate of return. The SUNY researchers indicate that a fuel should obtain a ratio of more than 5:1 to be worth pursuing. In contrast, Hall and John Day, ecologist and professor emeritus of oceanography at Louisiana State University, estimate hydropower’s potential return at roughly 40:1.
