Energy return on investment for various different energy sources Answered
We're used to thinking about the cost per unit of energy (e.g. $/gallon of gasoline) with the implicit assumption that cost is a rough indicator of what is required to obtain that energy. The Oil Drum has a nice piece on Energy Return on Investment (EROI) and the implications of using low EROI energy sources. To dive right in, it's instructive to think about the EROI of domestic oil production as a function of time:
100:1 in 1930
30:1 in 1970
11-18:1 in 2000
EROI on the Web part 2 of 5, (Provisional Results Summary, Imported Oil, Natural Gas)
Energy return on investment, sometimes called EROI and sometimes called EROEI, is thought by many, including myself, to be a critical issue for determining the past, present and future status of human society. It is usually considered in terms of energy return on energy investment, but it can also be considered in terms of energy return on monetary investment. While much of human progress has been attributed, rightfully, to technology, much of that technology has been a means of using more energy for human ends. This is true for fire, knife blades and spear points (energy concentrating devices), the development of agriculture and the increase in its productivity and, essentially all aspects of the industrial revolution.
EROI is simply the energy delivered by an energy-obtaining activity compared to the energy required to get it. If the numerator and denominator are expressed in the same units (barrels per barrel, MegaJoules per MegaJoule) the result is a dimensionless ratio, i.e. 100:1 or 10:1). Obviously a higher ratio implies a more desirable fuel than a lower one, other things being equal (which is rarely the case). The concept is extremely simple in theory but often very difficult in execution, mostly because society generally maintains its records in monetary rather than energy terms. Another problem is that the U.S. Government has not supported such studies in a consistent fashion and it is my perception that the quality of some energy records as are kept by e.g. the U.S. Departments of Energy and of Commerce appear to be deteriorating in recent years. Thus deriving the energy cost of getting energy (or most other things) is generally somewhat, and oftentimes exceedingly, difficult. A second problem is that the usual measure of the quantity of a fuel, its heat value, often does not give a full assessment of that fuel's ability to do economic or other work. Most simply electricity and thermal heat from e.g. coal or oil have a great difference in their ability to do work, such as we are willing to trade three or four heat units of coal or oil in a thermal plant for one thermal unit of higher quality electricity. Thus if the input and output fuels are of different quality then it is often thought desirable to weight in some way the inputs and the outputs. A third problem is that it is important to consider boundaries: how large should we draw the boundaries of the energy analysis for the inputs? We will consider these issues in far more detail in later publications but there are many reasons why it is important to make summaries of EROI available at this time even though many uncertainties exist in the numbers that we present here, and indeed with any numbers that might be possible to generate.