"Energy return on investment (EROI) is the ratio of the energy extracted or delivered by a process to the energy used directly and indirectly in that process."
Aggregation and the Role of Energy in the Economy from Ecological Economics 32 (2000) 301–317 by Cutler J. Cleveland, Robert K. Kaufmann, Center for Energy and Environmental Studies and Department of Geography, Boston University, 675 Commonwealth Avenue, Boston, MA 02215, USA and David I. Stern, Centre for Resource and Environmental Studies, Australian National Uni6ersity, Canberra ACT 0200, Australia
Methods for investigating the role of energy in the economy involve aggregating different energy flows. A variety of methods have been proposed, but none has received universal acceptance. This paper shows that the method of aggregation has crucial effects on the results of the analysis. We review the principal assumptions and methods for aggregating energy flows: the basic heat equivalents approach, economic approaches using prices or marginal product for aggregation, emergy analysis, and thermodynamic approaches such as exergy. We argue that economic approaches such as the index or marginal product method are superior because they account for differences in quality among fuels. We apply various economic approaches in three case studies in the US economy. In the first, we account for energy quality to assess changes in the energy surplus delivered by the extraction of fossil fuels from 1954 to 1992. The second and third case studies examine the importance of energy quality in evaluating the relation between energy use and GDP. First, a quality-adjusted index of energy consumption is used in an econometric analysis of the causal relation between energy use and GDP from 1947 to 1996. Second, we account for energy quality in an econometric analysis of the factors that determine changes in the energy:GDP ratio from 1947 to 1996. Without adjusting for energy quality, the results imply that the energy surplus from petroleum extraction is increasing, that changes in GDP drive changes in energy use, and that GDP has been decoupled from between aggregate energy use. All of these conclusions are reversed when we account for changes in energy quality.
"The "energy payback time" is a term used to measure the net energy value of a wind turbine or other power plant--i.e., how long does the plant have to operate to generate the amount of electricity that was required for its manufacture and construction? Several studies have looked at this question over the years and have concluded that wind energy has one of the shortest energy payback times of any energy technology. A wind turbine typically takes only a few months (3-8, depending on the average wind speed at its site) to "pay back" the energy needed for its fabrication, installation, operation, and retirement."
"If humanity were to use cellulose ethanol to match all of our present global oil usage (85 m barrels/day), we would need to cut down the vegetation every year from about 10% of all land including ice caps, deserts and mountain tops. People are talking with a straight face about converting millions of square miles in Africa and South America to fuel the global economy. 'Use drip irrigation; it's more efficient.' I kid you not.
"Since we in the USA use 5 times as much energy as the global average, we don't have enough land here to make it work. If we became 5 times more efficient than we are now, we could probably make do within our borders (125 mpg). Is that plausible? We might be able to do it if everyone carpooled, filling up every seat in the car. Is that plausible?
"In this crazy business, much consideration is being given to by-product biomass sources ("waste") such as sawdust, turkey offal or fast-food cooking oil. If we are to take any of these marginal schemes to scale, we have to wave aside consideration of most of the energy it takes to bring the sources to the processing plant. Is that plausible? If I'm producing valuable plywood or sugar, I can afford to use the residue to run my plant. In fact, paper mills have gone from one of the most energy-intensive industries to self-sufficient in the last few years by burning lignon that used to be dumped into streams. But the left-overs are just that-- not enough to make a meal for the whole family."
"BEIJING: Diners in China are being encouraged to change their habits in order to save the country's forests from destruction.
The aim is to curb the plunder of timber and protect the environment.
China makes 15 billion pairs of throwaway chopsticks a year, consuming some two million cubic metres of wood, equivalent to 10 million trees, which would occupy 46sq km."
[If there is insufficient timber to provide for chopsticks, how can there be sufficient biomass of any form to propel automobiles? Ed.]
"An exergy analysis of a Biomass Integrated Gasification – Fischer Tropsch process is presented. The analyses were done for an air-blown, atmospheric gasifier using poplar wood as feedstock. Results show that the rational (exergetic) efficiency is 51.2 % for the combined liquid and gaseous products. The effect of process parameters on the rational efficiency is demonstrated."