August 20, 2011 by Nate Hagens and Kenneth Mulder
Some excerpts from this article:
The 2 most important natural resources are water and energy. In most cases, each is required to procure the other. We use water directly through hydroelectric power generation at major dams, indirectly as a coolant for thermoelectric power plants, and as an input for the production of biofuels.
- The 2 largest consumers of water in the USA are agriculture and electric power plants.
- world-wide agriculture uses 90% of fresh-water
- If we count only fresh water, fully 81% of U.S. use is for crop irrigation.
- CORN: uses about 2,100 gallons of water per bushel which yields 2.7 gallons of corn-based ethanol. This means that 206 gallons of water is needed per gallon of ethanol
[Water shortages will only get worse if we adopt energy-production technologies that use a lot of water, like biofuels, and also lead to hunger as less food is produced. Water depends on energy: for example, in California water delivery uses over 15% of the state’s total electricity consumption.]
Fossil fuels use the least amount of water per unit of energy generated:
|Water requirements for energy production
(litres per megawatt hour)
|Oil shale surface retort||170-681|
|NGCC* power plant, closed loop cooling||230-30,300|
|Coal integrated gasification combined cycle||~900|
|Nuclear power plant, closed loop cooling||~950|
|Geothermal power plant, closed loop tower||1900-4200|
|Enhanced oil recovery||~7600|
|NGCC*, open loop cooling||28,400-75,700|
|Nuclear power plant, open loop cooling||94,600-227,100|
|Corn ethanol irrigation||2,270,000-8,670,000|
|Soybean biodiesel irrigation||13,900,000-27,900,000|
|*Natural Gas Combined Cycle|
Unlike energy, water can sometimes be recycled. For example, cooling water withdrawn for use by a nuclear power plant may be returned and withdrawn again farther downstream to irrigate biofuel crops.
Energy derived from finite and renewable resources is a function of multiple inputs including land, labor, and raw materials — any of which may become a limiting factor for energy production. A technology might have a high EROI and yet require sufficient levels of scarce, non-energy inputs as to be extremely restricted in potential scale. For example, the amount of land required for biofuels is between 100 and 1,000 times more than the land area required for conventional fossil fuels. In addition to non-energy inputs, energy technologies vary in their waste outputs and impact on environment. Within the biofuels class itself, there is a large disparity of pesticide and fertiliser requirements. For example, per unit of energy gained, soybean biodiesel requires just 2% of the nitrogen, 8% of the phosphorous, and 10% of the pesticides that are needed for corn ethanol, inputs that impact groundwater quality and stream runoff. As such, future refinements to an energy and water policy framework will probably have to look beyond energy and water supplies.
How much water does it take to provide energy?
- “Environmental, Economic, and Energetic Costs and Benefits of Biodiesel and Ethanol Biofuels”. Hill et al,. Proc. Acad. Nat. Sci. 103:11206-11210 (2006).
- “Burning Water: Energy Return on Water Invested”, Mulder, K., Hagens, N., Fisher, B. Volume 39, Number 1/February, 2010 AMBIO — Journal of Human Environment
- “The Water Intensity of the Plugged-In Automotive Economy”, Webber, M., King, C., Environmental Science & Technology 2008 42 (12), 4305-4311
- Cleveland, C. “Net Energy from the Extraction of Oil and Gas in the United States”. Energy, 2005, 30, 769–782.
- “Another Biofuels Drawback: The Demand for Irrigation”, Robert F. Service, Science 23 October 2009:Vol. 326. no. 5952, pp. 516 – 517