Thursday, July 2, 2009

Sustainable Energy Defined

A sustainable source of energy is renewable and environmentally benign.  While sustainable energy sources such as hydro, geothermal, wind, solar, oceanic (wave, tidal, current and temperature differential) are seemingly inexhaustible, this is not true for biomass.  Biomass is a sustainable source of energy as long as a crop is grown, burned for its energy content, and replaced by another.  Under these conditions, there is no net addition of carbon dioxide to the atmosphere because the carbon dioxide released from burning is absorbed in growing the replacement crop.  Deforestation adds carbon dioxide to the atmosphere as more biomass is burned than is replenished and is not sustainable; at some point the forest is gone.  Inexhaustible means that the source of energy is always present and never diminished, but that does not infer an infinite supply.  Inexhaustibility must be tempered with capacity limits.  Biomass is limited by the availability of arable land for non-food crops; solar power by whether the sun is shining and the number of solar arrays; wind power by whether the wind is blowing and the number of wind turbines; and hydropower by rainfall and the number of dams.

A major difference between conventional and sustainable sources of energy is reliability.  Electricity can be generated at the dispatcher’s whim up to a plant’s rated capacity for a generator fueled by fossil and biomass fuels, nuclear power and geothermal energy.  This is not true for other sources.  Hydropower depends on rainfall.  Wind and solar and wave power depend on the weather.  Tidal energy is predictable, but there is no guarantee that peaks in electricity generation from changing tides coincide with peaks in electricity demand.  Wind, solar, tidal and wave sources can certainly be tied into an electricity distribution grid and contribute to the electricity pool “weather permitting,” but they can only displace, not replace, conventional sources of energy.  Wind and solar energy, in particular, are being researched, developed and implemented heavily in states such as Colorado.

Source: (“Energy for the 21st Century,” Nersesian)

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