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site last updated: 6/26/2010

C a l i f o r n i a   P H O T O N

Renewability

The renewability of energy sources is, perhaps, the criterian most often used to classify them when discussing the future of energy and the need for a sustainable energy economy. A renewable energy source is one that is continually replenished.

Renewable sources currently account for a small fraction of total electricity production, and a smaller fraction of liquid fuels production. However, renewable energy sources present a much more diverse palatte of options than do fossil fuels. There are bio-fuel replacements for fossil coal and oil, and renewable energy is available everywere rather than only at the end of excavation and extraction equipment.

The following outline lists the larger types of energy sources. In the case of most reneable energy sources, there are both small- and large-scale generation technologies.

  • Non-Renewable energy sources
    • Fossil fuels: Fossil fuels are combusted to produce mechanical energy or heat for electricity generation.
      • Solid: coal
        • Surface or "strip" mining, including mountaintop removal
        • Underground mining
      • Fluid: oil and gas
        • Hydraulic extractions of oil and gas from subsurface geological formations
        • Tar sands surface mining and processing
    • Nuclear fuels: Radioactive isotobes of uranium are fissioned in nuclear reactors to produce heat for electricity generation,
      • U235
        • Surface mining of uranium and enrichment
  • Renewable energy sources
    • Solar: Sunlight is captured and converted directly to electricity, or used for space and/or water heating or electricity generation.
      • Panels, installed on building rooftops or other existing structures
      • Thermal plants or farms of panels, built on patches of land
    • Wind: Kinetic energy in wind is converted to mechanical energy which is used for electricity generation or pumping.
      • Small wind turbines, installed on various platforms
      • Large wind turbines, erected on tall poles in windy locations
    • Geothermal: Subsurface water is used as a thermal source or sink for space and water heating and cooling, and electricity generation.
      • Geotherml heat pump, in which water is cooled or heated by passing through underground coils
      • Ground-source heating, in which underground heat sources are exploited, in some cases by injecting water
    • Hydro: Kinetic energy in flowing water is converted to mechanical energy which is used for electricity generation or pumping.
      • Dam-less turbine installations and micro-hydro
      • Dams with generator-driving turbines
    • Biomass: Combustion of liquid and/or solid biomass from plant or animal sources is used as a thermal source for space and water heating, electricity generation, and in industrial processes, such as concrete manufacture.
      • Solid
        • Wood, straw, etc, from crops
        • Bio-coal from processing of agricultural by-products
      • Liquid and gaseous
        • Methane gas from landfills and sewage processing
        • Ethanol and methanol from fermentation of bio-solids
        • Bio-diesel from plant oils

Although non-renewable energy sources tend to have the greatest negative environmental impact, renewable energy sources may also have serious impacts. Large-scale hydropower projects devastate the ecology of rivers, large wind turbines kill airborne wildlife in large numbers, and biofuel production increases demands for arable lands.

Such impacts tend to diminish with increasing distribution of power generation, and consequent reductions in the scale of the power generation units.