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Today-Ch. 5

Today-Ch. 5. Hydropower Geothermal power Wave power Tidal power Ocean thermal power Biomass (more with Ch. 8). reminder. The Betz factor of 0.59 for the maximum fraction of wind power that can be extracted is NOT included in the text equation with the 6.1x10 -4.

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Today-Ch. 5

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  1. Today-Ch. 5 Hydropower Geothermal power Wave power Tidal power Ocean thermal power Biomass (more with Ch. 8)

  2. reminder • The Betz factor of 0.59 for the maximum fraction of wind power that can be extracted is NOT included in the text equation with the 6.1x10-4.

  3. GeothermalDeep heat from radioactive decay. Steam, geysers ‘Hot dry rock’, inject water

  4. Ocean power 1. Tidal energy Dams, build a pressure head Turbines in the flow 2. Wave 3. Ocean thermal

  5. Ocean thermal power Water is most dense at 4 deg C, and thus this is the temperature at the bottom of oceans. Build a heat engine, with surface warm water temps near 30 deg C. Too much plumbing, pumping, very poor Carnot efficiency. Instead– pump up cold water for AC.

  6. Biofuels Wood/pulp/woodwaste, cheaper, cleaner than coal, 7700 MWe Municipal waste Manure/farm waste Ethanol/Biodiesel--later

  7. Example Wood byproducts provide 7700 MWe per year. How much coal is thus not dug, hauled, and burned?

  8. numbers Assume efficiency =0.30. Coal holds 2.81x1010 J/ton. In one year, wood provides 7.7x103x106 J/sec x 3.16x107 sec = 24.3 x 1016 J of electrical energy At 30%, this needed 24.3x1016/0.30 =81.1x1016 J of heat. Tons of coal = J / (J/ton) =81.1x1016 J / 2.81x1010 J/ton=29 x106 tons (almost 3%)

  9. (10) You are deciding what kind of heating system to put into your new house in Boulder. Your choices are electrical heat (using power from burning coal at the Valmont plant at 32% • efficiency), burning coal in a home furnace at 80% efficiency, or installing a heat pump (driven by electricity) with a C. O. P. of three. • Compare and contrast the tons of coal needed to • provide 4 x 107 BTU per year.

  10. Next week-- Nuclear fission (and fusion) Chapter 6

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