chapter 28

Renewable energy use is gradually increasing.
- • Current world electricity generation is still dominated by fossil fuels.
  Renewables contribute 18% of the total, and may grow to 22.7% by 2035.
  Among renewables, biomass (fuels such as wood, charcoal, and animal waste) is by far the most common, followed by hydroelectric power.
- wind
  - • Wind turbines use air currents to turn rotor blades on top of a tower.
    Spinning blades turn a shaft; a gear box transfers energy to a generator, producing electricity.
    Wind is sporadic, and needs storage (batteries) for calm periods.
    Local residents may exhibit Not-in-my-backyard (NIMBY) syndrome, opposing these structures in the neighborhood.
- solar
  - • Solar energy is abundant. But like wind, sunshine is intermittent, and needs storage (batteries) when sun is not shining.
    - Passive solar
    - Solar thermal
    - Photovoltaic cells
  - • A passive solar house uses no moving parts but relies on exploitation of greenhouse effects.
    Strategic placement of windows and overhangs allow optimum solar heating in different seasons.
    Investment emphasis is in thermal mass for insulation instead of heating equipment and fuels.
  - • Solar thermal collectors use dark metal plates that absorb solar radiation to heat water for home use.
  - • Photovoltaic cells convert solar energy to electricity.
    Home installations can feed excess electricity not used by the home back to the grid and sold to the local utility.
- geothermal
  - • The U.S. is the current world leader in geothermal energy.
    Groundwater heated by magma may rise to the surface as geysers or hot springs.
    Dry steam geothermal power plants extend geothermal availability by pumping water down wells; the hot steam rises to spin turbines and generate electricity.
    This may not be sustainable if the groundwater is not recharged.
    Ground-source heat pumps can be used to manage building temperatures.
  - • Soil temperatures vary less than air temperatures and are nearly constant year round.
    Ground-source heat pumps take advantage of this temperature differences between the soil and air, by pumping water between ground and house.
    In summer, heat is transferred from the house to the ground.
    In winter, heat is transferred from the ground to the house.
- hydroelectric
- • Hydropower (hydroelectric power) uses the kinetic energy of moving water to turn turbines and generate electricity.
  Most hydropower is generated from reservoirs behind dams such as the Grand Coulee Dam.
  Dams fragment the river and destroy wildlife as well as human habitats.
- • A run-of-the-river hydroelectric system does not block water.
  A wall enhances the natural elevation of a river to allow falling water to turn turbines.
Energy efficiency can reduce dependency on fossil fuels.
- • Energy efficiency should be integral to reducing our energy needs.
  A 13-watt compact fluorescent light (CFL) bulb produces the same amount of light as a 60-watt incandescent bulb and lasts 10 times as long - consuming less than 1/3 of electricity.
  If every U.S. home replaces one incandescent with a CFL bulb, the energy saved can light 3 million homes and prevent release of greenhouse gases of 800,000 cars.