Topic 7 summary due: Wednesday, October 10 Describe the costs and benefits of two forms of alternative/renewable energy.

historical sources of energy muscle fire - wood & charcoal animal wind water steam wood coal petroleum

current sources of energy (worldwide use) overall oil - 35% coal - 29% natural gas – 24% nuclear – 5% Biomass - ? hydro - 6% Geothermal, wind, etc. – 1%

Chapter 20: Sustainable Energy

Conservation utilization efficiencies standard conservation techniques public transportation cars: engine & use efficiency homes industry energy conversion efficiencies (fig p. 448) fuel energy = useful energy + waste heat low percent useful energy yields can be improved efficiency table does not account for cost of pollution negawatt programs cogeneration

solar vast resource passive solar heat active solar heat high temp mirrors focus energy large and small scale photovoltaic sun’s energy separates electrons from atoms and moves them across a one-way barrier need energy storage

biomass sources crop residue & energy crops wood dung methane (source – digesters) alcohol (fuel and oxygenator) peat advantages renewable accessible use waste material disadvantages open fires - very wasteful pollutes combustion efficiency fuel wood shortages

hydropower pro very efficient no chemical pollution readily available in many areas water supply control flood control navigation recreation con blocks free flow siltation seepage water temp big dams are not efficient destroys habitat alternatives low-head run of the river micro-hydro (home use)

wind pro clean readily available con ugly hurt birds takes up space (less per watt than conventional) wind farms getting wind energy to users (map p. 466) home use

geothermal examples electricity generation heat pumps (p. 467) effects clean use up the resource depends on geothermal gradient

ocean tidal need high tidal range incoming and out going wave - difficult to harness ocean thermal electric conversion

Demand Matching Big issue with alternatives Production & availability does not always meet demand. Chart p. 467