Download Sustainable Energy: Efficiency and Renewable Sources - Prof. T. Dewitt and more Study notes Environmental Science in PDF only on Docsity! BESC 201, Introduction to Bioenvironmental Science Lecture 16 (31 October 2008) Chapter 20: Sustainable Energy Energy Use Efficiencies Most potential energy in fuel is lost as waste heat. In response to 1970’s oil prices, average US automobile gas- mileage increased from 13 mpg in 1975 to 28.8 mpg in 1988. o Falling fuel prices in the 1980’s discouraged further conservation. Today’s average new home uses half the fuel required in a house built in 1974. o Reducing air infiltration is usually the cheapest, quickest, and most effective way of saving household energy. New washing machines use 35% less water as of 2007. Superefficient Swedish houses consume 90% less energy than average US home. (E.g. thatch-roofs are common in Europe— contribute to insulation.) Power companies investing in negawatts of demand avoidance. o Conservation costs on average $350/kw o Nuclear Power Plant: $3,000 - $8,000/kw o Coal Power Plant: $1,000/kw Cogeneration Cogeneration - Simultaneous production of both electricity and steam, or hot water, in the same plant. o Increases net energy yield from 30-35% to 80-90%. o In 1900, half of electricity generated in US came from plants also providing industrial steam or district heating. o By 1970’s cogeneration fell to less than 5% of power supply. Solar Energy, A Vast Resource Average amount of solar energy arriving on top of the atmosphere is 1,330 watts per square meter. Amount reaching the earth’s surface is 10,000 times more than all commercial energy used annually. Until recently, this energy source has been too diffuse and low intensity to capitalize for electricity. Look on 2818, North of University Low tech solar… Passive Solar Heat - Using absorptive structures with no moving parts to gather and hold heat (greenhouses, pools, water tanks in Med) Active Solar Heat - Generally pump heat-absorbing medium through a collector, rather than passively collecting heat in a stationary object. Water heating consumes 15% of US domestic energy budget High tech solar… Parabolic mirrors – curved reflective surfaces that focus light to a concentrated point. Two techniques: charge attracts two H+ ions through the membrane, where they combine with an oxygen atom and two of the electrons from the external circuit to form a water molecule (H2O). This reaction in a single fuel cell produces only about 0.7 volts. To get this voltage up to a reasonable level, many separate fuel cells must be combined to form a fuel-cell stack. Chemistry of a Fuel Cell Anode side: Cathode side: 2H2 => 4H+ + 4e- O2 + 4H+ + 4e- => 2H2O Net reaction: 2H2 + O2 => 2H2O Biomass Plants capture about 0.1% of all solar energy that reaches the earth’s surface. About half the energy used in metabolism. Useful biomass production estimated at 15 - 20 times the amount currently obtained from all commercial energy sources. Renewable energy resources account for 18% of total world energy use, and biomass makes up three-quarters of that supply. Wood provides less than 1% of US energy, but provides up to 95% in poorer countries (note that historically US used to rely heavily on wood fuel). About 40% of world population depends on firewood and charcoal as their primary energy source. Of these, three- quarters do not have an adequate supply. Note also: Landfills produce up to 20% of atmospheric methane—this gas can be captured or mitigated Tidal generators (LUNAR energy—I should copyright this phrase!!!) Hybrid vehicles Prius & Civic hybrids (My family is dual career, so we need two cars, but both are hybrids —one of each type) Captures “waste” energy into batteries (e.g. braking nrg) Stored electric energy assists gas motor Electric part adds additional hp on top of gas engine, so the cars are “peppy” $4500 tax break, local perks such as use of HOV lanes Karma points too
