February 19, 2014
Chapter 17: Energy Efficiency and Renewable Energy
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Energy conservation - reducing or eliminating unnecessary waste of energy
Energy efficiency - one way to conserve by using less to accomplish same task (more work/unit of energy)
*Quickest, cheapest, cleanest way to provide more energy.
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*net energy efficiency
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Some strategies to improve energy efficiency in industry...
1. Cogeneration or combined heat and power (CHP) systems
2. Replace energy-wasting electric motors
3. Switch from incandescent to fluorescent lighting
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Strategies for improving energy efficiency in transportation
1. Fuel economy standards (CAFE--corporate average fuel economy standards)
2. More fuel-efficient cars• hindered by low gas prices (subsidies and tax
breaks, military protection)• government $ to allow people to buy fuel-efficient
vehicles
3. Redesign urban transportation system
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Hybrid Vehicles• gasoline-powered motor + electric motor
Plug-in hybrid• 2nd battery to plug in and charge
*where does electricity come from?
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Fuel cell in cars
2H2 + O2 2H2O
Advantages?
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Green Architecture: Energy efficient buildings• Capture solar energy• block out sun to reduce cooling costs• use efficient lighting• thermostats• insulation• living roofs
• LEED: Leadership in Energy and Environmental design> certifies buildings based on standards> *tax breaks, rebates, grants to encourage
meeting LEED standards?
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Alternative Forms of Energy• Solar• Hydropower*• Wind*• Biomass*• Geothermal• Hydrogen
*Indirect form of solar energy
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Hydropower• Water flowing from higher to lower elevation• Dams Reservoir Turbines• *US largest producer of electricity from hydropower
> 7% US, 50% west coast> Little room for expansion: 98% rivers already
dammed, some need to be taken down (silt)• micro-hydrogenerator
*Not true for US
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Hydropower• Tides
> Need big difference in high/low tide> expensive
• Waves• Ocean thermal energy conversion (OTEC)
> Large temperature difference between surface and deep water in tropical oceans
http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion
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Windpower• difference in solar
heating of earth• Taller = more reliable
wind
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Windpower: expansion?• Anemometers
> wind speed at different heights• Locations?
> land– in US: midwestern states could potentially
supply all of nation's electricity needs> offshore*
– winds are stronger and steadier– sounds– high cost
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Biomass• Directly burn organic materials (plants, animal
waste) or convert into liquid/gaseous biofuels
• mostly burned for heat not to generate electricity
• 95% energy in poorest countries
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Biomass• Plants are potentially plentiful
> sustainable harvest> biomass plantation
– depletes soils, degrade biodiversity• Other sources?
> crop residue> animal manure
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Biomass: Liquid biofuels • Ethanol produced by fermentation and distillation
of sugars (starch and cellulose can be broken down)> microbes> cellulosic ethanol> sugar cane and switchgrass rather than corn?
• Replace gasoline and diesel• Environmental impacts?
*Made affordable by government subsidies!
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Biodiesel• alcohol + vegetable oil
*Environmental impacts of conventional farming
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Geothermal Energy• Heat stored in soil, underground rocks, and fluids
in earth's mantle> original formation> radioactive decay
• Using just 1% stored heat in uppermost 5km of earth's crust provide 250x more energy than in all earth's oil and natural gas reserves
*Geothermal energy most available at volcanoes: boundaries of plates and hot spots
*US biggest producer
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Geothermal Energy• Hydrothermal reservoirs
> dry steam> wet steam> hot water
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Geothermal Energy
Geothermal heat pump (GHP)• difference in surface and underground temperature• fluid flowing through pipes• Winter: Heat from underground to home• Summer: Heat from home to underground
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Geothermal Energy
Geothermal heat pump (GHP)• energy-efficient, reliable, environmentally clean• no pollutants, no CO2
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Turning Geothermal Energy into Electricity
1. Dry steam
2. Flash steam
3. Binary cycle
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*Recirculate hot water back into ground to slow depletion
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Hydrogen gas (H2)• H2 + O2 H2O• Where is the hydrogen?
> Locked up in water, organic compounds> Energy and money to produce* low energy
yield> Fuel cells are expensive> Whether it produces less air pollution than fossil
fuel depends on how hydrogen is produced– burning fossil fuels v. hydro/wind/solar power
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Hydrogen• How to apply technology?
> home fueling units> energy farmers not energy hunter-gatherers> nanomaterials> store hydrogen in tanks or carbon nanofibers
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Sustainable Energy Strategy• Takes at least 50 years + $$ to phase in new
energy alternatives to 10-20% total energy use• Things to consider:
> Resource> Net energy yield> $$ required?> Government research and subsidies> Environmental effects
*US
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Trends:• shift from large centralized macropower systems to
smaller, decentralized micropower systems> diversity of energy resources
• energy efficiency + natural gas + sustainably produced biofuel to transition to renewable-energy resources
• continued use of fossil fuels + reduce harm while phase-in renewable energy
February 19, 2014
Policy to shift to more sustainable energy resources1. Keep price of sustainable energy resources low
> research subsidies, tax breaks2. Keep energy prices artificially high to discourage
use of a resource> eliminate tax breaks and subsidies, restrictive
regulation, add tax on use3. Consumer education
February 19, 2014
Tuesday (2/18):• Guest presentation on using solar power• Finish up chapter 17
Thursday (2/20): Start Chapter 18
Monday (2/24): Unit 6 Test (Chapter 16 and 17) *including calculations
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