energy alternatives

Energy Alternatives

NUCLEAR ENERGY

Fission

• Nuclear energy = energy holding protons and neutrons together

• Nuclear energy → thermal energy → electricity• In nuclear power plants, nuclear fission drives the

release of energy• In fission, a large, unstable nucleus (U-235 or U-238),

is made to break apart, releasing energy• Radioisotopes are atoms of a certain element that

emit subatomic particles and radiation to become stable

Fission

• Each radioisotope has a certain half-life of decay• Half-life is the time it takes for half of the

original amount of radioactive isotope to decay• After several years, rods must be replaced due

to decay and consumption• Fuel rods can be processed to extract more

energy, but they are usually disposed of as radioactive waste

Fission

• Breeder reactors make use of 238U which can generate more power (it is more abundant than 235U)

• Breeder reactors use liquid Na as coolant – more dangerous

• Breeder reactors can generate plutonium to be used in nuclear weapons

Fusion

• Fusion involves the synthesis of heavier elements from lighter ones under high temperature and pressure

• Hydrogen isotopes (deuterium and tritium) are fused to form helium

• Have not achieved break-even energy• Energy is cleaner, resources are plentiful (water)

Nuclear Advantages & Disadvantages

• Clean energy (no emissions)• More bang for your buck means less mining• Disposal of waste is a huge problem; most is

stored on site• Accidents, sabotage could be catastrophic• 439 operating plants world-wide

Small Risks of Large Accidents

• 1979 – Three Mile Island in Pennsylvania• Metal surrounding the fuel rods melted down,

releasing radiation• It did not escape containment (some gases were

vented)• Clean-up lasted years• No significant health risks

Small Risks of Large Accidents

• 1986 – an explosion at the Chernobyl plant (Ukraine) caused most severe nuclear pp disaster in the world

• Clouds of radioactive debris spewed into the atmosphere

• Fallout carried over most of northern hemisphere

• 30-km radius contaminated

Waste Disposal & Other Problems

• Waste remains dangerous for thousands of years (remember half-life?)

• Currently, waste is held in temporary storage on-site• Yucca mountain in Nevada has been chosen for

storage beginning in 2010• More expensive than expected• Plants have aged more quickly• Shutting down plants more expensive than the

original construction

BIOMASS ENERGY

Biomass Energy• Biomass consists of the organic material that

makes up living organisms• Biomass energy involves burning many types of

plant and animal matter• Includes: wood, charcoal, combustible animal

waste• Fuelwood and other traditional biomass sources

= 80% of all renewable energy used worldwide• Renewable if not overharvested!

Biomass Energy

• Biopower generates electricity in power plants• Biomass sources can be converted to biofuels• Many new biomass resources are waste

products from preexisting industry• Organic components form municipal landfills,

animal waste from feedlots and ag residue can be major bioenergy resources

Biofuels

• Ethanol is produced by fermenting biomass• Used in gasoline to reduce emissions• E-85 is 85% ethanol and 15% gasoline• Biodiesel is produced from vegetable oil, used

cooking grease or animal fat• Traditional diesel engines can run on 100%

biodiesel

Environmental and Economic Benefits

• Carbon-neutral, releasing no net carbon into the air• Is the product of recent photosynthesis, so carbon

released balances the carbon taken up• Capturing landfill gas for biofuels also reduces

greenhouse gases• Ethanol additives to gasoline reduces pollution• Economic support of rural areas, reduce

dependence on oil, etc.• Human health benefits

Drawbacks

• Burning biomass in traditional ways for cooking and heating leads to health hazards from indoor pollution

• Unsustainable harvesting leads to deforestation, erosion, and desertification

• Growing biofuel crops leads to monoculture agriculture

• Growing biofuel crops requires large energy inputs

HYDROELECTRIC POWER

Hydroelectric Power

• Kinetic energy of moving water powers turbines to generate electricity

• Most of our energy comes from impounding water behind dams and letting water pass through dams

• An alternative is run-of-river approach, in which electricity is generated w/out disrupting water flow (susceptible to seasonal changes)

Hydroelectric Power

• Hydropower is widely used• Hydropower is clean and renewable• Negative impacts include habitat destruction,

disruption of natural flooding, sediments trapped behind the dam, thermal pollution downstream, fragmentation of the river

• No room for expansion – all capable rivers already dammed (98% in US)

“NEW” RENEWABLE ENERGY

Currently Provide Little of Our Power

• 80% of world’s energy sources are fossil fuels

• US electricity generation from renewables:–75% hydropower–17.5% biomass–4.2% geothermal–4.1% wind–0.1% solar

Currently Provide Little of Our Power

• Transition cannot be immediate, but it must be soon:– Expensive– Technology must be developed– Lack of infrastructure to transfer energy– Labor intensive (good for economy – jobs)–Development is underfunded

SOLAR ENERGY

Solar Energy

• Potential is tremendous; the sky is the limit!

• Passive solar heating: buildings and materials are chosen to maximize direct absorption of sunlight in winter

• Active solar energy collection uses technological devices to focus, move, or store energy

Solar Energy

• Passive: heat-absorbing materials, low, south-facing windows, even vegetation• Active: uses solar panels or flat-plate solar

collectors• Concentrating solar rays magnifies energy

received• Photovoltaic (PV) cells convert sunlight into

electricity

Solar Energy

• PV cells made of silicon enriched with P and B• Solar power is little used, but growing fast• Sales of PV growing by 28% each year in US• Limitless supply of energy (well, at least 4

billion years more)• PVC’s use no fuel, are quiet, little

maintenance, do not require a turbine or generator

Solar Energy

• Enable local, decentralized control over power

• No pollution• Location and cost are major drawbacks• Need a sunny region

WIND ENERGY

Wind Energy

• Indirect solar energy!• Wind turbines convert KE of wind into

electricity• Over 800 years of use, first generation of

electricity in late 1800’s• Most turbines are erected in groups called

wind farms

Wind Energy

• Designed to begin turning at specific wind speeds

• Offshore sites more productive• No emissions are produced• More energy efficient than conventional• Can be used on many scales• Landowners can lease land

Wind Energy

• Up-front costs are large, but low lifetime costs for upkeep

• Generation relies on wind• Good wind resources not always near

populated areas• Threat to birds (not owls – they’re too

smart)

Wind Energy

• Noise is an issue for those who live nearby• Wind is intermittent

GEOTHERMAL ENERGY

Geothermal Energy

• Originates from deep underground• Radioactive decay of elements and high

pressures generates heat; rises to sfc• Requires well-drilling 100’s to 1000’s of

meters to tap heated groundwater• Can be used directly for heating homes,

etc

Geothermal Energy

• Can also be used to drive a heat pump • Ground Source Heat Pumps (GSHP) are 50-

70% more efficient than conventional• Reduces emissions• Water is loaded with salts that lead to corrosion

of equipment• Use in particular areas only

OCEAN ENERGY SOURCES

Ocean Energy Sources

• Harnessing energy from tides and ocean waves

• Other: currents, chemical gradients (salinity), and immense thermal energy

HYDROGEN

Hydrogen Fuel Cells

• Shows promise as a vehicle for storing electricity conveniently in large quantities

• Produced from water through electrolysis• Fuel cells produce electricity by

combusting hydrogen• Hydrogen is most abundant element in

universe

Hydrogen Fuel Cells

• It is clean and nontoxic• May produce a few pollutants and

greenhouse gases, depending on source of H

• Fuel cells are quiet, non-polluting and allow energy to be stored in the form of H

• Energy efficient