Alternative energy sources - renewable and ~ low impact on the environment
Combine two isotopes to make a larger one and harness the resultant energy (similar in amount to nuclear fission).
Main process in stars (our sun) and hydrogen bomb (uncontrolled reaction)
The typical nuclear fusion reaction achievable on Earth is the combination of heavy Hydrogen isotopes to produce Helium:
2 H + 3 H (deuterium + tritium) He + neutron
+ energy (17.6 million electron volts)
There has only been limited success in achieving controlled nuclear fusion because
Extremely high temperatures required
>100 million °C
Reactions can be maintained over only fractions of a second
Reaction requires more energy than the amount released
Future technology may find a way, but it is currently not useful
enormous potential source of energy (essentially unlimited , the oceans have vast amounts of deuterium)
low environmental costs
no CO 2 emissions
non-hazardous, benign by-products = Helium
technology currently not available...
technology may NEVER exist...
or may not ever be economical (e.g., requires more energy than it creates)
Involves tapping heat generated deep in the earth, usually due to active or dormant volcanism
A sustainable resource as long as it is not extracted faster than it is naturally replenished.
Need the following geologic conditions for a potentially economic source of geothermal energy:
recent volcanic activity (magma body within 3-10 km of the surface)
impermeable cap rock
Three types of power plants are used to generate power from geothermal energy:
Dry steam plants
take steam out of fractures in the ground
and use it to directly drive a turbine that spins a generator.
take hot water, usually at temperatures over 200°C, out of the ground
and allows it to boil as it rises to the surface
then separates the steam phase in steam/water separators
and then runs the steam through a turbine.
the hot water flows through heat exchangers, boiling an organic fluid that spins the turbine.
The condensed steam and remaining geothermal fluid from all three types of plants are injected back into the hot rock to pick up more heat
Vast potential energy resource
Easy to find sources of heat
~ Clean resource:
little air pollution
few CO 2 emissions
no solid waste
Wastewater disposal is a problem (often a saline brine - rich in toxic elements),
Subsidence during groundwater extraction (reduced permeability in aquifer),
Can produce earthquakes during forced injection (Rocky Mountain Arsenal)
Rocky Mountain Arsenal
From April 1962 to November 1965, several hundred earthquakes occurred in the Denver, CO, area
The source of the earthquakes was traced to the Rocky Mountain Arsenal, which was manufacturing materials for chemical warfare
Liquid waste from the manufacturing process was being pumped down a deep disposal well to a depth of about 3600 m
The rock receiving the waste was highly fractured metamorphic rock
Injection of the new liquid increased the fluid pressure, causing slippage along fractures
When the injection of the waste stopped, so did the earthquakes
Geothermal Heat Pumps
Take advantage of the stable Earth temperature of 45-58 F (7.2-14.4 C) just a few feet below the surface
GHP's circulate water or other liquids through pipes buried in a continuous loop (either horizontally or vertically) next to a building.
Depending on the weather, the system is used for heating or cooling.
Earth's heat (the difference between the earth's temperature and the colder temperature of the air) is transferred through the buried pipes into the circulating liquid and then transferred again into the building.
During hot weather, the continually circulating fluid in the pipes 'picks up' heat from the building - thus helping to cool it - and transfers it into the earth
GHP's use very little electricity and are very easy on the environment.
In the U.S., the temperature inside over 300,000 homes, schools and offices is kept comfortable by these energy saving systems, and hundreds of thousands more are used worldwide.
The U.S. Environmental Protection Agency has rated GHP's as among the most efficient of heating and cooling technologies
GHP’s can be used worldwide
Unlike other kinds of geothermal heat, shallow ground temperatures are not dependent upon tectonic plate activity or other unique geologic processes.
Thus geothermal heat pumps can be used to help heat and cool homes anywhere
How much geothermal energy is there?
Thousands more megawatts of power than are currently being produced could be developed from already-identified hydrothermal resources.
With improvements in technology , much more power will become available.
Usable geothermal resources will not be limited to the "shallow" hydrothermal reservoirs at the crustal plate boundaries.
Much of the world is underlain (3-6 miles down), by hot dry rock - no water, but lots of heat.
Scientists have experimented with piping water into this deep hot rock to create more hydrothermal resources for use in geothermal power plants.
As drilling technology improves, allowing us to drill much deeper, geothermal energy from hot dry rock could be available anywhere.
At such time, we will be able to tap the true potential of the enormous heat resources of the earth's crust.
Renewable resource; many forms including:
Direct solar energy
architectural designs use solar energy to heat and cool homes
solar panels used to heat water to drive turbines
mirrors move and track the sun
focus rays on receiver (> 1000 °C)
cylindrical reflector focuses rays on heating element
photovoltaic (solar) cells to generate electricity
cells contain a material that becomes unstable when struck by light
emits electricity as the crystalline lattice reorganizes itself
low conversion efficiency: 10-12% in silicon cells, 4-6% in cadmium/copper cells
AND high cost per kwh
Indirect solar energy - heat from solar energy drives other Earth systems which can be harnessed
Moving water - hydroelectric power
tides - use energy of tidal forces to drive turbines
focus water flow using locks, gates
ocean currents and waves
difficult to concentrate (funnels/horns) and utilize
rivers - dams trap the water in a reservoir, force water to flow past turbines
constructed to increase height from which water drops
provides a constant flow of water through turbines
80-90% efficient in converting energy to electricity
35-40% for fossil fuels
30% for nuclear fuels
Harness energy of falling water
Require dams to create reservoirs
In addition to power generation, also control flooding and water supply
Energy from organisms or their remains
agriculture - burn or compost vegetation
urban waste - methane gas from decay, collect and use as natural gas
ethyl alcohol - derived from corn, added to gasoline
Harness wind energy using " wind farms " with huge windmills
Wind-electric potential: 48 contiguous U.S. states (% of each state’s energy need). 12 states could provide ~90 % of the total U.S. energy need
Advantages of Solar Power (both direct and indirect)
free and renewable
no CO 2 emissions or other pollutants - except biomass
Disadvantages - direct solar energy
expensive - difficult to store electricity
cost per kilowatt hour (kwh) is 5-6 times that of other methods but costs may decrease in the future
intermittent and localized
construction of facilities involves semiconductor manufacture
mining and manufacturing hazards and costs
large arrays affect landscape aesthetics
Disadvantages – indirect solar energy
dams cause numerous environmental problems to river systems
change stream velocity
inhibit fish migrations
large projects displace humans and animals
Three Gorges Dam, China
dam failures result in catastrophic floods
windmills are eyesores, noisy, and affect media reception
wood is renewable but not necessarily sustainable as a resource
adds greenhouse gases and other forms of air pollution
Three Gorges Dam Project
Will be the world’s largest dam
Artist’s drawing of what the finished project will look like
Some facts about the Three Gorges project:
Project expected to take 17 years; completion expected in 2009.
The Three Gorges Reservoir will inundate 632 square kilometers (395 square miles) of land.
An estimated 1.2 million people will be resettled by the dam
The project's 26 hydropower turbines are expected to produce 18.2 million kilowatts, up to one-ninth of China's output.
Source: Chinese government
What will it cost?
Chinese Government estimate: $25 billion
Forced resettlement (jobs, culture, housing)
Loss of farmland, historical sites, tourism
sediment pollution and erosion
sediment-filled reservoir = no flood control capacity
Three attractive advantages:
mostly present in molecules combined with other elements (i.e., H 2 O, CH 4 )
Combustion provides large quantities of heat
Waste products = just water
How is hydrogen separated?
Pass electric current through water
Collect pure oxygen (O 2 ) and hydrogen (H 2 )
Relatively infinite supply of water, but the process does require electricity (fossil fuel? hydro? solar?)
Usually takes more energy to separate hydrogen than you receive from it as a fuel.
More of an energy carrier
How could it be used as an energy resource (for example, in automobile engines)?
combustion (like gasoline)
fuel cells (hydrogen and oxygen vigorously react to produce electricity and heat)
electric motor in cars
very dangerous, highly explosive
needs to be highly pressurized or as a liquid
difficult to safely store and transport
simple technology could mean on-site manufacturing