Renewables Flashcards
The process by which large nuclei are split into smaller ones is called nuclear
Fission
About 95% of the uranium reserves around the world are found in
sedimentary and metasedimentary rocks
Nuclear fusion reactors would
Involve far fewer radiation hazards than fission reactors
A breeder reactor
Converts more-common isotopes, such as uranium-238, to fissionable fuel during normal operation
The sun generates its tremendous energy output by
Nuclear fusion
Given that a region has an average annual air temperature of 13 C, what would the subsurface temperature be at a depth of 2 km? Assume the geothermal gradient is the same as the world average geothermal gradient, which is approximately 30 C per kilometer.
73 C
Which of the following energy sources is particularly associated with plate boundaries?
Geothermal Power
Limitations of wind and solar energy include all of the following except
Both are low pollution forms of energy production
Hydropower plants
Are used exclusively for generating electricity
Which of the following renewable energy sources provides the greatest share of energy consumed in the U.S.?
Conventional hydropower
Solar Energy
Abundant solar energy reaches the Earth’s
surface (enough to meet all our energy needs)
How is solar energy used?
Solar Heating •Passive solar heating: no mechanical assistance •Active solar heating: mechanical circulation of solar-heated water
Why isn’t solar widely used?
Efficiency is still pretty low (and cost is high!)!
•Even in areas of strongest sunlight in the US, incident radiation is ~250
watts/m2.
•If solar cells are operating at 20% efficiency, only 50 watts/m2 would be generated.
•SO…it would take 2 m2 of solar cells to power a 100-watt lightbulb!!
•A 100 mW power plant would require 2 km2 of both land and mineral
(usually toxic materials like gallium and arsenic) resources.
Storing solar electricity is complicated
• For individual homeowners, batteries work but power companies need better storage capabilities.
Renewables Portfolio Standard
“RPS”
Utilities must generate 20% of total
electricity capacity from renewable
resources by 2020.
With the property tax exemption in place,
you won’t have to pay a single extra
penny in property taxes for that home
value increase.
Wind Energy
- The winds are ultimately powered by the sun, and thus wind energy can be viewed as a variant of solar energy
- Clean and renewable energy resource
- Many technological improvements have increased the energy production from windmills
- Areas of best wind generation potential tend to be far from population centers that would benefit from them
- “Wind Farms” are large scale operations producing about 1 megawatt per windmill
- Abundant small scale windmills involve small wind turbines lifting water on a ranch or farm
Geothermal Energy
- The earth contains a great deal of heat, most of it left over from its early history, some generated by decay of radioactive elements in the earth
- Interior of the earth is very hot
- Abundant source of heat and hot water
- Magma rising into the crust bring abundant heat up into the crust as geothermal energy
- Heat escaping from the magma heats water and the water convectively circulates
Many areas away from plate boundaries have
high geothermal gradients
• These areas contain hot-dry-rock type
geothermal resources
• Deep drilling into such rocks may produce
appreciable amounts of geothermal energy
Geothermal Heat Pumps (GHPs) Direct-Use Piped Hot Water Warms Greenhouses and Melts Sidewalk Snow
In the U.S., most geothermal reservoirs are located in the western states, Alaska, and Hawaii.
•Hot water near Earth’s surface can be piped directly into facilities
•Some cities pipe the hot water under roads and sidewalks to melt snow.
District heating applications use networks of piped hot water to heat buildings in whole communities. For more information on direct use of geothermal energy
Hydropower
• Hydroelectric power produces less than 5% of U.S. energy requirement
• Hydropower is a clean fuel source..
• Hydropower is generally available as needed; engineers can control the flow of water through the turbines to produce electricity on demand.
• Most hydropower installations are required to provide some public access to the reservoir to allow the public to take advantage of these opportunities. Other benefits may include
water supply and flood control.
•There are many ecological and environmental impacts of large dams
Impoundment:
The most common type of hydroelectric
power plant. It is typically a large hydropower system, and uses a dam to store river water in a reservoir.
Hydropower Disadvantages
Fish populations can be impacted if fish cannot migrate
upstream
•Hydropower can impact water quality and flow. Hydropower plants can cause low dissolved oxygen levels in the water
•Hydropower plants can be impacted by drought. When water is not available, the hydropower plants can’t produce electricity.
•New hydropower facilities impact the local environment and may compete with other uses for the land. Those alternative uses may be more highly valued than electricity generation.
•Effect erosion rates
Bowersock Mills and Power Company
The Bowersock Mills & Power Company is the only operating hydroelectric plant in Kansas,
•Bowersock provides river flow and public water services to the city of Lawrence, KS, and generates 2.35 MW of power each year.
•The clean, renewable electricity produced by the plant’s seven generators flows into the electrical grid and is purchased by the Kansas
Power Pool providing enough power for approximately 1,800 homes.
•The new powerhouse will replace the spillway on the north end of the dam, and will house four additional turbine/generators, for a total
capacity addition of 4.6 MW.
Tidal Power
Although not yet widely used, tidal power has
potential for future electricity generation.
Tides are more predictable than wind energy
and solar power. Historically, tide mills have
been used, both in Europe and on the Atlantic
coast of the USA.
Biomass
Biomass refers to the total mass of all the organisms living on earth
• Biomass energy uses discarded waste material that is burned as a fuel to produce energy
• Biomass fuels include wood, paper, crop waste, and other combustible waste
• Alcohol, as a fuel, is produced from grains, such as corn
–Mixed with gasoline to form gasohol
–Qualifies as a renewable resource
Sustainable, low-carbon biomass can provide a significant fraction of the new
renewable energy we need. Without sustainable, low-carbon biopower, it will likely
be more expensive and take longer to transform to a clean energy economy.
Among beneficial resources, the most effective and sustainable biomass resources will vary
from region to region and also depend on the efficiency of converting biomass to its final
application, be it for biopower, biofuels, bioproducts, or heat.
Energy Crops
Grasses
Crop Residue
Manure
Woody Biomass
Forest Residues/Forest Treatments/Thinned Trees/Short-rotation Trees
Urban Waste
advantages of biomass
• Theoretically inexhaustible fuel source
• When direct combustion of plant mass is not used to generate energy (i.e. fermentation, pyrolysis, etc. are used instead), there is minimal environ. impact
• Alcohols and other fuels produced by biomass are efficient, viable, and relatively
clean-burning
• Available throughout the world
disadvantages of biomass
• Could contribute a great deal to global warming and particulate pollution if
directly burned
• Still an expensive source, both in terms of producing the biomass and converting
it to alcohols
• On a small scale there is most likely a net loss of energy–energy must be put in
to grow the plant mass
Nuclear Energy; Radioactive Isotopes
The forces that bind protons and neutrons together in the nucleus are usually strong. In some cases, these forces are not strong enough, and the nuclei spontaneously break apart (decay) = radioactivity •Only certain isotopes are radioactive
Nuclear Energy
Based on an induced fission reaction. A slow-moving neutron is absorbed by the nucleus of a Uranium-235 atom, which in turn splits into fast moving lighter elements (fission products) and releases three free neutrons.
Nuclear Energy
chain reactions
In order for a chain reaction to occur, three things must happen:
1.The sample must be mostly uranium-235 atoms. Any other atoms could
absorb the neutrons without undergoing fission, and the chain reaction stops.
2.The sample of uranium-235 atoms must be large enough. If the sample is too
small, too many of the atoms are on the outside, and the neutrons fly off in other
directions rather than hitting a uranium-235 atom.
3.The atoms must be held together long enough for lots of fission reactions
to occur. If it explodes too quickly, not many fission reactions will start, and the
explosion will be small
Nuclear Energy Bomb
It is important not to let the chain reaction used in a nuclear reactor get out of control and
create a nuclear explosion. To do this, uranium that is only 3% enriched is used. This is
just enough to keep the chain reaction going, but not let it grow out of control and explode.
Also, control rods which absorb neutrons can be lowered or raised from the reactor, slowing
it down or speeding it up
Radioisotopes
Radioisotopes with short half-lives (a few
years to hundreds of years) present the most
risk
•Radioactive enough to cause harm
•Persistent in the environment long enough to require management
Nuclear Waste Disposal
Nuclear Waste Policy Act of 1982: establish a high-level
disposal site in the west
•Yucca Mountain Attractive Characteristics:
•Rhyolitic tuff host rock
•Arid climate
•Low population density (but Las Vegas is 60 miles to the
southeast)
•Low regional water table
•Apparent geologic stability
Yucca Mountain
Funding for development of Yucca Mountain waste site was terminated effective with the 2011 federal budget passed by Congress on April 14, 2011. This leaves the United States without any long term storage site for its high level radioactive waste, currently stored on-site at various nuclear facilities around the country. In the meantime, failure to perform to contractual requirements will cost the taxpayer $11 billion by 2020.
