Post on 07-Aug-2018
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Hydropower
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Basics•this is a form of solar energy, as the sun drives water
evaporation from the ocean and winds carry the moisture
overland
•largest form of alternative energy used today (but only 2%
of global energy)
•industrialized countries have already tapped most of their
potential
•non-industrialized countries have most of the untapped
potential
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More basics
•Energy is converted from potential energy of water at some
height to other forms of energy as water drops... electrical
energy, mechanical energy....
•most water power is tapped via dams ... these hold enough
water to outlast periodic droughts and help to control flooding
•tidal power and wave power are an ocean forms of water
power
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Dams
Ultimate source of
power is the sun;
aided by gravity.
Solar energyevaporates water
Water falling on
land flows
downhill
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DamsTrap water flowing downhill and use the energy to turn turbines
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DamsTrap water flowing downhill and use the energy to turn turbines
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Dams
Height of dam and mass of water behind the dam
determine useful energy.
Efficiency is very good to excellent, generally 80 to
90% efficient in converting potential energy to
electrical energy.
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Costs of hydropower
•Hydroelectric is less than half the cost of fossil fuel derived
electricity.
•Note that the difference is in fuel costs.
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Hydropower: USHydropower is the #1 alternative energy source (but
biomass is close…)
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Hydropower:
US
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Global
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History of hydropower
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History of hydropower
Percentage of electricity from hydropower has declined
because the total amount of electricity produced has risen,
while electricity for hydropower remained nearly constant
Very little new hydropower added after 1975
Fluctuations in amount of hydropower after 1975 are due
variations in rainfall… climate
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Pros and Cons of hydropower
Pros:
•very clean•cheap
•flood control (primary reason for dams)
•multiple crops per year possible
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Pros and Cons of hydropower Cons:
•potential is limited globally to about 5 to 10% of energy needs
•dependability is an issue; prolonged droughts can cut electrical
production in half or more
•dams have drawbacks, including...
!loss of nutrient flow down river
!loss of sediment flow down river
!sedimentation behind the dam limits lifetime of the dam
flooding of scenic areas
!ecosystem below the dam is usually changed by having
colder, nutrient poor water
!aesthetics… loss of wild rivers
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Potential for hydropower
Industrialized world is about tapped out… maybe a
30% increase possible.
•currently 3% of total energy
•so 5% of today's energy is possible
•but as needs increase, this percentage goes down
•maximum of 3% is realistic
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Potential for hydropower
Developing world has more potential
•less than 1% of energy from hydropower
today
•could be as much as 10%
•as developing countries develop, however,
this percentage will drop, maybe 5% or less.
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Tidal power
Form of hydropower, but uses gravitational
energy, the pull of the moon on water
Concept is simple.
•build a dam across an inlet with a large tidal
range, or
•Build an enclosure that can be filled duringhigh tide
•Capture wave energy
•Use underwater propellers
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Tidal power: propeller systems
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Tidal power: wave systems
Air driven
Water driven
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Tidal power:
enclosuresPower can be generated
with both rising and
falling tide…
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Tidal power: issues
Tides cycle every 12.5 hours, so daily peak production
times and slack times vary, this causes a mismatch in
supply and demand, as industrial demand is high during
the day and low at night.
Tides vary seasonally and monthly as well.
The tidal range is about 2 feet to about 20 feet, thehigher the tide, the more useful the energy (remember
height of dam issue!).
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Tidal power: issues
Due to low height of water and slack times in
production, tidal dams produce about 1/3rd the power of
river dams.
Tidal power is cheap, less than 1/5th the cost of fossil
fuel power.
Problems include hindered ship traffic and ecological
damage to marine ecosystems and especially migrating
fish species.
Wave generating systems dependent on weather
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Tidal power: bottom line
Tidal power has a potential equal to only 1 to 2
percent of current global energy use, but , it is
useful in certain coastal settings, and is verycheap to produce and maintain.