Basics•this is a form of solar energy, as the sun drives waterevaporation from the ocean and winds carry the moistureoverland
•largest form of alternative energy used today (but only 2%of global energy)
•industrialized countries have already tapped most of theirpotential
•non-industrialized countries have most of the untappedpotential
More basics
•Energy is converted from potential energy of water at someheight to other forms of energy as water drops... electrical
energy, mechanical energy....
•most water power is tapped via dams ... these hold enoughwater to outlast periodic droughts and help to control flooding
•tidal power and wave power are an ocean forms of waterpower
Dams
Ultimate source ofpower is the sun;aided by gravity.
Solar energyevaporates water
Water falling onland flowsdownhill
Dams
Height of dam and mass of water behind the damdetermine useful energy.
Efficiency is very good to excellent, generally 80 to90% efficient in converting potential energy toelectrical energy.
Costs of hydropower
•Hydroelectric is less than half the cost of fossil fuel derivedelectricity.•Note that the difference is in fuel costs.
History of hydropower
Percentage of electricity from hydropower has declinedbecause 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 duevariations in rainfall… climate
Pros and Cons of hydropower
Pros:•very clean•cheap •flood control (primary reason for dams)•multiple crops per year possible
Pros and Cons of hydropowerCons:•potential is limited globally to about 5 to 10% of energy needs•dependability is an issue; prolonged droughts can cut electricalproduction in half or more
•dams have drawbacks, including...loss of nutrient flow down riverloss of sediment flow down riversedimentation behind the dam limits lifetime of the damflooding of scenic areasecosystem below the dam is usually changed by havingcolder, nutrient poor wateraesthetics… loss of wild rivers
Potential for hydropower
Industrialized world is about tapped out… maybe a30% 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
Potential for hydropower
Developing world has more potential•less than 1% of energy from hydropowertoday•could be as much as 10%•as developing countries develop, however,this percentage will drop, maybe 5% or less.
Tidal power
Form of hydropower, but uses gravitationalenergy, the pull of the moon on water
Concept is simple.•build a dam across an inlet with a large tidalrange, or•Build an enclosure that can be filled duringhigh tide•Capture wave energy•Use underwater propellers
Tidal power: issues
Tides cycle every 12.5 hours, so daily peak productiontimes and slack times vary, this causes a mismatch insupply and demand, as industrial demand is high duringthe 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 (rememberheight of dam issue!).
Tidal power: issuesDue to low height of water and slack times inproduction, tidal dams produce about 1/3rd the power ofriver dams.
Tidal power is cheap, less than 1/5th the cost of fossilfuel power.
Problems include hindered ship traffic and ecologicaldamage to marine ecosystems and especially migratingfish species.
Wave generating systems dependent on weather