Hydropower

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

DamsTrap water flowing downhill and use the energy to turn turbines

DamsTrap water flowing downhill and use the energy to turn turbines

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.

Hydropower: USHydropower is the #1 alternative energy source (butbiomass is close…)

Hydropower:US

Global

History of hydropower

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: propeller systems

Tidal power: wave systems

Air driven

Water driven

Tidal power:enclosures

Power can be generatedwith both rising andfalling tide…

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

Tidal power: bottom line

Tidal power has a potential equal to only 1 to 2percent of current global energy use, but, it isuseful in certain coastal settings, and is verycheap to produce and maintain.