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    2010

    RAYAT INSTITUTE OF ENGINEERING AND

    INFORMATION TECHNOLOGY

    11/10/2010

    HYDROELECTRICITY

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    HYDROELECTRICITY

    CONTENTS:

    INTRODUCTION

    GENERATINGMETHODS

    SIZES AND CAPACITIES OF HYDROELECTRIC FACILITIES

    CALCULATING THEAMOUNT OF POWER AVAILABLE

    ADVANTAGES AND DISADVANTAGES

    WORLD HYDROELECTRIC CAPACITY

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    HYDROELECTRICITYINTRODUCTION

    Hydroelectricity is the term referring to electricity generated by hydropower;

    the production of electrical power through the use of the gravitational force of

    falling or flowing water. It is the most widely used form of renewable energy.

    Once a hydroelectric complex is constructed, the project produces no direct

    waste, and has a considerably lower output level of the greenhouse gas carbon

    dioxide (CO2) than fossil fuel powered energy plants. Worldwide, an installed

    capacity of 777 GW supplied 2998 TWh of hydroelectricity in 2006.This was

    approximately 20% of the world's electricity , and accounted for about 88% of

    electricity from renewable sources

    ]

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    HYDROELECTRICITYEnergy is the most important thing in this world. All living plants, animals

    (organisms) on this earth require energy to perform any type of work. The

    capacity to do a work is energy. The energy may require in smaller amount or in

    larger amount depending upon the nature of work to be performed.

    The different things from which we get the energy are called as Energy Sources.

    This is the simplest meaning of energy sources. There are two types of energysources:

    1. Conventional OR Non-Renewable Energy Sources

    2. Non-Conventional OR Renewable Energy Sources

    1. Conventional OR Non-Renewable Energy Sources:

    The energy sources, which we are using from long time and which are in danger

    of exhausting, are called as Conventional OR Non-Renewable Energy Sources.

    They are not renewed by Nature and they are perishable, are going to get

    exhausted one day.

    e. g. coal, petroleum products, nuclear fuels etc.

    2. Non-Conventional OR Renewable Energy Sources:

    These are the energy sources whose utilization technology is not yet fully

    developed. These are the sources, which can be recovered and reused. i. e. they

    can be used again and again to generate energy because of the renewal of their

    energy

    We are going to consider one of the ways of generation of energy from non -

    conventional energy namely hydroelectric energy. As name suggest, it is the

    energy obtained from water.

    The main principle used in this type is the kinetic energy of falling water is

    converted into electric energy using turbines.

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    HYDROELECTRICITYHistory of hydro power development:

    The first recorded use of water power was a clock, built around 250 BC. Sincethat time, humans have used falling water to provide power for grain and sawmills, as well as a host of other applications. The first use of moving water to

    produce electricity was a waterwheel on the Fox River in Wisconsin in 1882, twoyears after Thomas Edison unveiled the incandescent light bulb. The first ofmany hydro electric power plants at Niagara Falls was completed shortlythereafter. Hydro power continued to play a major role in the expansion ofelectrical service early in this century, both in North America and around theworld. Contemporary Hydro-electric power plants generate anywhere from a fewkW, enough for a single residence, to thousands of MW, power enough to s upplya large city.Early hydro-electric power plants were much more reliable and efficient than thefossil fuel fired plants of the day. This resulted in a proliferation of small tomedium sized hydro-electric generating stations distributed wherever there wasan adequate supply of moving water and a need for electricity. As electricitydemand soared in the middle years of this century, and the efficiency of coal andoil fueled power plants increased, small hydro plants fell out of favor. Most newhydro-electric development was focused on huge "mega-projects".The majority of these power plants involved large dams which flooded vast areasof land to provide water storage and therefore a constant supply of electricity. InRecent years, the environmental impacts of such large hydro projects are beingidentified as a cause for concern. It is becoming increasingly difficult fordevelopers to build new dams because of opposition from environmentalists andpeople living on the land to be flooded. This is shown by the opposition toprojects such as Great Whale (James Bay II) in Quebec and the Gabickovo-Nagymaros project on the Danube River in Czechoslovakia.Hydropower generation is an improvarient of primitive water wheel for grindingcereals. As hydro-electric power it emerged in USA in1882, followed by sweedenand Japan. In India, hydropower plant OF 130kw installed capacity wascommissioned in 1897 at sidrapong at Dargiling in West Bengal and followed by4.5MW plant at sivsamudram in Karnataka in 1902.during period between twoworld wars, a number of hydro power plants such as 48MW, atJogindernagar(H.P.),17.4MW ganga power plant(U.P.), 38.75MWpykaraand30MWmatter(Chnnai)were commissioned,from installed capacity of 1362MW,outof which hydropower was 508 MW in 1947,the pace of growth has been rapid inpost independence era. The hydal install capacity by the end 2001 is 25,574MW,out of total capacity of 102907MW.

    Hydroelectric power:Electricity produced from generators driven by water turbines that convert the

    energy in falling or fast-flowing water to mechanical energy. Water at a higherelevation flows downward through large pipes or tunnels (penstocks). The fallingwater rotates turbines, which drive the generators, which convert the turbines'mechanical energy into electricity. The advantages of hydroelectric power oversuch other sources as fossil fuels and nuclear fission are that it is continuallyrenewable and produces no pollution. Norway, Sweden, Canada, and Switzerlandrely heavily on hydroelectricity because they have industrialized areas close tomountainous regions with heavy rainfall.

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    HYDROELECTRICITYThe U.S., Russia, China, India, and Brazil get a much smaller proportion of theirelectric power from hydroelectric generation. See also tidal power.Water is needed to run a hydroelectric generating unit. Its held in a reservoir orlake behind the dam and the force of the water being released from the reservoirthrough the dam spins the blades of a turbine. The turbine is connected to thegenerator that produces electricity. After passing through the turbine, the water

    reenters the river on the downstream side of the dam.The capability to produce and deliver electricity for widespread consumption wasone of the most important factors in the surge of American economic influenceand wealth in the late nineteenth and early twentieth centuries. Hydroelectricpower, among the first and simplest of the technologies that generatedelectricity, was initially developed using low dams of rock, timber, or graniteblock construction to collect water from rainfall and surface runoff into areservoir. The water was funneled into a pipe (or pen-stock) and directed to awaterwheel (or turbine) where the force of the falling water on the turbineblades rotated the turbine and its main shaft. This shaft was connected to agenerator, and the rotating generator produced electricity. One gallon (about 3.8liters) of water falling 100 feet (about 30 meters) each second produced slightly

    more than 1,000 watts (or one kilowatt) of electricity, enough to power ten 100-watt light bulbs or a typical hairdryer.There are now three types of hydroelectric installations: storage, run -of-river,and pumped-storage facilities. Storage facilities use a dam to capture water in areservoir. This stored water is released from the reservoir through turbines atthe rate required to meet changing electricity needs or other needs such as floodcontrol, fish passage, irrigation, navigation, and recreation. Run-of-river facilitiesuse only the natural flow of the river to operate the turbine. If the conditions areright, this type of project can be constructed without a dam or with a lowdiversion structure to direct water from the stream channel into a penstock.Pumped-storage facilities, an innovation of the 1950s, have specially designedturbines. These turbines have the ability to generate electricity the conventionalway when water is delivered through penstocks to the turbines from a reservoir.They can also be reversed and used as pumps to lift water from the powerhouseback up into the reservoir where the water is stored for later use. During thedaytime when electricity demand suddenly increases, the gates of the pumped -storage facility are opened and stored water is released from the reservoir togenerate and quickly deliver electricity to meet the demand. At night whenelectricity demand is lowest and there is excess electricity available from coal ornuclear electricity generating facilities the turbines are reversed and pump waterback into the reservoir. Operating in this manner, a pumped-storage facilityimproves the operating efficiency of all power plants within an electric system.Hydroelectric developments provide unique benefits not available with otherelectricity generating technologies. They do not contribute to air pollution, acidrain, or ozone depletion, and do not produce toxic wastes. As a part of normaloperations many hydroelectric facilities also provide flood control, water supplyfor drinking and irrigation, and recreational opportuni ties such as fishing,swimming, water-skiing, picnicking, camping, rafting, boating, and sightseeing.

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    HYDROELECTRICITYHydro electric power plant

    Installations (e.g. Dams) to a large extent. Manufacturers have Been quickenough to develop package designs for small un its. These are also called asSmall Scale Hydroelectric Power Plants. These facilities can supply in principle

    significant amounts of electricity for irrigation, or potable water pumping lightingor health or educational purpose. The total potential amount of such a resourcesis poorly documented but is apt to be large.Up to 1972, hydro engineers concentrated on developing the larger sites, wherethe economy of scale enabled the production of energy at a cost low enough tocompete thermal power etc. But the shortage of fuel, high cost of fuels neededfor many of the other plants made the engineers to pay attention to thenaturally occurring renewable sources which can be efficiently used as energysources. Moreover, the remarkable advancement in the technol ogy ofdevelopment of turbines suitable for utilizing small falls and small dischargesfrom RIVERS increased the chances of development of small hydral For manysmall hydro plants of less than 500 kW capacity, electronic load controllers have

    been developed to replace the governor. These controllers maintain a constantload on the turbine and hence constant flow, surplus power is diverted to aresistor and either wasted or used to heat water.The advantage of Hydro Power Plants operation in hilly areas and remote areasand the elimination of long transmission system, & lesser gestation periods havelent added attraction. It has little or no adverse environmental impact, effects onstream ecology.In India, the potential of small hydropower is estimated to be 5000MW at present, while further investigations and surveys are expected to indicatea higher potential. Small Hydropower is covered in renewable programme. Thealternate hydro-energy center at Roorki works on the development of solarhydropower system as well as Hybrid Hydro systems. If small hydropower

    stations are set up all over the country, decentralized availability of power willbecome possible.Many countries now have active small hydro development and ruralelectrification programmes, due to the several advantages offered by theseplants.There is no formal definition of a small hydro plant but this may generally betaken as power station or plant having output up to 5000 kW. Some associatethe concept of small hydro with low head say up to 1 5 m. This may not generallybe true as there is no restriction on head for these power plants. Stations up tooutput 1000 kW are called micro and up to 5000 kW as mini power plants.Conceptually these power plants can be categorized into two types:1) One utilizing small discharges but having high head2) One utilizing large discharges but having comparatively smaller head. Hydro -electric power plants convert the kinetic energy contained in falling water intoelectricity. The energy in flowing water is ultimately derived from the sun, and istherefore constantly being renewed. Energy contained in sunlight evaporateswater from the oceans and deposits it on land in the form of rain. Differences inland elevation result in rainfall runoff, and allow some of the original solarenergy to be captured as hydro-electric power.Hydro power is currently the world's largest renewable source of electricity,accounting for 6% of worldwide energy supply or about 15% of the world'selectricity. In Canada, hydroelectric power is abundant and supplies 60% of our

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    HYDROELECTRICITYelectrical needs. Traditionally thought of as a cheap and clean source ofelectricity, most large hydro-electric schemes being planned today are comingup against a great deal of opposition from environmental groups and nativepeople.

    Hydro-electric Power Plants:Hydroelectric energy is produced by the force of falling water. The capacity toproduce this energy is dependent on both the available flow and the height fromwhich it falls. Building up behind a high dam, water accumulates potentialenergy. This is transformed into mechanical energy when the water rushes downthe sluice and strikes the rotary blades of turbine. The turbine's rotation spinselectromagnets which generate current in stationary coils of wire . Finally, thecurrent is put through a transformer where the voltage is increased for longdistance transmission over power lines.Hydro-electric power plants capture the energy released by water falling througha vertical distance, and transform this energy into useful electricity. In general,

    falling water is channeled through a turbine which converts the water's energyinto mechanical power. The rotation of the water turbines is transferred to agenerator which produces electricity. The amount of electr icity which can begenerated at a hydro-electric plant is dependant upon two factors. These factorsare (1) the vertical distance through which the water falls, called the "head", and(2) the flow rate, measured as volume per unit time. The electricity pro duced isproportional to the product of the head and the rate of flow. The following is anequation which may be used to roughly determine the amount of electricitywhich can be generated by a potential hydro -electric power site:POWER (kW) = 5.9 x FLOW x HEADIn this equation, FLOW is measured in cubic meters per second and HEAD ismeasured in meters.

    Based on the facts presented above, hydroelectric power plants can generally bedivided into two categories. "High head" power plants are the most common andgenerally utilize a dam to store water at an increased elevation. The use of adam to impound water also provides the capability of storing water during rainyperiods and releasing it during dry periods. This results in the consistent andreliable production ofElectricity, able to meet demand. Heads for this type of power plant may begreater than 1000 m. Most large hydroelectric facilities are of the high headvariety. High head plants with storage are very valuable to electric utilitiesbecause they can be quickly adjusted to meet the electrical demand on adistribution system.

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    HYDROELECTRICITYDifferent classifications of Hydroelectric power plants:

    1) Depending upon Capacity to generate power:

    Size unit size Installation

    Micro upto 100 kW 100 kW

    Mini 101 to 1000 kW 2000 kW

    Small 1001 to 6000 kW 15000 kW

    2) Depending on head:

    Ultra low head: Below3 meters,

    Low head : Less than 30 meters,

    Medium head: Between 30 to 75 meters,

    High head : Above 75 meters,

    Selection of site for Hydro Power Plants:

    1. Large quantity of water at a reasonable head should be available

    2. The site should provide strong and high mountains on the two sides of the

    river reservoir with minimum gap for economical dam construction.

    3. The rainfall should be sufficient to maintain desired water level in the

    reservoir throughout the year.

    4. The catchments area for the reservoir to collect rainwater should be large.

    5. There should not be any possibility of leakage of water in future.

    6. The site should have firm rock for foundation.

    Basic components of a hydroelectric power plant:

    a) Diversion and intake

    b) Desilting chamber

    c) Water conducting system

    d) Balancing reservoir

    e) Surge tank (if necessary)f) Penstock

    g) Power house: turbine, generator, protection and control equipment,

    dewatering, drainage system, auxiliary, power system, grounding, emergency

    and standby power system, lighting and ventilation

    Tail race channel.

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    HYDROELECTRICITY Diversion structure:

    The diversion structure provided should be simple in construction as well as

    economical. It should involve minimum maintenance. Depending upon the type

    of river bed the diversion structure may be of two-type viz. Boulder weir and

    Trench type weir. It is usually constructed in re-enforced concrete or masonry.

    Water conductor system:

    Water conducting system is the very important component of hydro -power plant.

    The type of water conductor system depends on the site conditions and the

    materials available. The design of the water conduction system should ensure

    minimum head loss, adequate velocity of flow so that silt does not settle down.

    The material of construction should be such that loss due to seepage is also

    minimized. The most commonly used channel section is trapezoi dal.

    Desalting tank:

    Desilting tank is provided usually in the initial reaches of water conductor to trap

    the suspended silt load and pebbles etc ; so as to minimize the erosion damages

    to the turbine runner. The size of silt particles to be trapped f or medium headpower stations is from 0.2 to 0.5 mm and for high head it is from 0.1 to 0.2 mm.

    The depth of tank may be kept between 1.5 to 4 m. The horizontal flow velocity

    should not exceed 0.4 to 0.6 m/s.

    Layout of hydro power plants:

    The layout of hydro power plants envisages positioning of the various

    components of the plant to insure optimum use of available space for its efficient

    and convenient erection, operation and maintenance.

    Power house:The power is positioned at the toe of the concrete masonry dam where the

    suitable rock to lay foundation is available each turbine is fed by a separate

    penstock which is embedded inside the non-overflow section of the dam. The

    power house separated from the dam expansion joints. With a view to minimize

    the fluctuations in the tail water level. Especially due to ski jump trajectory, the

    power go use maybe located further downstream and fed through a tunnel

    branching into individual penstocks near the powerhouse.

    The powerhouse may be located at the underground, led through pressure shafts

    or pressure tunnels with surge tank. The power house may be located below the

    ski jump bucket itself. In the case of earth and rock fill dams, the power house is

    separated from the dam founded on suitable location and fed by pe nstock sgenerally taken out from a tunnel earlier used as diversion tunnel. Sometimes

    penstock may be laid in trench excavated below the dam buried in concrete.

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    HYDROELECTRICITYTypes of powerhouses:

    Surfaces power house:

    It is the best choice when sufficient area is available to accommodate the

    powerhouse within economical and convenient excavation. The there are three

    types of surface powerhouse depending on superstructure are outdoor, semi out

    door, indoor types

    Semi-underground power house:

    The surface with setting of turbines below the minimum tail water level may

    involve substantial excavation and then backfilling with concrete to facilitate

    construction of high retaining walls for protections against floods. In this type

    vertical shafts are driven in rock for housing part of draft tube, spiral casings

    turbines and generators.

    Submersible powerhouse:

    In this type of power plant which is incorporated in the body of spillway beneath

    the crest. The head water elevation is incorporated in the body of spillway

    beneath the crest. The head water elevation is maintained with the help of

    vertical lift crest gates. It has advantages of economy because separate

    powerhouse structure is avoided in this arrangement.

    Hydroelectric power: How it works:

    So just how do we get electricity from water? Actually, hydroelectric and coal-

    fired power plants produce electricity in a similar way. In both cases a power

    source is used to turn a propeller-like piece called a turbine, which then turns a

    metal shaft in an electric generator which is the motor that produces electricity.

    A coal-fired power plant uses steam to turn the turbine blades; whereas a

    hydroelectric plant uses falling water to turn the turbine. The resu lts are the

    same.

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    HYDROELECTRICITYFrancis turbine:

    The theory is to build a dam on a large river that has a large drop in elevation

    (there are not many hydroelectric plants in Kansas or Florida). The dam storeslots of water behind it in the reservoir. Near the bottom of the dam wall there is

    the water intake. Gravity causes it to fall through the penstock inside the dam.

    At the end of the penstock there is a turbine propeller, which is turned by the

    moving water. The shaft from the turbine goes up into the generato r, which

    produces the power.

    Power lines are connected to the generator that carry electricity to your home

    and mine. The water continues past the propeller through the tailrace into the

    river past the dam. By the way, it is not a good idea to be playing in the water

    right below a dam when water is released!

    Impulse Turbines: The Pelton Wheel:

    The impulse turbine is very easy to understand. A nozzle transforms water under

    a high head into a powerful jet. The momentum of this jet is destroyed by

    striking the runner, which absorbs the resulting force. If the velocity of the water

    leaving the runner is nearly zero, all of the kinetic energy of the jet has been

    transformed into mechanical energy, so the efficiency is high.

    A practical impulse turbine was invented by Lester A.

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    HYDROELECTRICITYPelton (1829-1908) in California around 1870. There were high-pressure jets

    there used in placer mining, and a primitive turbine called the hurdy -gurdy, a

    mere rotating platform with vanes, had been used since the '60's, driven by such

    jets. Pelton also invented the split bucket, now universally used , in 1880. Pelton

    is a trade name for the products of the company he originated, but the term is

    now used generically for all similar impulse turbines.

    Reaction Turbines: The Lawn Sprinkler:

    By contrast with the impulse turbine, reaction turbines are di fficult to understand

    and analyze, especially the ones usually met with in practice. The modest lawn

    sprinkler comes to our aid, since it is both a reaction turbine, and easy to

    understand. It will be our introduction to reaction turbines. In the impulse

    turbine, the pressure change occurred in the nozzle, where pressure head was

    converted into kinetic energy. There was no pressure change in the runner,

    which had the sole duty of turning momentum change into torque. In the

    reaction turbine, the pressure change occurs in the runner itself at the same

    time that the force is exerted. The force still comes from rate of change of

    momentum, but not as obviously as in the impulse turbine.

    The duty of the lawn sprinkler is to spread water; its energy output as a tur bine

    serves only to move the sprinkler head. It is a descendant of Hero's aeolipile,

    the rotating globe with two bent jets that was quite a sensation in ancient times,

    though this worked with steam, not water. The lawn sprinkler seems directly

    descended from Rev. Robert Barker's proposed mill of 1740. He used two jets at

    right angles to the radius. A later improvement fed water from below to balance

    the weight of the runner and reduce friction. Barker's mills only appeared as

    models, and were never commercially offered. The flow of water in a lawnsprinkler is radially outward. Water under pressure is introduced at the centre,

    and jets of water that can cover the area necessary issue from the ends of the

    arms at zero gauge pressure. The pressure decrease occurs in the sprinkler

    arms. Though the water is projected at an angle to the radius, the water from an

    operating sprinkler moves almost along a radius. If you have such a sprinkler,

    by all means observe it in action.

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    HYDROELECTRICITYThe jets do not impinge on a runner; in fact, they are leaving the runner, so

    their momentum is not converted into force as in the impulse turbine. The force

    on the runner must act in reaction to the creation of the momentum instead,

    which is, of course, the origin of the name of the reaction turbine.

    Total annual cost of hydro power project:

    Total annual cost of hydro power project consists of three elements:

    1. Fixed charges it includes fixed charges on plant interest taxes insurances

    depreciation and obsolescence

    2. Operation and maintenance cost

    It includes operating cost, fuel cost, supervisory, labor maintenance, repair and

    miscellaneous expenses .the annual operation and maintenance cost is roughly

    proportional to the capacity of plant and the number of unit installed. The annual

    maintenance cost is usually taken as 1.5% of capital cost.

    3. Transmission cost

    It covers the cost of transmission facilities to connect the power generated tothe system load.

    "Low head" hydroelectric plants are power plants which generally utilize heads of

    only a few meters or less. Power plants of this type may utilize a low dam or

    weir to channel water, or no dam and simply use the "run of the river". Run of

    the river generating stations cannot store water, thus their electric output varies

    with seasonal flows of water in a river. A large volume of water must pass

    through a low head hydro plant's turbines in order to produce a useful amount of

    power. Hydro-electric facilities with a capacity of less than about 25 MW (1 MW

    = 1,000,000 Watts) are generally referred to as "small hydro", although hydro-

    electric technology is basically the same regardless of generating capacity.

    "Pumped Storage" is another form of hydro-electric power. Pumped storage

    facilities use excess electrical system capacity, generally available at night, to

    pump water from one reservoir to another reservoir at a higher elevation. During

    periods of Peak electrical demand, water from the higher reservoir is released

    through turbines to the lower reservoir, and electricity is produced (Figu re 2).

    Although pumped storage sites are not net producers of electricity - it actually

    takes more electricity to pump the water up than is recovered when it isreleased - they are a valuable addition to electricity supply systems. Their value

    is in their ability to store electricity for use at a later time when peak demands

    are occurring. Storage is even more valuable if intermittent sources of electricity

    such as solar or wind are hooked into a system.

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    HYDROELECTRICITY

    Future Directions for the Hydroelectric Industry:

    The hydroelectric industry has been termed "mature" by some who charge that

    the technical and operational aspects of the industry have changed little in the

    past 60 years. Recent research initiatives counter this label by establishing newconcepts for design and operation that show promise for the industry. A multi -

    year research project is presently testing new turbine designs and will

    recommend a final turbine blade configuration that will allow safe passage of

    more than 98 percent of the fish that are directed through the turbine. The DOE

    also recently identified more than 30 million kilowatts of untapped hydroelectric

    capacity that could be constructed with minimal environmental effects at existing

    dams that presently have no hydroelectric generating f acilities, at existing

    hydroelectric projects with unused potential, and even at a number of sites

    without dams. Follow-up studies will assess the economic issues associated with

    this untapped hydroelectric resource. In addition, studies to estimate the

    hydroelectric potential of undeveloped, small capacity, dispersed sites that could

    supply electricity to adjacent areas without connecting to a regional electric

    transmission distribution system are proceeding. Preliminary results from these

    efforts have improved the visibility of hydroelectric power and provide

    indications that the hydroelectric power industry will be vibrant and important to

    the country throughout the next century.

    The theoretical size of the worldwide hydro power is about four times greate r

    than that which has been exploited at this time. The actual amount of electricity

    which will ever be generated by hydro power will be much less than the

    theoretical potential. This is due to the environmental concerns outlined above,

    and economic constraints. Much of the remaining hydro potential in the worldexists in the developing countries of Africa and Asia. Harnessing this resource

    would require billions of dollars, because hydro -electric facilities generally have

    very high construction costs. In the past, the World Bank has spent billions of

    foreign aid dollars on huge hydro-electric projects in the third world. Opposition

    to hydro power from environmentalists and native people, as well as new

    environmental assessments at the World Bank will restrict the amount of money

    spent on hydro-electric power construction in the developing countries of the

    world.

    In North-America and Europe, a large percentage of hydro power potential has

    already been developed. Public opposition to large hydro schemes will p robably

    result in very little new development of big dams and reservoirs. Small scale andlow head hydro capacity will probably increase in the future as research on low

    head turbines, and standardized turbine production, lowers the costs of hydro -

    electric power at sites with Companies have to dig up the Earth or drill wells to

    get the coal, oil, and gas

    for nuclear power plants there are waste-disposal problems

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    HYDROELECTRICITYLow heads. New computerized control systems and improved turbines may allow

    more electricity to be generated from existing facilities in the future. As well,

    many small hydro electric sites were abandoned in the 1950's and 60's when the

    price of oil and coal was very low, and their environmental impacts unrealized.

    Increased fuel prices in the future could result in these facilities being

    refurbished.

    Advantages:

    1. Renewable source of energy thereby saves scares fuel reserves.

    2. Economical source of power.

    3. Non-polluting and hence environment friendly.

    4. Reliable energy source with approximately 90% availability.

    5. Low generation cost compared with other energy sources.

    6. Indigenous, inexhaustible, perpetual and renewable energy source.

    7. Low operation and maintenance cost.

    8. Possible to build power plant of high capacity.

    9. Plant equipment is simple.10. Socio-economic benefits being located usually remote areas.

    11. Higher efficiency, 95%to98%.

    12. Fuel is not burned so there is minimal pollution

    13. Water to run the power plant is provided free by nature

    14.It's renewable - rainfall renews the water in the reservoir, so the fuel is

    almost always there.

    Disadvantages:

    1. Susceptible to vagaries of nature such as draught.

    2. Longer construction period and high initial cost.

    3. Loss of large land due to reservoir.

    4. Non-availability of suitable sites for the construction of dam.

    5. Displacement of large population from reservoir area and rehabilitation.

    6. Environmental aspect reservoirs verses river ecology.

    7. High cost of transmission system for remote sites.

    8. They use up valuable and limited natural resources

    9. They can produce a lot of pollution

    10.Companies have to dig up the Earth or drill wells to get the coal, oil, and gas

    11.For nuclear power plants there are waste-disposal problems

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    HYDROELECTRICITYCASESTUDYEXAMPLE

    KOYNA DAM, KOYNA NAGAR

    Koyna Dam is one of the largest dams in Maharashtra, India. It is located in

    Koyna Nagar, nestled in the Western Ghats on the state highway betweenChiplun and Karad, Maharashtra. The dam supplies water to westernMaharashtra as well as cheap hydroelectric power to the neighbouring areas witha capacity of 1,920 MW. The Koyna project is actually composed of four dams,with the Koyna dam having the largest catchment area.The catchment area dams the Koyna River and forms a huge lake theShivsagar Lake whose length is 50 kilometres. Completed in 1963, it is one ofthe largest civil engineering projects commissioned after Indian independence.The Koyna electricity project is run by the Maharashtra State Electricity Board.Most of the generators are located in excavated caves a kilometre deep, insidethe heart of the surrounding hills.The dam is blamed for the spate of earthquakes in the recent past. In 1967 a

    devastating earthquake almost razed the dam, with the dam developing majorcracks. Geologists are still uncertain if the Koyna Dam is responsible for thespate in seismic activity.

    Koyna Dam is one of the largest damsinMaharashtra,India. It is located i n KoynaNagar, nestled in the Western Ghats on the state highway between Chiplun andKarad,Maharashtra. The dam supplies water to western Maharashtra as well ascheap Hydro electric power to the neighbouring areas with a capacity of 1,920MW. The Koyna project is actually composed of four dams, with the Koyna damhaving the largest catchment area.

    The catchment area dams the Koyna River and forms a huge lake theShivsagar Lake whose length is 50 kilometres. Completed in 1963, it is one ofthe largest civil engineering projects commissioned after Indian independence.The Koyna electricity project is run by theMaharashtra State Electricity Board.Most of the generators are located in excavated cavesa kilometre deep, insidethe heart of the surrounding hills.

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    HYDROELECTRICITYThe dam is blamed for the spate of earthquake in the recent past. In 1967 adevastating earthquake almost razed the dam, with the dam developing majorcracks. Geologists are still uncertain if the Koyna Dam is responsible for thespate in seismic activity.Statistics Storage:

    o Gross storage: 98.78 TMCo Live: 93.65 TMCo Dead: 5.125 TMC Length: 1807.22 m Height: 85.35 m Year of completion: 1963The Koyna Dam in Maharashtra

    The resovoir behind the dam is 50 km in length.Gravitational potential energy is stored in the water above the dam. Because ofthe great height of the water, it will arrive at the turbines at high pressure,which means that we can extract a great deal of energy from it. The water thenflows away downriver as normal.In mountainous countries such as Switzerland and New Zealand, hydro -electricpower provides more than half of the country's energy needs.An alternative is to build the station next to a fast -flowing river. However withthis arrangement the flow of the water cannot be controlled, and water cannotbe stored for later use.

    Hydro-electric power stations can produce a great deal of power very cheaply.When it was first built, the huge "Hoover Dam", on the Colorado river, suppliedmuch of the electricity for the city of Las Vegas; however now Las Vegas hasgrown so much, the city gets most of its energy from other sources.There's a good explanation of how hydro power works atAlthough there are many suitable sites around the world, hydro -electric damsare very expensive to build. However, once the station is built, the water comesfree of charge, and there is no waste or pollution.

    1962 - 1963

    Height of dam: 103 meters

    Water storage: 2,797.400 kmVolume of dam: 1,555.000 mWidth of dam: 808 mSlope at water side: 24:1Length of 60 km

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    HYDROELECTRICITYLake tapping at Koyna:

    ________________________________________

    In a major technological breakthrough, the engineers of Koyna hydroelectricproject today successfully performed the `lake tapping' operatio ns at Shivaji

    Sagar reservoir of the dam. This operation or `lake tapping' using Norwegiantechnology will pave the way for the commissioning of the 1,000 MW stage fourof the Koyna hydroelectric project, which would take total generation capacity to1,920 MW by this year end.Enthusiasm reigned on the banks of Shivaji Sagar reservoir, as people fromneighbouring villages flocked the lake to witness the `lake tapping', the first ofits kind in Asia.Standing on the hilly terrain of the Koyna backwater, pe ople were all ears to theannouncements made by Shrikant Huddar, chief engineer of the Koyna Hydelproject. And as Huddar instructed his subordinates to switch on the Konsbergsunderwater cameras, the countdown for the million dollar blast had begun.Beginning from 10, Huddar launched his countdown and just after he had

    announcedzero, within a fraction of a second after Chief Minister Narayan Ranehad switched knobs activating the blastings, hundreds of people felt waves oftremors passing under their feet.

    Suddenly, a mushroom flower-like cloud of water erupted from Shivaji Sagarreservoir, and ripples after ripples hit the banks. Soon after the ripples hit thebanks, villagers standing on the banks lifted the water from the reservoir andgently applied it to their foreheads. No one could hear the sound of the blasts,but they had certainly felt it deep inside their hearts. Certainly it was a momentto cherish.Planned for 1000 MW power generation, the fourth stage of Koyna hydro electricproject, envisages that the water will be tapped by piercing the Koyna reservoir,

    following which it will be carried through a 4.25 km-long head race tunnel intothe underground power house. The water will be finally released in KolkewadiLake of stage III.Speaking on the occasion after the blasts had been conducted, ministers EknathKhadase,Anna Dange, Harshvardhan Patil, Deputy Chief Minister GopinathMunde and Chief Minister Narayan Rane were all praise for the State irrigationdepartment. While Irrigation Minister Khadse said such blasts could be replicatedin future to generate more power, Rural Development Minister Anna Dangeactually coined a couplet describing the event.Munde, who also holds the energyportfolio, expressed his gratitude to irrigation department fo r inviting him towitness the `lake tapping'. He also said the `event' was a major leap towardsthe State Government's dream to be self-sufficient in power generation.``At present there is a shortage of nearly 1000-1500 MW of power in the State.This difference will be reduced after the Koyna fourth stage starts generating1000 MW power,'' he said. Chief Minister was also all praise for the irrigationdepartment and said this development would go a long way in providing excesspower for the State.The Koyana dam is at Koynanagar in Patan tehsil of Satara district intheSahyadaris. Its Shivaji Sagar reservoir has a capacity of 2,797 million cubicmetres of water. The Rs 1,300 crore stage-four project is a World Bank fundedproject having commenced in 1992.

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    H C C

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    H C C

    Turbine row in a power s

    ation

    Crosssection of a conventional hydroelectric dam

    A typical turbine and generator

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    HYDROELECTRICITY

    Generating methods:

    Conventional:

    Most hydroelectric power comes from the potential energy of dammed waterdriving a water turbine and generator. The power extracted from the waterdepends on the volume and on the difference in height between the source andthe water's outflow. This height difference is called the head. The amount ofpotential energy in water is proportional to the head. To deliver water to aturbine while maintaining pressure arising from the head, a large pipe called apenstock may be used.

    Pumped-storage:

    This method produces electricity to supply high peak demands by moving waterbetween reservoirs at different elevations. At times of low electrical demand,excess generation capacity is used to pump water into the higher reservoir.When there is higher demand, water is released back into the lower reservoirthrough a turbine. Pumped-storage schemes currently provide the mostcommercially important means of large-scale grid energy storage and improvethe daily capacity factor of the generation system.

    Run-of-the-river:

    Run-of-the-river hydroelectric stations are those with smaller reservoircapacities, thus making it impossible to store water.

    Tide:

    A tidal power plant makes use of the daily rise and fall of water due to tides;

    such sources are highly predictable, and if conditions permit construction ofreservoirs, can also be dispatchable to generate power during high demandperiods. Less common types of hydro schemes use water's kinetic energy orundammed sources such as undershot waterwheels.

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    HYDROELECTRICITY

    Sizes and capacities of hydroelectric facilities:

    Large and specialized industrial facilities

    The Three Gorges dam ,china seen here from space, is the largest operating

    hydroelectric power stations at an installed capacity of 22,500 MW.

    Although no official definition exist for the capacity range of large hydroelectricpower stations, facilities from over a few hundred megawatts to more than10GW is generally considered large hydroelectric facilities. Currently, only threefacilities over 10GW (10,000MW)are in operation worldwide; Three Gorges Damat 22.5 GW, Itaipu Dam at 14 GW, and Guri Dam at 10.2 GW. Large-scale

    hydroelectric power stations are more commonly seen as the largest powerproducing facilities in the world, with some hydroelectric facilities capable ofgenerating more than double the installed capacities of the current largestnuclear power stations.

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    While many hydroelectric projects supply public electricity networks, some arecreated to serve specific industrial enterprises. Dedicated hydroelectric projectsare often built to provide the substantial amounts of electricity needed foraluminium electrolytic plants, for example. The Grand Coulee Dam switched to

    support Alcoa aluminium in Bellingham, Washington, United States for AmericanWorld WarII airplanes before it was allowed to provide irrigation and power tocitizens (in addition to aluminium power) after the war.

    In Suriname, the Brokopondo Reservoir was constructed to provide electricityfor the Alcoa aluminium industry. New Zealand's Manppouri Power Station wasconstructed to supply electricity to the aluminium smelter at Tiwai Point.

    The construction of these large hydroelectric facilities and the changes it makesto the environment, are often too a t very large scales, creating just as much

    damage to the environment as at helps it by being a renewable resource. Manyspecialized organizations, such as the International Hydropower Association, lookinto these matters on a global scale.

    Small

    Small hydro is the development of hydroelectric power on a scale serving a smallcommunity or industrial plant. The definition of a small hydro project varies buta generating capacity of up to 10 megawatts (MW) is generally accepted as theupper limit of what can be termed small hydro. This may be stretched to 25 MW

    and 30 MW in Canada and the United States. Small-scale hydroelectricityproduction grew by 28% during 2008 from 2005, raising the total world small -hydro capacity to 85GW Over 70% of this was in China (65 GW), followed byJapan (3.5 GW), the United States (3 GW), and India (2 GW).

    Small hydro plants may be connected to conventional electrical distributionnetworks as a source of low-cost renewable energy. Alternatively, small hydroprojects may be built in isolated areas that would be uneconomic to serve from anetwork, or in areas where there is no national electrical distribution network.Since small hydro projects usually have minimal reservoirs and civil constructionwork, they are seen as having a relatively low environmental impact comparedto large hydro. This decreased environmental impact depends strongly on the

    balance between stream flow and power production.

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    Micro

    A micro-hydro facility.

    Micro hydro is a term used for hydroelectric power installations that typicallyproduce up to 100KW of power. These installations can provide power to anisolated home or small community, or are sometimes connected to electricpower networks. There are many of these installations around the world,particularly in developing nations as they can provide an economical source ofenergy without purchase of fuel.Micro hydro systems complement photovoltaicsolar energy systems because in many areas, water flow, and thus availablehydro power, is highest in the winter when solar energy is at a minimum.

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    HYDROELECTRICITYPico

    Pico hydro is a term used for hydroelectric power generation of under 5KW. It isuseful in small, remote communities that require only a small amount ofelectricity. For example,to power one or two fluorescent light bulbs and a TV orradio for a few homes. Even smaller turbines of 200-300W may power a single

    home in a developing country with a drop of only 1 m (3 ft).

    Pico-hydro setups typically are run-of-the-river, meaning that dams are notused, but rather pipes divert some of the flow, drop this down a gradient, andthrough the turbine before being exhausted back to the stream.

    Calculating the amount of available power:

    A simple formula for approximating electric power produc tion at a hydroelectricplant is: P= hrgk, where

    y Pis Power in watts,y is the density of water (~1000 kg/m3),y h is height in meters,y ris flow rate in cubic meters per second,y g is acceleration due to gravity of 9.8 m/s2,y kis a coefficient of efficiency ranging from 0 to 1. Efficiency is often

    higher (that is, closer to 1) with larger and more modern turbines.

    Annual electric energy production depends on the available water supply. Insome installations the water flow rate can vary by a factor of 10:1 over thecourse of a year.

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    Advantages and disadvantages of hydroelectricity:

    Advantages

    The festiniog Power Station can generate 360MW of electricity within 60 seconds

    of the demand arising.

    Economics

    The major advantage of hydroelectricity is elimination of the cost of fuel. Thecost of operating a hydroelectric plant is nearly immune to increases in the costof fossil fuels such as oil, natural gas or coal, and no imports are needed.

    Hydroelectric plants also tend to have longer economic lives than fuel -firedgeneration, with some plants now in service which were built 50 to 100 yearsago. Operating labor cost is also usually low, as plants are automated and havefew personnel on site during normal operation.

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    Where a dam serves multiple purposes, a hydroelectric plant may be added withrelatively low construction cost, providing a useful revenue stream to offset thecosts of dam operation.

    It has been calculated that the sale of electricity from the Three Gorges Damwill cover the construction costs after 5 to 8 years of full generation.

    CO2 emissions

    Since hydroelectric dams do not burn fossil fuels, they do not directly producecarbon dioxide. While some carbon dioxide is produced during manufact ure andconstruction of the project, this is a tiny fraction of the operating emissions ofequivalent fossil-fuel electricity generation. One measurement of greenhouse gasrelated and other externality comparison between energy sources can be foundin the ExternE project by the Paul Scherrer Institute and the University ofStuttgart which was funded by the European Commission. According to this

    project, hydroelectricity produces the least amount of greenhouse gases andexternality of any energy source.Coming in second place was wind, third wasnuclear energy, and fourth was solar photovoltaic.The extremely positivegreenhouse gas impact of hydroelectricity is found especially in temperateclimates. The above study was for local energy in Europe presumably similarconditions prevail in North America and Northern Asia, which all see a regular,natural freeze/thaw cycle (with associated seasonal plant decay and regrowth.

    Other uses of the reservoir

    Reservoirs created by hydroelectric schemes often provide facil ities for watersports, and become tourist attractions themselves. In some countries,

    aquaculture in reservoirs is common. Multi-use dams installed for irrigationsupport agriculture with a relatively constant water supply. Large hydro damscan control floods, which would otherwise affect people living downstream of theproject.

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    HYDROELECTRICITYDisadvantages

    Ecosystem damage and loss of land

    Hydroelectric power stations that uses dams would submerge large areas of land

    due to the requirement of a reservoir.

    Large reservoirs required for the operation of hydroelectric power stations resultin submersion of extensive areas upstream of the dams, destroying biologicallyrich and productive lowland and riverine valley forests, marshland andgrasslands. The loss of land is often exacerbated by the fact that reservoirscause habitat fragmentation of surrounding areas.

    Hydroelectric projects can be disruptive to surrounding aquatic ecosystems bothupstream and downstream of the plant site. For instance, studies have shownthat dams along the Atlantic and Pacific coasts of North America have reducedsalmon populations by preventing access to spawning grounds upstream, even

    though most dams in salmon habitat have fish ladders installed. Salmon spawnare also harmed on their migration to sea when they must pass throughturbines. This has led to some areas transporting smolt downstream by bargeduring parts of the year. In some cases dams, such as the Marmot Dam, havebeen demolished due to the high impact on fish.Turbine and power-plant designsthat are easier on aquatic life are an active area of research. Mitigationmeasures such as fish ladders may be required at new projects or as a conditionof re-licensing of existing projects.

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    HYDROELECTRICITYGeneration of hydroelectric power changes the downstream river environment.Water exiting a turbine usually contains very little suspended sediment, whichcan lead to scouring of river beds and loss of riverbanks.Since turbine gates areoften opened intermittently, rapid or even daily fluctuat ions in river flow areobserved. For example, in the Grand Canyon, the daily cyclic flow variationcaused by Glen Canyon Dam was found to be contributing to erosion of sand

    bars. Dissolved oxygen content of the water may change from pre-constructionconditions. Depending on the location, water exiting from turbines is typicallymuch warmer than the pre-dam water, which can change aquatic faunalpopulations, including endangered species, and prevent natural freezingprocesses from occurring. Some hydroelectric projects also use canals to divert ariver at a shallower gradient to increase the head of the scheme. In some cases,the entire river may be diverted leaving a dry riverbed. Examples include theTekapo and Pukaki Rivers in New Zealand.

    Flow shortage

    Changes in the amount of river flow will correlate with the amount of energy

    produced by a dam. Lower river flows because of drought, climate change orupstream dams and diversions will reduce the amount of live storage in areservoir therefore reducing the amount of water that can be used forhydroelectricity. The result of diminished river flow can be power shortages inareas that depend heavily on hydroelectric power.

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    H CTRICITY

    Meth

    ne emissions (f

    om reservoirs)

    The Hoover Dam in United States is a large conventional dammed-hydro facility,

    with an installed capacity of up to 2,080M

    Lower positive impacts are found in

    the tropical regions, as it has been noted that the reservoirs of power plants in

    tropical regionsmay produce substantial amounts ofmethane. This is due to

    plant material in flooded areas decaying in an anaerobic environment, andforming methane, a very potent greenhouse gas. According to the World

    Commission on Dams report,where the reservoir is large compared to the

    generating capacity (less than 100 watts per s uare metre ofsurface area) and

    no clearing of the forests in the area was undertaken prior to impoundment of

    the reservoir, greenhouse gas emissions from the reservoir may be higher than

    those of a conventional oil-fired thermal generation plant.

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    HYDROELECTRICITYAlthough these emissions represent carbon already in the biosphere, not fossil

    deposits that had been sequestered from the carbon cycle, there is a greater

    amount of methane due to anaerobic decay, causing greater damage than would

    otherwise have occurred had the forest decayed naturally.

    In boreal reservoirs of Canada and Northern Europe, however, greenhouse gasemissions are typically only 2% to 8% of any kind of conventional fossil -fuelthermal generation. A new class of underwater logging operation that targetsdrowned forests can mitigate the effect of forest decay.

    In 2007, International Rivers accused hydropower firms for cheating with fakecarbon credits under the Clean Development Mechanism, for hydropowerprojects already finished or under construction at the moment they applied to

    join the CDM. These carbon credits of hydropower projects under the CDM indeveloping countries can be sold to companies and governments in richcountries, in order to comply with the Kyoto protocol.

    Relocation

    Another disadvantage of hydroelectric dams is the need to relocate the peopleliving where the reservoirs are planned. In February 2008, it was estimated that40-80 million people worldwide had been physically displaced as a direct resultof dam construction. In many cases, no amount of compensation can replaceancestral and cultural attachments to places that have spiritual value to thedisplaced population. Additionally, historically and culturally important sites canbe flooded and lost.

    Such problems have arisen at the Aswan Dam in Egypt between 1960 and 1980,the Three Gorges Dam in China, the Clyde Dam in New Zealand, and the Ilisu

    Dam in Turkey.

    Failure hazard

    Because large conventional dammed-hydro facilities hold back large volumes ofwater, a failure due to poor construction, terrorism, or other causes can becatastrophic to downriver settlements and infrastructure. Dam failures havebeen some of the largest man-made disasters in history. Also, good design andconstruction are not an adequate guarantee of safety. Dams are temptingindustrial targets for wartime attack, sabotage and terrorism, such as OperationChastise in World War II.

    The Banqiao Dam failure in Southern China directly resulted in the deaths of26,000 people, and another 145,000 from epidemics. Millions were lefthomeless. Also, the creation of a dam in a geologically inappropriate locationmay cause disasters like the one of the Vajont Dam in Italy, where almost 2000people died, in 1963.

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    Smaller dams and micro hydro facilities create less risk, but can form continuinghazards even after they have been decommissioned. For example, the smallKelly Barnes Dam failed in 1967, causing 39 deaths with the Toccoa Flood, tenyears after its power plant was decommissioned in 1957.

    Comparison with other methods of power generation

    Hydroelectricity eliminates the flue gas emissions from fossil fuel combustion,including pollutants such as sulphur dioxide, nitric oxide, carbon monoxide, dust,and mercury in the coal. Hydroelectricity also avoids the hazards of coal miningand the indirect health effects of coal emissions. Compared to nuclear power,hydroelectricity generates no nuclear waste, has none of the dangers associatedwith uranium mining, nor nuclear leaks. Unlike uranium, hydroelectricity is also arenewable energy source.

    Compared to wind farms, hydroelectricity power plants have a more predictableload factor. If the project has a storage reservoir, it can be dispatched togenerate power when needed. Hydroelectric plants can be easily regulated tofollow variations in power demand.

    Unlike fossil-fuelled combustion turbines, construction of a hydroelectric plantrequires a long lead-time for site studies, hydrological studies, andenvironmental impact assessment. Hydrological data up to 50 years or more isusually required to determine the best sites and operating regimes for a largehydroelectric plant. Unlike plants operated by fuel, such a s fossil or nuclearenergy, the number of sites that can be economically developed for hydroelectric

    production is limited; in many areas the most cost effective sites have alreadybeen exploited. New hydro sites tend to be far from population centres andrequire extensive transmission lines. Hydroelectric generation depends onrainfall in the watershed, and may be significantly reduced in years of lowrainfall or snowmelt. Long-term energy yield may be affected by climate change.Utilities that primarily use hydroelectric power may spend additional capital tobuild extra capacity to ensure sufficient power is available in low water years.

    Environmental Impacts:

    Hydro-electric power plants have many environmental impacts, some of which

    are just beginning to be understood. These impacts, however, must be weighedagainst the environmental impacts of alternative sources of electricity. Untilrecently there was an almost universal belief that hydro power was a clean andenvironmentally safe method of producing e lectricity. Hydro-electric powerplants do not emit any of the standard atmospheric pollutant s such as carbondioxide or sulphur dioxide given off by fossil fuel fired power plants. In thisrespect, hydro power is better than burning coal, oil or natural gas to produceelectricity, as it does not contribute to global warming or acid rain.

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    HYDROELECTRICITYSimilarly, hydro-electric power plants do not result in the risks of radioactivecontamination associated with nuclear power plants.A few recent studies of large reservoirs created behind hydro dams havesuggested that decaying vegetation, submerged by flooding, may give offquantities of greenhouse gases equivalent to those from other sources ofelectricity. If this turns out to be true, hydro-electric facilities such as the James

    Bay project in Quebec that flood large areas of land might be significantcontributors to global warming. Run of the river hydro plants without dams andreservoirs would not be a source of these greenhouse gases.The most obvious impact of hydro-electric dams is the flooding of vast areas ofland, much of it previously forested or used for agriculture. The size of reservoirscreated can be extremely large. The La Grande project in the James Bay regionof Quebec has already submerged over 10,000 square kilometers of land; and iffuture plans are carried out, the eventual area of flooding in northern Quebecwill be larger than the country of Switzerland. Reservoirs can be used forensuring adequate water supplies, providing irrigation, and recreat ion; but inseveral cases they have flooded the homelands of native peoples, whose way oflife has then been destroyed. Many rare ecosystems are also threatened by

    hydro-electric development.Large dams and reservoirs can have other impacts on a watershed . Damming ariver can alter the amount and quality of water in the river downstream of thedam, as well as preventing fish from migrating upstream to spawn. Theseimpacts can be reduced by requiring minimum flows downstream of a dam, andby creating fish ladders which allow fish to move upstream past the dam. Silt,normally carried downstream to the lower reaches of a river, is trapped by adam and deposited on the bed of the reservoir. This silt can slowly fill up areservoir, decreasing the amount of water which can be stored and used forelectrical generation. The river downstream of the dam is also deprived of siltwhich fertilizes the river's flood-plain during high water periods.Bacteria present in decaying vegetation can also change mercury, present inrocks underlying a reservoir, into a form which is soluble in water. The mercuryaccumulates in the bodies of fish and poses a health hazard to those whodepend on these fish for food. The water quality of many reservoirs also poses ahealth hazard due to new forms of bacteria which grow in many of the hydrorivers. Therefore, run of the river type hydro plants generally have a smallerimpact on the environment

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    World hydroelectric capacity

    World renewable energy share as at 2008, with hydroelectricity more than 50%

    of all renewable energy sources.

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    World renewable energy potential.

    The ranking of hydro-electriccapacity is either by actual annual energyproduction or by installed capacity power rating. A hydro-electric plant rarelyoperates at its full power rating over a full year; the ratio between annual

    average power and installed capacity rating is the capacity factor. The installedcapacity is the sum of all generator nameplate power ratings. SourcescamefromBP Statistical Review.

    Brazil, Canada, Norway, Paraguay, Switzerland and Venezuela are the onlycountries in the world where the majority of the internal electric energyproduction is from hydroelectric power. Paraguay produces100

    of its

    electricity from hydroelectric dams, and exports 90

    of its production to Braziland to Argentina. Norway produces 9899% of its electricity from hydroelectricsources.

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    HYDROELECTRICITY

    Ten ofthe largesthy roelectric producers as at 2009

    Country

    Annual

    hy

    roelectric

    production (TWh)

    Installed

    capacity

    (GW)

    Capacity

    factor

    % of

    total

    capacity

    China 585.2 196.79 0.37 22.25

    Canada 369.5 88.974 0.59 61.12

    Brazil 363.8 69.080 0.56 85.56

    United

    States250.6 79.511 0.42 5.74

    Russia 167.0 45.000 0.42 17.64

    Norway 140.5 27.528 0.49 98.25

    India 115.6 33.600 0.43 15.80

    Venezuela 86.8 67.17

    Japan 69.2 27.229 0.37 7.21

    Sweden 65.5 16.209 0.46 44.34