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Hydroelectric Power 1. 2 Scenario......... It is the most widely used form of renewable energy Worldwide, an installed capacity of 777 GWe supplied 2998.

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Presentation on theme: "Hydroelectric Power 1. 2 Scenario......... It is the most widely used form of renewable energy Worldwide, an installed capacity of 777 GWe supplied 2998."— Presentation transcript:

1 Hydroelectric Power 1

2 2 Scenario......... It is the most widely used form of renewable energy Worldwide, an installed capacity of 777 GWe supplied 2998 TWh of hydroelectricity in 2006GWe This was approximately 20% of the world's electricity, and accounted for about 88% of electricity from renewable sources

3 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 3

4 4 Six Important Components of Hydroelectric Power Plants 1.Dam 2.Reserviour 3.Intake or Control Gates 4.Penstock 5.Turbine 6.Generator

5 5 A typical turbine and generator

6 6 How much power???? – The power extracted from the water depends on the volume and on the difference in height between the source and the water's outflow – This height difference is called the head Low Head Power Generation Medium Head Power Generation High Head Power Generation

7 7 Hydro powers managemant

8 8 Pumped-storage This method produces electricity to supply high peak demands by moving water between 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 reservoir through a turbine Pumped-storage schemes currently provide the most commercially important means of large-scale grid energy storage and improve the daily capacity factor of the generation system

9 9 Run-of-the-river Run-of-the-river hydroelectric stations are those with small or no reservoir capacity, so that the water coming from upstream must be used for generation at that moment, or must be allowed to bypass the dam.

10 10 Tide A tidal power plant makes use of the daily rise and fall of ocean water due to tides; such sources are highly predictable, and if conditions permit construction of reservoirs, can also be dispatchable to generate power during high demand periods

11 11 Underground An underground power station makes use of a large natural height difference between two waterways, such as a waterfall or mountain lake An underground tunnel is constructed to take water from the high reservoir to the generating hall built in an underground cavern near the lowest point of the water tunnel and a horizontal tailrace taking water away to the lower outlet waterway

12 12 Sizes and capacities of hydroelectric facilities The Three Gorges Dam in China is the largest operating hydroelectric power station, at 22,500 MW

13 13 large hydroelectric large hydroelectric power stations, facilities from over a few hundred megawatts to more than 10 GW are generally considered large hydroelectric facilities Currently, only three facilities over 10 GW (10,000 MW) are in operation worldwide; Three Gorges Dam at 22.5 GW, Itaipu Dam in South America at 14 GW, and Guri Dam in Venezuela at 10.2 GW

14 14 Small Small hydro is the development of hydroelectric power on a scale serving a small community or industrial plant The definition of a small hydro project varies but a generating capacity of up to 10 megawatts (MW) is generally accepted as the upper 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 hydroelectricity production grew by 28% during 2008 from 2005, raising the total world small-hydro capacity to 85 GW Over 70% of this was in China (65 GW), followed by Japan (3.5 GW), the United States (3 GW), and India (2 GW)

15 15 Micro Micro hydro is a term used for hydroelectric power installations that typically produce up to 100 KW of power These installations can provide power to an isolated home or small community, or are sometimes connected to electric power networks There are many of these installations around the world, particularly in developing nations as they can provide an economical source of energy without purchase of fuel Micro hydro systems complement photovoltaic solar energy systems because in many areas, water flow, and thus available hydro power, is highest in the winter when solar energy is at a minimum.

16 16 A micro-hydro facility in Vietnam

17 17 Pico Pico hydro is a term used for hydroelectric power generation of under 5 KW It is useful in small, remote communities that require only a small amount of electricity For example, to power one or two fluorescent light bulbs and a TV or radio for a few home 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 not used, but rather pipes divert some of the flow, drop this down a gradient, and through the turbine before returning it to the stream

18 18 Pico hydroelectricity in Mondulkiri, Cambodia

19 19 Advantages and disadvantages of hydroelectricity

20 20 Advantages Economics The major advantage of hydroelectricity is elimination of the cost of fuel The cost of operating a hydroelectric plant is nearly immune to increases in the cost of fossil fuels such as oil, natural gas or coal, and no imports are needed Hydroelectric plants have long economic lives, with some plants still in service after 50–100 years

21 21 CO2 emissions Since hydroelectric dams do not burn fossil fuels, they do not directly produce carbon dioxide Hydroelectricity produces the least amount of greenhouse gases and externality of any energy source Coming in second place was wind, third was nuclear energy, and fourth was solar photovoltaic

22 22 Other uses of the reservoir water sports, become tourist attractions aquaculture in reservoirs irrigation support Large hydro dams can control floods

23 23 Disadvantages Ecosystem damage and loss of land ( submersion of extensive areas ) Salmon are also harmed on their migration to sea when they must pass through turbines

24 24 After turbine Generation of hydroelectric power changes the downstream river environment Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks Since turbine gates are often opened intermittently, rapid or even daily fluctuations in river flow are observed. For example, in the Grand Canyon, the daily cyclic flow variation caused by Glen Canyon Dam was found to be contributing to erosion of sand bars

25 25 Siltation When water flows it has the ability to transport particles heavier than itself downstream This has a negative effect on dams and subsequently their power stations, particularly those on rivers or within catchment areas with high siltation Siltation can fill a reservoir and reduce its capacity to control floods along with causing additional horizontal pressure on the upstream portion of the dam Eventually, some reservoirs can become completely full of sediment and useless or over-top during a flood and fail

26 26 The Hoover Dam in the United States is a large conventional dammed-hydro facility, with an installed capacity of 2,080 MW

27 27 Relocation Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned In February 2008 it was estimated that 40-80 million people worldwide had been physically displaced as a direct result of dam construction

28 28 Ten of the largest hydroelectric producers as at 2009. [31][32] [31][32] Country Annual hydroelectric production (TWh)TWh Installed capacity (GW)GW Capacity factor % of total capacity China 652.05196.790.3722.25 Canada 369.588.9740.5961.12 Brazil 363.869.0800.5685.56 United States 250.679.5110.425.74 Russia 167.045.0000.4217.64 Norway 140.527.5280.4998.25 India 115.633.6000.4315.80 Venezuela 85.9614.6220.6769.20 Japan 69.227.2290.377.21 Sweden 65.516.2090.4644.34

29 29 Francis Runner, Grand Coulee Dam

30 30 Three Gorges Dam Francis turbine runner

31 31 Francis Turbine (exterior view) attached to a generator

32 32 Theory of operation Flowing water is directed on to the blades of a turbine runner, creating a force on the blades Since the runner is spinning, the force acts through a distance (force acting through a distance is the definition of work) In this way, energy is transferred from the water flow to the turbine Water turbines are divided into two groups; reaction turbines and impulse turbines The precise shape of water turbine blades is a function of the supply pressure of water, and the type of impeller selected.

33 33 Reaction turbines Reaction turbines are acted on by water, which changes pressure as it moves through the turbine and gives up its energy They must be encased to contain the water pressure (or suction), or they must be fully submerged in the water flow Newton's third law describes the transfer of energy for reaction turbines. Most water turbines in use are reaction turbines and are used in low (<30m/98 ft) and medium (30-300m/98– 984 ft)head applications. In reaction turbine pressure drop occurs in both fixed and moving blades.

34 34 Impulse turbines Impulse turbines change the velocity of a water jet. The jet pushes on the turbine's curved blades which changes the direction of the flow The resulting change in momentum (impulse) causes a force on the turbine blades. Since the turbine is spinning, the force acts through a distance (work) and the diverted water flow is left with diminished energy Prior to hitting the turbine blades, the water's pressure (potential energy) is converted to kinetic energy by a nozzle and focused on the turbine No pressure change occurs at the turbine blades, and the turbine doesn't require a housing for operation Newton's second law describes the transfer of energy for impulse turbines Impulse turbines are most often used in very high (>300m/984 ft) head applications

35 35 Newton’s Laws of Motion Newton's First Law of Motion: I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. Newton's Second Law of Motion: II. The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors in this law the direction of the force vector is the same as the direction of the acceleration vector. Newton's Third Law of Motion: III. For every action there is an equal and opposite reaction.

36 36 Power The power available in a stream of water is; where: P = power (J/s or watts) η = turbine efficiency ρ = density of water (kg/m³) g = acceleration of gravity (9.81 m/s²) h = head (m) For still water, this is the difference in height between the inlet and outlet surfaces Moving water has an additional component added to account for the kinetic energy of the flow The total head equals the pressure head plus velocity head. = flow rate (m³/s)

37 37 Pumped storage Some water turbines are designed for pumped storage hydroelectricity They can reverse flow and operate as a pump to fill a high reservoir during off-peak electrical hours, and then revert to a turbine for power generation during peak electrical demand This type of turbine is usually a Deriaz or Francis in design Efficiency Large modern water turbines operate at mechanical efficiencies greater than 90% (not to be confused with thermodynamic efficiency).

38 38 Types of water turbines Various types of water turbine runners. From left to right: Pelton Wheel, two types of Francis Turbine and Kaplan Turbine

39 39 Reaction turbines: Francis Kaplan, Propeller, Bulb, Tube, Straflo Tyson Gorlov Impulse turbine Waterwheel Pelton Turgo Michell-Banki (also known as the Crossflow or Ossberger turbine) Jonval turbine Reverse overshot water-wheel Archimedes' screw turbine

40 40 Design and application

41 41 Turbine selection is based mostly on the available water head, and less so on the available flow rate In general, impulse turbines are used for high head sites, and reaction turbines are used for low head sites Kaplan turbines with adjustable blade pitch are well-adapted to wide ranges of flow or head conditions, since their peak efficiency can be achieved over a wide range of flow conditions. Small turbines (mostly under 10 MW) may have horizontal shafts, and even fairly large bulb-type turbines up to 100 MW or so may be horizontal Very large Francis and Kaplan machines usually have vertical shafts because this makes best use of the available head, and makes installation of a generator more economical Pelton wheels may be either vertical or horizontal shaft machines because the size of the machine is so much less than the available head Some impulse turbines use multiple water jets per runner to increase specific speed and balance shaft thrust.

42 42 Typical range of heads Hydraulic wheel turbine Archimedes' screw turbine Kaplan_________________ Francis 10 < H < 350 Pelton 50 < H < 1300 Turgo 50 < H < 250 0.2 < H < 4 (H = head in m) 1 < H < 10 2 < H < 40

43 43 Specific speed The specific speed n s of a turbine characterizes the turbine's shape in a way that is not related to its size This allows a new turbine design to be scaled from an existing design of known performance The specific speed is also the main criteria for matching a specific hydro site with the correct turbine type The specific speed is the speed with which the turbine turns for a particular discharge Q, with unit head and thereby is able to produce unit power.

44 44 Affinity laws Affinity Laws allow the output of a turbine to be predicted based on model tests A miniature replica of a proposed design, about one foot (0.3 m) in diameter, can be tested and the laboratory measurements applied to the final application with high confidence Affinity laws are derived by requiring similitude between the test model and the application Flow through the turbine is controlled either by a large valve or by wicket gates arranged around the outside of the turbine runner Differential head and flow can be plotted for a number of different values of gate opening, producing a hill diagram used to show the efficiency of the turbine at varying conditions

45 45 Runaway speed The runaway speed of a water turbine is its speed at full flow, and no shaft load The turbine will be designed to survive the mechanical forces of this speed The manufacturer will supply the runaway speed rating.

46 46 Environmental impact Water turbines are generally considered a clean power producer, as the turbine causes essentially no change to the water They use a renewable energy source and are designed to operate for decades They produce significant amounts of the world's electrical supply Historically there have also been negative consequences, mostly associated with the dams normally required for power production Dams alter the natural ecology of rivers, potentially killing fish, stopping migrations, and disrupting peoples' livelihoods.

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