Large Hydroelectric. Suvagata Chakraborty. Types of Hydro projects. 1) Large Hydro 2) Small Hydro. Difference. Principals of Hydroelectric Power Stations.
Large Hydroelectric SuvagataChakraborty
Types of Hydro projects • 1) Large Hydro • 2) Small Hydro
Principals of Hydroelectric Power Stations • To harness the power of water flowing down from a high level, where huge generators convert the potential energy of falling or fast moving water into electrical energy (known as Hydroelectricity or hydroelectric power) • It is the most widely used form of renewable energy. • to calculate the amount of available hydro power. • The two vital factors to consider are the flow and the head of the stream or river. The flow is the volume of water which can be captured and re-directed to turn the turbine generator, and the head is the distance the water will fall on its way to the generator. The larger the flow - i.e. the more water there is, and the higher the head - i.e. the higher the distance the water falls - the more energy is available for conversion to electricity.
Power = Flow x Head x Efficiency x Gravity where power is measured in Watts, head in meters, flow in liters per second, and acceleration due to gravity in meters per second per second. • A low head site has a head of below 10 meters. In this case we need to have a good volume of water flow if we are to generate much electricity. A high head site has a head of above 20 meters. In this case you can get away with not having a large flow of water, because gravity will give what we have an energy boost.
Dams Dams are structures built over rivers to stop the water flow and form a reservoir. The reservoir stores the water . The dams should be water-tight and should be able to withstand the pressure exerted by the water on it. Typically a large dam is classified as being higher than 50-65 feet (15-20 meters) while major dams are those over 492-820 feet (150-250 meters). • Around 5,300 (11%) of the world’s 48,000 large dams were built solely for hydropower. Further 13,300 (28%) were built for more than one function. Many of these multipurpose dams, especially the larger ones, have a hydropower function
Dams The various types of dams (by structure)are: • Gravity Dams Gravity dams are huge dams that are constructed to hold back water using only their own weight. To do this, they are constructed using extensive amounts of concrete, making them difficult and expensive to build. The Grand Coulee Dam in the U.S. state of Washington is a gravity dam.
Dams 2) Arch Dam One of the most common types of major dams is the arch dam. These masonry or concrete dams are ideal for narrow and/or rocky locations because their curved shape easily holds back water via gravity without the need for a lot of construction materials. Arch dams can have one large single arch or they can have multiple small arches separated by concrete buttresses. The Hoover Dam which is on the border of the U.S. states of Arizona and Nevada is an arch dam.
Dams 3) Buttress dam • Another type of dam is the buttress dam. These can have multiple arches, but unlike a traditional arch dam, they can be flat as well. Normally buttress dams are made of concrete and feature a series braces called buttresses along the downstream side of the dam to prevent the natural flow of water. The Daniel-Johnson Dam in Quebec, Canada is a multiple arch buttress dam.
Dams 4) Embankment dam • In the U.S., the most common type of dam is the embankment dam. These are large dams made out of soil and rock which use their weight to hold back water. To prevent water from moving through them, embankment dams also have a thick waterproof core. The Tarbela Dam in Pakistan is the world’s largest embankment dam.
Spillway and Flood gate • SpillwayA spillway could be called as a way for spilling of water from dams. It is used to provide for the release of flood water from a dam. It is used to prevent over toping of the dams which could result in damage or failure of dams. Spillways could be controlled type or uncontrolled type. The uncontrolled types start releasing water upon water rising above a particular level. But in case of the controlled type, regulation of flow is possible. • Floodgates are devices that are designed to allow for the controlled flow of water from various types of water systems. The floodgate is a common component in all sorts of systems ranging from reservoirs, dams, and spillways. Essentially, any human constructed system that is used to control the level and flow of water in a river, lake, or stream will be equipped with some type of floodgate.
Penstock and Surge Tank • Penstock and TunnelPenstocks are pipes which carry water from the reservoir to the turbines inside power station. They are usually made of steel and are equipped with gate systems. Water under high pressure flows through the penstock. A tunnel serves the same purpose as a penstock. It is used when an obstruction is present between the dam and power station such as a mountain. • Surge TankSurge tanks are tanks connected to the water conductor system. It serves the purpose of reducing water hammering in pipes which can cause damage to pipes. The sudden surges of water in penstock is taken by the surge tank, and when the water requirements increase, it supplies the collected water thereby regulating water flow and pressure inside the penstock.
Power Station/House • Power StationPower station contains a turbine coupled to a generator. The water brought to the power station rotates the vanes of the turbine producing torque and rotation of turbine shaft. This rotational torque is transferred to the generator and is converted into electricity. The used water is released through the tail race.
Turbines • As water sources vary, water turbines have been designed to suit different locations. The design used is determined largely by the head and quantity of water available at the particular site. • The three main types are: Pelton wheels, Francis turbines, and Kaplan or propeller type turbines
The Pelton wheel • The Pelton wheel is used where a small flow of water is available with a ‘large head’. The Pelton wheel has small ‘buckets’ all around its rim. Water from the dam is fed through nozzles at very high speed hitting the buckets, pushing the wheel around.
The Francis turbine • The Francis turbine is used where a large flow and a high or medium head of water is involved. This wheel is called a ‘runner’. A circle of guide vanes surround the runner and control the amount of water driving it. Water is fed to the runner from all sides by these vanes causing it to spin.
Propeller or Kaplan turbines • Propeller type turbines are designed to operate where a small head of water is involved. These turbines resemble ship’s propellers. However, with the Kaplan turbines the angle (or pitch) of the blades can be altered to suit the water flow.The variable pitch feature permits the machine to operate efficiently over a range of heads, to allow for the seasonal variation of water levels in a dam.
Hydroelectric generator • It is a low-speed synchronous generator driven by water turbines. Hydro generators may have a horizontal or vertical shaft. The horizontal units are usually small with speeds of 300–1200 revolutions per minute (rpm). The vertical units are usually larger(<100 rpm) and more easily adapted to small hydraulic heads. The rotor diameters range from 2 to 62 ft (0.6 to 19 m) and capacities from 50 to 900,000 kVA. The generators are rated in kVA (kilovolts times amperes). The kilowatt output is the product of kVA and power factor. For large generators a rating of 0.9–0.95 is common with the machines able to operate up to 1.0 when the load requires. The generators may also supply reactive power.
Advantages • Flexibility Hydro is a flexible source of electricity since plants can be ramped up and down very quickly to adapt to changing energy demandslike peak demands, maintain the system voltage levels, and quickly re-establish supply after a blackout. Energy generated by hydroelectric installations can be injected into the electricity system faster than that of any other energy source. The capacity of hydroelectric systems to reach maximum production from zero in a rapid and foreseeable manner makes them exceptionally appropriate for addressing alterations in the consumption and providing ancillary services to the electricity system, thus maintaining the balance between the electricity supply and demand.
Low power costs No cost of fuel. Hydroelectric plants have long economic lives, 50–100 years. Operating labor cost is also usually low, as plants are automated and have few personnel on site during normal operation. So construction costs will be covered after 5 to 8 years of full generation.
The Three Gorges Dam is the world's largest power station in terms of installed capacity (22,500 MW), over Yangtze River • Itaipu Dam, capacity(14,000 MW), located at Paraná River on the border section between Brazil and Paraguay
Its resources are widely spread around the world. Potential exists in about 150 countries, and about 70 per cent of the economically feasible potential remains to be developed. This is mostly in developing countries. • It is a proven and well advanced technology (more than a century of experience), with modern power plants providing the most efficient energy conversion process (> 90 per cent), which is also an important environmental benefit.
Hydroelectricity helps fight climate changes. The hydroelectric life cycle produces very small amounts of greenhouse gases (GHG). In emitting less GHG than power plants driven by gas, coal or oil, hydroelectricity can help retard global warming. Although only 33% of the available hydroelectric potential has been developed, today hydroelectricity prevents the emission of GHG corresponding to the burning of 4.4 million barrels of petroleum per day worldwide.
Hydroelectricity contributes to the storage of drinking water. Hydroelectric power plant reservoirs collect rainwater, which can then be used for consumption or for irrigation. In storing water, they protect the water tables against depletion and reduce our vulnerability to floods and droughts.
Disadvantages • Disturbance of habitat The formation of large and huge dams destroys the living beings around them. Local life is disturbed as human can’t live in such a flooded area and plants are destroyed. People living nearby have to relocate.
Emission of methane and carbon dioxide The reservoir of water for hydroelectric power releases a large amount of carbon dioxide and methane. The area around the dam is filled with water. The plants and trees in them start rotting and decompose by other method without the use of oxygen . So this type of decomposition dumps a great amount of methane and carbon dioxide which increase pollution.
Limited use As the hydroelectric power is produced by the water which depend on the yearly rain falls so only those areas can use this method which receives a good amount of rainfall water because this method needs a huge reservoir of water. • Installation costs Although the effective cost is zero but the manufacturing and building a dam and installation of the turbines is very costly due to which many countries do not employ this alternative source of energy
Effects on agriculture Making dams on rivers affect the amount, quality and temperature of water that flow in streams which has drastic effects on agriculture and drinking water. • Fish killing The water while flowing through the dam collects nitrogen which can damage and also kills fish. They can also damage the reproduction of fishes thus eliminating the whole species of fishes.
Including large hydro in renewables initiatives would crowd out funds for new renewables • Large hydro plants are among the most expensive infrastructure projects on the planet, with major projects costing in the billions and even tens of billions of dollars. Including subsidies for large hydro in renewables schemes could thus consume the lion’s share of funds available to promote renewables.
References • http://www.see.murdoch.edu.au/resources/info/Tech/hydro/large.html • http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_power_stations • http://www.conserve-energy-future.com/Disadvantages_HydroPower.php • http://energyfuture.wikidot.com/hydropower-resources • http://www.energytoolbox.org/gcre/mod_4/gcre_hydropower.pdf • http://ga.water.usgs.gov/edu/hydroadvantages.html • http://geography.about.com/od/waterandice/a/damsreservoirs.html
Small Hydroelectric Md Rakib Ur Rahman
Small Hydroelectric • Small hydroelectric generation is a renewable and decentralized source of electricity, which is typically employed with very minimal environmental impact. • Unlike large hydroelectric projects requiring the damming of rivers, small hydro projects simply divert a portion of a river or creek’s flow or are constructed on pre-existing diversions, such as raw water distribution systems
Small Hydroelectric • Small hydropower facilities can produce 100 – 30,000 kilowatts (kW) of electricity. • Small hydropower facilities may involve a small dam, or be a diversion of the main stream, or be a run-of-the-river system
What do small hydro systems provide? • Electricity for • Central grids • Isolated-grids • Remote power supplies Beyond their ability to provide electricity they have number of attributes that make Small Hydro more attractive: • Reliability • Very low operating cost • Reduced exposure to energy price volatility
Head (m) Head (m) Flow (m3/s) Power in kW » 7 x Head x Flow Small Hydro System Description
“Small” Hydro Projects • “Small” is not universally defined • Size of project related not just to electrical capacity but also to whether low or high head.
Classification Depending on The Head The objective of a hydropower scheme is to convert the potential energy of a mass of water, flowing in a stream with a certain fall to the turbine (termed the "head"), into electric energy at the lower end of the scheme, where the powerhouse is located. The power output from the scheme is proportional to the flow and to the head. Schemes are generally classified according to the “Head”: • High head: 100-m and above • Medium head: 30 - 100 m • Low head: 2 - 30 m These ranges are not rigid but are merely means of categorizing sites. Schemes can also be defined as: • Run-of-river schemes • Schemes with the powerhouse located at the base of a dam • Schemes integrated on a canal or in a water supply pipe
Types of Small Hydro Projects • Type of grid • Central-grid • Isolated-grid or off-grid • Type of civil works • Run-of-river • No water storage • Power varies with flow available from river: lower firm capacity • Reservoir • Higher firm capacity year-round • Significant damming usually required
Components: Civil Works • Typically account for 60% of plant initial costs • Diversion dam or weir • Low dam of simple construction for run-of-river • Concrete, wood, masonry • Cost of dam alone can render project unviable • Water passage • Intake with trashrack and gate; tailrace at exit • Excavated canal, underground tunnel and/or penstock • Valves/gates at turbine entrance/exit, for maintenance • Power house • Houses turbine, mechanical, and electrical equipment