Module 3.pptx energy engineering module 3

Energy engineering

1. Module 3 : Geothermal Energy, Tidal Energy, Wind Energy Geothermal Energy : Forms of geothermal energy, Dry steam, wet steam, hot dry rock and magmatic chamber systems. Tidal Energy: Tidal power, Site selection, Single basin and double basin systems, Advantages and disadvantages of tidal energy. Wind Energy: Wind energy-Advantages and limitations, wind velocity and wind power, Basic components of wind energy conversion systems, horizontal and vertical axis wind mills, coefficient of performance of a wind mill rotor, Applications of wind energy.

2. Geothermal Energy: “Geo” means earth and “ therm ” means heat energy i.e. geothermal energy is heat energy from the earth. Geothermal energy is recoverable in some form such as steam or hot water. The earth crust now averages about 20 to 40 km in thickness. Below that crust, the molten mass called magma , is still in the process of cooling. Earth tremors caused the magma to come close to the earth’s surface in certain places and crust fissures to open up . The hot magma near the surface thus causes active volcanoes ,hot springs and geysers where water exists. It also causes the steam to vent through the fissures ( fumaroles) . A typical geothermal field is shown in the figure.

3. The hot magma near the surface (A) solidifies into igneous rock (B). The heat of the magma is conducted upward to this igneous rock. The ground water that finds its way down to this rock through fissures in it will be heated by the heat of the rock or by mixing with hot gases and steam emanating from the magma . The heated water will then rise convectively upward and into a porous and permeable reservoir(C) above the igneous rock. This reservoir is capped by a layer of impermeable(not allowing liquid or gas to pass through) solid rock D that traps the hot water in the reservoir . The solid rock however has fissures E that acts as vent of the giant underground boiler . The vents show up at the surface as geysers, fumaroles F . or hot springs G. A well H traps steam from the fissures for use in a geothermal power plant. It can be seen that geothermal steam is of two kinds: that originating from the magma itself , called magmatic steam , and that from the ground water heated by the magma called meteoritic steam. The latter is the largest source of geothermal steam Application of geothermal energy: There are three main applications of the steam and hot water from the wet geothermal reservoirs: 1) Generation of electric power 2) Industrial process heat and 3) Space heating for various kinds of buildings. The major benefit of geothermal energy is its varied application and versatility.

4. Advantages: 1) Geothermal energy is renewable source of energy. 2) Geothermal energy is least polluting compared to other conventional energy sources. 3) Geothermal plants have higher annual load factors. 4) It is cheaper compared to the energies obtained from other sources. 5) The greatest advantage of geothermal power is that it can be used in multiple uses. Disadvantages: 1) Overall efficiency for power production is low. 2) The withdrawal of large amounts of steam or water from a hydrothermal reservoir may result in surface subsidence (Large caving or sinking of land). 3) The gases present in the steam must be removed by chemical action before discharging into atmosphere. 4) Drilling operation is noisy. 5) Large areas are needed for exploitation of geo thermal energy as much of it is diffused(spread in all directions). Forms of geothermal energy: There are three basic kinds of geothermal sources a) Hydro-thermal b) Geo-pressured and c) Petro-thermal

5. a) Hydrothermal sources : Hydrothermal sources are those in which water is heated by contact with the hot rock. Hydrothermal systems are in turn subdivided into 1) Vapor dominated and 2) Liquid dominated. Vapor dominated : In these systems the water is vaporized into steam that reaches the surface in a relatively dry condition at about 205 degree C and rarely above 8 bar. This system is the most suitable for use in turboelectric power plants, with least cost. It does, however, suffer problems similar to those encountered by all geothermal systems, namely , the presence of corrosive gases and erosive material and environmental problems . Vapor dominated systems, however , are a rarity . These systems account for about 5 percent of all geothermal sources. 2 ) Liquid dominated systems: In these systems the hot water circulating and trapped underground is at a temperature range 174 to 315 degree C at high pressures(> 8 bar). When tapped by wells drilled in the right places and to the right depths, the water flows either naturally to the surface or is pumped up to it . The drop in pressure usually to 8 bar or less, causes it to partially flash to a two phase mixture of low quality , liquid dominated. It contains relatively large concentrations of dissolved solids ranging between 3000 to 25000 ppm and sometimes higher. The power production is adversely affected by these solids due to formation of scaling, reducing flow and heat transfer. The liquid dominated systems however are much more plentiful than vapor dominated systems

6. b) Geo pressured systems: Geo-pressured systems are sources of water, or brine, that has been heated in a manner similar to hydrothermal water, except that geo-pressured water is trapped in much deeper underground aquifers( body of rock that holds ground water), at depth between 2400 m to 9100 m . This water is relatively at low temperature(160 degree C) and under very high pressure of 1000 bar. It has relatively high salinity. In addition , it is saturated with natural gas , mostly methane CH4 . Such water is thought to have thermal and mechanical potential to generate electricity. Temperature, however is not high enough and the depth so great that there is little economic justification of drilling for this water for its thermal potential alone. However it is possible to generate electricity by recovering dissolved methane c)Petro thermal systems: Magma lying closes the earth’s surface heats overlying rock. When no ground water exists, there is simply hot dry rock (HDR) . The known temperatures of HDR vary between 150 to 290 degree C . This energy is called petro thermal energy, represents by far the largest source of geothermal energy of any type. Much of the HDR occurs at relatively moderate depths, but it is largely impermeable. In order to extract thermal energy out of it , water will have to be pumped into it and back out to the surface. It is necessary for the heat transport mechanism that a way be found to render the impermeable rock into a permeable structure with a large heat transfer surface. Rendering the rock permeable is to be done by fracturing it. Fracturing methods that have been considered involve drilling wells into the rock and then fracturing by (1) high pressure water (2) Nuclear explosives

7. Dry steam System(Vapor dominated power plant): Vapor dominated geothermal systems are the most developed of all geothermal systems. They have the lowest cost and the least number of problems. The vapor dominated power plant is as shown in the fig. Dry steam from the well (1) at 200 degree C is used . It is nearly saturated and may have a shut off pressure up to 35 bar. Pressure drops through the well causes it to slightly superheat at the well head 2. The pressure there rarely exceeds 7 bar . It then goes through a centrifugal separator to remove particulate matter and then enters the turbine after additional pressure drop 3. Processes 1-2 and 2-3 are essentially throttling process with constant enthalpy. The steam expands through the turbine and enters the condenser at 4. The condenser used is of direct contact type. Turbine exhaust steam at 4 mixes with cooling water (7) that comes from a cooling tower. The mixture of 7 and 4 is saturated water (5) that is pumped to the cooling tower (6) . The greater part of the cooled water at 7 is recircualted to the condenser. The balance, which would normally be returned to the cycle in a conventional plant, is rejected in to the ground either before or after the cooling tower. No makeup water is necessary

8. Wet steam System ( Liquid dominated systems): In these systems the hot water circulating and trapped underground is at a temperature range 174 to 315 degree C. When tapped by wells drilled in the right places and to the right depths, the water flows either naturally to the surface or is pumped up to it . The drop in pressure usually to 8 bar or less, causes it to partially flash to a two phase mixture of low quality , liquid dominated. It contains relatively large concentrations of dissolved solids ranging between 3000 to 25000 ppm and sometimes higher. The power production is adversely affected by these solids due to formation of scaling, reducing flow and heat transfer. The liquid dominated systems however are much more plentiful than vapor dominated systems. Liquid dominated power plants: The two different methods are used for generating power i ) The flashed system ii) Binary cycle system i ) The flashed system: The schematic diagram of this system is as shown in the figure. The water from the underground reservoir at 1 reaches the well head at 2 at a lower pressure. Process 1-2 is essentially a constant enthalpy throttling process that results in two phase mixture of low quality at 2. This is further throttled in flash separator resulting in a still low but slightly higher quality at 3. This mixture is now separated in to dry saturated steam at 4 and saturated brine at 5. The latter is rejected in to the ground. The dry steam usually at pressure of less than 8 bar , is expanded in a turbine to 6 and mixed with cooling water in direct contact condenser with mixture at 7 is going to a cooling tower. The greater part of the cooled water at 7 is recircualted to the condenser. Remaining portion of the mixture is rejected in the ground. In order to improve the efficiency in splashing two stages flashing is used instead of single stage flashing (double flash).

9. ii) Binary cycle system: The figure shows the schematic diagram of binary cycle system. Hot water or brine from the underground reservoir circulates through a heat exchanger and is pumped back to the ground. In the heat exchanger it transfers its heat to the organic fluid thus converting it to superheated vapor that is used in a standard closed Rankine cycle . The vapor drives the turbine and is condensed in a surface condenser ; the condensate is pumped back to the heat exchanger . The condenser is cooled by the water from the natural source, if available, or a cooling tower circulation system. The blow down from the tower may be rejected to the ground with cooled brine. Makeup of the cooling tower water must be provided. In binary cycle there is no problems of corrosion or scaling . Such problems are confined to well casing and the heat exchanger . The heat exchanger is shell and tube unit so that no contact between brine and working fluid takes place

10. Hot dry rock geothermal energy : Hot dry rock (HDR) is an extremely abundant source of geothermal energy that is difficult to access. A vast store of thermal energy is contained within hot – but essentially dry and impervious crystalline basement rocks found almost everywhere deep beneath Earth's surface

11. magmatic chamber systems. Magmatic chamber systems:

12. Tidal Energy: Tidal energy is a form of power produced by the natural rise and fall of tides caused by the gravitational interaction between Earth, the sun, and the moon. Tidal currents with sufficient energy for harvesting occur when water passes through a constriction, causing the water to move faster. Using specially engineered generators in suitable locations, tidal energy can be converted into useful forms of power, including electricity. Other forms of energy can also be generated from the ocean, including waves, persistent ocean currents, and the differences in temperature and salinity in seawater. Suitable locations for capturing tidal energy include those with large differences in tidal range, which is the difference between high tide and low tides, and where tidal channels and waterways become smaller and tidal currents become stronger. SITE Selection: The site selection plays an important role in the entire life cycle of a tidal power plant (TPP) project. However, some problems decrease the evaluation quality of TPP site selection: (a) suitable and effective methods are scarce since the TPP site selection involves multiple forms of data; (b) there is no comprehensive evaluation index system due to the unilateralism of existing criteria. Propose a novel method based on interval number with probability distribution weighted operation and stochastic dominance degree. It takes all stakeholders’ preferences into consideration and can simultaneously deal with different forms of data in the TPP site selection; then, a comprehensive evaluation index system for TPP site selection is constructed on the basis of academic literature, feasibility research reports and expert opinions in different fields. It takes the factors of construction conditions, existing policies, social impacts as well as ecological and environmental impacts which reflects the inherent characteristics of TPP site selection fully into account.

13. Harnessing tidal energy: The power generation from tides involves flow between an artificially developed basin and the basic scheme can be elaborated by having two or more basins. Accordingly we can have two different types of arrangements . 1) Single basin arrangement 2) Double basin arrangement. 1) Single basin or pool system : The simple – pool tidal system has one pool or basin behind a dam that is filled from the ocean at high tide and emptied to it at low to tides. Both filling and emptying processes take place during short periods of time: the filling when ocean is at high tide while the water in the pool is at low tide level, the emptying when the ocean is at low tide and the pool at high tide level. The flow of water in both directions is used to drive a number of reversible water turbines, each driving an electrical generator. Electric power would thus be generated during two short periods during each tidal period, of 12 h, 25 min or once every 6h, 12.5 min. The generation of power in a single basin system can be carried out either as a) Single ebb – cycle system or b) Single tide cycle system or c) Double cycle system.

14. a) Single ebb – cycle system: When high tide comes , the sluice gates are opened to permit the sea water to enter the basin or reservoir, while the turbines sets are shut. The reservoir thus starts filling while its level rises, till the maximum tide level is reached. At the beginning of the ebb tide the sluice gates are closed. Then the generation of power takes place when the sea is ebbing (Flowing back of tide) and the water from the basin flows through the turbine in to the lower level sea. The generation of power can be continued till there is sufficient head difference between the level of water in the reservoir and the sea. The turbines are closed when the level of water becomes same on both the sides; sluice gates are opened to repeat the cycle. b) Single tide cycle system: In a single tide cycle system , the generation of power is carried out when sea at flood tide. The water of the sea is admitted in to the basin through the turbines. As the flood tide period is over and the sea level starts falling again, the generation is stopped. The basin is drained in to the sea through the sluice ways. This system needs large size plant, operating for short period and hence less efficient as compared to ebb tide operation. c) Double cycle system: In this system power generation is carried out during both high tide as well as ebb tides. The flow of water in both the directions is used to drive a number of reversible water turbines, each driving an electrical generator. Electric power would thus be generated during two short period during each tidal period of 12 h, 25 min or once every 6h, 12.5 min

15. 2) Double basin arrangement: Two basin system is one that is much less dependent on tidal fluctuation but at the expense of more complex and hence more costly dam construction. A inland basin is enclosed by dam A and divides into a high pool and a low pool by dam B. By proper gating in the dam A, the high pool gets periodically filled at high tide from the ocean and the low pool gets periodically emptied at low tide. Water flows from the high to the low pool through the turbines that are situated in the dam B. The power generation thus continues simultaneously with the filling up the high pool. The capacities of these two pools are large enough in relation to the water flow between them that the fluctuations in the head are minimized, which results in continuous and much more uniform power generation. At the end of the flood tide when high pool is full and the water level in it is maximum, its sluice gates are closed. When ebb tide level gets lower than the water level in low pool , its sluice gates are opened whereby the water level in low pool, which was rising and reducing the operating head, starts falling with the ebb. This continues until the head and water level in high pool is sufficient to run the turbines. With the next flood tide cycle repeats. With this twin pool system, a longer and more continuous period of generation per day is possible.

16. Advantages of tidal power: 1) Tidal power is inexhaustible in nature. 2) Tidal power generation is free from pollution. 3) The requirement of valuable land is less. 4) Peak power demand can be met if it effectively works in combination with hydroelectric or thermal system. 5) It can provide better recreational facilities to visitors and holiday makers, in addition to the possibility of fish farming in the tidal basins. Limitations of tidal power: 1) Generating power is always dependent on the tidal range. 2) The generating efficiency of the turbines affected by the variations in the operating head. 3) Power generation is intermittent in nature. 4) The selecting of suitable turbine operating under varying head condition is difficult. 5) Load sharing of power with the grid is very difficult due variation in power cycle. 6) Maintenance cost of the machinery is high due to the corrosive nature of sea water. 7) Construction in sea is found difficult 8) Cost of power generation is not favorable compared to other sources of energy. 9) It may affect fishing and navigation.

17. Wind Energy : Wind energy is another potential source of energy. Winds are the motion of air caused by un- even heating of the earth‘s surface by the sun and rotation of the earth. It generates due to various global phenomena such as air-temperature difference associated with different rates of solar heating. Since the earth‘s surface is made up of land, desert, water, and forest areas, the surface absorbs the sun‘s radiation differently. Locally, the strong winds are created by sharp temperature difference between the land and the sea. Wind resources in India are tremendous. They are mainly located near the sea coasts. Its potential in India is estimated to be of 25 × 10 3 MW. According to a news release from American Wind Energy Association. The installed wind capacity in India in the year 2000 was 1167 MW and the wind energy production was 2.33 × 10 6 MWh . This is 0.6% of the total electricity production. ADVANTAGES OF WIND ENERGY : Wind energy has a number of different benefits. We can use it for a variety of purposes, primarily for the production of clean and renewable electricity. Let’s jump right in and take a look at the different advantages wind energy has. 1. Wind Energy Is Renewable & Sustainable Wind energy itself is both renewable and sustainable. The wind will never run out, unlike reserves of fossil fuels (such as coal, oil, and gas.) This makes it a good choice of energy for a sustainable power supply. 2. It’s Also Environmentally Friendly Wind energy is one of the most environmentally friendly energy sources available today. This is based on the simple reason that wind turbines don’t create pollution when generating electricity. Most non-renewable energy sources need to be burnt.

18. This process releases gases such as carbon dioxide (CO2) and methane (CH4) into the atmosphere. These gases are known to contribute to climate change. In contrast, wind turbines produce no greenhouse gases when generating electricity. We should note that both noise and visual pollution are environmental disadvantages of wind turbines. However, these factors don’t have a negative impact on the earth, water table or the quality of the air we breathe. 3. It Can Reduce Fossil Fuel Consumption Generating electricity from wind energy reduces the need to burn fossil fuel alternatives such as coal, oil, and gas. This can help to conserve dwindling supplies of the earth’s natural resources. As a result, they will last longer and help to support future generations. 4. Wind Energy is Free Unlike most non-renewable energy sources, wind energy is completely free. Anyone can make use of the wind and it will never run out. This makes wind energy a viable option for generating cheap electricity. 5. It Has A Small Footprint Wind turbines have a relatively small land footprint. Although they can tower high above the ground, the impact on the land at the base is minimal. Wind turbines are often constructed in fields, on hills or out at sea. At these locations, they pose hardly any inconvenience to the surrounding land. Farmers can still farm their fields, livestock can still graze the hills and fishermen can still fish the sea. Land surrounding wind turbines can be used for other purposes such as agriculture. 6. Both Industrial & Domestic Wind Turbines Exist. Wind turbines aren’t just limited to industrial-scale installations (such as wind farms.) They can also be installed on a domestic scale. As a result, many landowners opt to install smaller, less powerful wind turbines. This can help to provide a portion of a domestic electricity supply. Domestic wind turbines are often coupled with other renewable energy technologies. You can often find them installed alongside solar panels and geothermal heating systems.

19. 7. Wind Energy Can Provide Power For Remote Locations Wind turbines can play a key role in helping to bring power to remote locations. This can help to benefit everything from small off-grid villages to remote research facilities. It might be impractical or too expensive to hook such locations up to traditional electricity supplies. In these cases, wind turbines could have the answer. Wind turbines can be used to generate power in remote locations. 8. Wind Technology is Becoming Cheaper, The first-ever wind turbine started generating electricity in 1888. Since then, they have become more efficient and have come down in price. As a result of this, wind power is becoming much more accessible. Government subsidies are also helping to reduce the cost of wind technologies. Many countries across the world now provide incentives for the construction of wind turbines. In addition, incentives are sometimes available for domestic users to supply electricity back to the grid. 9. It Is Also Low Maintenance : Wind turbines are fairly low in maintenance. A new wind turbine can last a long time prior to it requiring any maintenance. Although older turbines can come up against reliability issues, technological advancements are helping to improve overall reliability. 10. It Has Low Running Costs As wind energy is free, running costs are often low. The only ongoing cost of wind energy is for the maintenance of wind turbines, but they are low maintenance in nature anyway. 11. Wind Energy Has Huge Potential Wind energy has huge potential. It’s both renewable and sustainable and is present in a wide variety of places. Although wind turbines aren’t cost-effective at every location, the technology isn’t limited to just a handful of locations. This is an issue that can affect other renewable energy technologies – such as geothermal power stations.

20. 12. It Can Increase Energy Security By using wind energy to generate electricity, we are helping to reduce our dependency on fossil fuel alternatives. In many cases, a country will source some or all of its fossil fuels from another country. War, politics and overall demand often dictate the price of these natural resources. This can sometimes cause serious economic problems or supply shortages. By using local renewable energy sources, a country can reduce its dependency on external supplies of natural resources. As a direct result of this, the country can increase its energy security. 13. The Wind Energy Industry Creates Jobs. The wind energy industry has boomed since wind turbines became commercially available. As a result of this, the industry has created jobs all over the world. Jobs now exist for the manufacturing, installation, and maintenance of wind turbines. You can even find jobs in wind energy consulting. This is a job where specialist consultants determine whether a wind turbine installation is going to be profitable. According to recent data released by the International Renewable Energy Agency (IRENA), the renewable energy industry employed over 10 million people worldwide in 2017. Of these jobs, 1.15 million were in the wind power industry. China leads the way in providing over 500,000 of these jobs. Germany is in second place with around 150,000 jobs and the United States are a close third with around 100,000 wind energy jobs.

21. DISADVANTAGES OF WIND ENERGY: We’ve had a look at the advantages, so now let’s take a look at the disadvantages of wind energy. Wind energy has a number of drawbacks and cons, with the NIMBY (not in my backyard) factor playing a large role. 1. The Wind Fluctuates Wind energy has a similar drawback to solar energy in that it is not constant. Although wind energy is sustainable and will never run out, the wind isn’t always blowing. This can cause serious problems for wind farm developers. They will often spend a significant amount of time and money investigating whether a particular site is suitable for wind power. For a wind turbine to be efficient, it needs to have an adequate supply of wind energy. For this reason, we often find wind turbines on top of hills or out at sea. In these locations, there are fewer land obstacles to reduce the force of the wind. 2. Installation is Expensive Although costs are reducing over time, wind turbines are still expensive. First, an engineer must carry out a site survey. This may involve having to erect a sample turbine to measure wind speeds over a period of time. If deemed adequate, a wind turbine then needs to be manufactured, transported and erected on top of a pre-built foundation. All of these processes contribute to the overall cost of installing wind turbines. When we take the above into account for offshore wind farms, the costs become much greater. Installing structures out at sea is far more complex than on land. Some companies have even commissioned bespoke ships capable of transporting and installing wind turbines at sea. Installing wind turbines is an expensive process.

22. 3. Wind Turbines Pose A Threat to Wildlife. We often hear that wind turbines pose a threat to wildlife – primarily birds and bats. However, researchers now believe that they pose less of a threat to wildlife than othermanmade structures. Installations such as cell phone masts and radio towers are far more dangerous to birds than wind turbines. Nevertheless, wind turbines still contribute to mortality rates among bird and bat populations. 4. Wind Turbines Create Noise Pollution One of the most common disadvantages of wind turbines is the noise pollution they generate. You can often hear a single wind turbine from hundreds of meters away. Combine multiple wind turbines with the right wind direction and the audible effects can be much greater. This issue is one of the biggest impacts of wind energy. Noise pollution from wind turbines has ruined the lives of many homeowners. Although steps are often taken to install them away from dwellings, they do sometimes get built too close to where people live. This is why new wind farms often come up against strong public objection. 5. They Also Create Visual Pollution Another common drawback of wind turbines is the visual pollution they create. Although many people actually like the look of wind turbines, others don’t. These people see them as a blot on the landscape. This, however, tends to come down to personal opinion. As we build more wind farms, public acceptance is becoming more common. Some people see wind turbines as ‘visual pollution’.

23. Classification of Wind Turbine: Wind turbines are classified into two types 1.)Horizontal Axis Wind Turbine (HAWT) 2.)Vertical Axis Wind Turbine (VAWT)

24. HAWT have emerged as the most common successful type of turbines. The details of the most common three-blade rotor, horizontal axis wind turbine is Shown above. The main parts are as follows – a)Turbine blades: •They are made of high-density wood or glass fiber composites. •The blades are slightly twisted from the outer tip to the root to reduce the tendency to stall. •The blades have to be designed to with stand wind turbulence, gust, gravitational forces and directional changes in the wind. •The diameter of a modern HWAT may be up to 100 m. b)Hub: •It is the central solid portion of the rotor wheel. •All blades are attached to the hub. •The mechanism for pitch angle control is provided inside the hub. c)Nacelle : •The nacelle houses the rotor brakes, gearbox, generator and electrical switch gear and control. •The rotor is attached to the nacelle and is mounted on the top of a tower. •Brakes are used to stop the rotor when power generation is not desired. •The gearbox sets up the rotor rpm to meet that of the generator.

25. d)Yaw-control Mechanism : •The mechanism to adjust the nacelle around the vertical axis to keep it facing the wind is provided at the base of the nacelle. e)Tower : •The tower supports the nacelle and rotor. •Both steel and concrete towers are used. •The construction can be either tubular or lattice type

26. The main attractions of VWAT are : -It can accept wind from any direction thus eliminating the need of yaw control -The gearbox, generator, etc., are located at the ground thus eliminating the heavy nacelle at the top of the tower, simplifying the design. -Its inspection and maintenance is easier -It also reduces the overall cost. The main components of VWAT ( Darrieus - type rotor) are Tower (or Rotor shaft) : The tower is a hollow vertical rotor shaft, which rotates freely about the vertical axis between the top and bottom bearings. -It is installed above a support structure. -The upper part of the tower is supported by guy ropes. -The height of the tower of a large turbine is around 100 m. Blades : It has two or three thin, curved blades shaped like an eggbeater in a profile, with blades curved in a form that minimizes the bending stress caused by centrifugal forces – the so called ‘ Troposkien ’ shaft. -The blades have an airfoil cross section with constant chord length. Support Structure :The support structure is provided at the ground to support the weight of the rotor. -Gearboxes, generator, brakes, electrical switchgear and controls are housed within the structure.

27. Wind Velocity and Wind power: Wind power is generated by the force wind exerts on the blades of a turbine, causing the turbine's shaft to rotate at a speed of 10 to 20 revolutions per minute (rpm). The rotor shaft is connected to a generator that converts mechanical energy into electrical energy. The amount of energy generated by a wind turbine depends on: ● wind speed (main factor) ● the area swept by the blades ● air density Wind turbines require: a minimum wind speed (generally 12-14 km/h) to begin turning and generate electricity ● strong winds (50-60 km/h) to generate at full capacity ● winds of less than 90 km/h; beyond that speed, the turbines must be stopped to avoid damage. Wind power is the generation of electricity from wind. Wind power harvests the primary energy flow of the atmosphere generated from the uneven heating of the Earth’s surface by the Sun. Therefore, wind power is an indirect way to harness solar energy. Wind power is converted to electrical energy by wind turbines.

28. Wind Speed : With reference to graph Arbitrary power curve of a 1 MW wind turbine compared to wind speed. Notice the cut out speed. Wind speed largely determines the amount of electricity generated by a turbine. Higher wind speeds generate more power because stronger wind sallow the blades to rotate faster. Faster rotation translates to more mechanical power and more electrical power from the generator. The relationship between wind speed and power for a typical wind turbine is shown in graph

29. Turbines are designed to operate within a specific range of wind speeds. The limits of the range are known as the cut-in speed and cut-out speed.[5] The cut-in speed is the point at which the wind turbine is able to generate power. Between the cut-in speed and the rated speed, where the maximum output is reached, the power output will increase cubically with wind speed. For example, if wind speed doubles, the power output will increase 8 times. This cubic relationship is what makes wind speed such an important factor for wind power. This cubic dependence does cut out at the rated wind speed. This leads to the relatively flat part of the curve in graph, so the cubic dependence is during the speeds below 15 m/s (54 kph ). The cut-out speed is the point at which the turbine must be shut down to avoid damage to the equipment. The cut-in and cut-out speeds are related to the turbine design and size and are decided on prior to construction. Application of Wind Energy : The wind energy is used to propel the sailboats in river and seas to transport men and materials from one place to another. Wind energy is used to run pumps to draw water from the grounds through wind mills. Wind energy has also been used to run flourmills to grind the grains like wheat and corn into flour. Now-a-days wind energy is being used to generate electricity

30. Coefficient of performance, CP, also called the power coefficient of a wind turbine: The coefficient of performance, CP, also called the power coefficient of a wind turbine, is defined as the ratio of the power captured by the rotor of the wind turbine, PR, divided by the total power available in the wind, P, just before it interacted with the rotor of the turbine. A maximum of 59.3% of the available wind power can be converted to mechanical power at ideal conditions, whatever the energy conversion device is. Real wind generators do not reach this theoretical optimum; however, good systems have power coefficients Cp  between 0.4 and 0.5 .

31. QUESTION FROM PREVIOUS YEAR VTU QUESTION PAPERS 1.Explain the methods of harnessing wind energy. Explain the horizontal axis wind mill [6m][8m][6m][6m] 2.Name the basic components of a wind electric system [3m] 3.Explain the method of harnessing wind energy using vertical axis wind mill with a neat sketch [8m][8m] 4.What are the major problems associated with wind power ? [3m] Problems – 1. Wind at 1 standerd atmosphere pressure and 15 deg c has a velocity of 20 m/s. The turbine diameter 100 m and its operating speed is 45 rpm at maximum efficiency. Calculate · The total power density in the wind stream · The total power in MW available · The maximum obtainable power density [6m] -Wind at 1 standerd atmospheric pressure and 15 ˚c has a velocity of 15 m/s . the turbine has a diameter of 120 m and its operating speed in 40 rpm at maximum efficiency. Calculate: The total power density in the wind stream · Maximum obtainable power density (assuming the η = 35 %), Total power and torque 2. A 10 m/sec wind is at 1 standard atm pressure at 15˚c calculate · The total density of wind stream · Maximum obtainable power density · A reasonable obtainable power density in W/m2 · Total power produced (in kW) if turbine diameter is 120m assume η= 40% -A horizontal shaft, proprller type wind turbine is located in area having following wind charecterisitcs : Speed of wind 10 m/s at 1 atm and 15 ˚c calculate the following · Total power density in wind stream w/m2 · Maximum possible obtainable power density in w/m2 · Acxtual obtainable power density in w/m2 assuming 40 % efficiency · Total power from the wind turbine of 120 m [Similar problem asked in - june 2015[10m]/ june 2016[10m] ]