IA 3206 Non-Conventional Energy Sources And Their Applications PDF

IA 3206 Non-Conventional Energy Sources and Their Applications Gihan Amarasinghe Department of Instrumentation and Automation Technology University of Colombo 1 Wind Energy 2 2019  Denmark case study...

IA 3206 Non-Conventional Energy Sources and Their Applications Gihan Amarasinghe Department of Instrumentation and Automation Technology University of Colombo 1 Wind Energy 2 2019  Denmark case study 3 https://youtu.be/PfvqGwoZAq8 Wind power generates 140% of Denmark's electricity demand | Wind power | The Guardian Fri 10 Jul 2015  Sri Lanka Wind Resource Distribution Commissioned Wind Farms by 2014 By 2022 total wind capacity is 252 MW  New Developments Group firm Adani Green Energy Ltd (AGEL) will set up two wind farms in Sri Lanka’s Mannar town and Pooneryn village in the northern provide with a total installed capacity of 484 megawatt at an investment of about $740 million. Mannar Wind Farm Phase II Wind Energy Applications 8 Wind Turbines Wind turbines deliver their power through a revealing shaft, and in this respect, they are like other prime movers such as diesel engine and stream turbines. A generator can be coupled to this shaft. The wind power is uncontrollable and unpredictable. 9  Energy Availability in Wind 1 𝐾𝑖𝑛𝑒𝑡𝑖𝑐 𝐸𝑛𝑒𝑟𝑔𝑦 = 𝑚𝑉 2 2 1 𝑑𝑚 2 𝑃𝑜𝑤𝑒𝑟 𝐸𝑛𝑒𝑟𝑔𝑦 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑡𝑖𝑚𝑒 = 𝑉 2 𝑑𝑡 l 𝑑𝑚 𝑑𝑙 𝑅𝑎𝑡𝑒 𝑜𝑓 𝑐ℎ𝑎𝑛𝑔𝑒 𝑜𝑓 𝑚𝑎𝑠𝑠 = = ρ𝐴 = ρ𝐴𝑉 𝑑𝑡 𝑑𝑡 𝟏 𝑷 = 𝝆𝑨𝑽𝟑 𝟐  𝟏 𝑷 = 𝝆𝑨𝑽𝟑 𝟐 Wind speed increases with height above the ground because of the earth’s boundary layer. This effect is modelled using a power law relation 11  Maximum Power Conversion A German physicist Albert Betz concluded in 1919 that no wind turbine can convert more than 16/27 (59.3%) of the kinetic energy of the wind into mechanical energy turning a rotor. At present, this is known as the Betz limit or Betz’ law. Why can’t the turbine extract all of the kinetic energy in the wind? What should be the ratio of downwind to upwind? There must be some ideal slowing of the wind that will result in maximum power extracted by the turbine Betz showed (using kinetic energy difference relationship) that an ideal turbine would slow the wind to the 1/3 of its original speed.  Modern wind machines operate at a slightly low practical non- ideal performance coefficient. 𝑉𝑜𝑢𝑡 𝑏= 𝑉𝑖𝑛  It is shown theoretically that any windmill can only possibly extract a maximum of 59.3% of the power from the wind (this is known as the Betz limit). In reality, this figure is usually around 45% (maximum) for a large electricity producing turbine and around 30%-40% for a wind pump. Therefore, modifying the formula for ‘power in the wind’, it can be said that the power that is produced by the wind machine can be given by the following formula: It is also worth bearing in mind that a wind machine will only operate at its maximum efficiency for a fraction of the time it is running, due to the variations in the wind speed. Relationship between wind speed, power, and height 15  Wind Potential For a wind energy system to be feasible, there must be an adequate wind supply. A wind energy system usually requires an average annual wind speed of at least 15 km/h. Seasonal and diurnal variations exist. The towers are generally placed 100 m away from the nearest obstacle. The middle of the rotor is placed 10 m above any obstacle that is within 100 m. 16  Wind Characteristics Even small errors in estimation of wind speed can have large effects on the energy yield and lead to poor choices for turbine and site. The following are the site-specific wind characteristics that are pertinent to wind turbines: 17 Wind Turbine Power 18 Wind Turbine Power Output Variation with Steady Wind Speed Cut-in speed: The speed at which the turbine first starts to rotate and generate power is called the cut-in speed and is typically between 3 and 4 m/s. Rated output power and rate output wind speed: As the wind speed rises above the cut-in speed, the level of electrical output power rises rapidly, and the power output reaches the limit that the electrical generator is capable of. Cut-out speed: As the speed increases above the rate output wind speed, the forces on the turbine structure continue to rise and, at some point, there is a risk of damage to the rotor. As a result, a braking system is employed to bring the rotor to a standstill.  Parts of a Wind Turbine 1. The nacelle contains the key components of the wind turbine, including the gearbox and the electrical generator. 2. The tower of the wind turbine carries the nacelle and the rotor. Generally, it is an advantage to have a high tower, since wind speeds increase farther away from the ground. 3. The rotor blades capture wind energy and transfer its power to the rotor hub. 4. The generator converts the mechanical energy of the rotating shaft to electrical energy. 5. The gearbox increases the rotational speed of the shaft for the generator.  Blade Count Aerodynamic efficiency increases with number of blades but with diminishing return. Increasing the number of blades from one to two yields a 6% increase in aerodynamic efficiency, whereas increasing the blade count from two to three yields only an additional 3% in efficiency. Further increasing the blade count yields minimal improvements in aerodynamic efficiency and sacrifices too much in blade stiffness as the blades become thinner. Tip speed ratio is the ratio between the rotational speed of the tip of the blade and the actual velocity of the wind. A high tip speed ratio is better, but not to the point where the machine becomes noisy and highly stressed.  Classification of Wind Machines Horizontal axis Vertical axis Vertical-Axis Wind Turbines (VAWT) This system was adapted for purposes such as water pumping and grain grinding (which slow rotation and high torque are essential). The differential drag causes the Savonius turbine to spin. Not good for generating large amounts of electricity. The drag-based VAWTs usually turn below 100 RPM. One might use a gearbox, but then efficiency suffers, and the machine may not start at all easily. Easy maintenance ( all the working parts are at ground level). Placement (No calculations for wind direction and speed are required as It will capture the wind from any placement). Its small rotation translates into quiet operation that will produce small but steady electricity. Because of the torque yield of a Savonius wind turbine, the bearings used must be very sturdy and may require servicing every couple of years. Savonius Low efficiency (~15 %)  Vertical-Axis Wind Turbines (VAWT) This arrangement is equally effective no matter which direction the wind is blowing. The generator and transmission devices are located at ground level. Maintenance is not simple since it usually requires rotor removal. The rotor is supported by guy ropes taking up large land extensions. The efficiency is not very remarkable. The Darrieus is not a self-starting turbine, the starting torque is very low, but it can be reduced by using three or more blades that result in a high solidity for the rotor. Darrieus Giromill Advantages of VAWT Disadvantages of VAWT Horizontal-axis Wind Turbines The main rotor shaft and electrical generator are placed at the top of a tower, and they must be pointed into the wind. Most large wind turbines have a gearbox, which turns the slow rotation of the rotor into a faster rotation that is more suitable to drive an electrical generator. Wind turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Nowadays, almost all commercial wind turbines connected to grid have horizontal-axis two-bladed or three-bladed rotors. There is also a yaw mechanism that turns the rotor and nacelle. Advantages of HAWT Disadvantages of HAWT Design Calculations Wind Speed Impact on Tower Height and Friction  Micro Siting Micro siting involves laying out the turbine and its accessories at optimum locations at the selected site. Turbines are placed in rows with the direction of incoming wind perpendicular to it. When several turbines are installed in clusters, the turbulence due to the rotation of blades of one turbine may affect the nearby turbines. In order to minimize the effect of rotor induced turbulence, A spacing of 3 DT to 4 DT is provided within the rows. The spacing between the rows may be around 10 DT. Hence the wind stream passing through one turbine is restored before it interacts with the next turbine. It is a usual practice to leave a clearance of (hT+ DT) from the roads.  Wind Rose A wind rose is a graphic tool used by meteorologists to give a succinct view of how wind speed and direction are typically distributed at a particular location.  Average Power in the Wind It is Important to know the capacity factor at the average wind speed of the intended site, or annual energy output. Average Wind Power: Wind Speed Histogram Example If the velocity is presented in the form of frequency distribution, the average and standard deviation are given by Model Wind Speed  Example A wind turbine with cut in velocity 4 m/s and cut out velocity 25 m/s is installed at a site with Weibull shape factor 2.4 and scale factor 9.8 m/s. a) Calculate the number of hours per year that wind turbine output is zero. b) Estimate the probability of wind velocity to exceed 35 m/s at this site.  Answer When wind speed is less than 4 m/s and greater than 25 m/s wind output is zero. Probability of wind speed being between 4 and 25 m/s is, 4 2.4 25 2.4 −( ) − P 4 < 𝑉 < 25 = 𝑒 9.8 −𝑒 9.8 = 0.89 Number of hours with zero power =(1- 0.89) * 8760 = 963 hours 35 −(9.8)2.4 𝑃 𝑉 > 35 = 𝑒 = 6.0628 e-10  Example Estimate the average power density in the wind at a height of 50 m, when the average wind speed at 10 m height is 6 m/s. Assume Rayleigh statistics. Standard friction coefficient is 1/7 and air density is 1.225 kg/m3. Example Capacity Factor Annual Energy Generation Speed On-shore And Off-shore Wind Turbine Foundation  Considerations and Guidelines for Site Selection Hill effect Roughness or the amount of friction that earth’s surface exerts on wind Tunnel effect Turbulence Variations in wind speed Wake Wind obstacles Wind shear  Turbine Controls The purpose of pitch control is to maintain the optimum blade angle to achieve certain rotor speeds or power output. Pitch adjustment can be used to stall and furl. By stalling a wind turbine, you increase the angle of attack, which causes the flat side of the blade to face further into the wind. Furling decreases the angle of attack, causing the edge of the blade to face the oncoming wind. Pitch angle adjustment is the most effective way to limit output power by changing aerodynamic force on the blade at high wind speeds.  Yaw refers to the rotation of the entire wind turbine in the horizontal axis. Yaw control ensures that the turbine is constantly facing into the wind to maximize the effective rotor area and, as a result, power. Because wind direction can vary quickly, the turbine may misalign with the oncoming wind and cause power output losses.  Active vs. Passive Yaw Active Yaw - all medium & large turbines produced today, & some small turbines. Anemometer on nacelle tells controller which way to point rotor into the wind. Yaw drive turns gears to point rotor into wind. Passive Yaw - Most small turbines Wind forces alone direct rotor Tail vanes Downwind turbines Homework Fixed-speed fixed-pitch Fixed-speed variable-pitch Variable-speed fixed-pitch Variable-speed variable-pitch Wind Turbine Generator Technologies Wind Plant Costs  Levelized Cost LCOE (Levelized Cost of Energy): Constant unit cost (per kWh) of a payment stream that has the same present value as the total cost of building and operating a generating plant over its life. Annual Cost divided by annual energy delivered Unit: USD/kWh Annual cost : Spread the capital cost out over the lifetime Add the annual O&M cost Unit: USD/Year  Example 900 W small wind turbine with 2.13 m blade costs USD1600. By the time the system is installed and operational, it costs a total of USD2500, which is to be paid from with a 15 yrs , at 7% interest. O&M costs is $100/yr. Average wind speed at hub height is 6.7 m/s. Estimate the cost per kWh (LCOE) over the 15-year period.  Example A wind farm project has 40 numbers of 1500 kW turbines with 64-m blades. Capital cost of wind farm is USD 60 million, and the O&M cost is USD1.8 million/yr. The project will be financed with a USD45 million, 20-yr loan at 7% plus an equity investment of USD15million that needs a 15% return. Turbines are exposed to averaging 8.5 m/s wind speed. What price would the electricity have to sell for to make the project viable?  Limitations of Wind Power Power density is very low. Needs a very large number of windmills to produce modest amounts of power. Cost. Environmental costs. Material and maintenance costs. Noise, birds and appearance.  Reference Singh, Sobh Nath. Non Conventional Energy Resources. Pearson Education India, 2015.