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Wind energy
- 1. Wind Energy Fundamentals& Design Considerations For Wind Turbines
- 2. Index Introduction Powerin Wind Power Coefficient Wind Turbine Types Design Consideration
- 3. Introduction The windis a free, clean, and inexhaustible energy source. It has served mankind well for many centuries by propelling ships and driving wind turbines to grind grain and pump water. Interest in wind power lagged, however, when cheap and plentiful petroleum products became available after World War II. The high capital costs and the uncertainty of the wind placed wind power at an economic disadvantage. Then in 1973, the Arab nations placed an embargo on petroleum. The days of cheap and plentiful petroleum were drawing to an end.
- 4. People beganto realize that the world’s oil supplies would not last forever and that remaining supplies should be conserved for the petrochemical industry. The use of oil as a boiler fuel, for example, would have to be eliminated. Other energy sources besides oil and natural gas must be developed, wind energy being one of them. Global wind power potential is of the order of 11,000 GW. It is about 5 times the global installed power generation capacity. This excludes offshore potential as it is yet to be properly estimated.
- 5. About 25,000MW is the global installed wind power capacity. It is about 1% of global installed power generation capacity. Wind produces about 50 billion kWh per year globally with the average utilization factor of 2000 hours per year. Global wind power growth trends from 1980 to 1995 are shown in Figure 1 and the country wise details of installed wind power capacity from 1998 to 2001 is given in Table 1.
- 8. Power in Wind WindPower depends on: amount of air (volume) speed of air (velocity) mass of air (density) flowing through the area of interest (flux) Kinetic Energy definition: KE = ½ * m * 𝑣2 Power is K.E per unit time: P = ½ * 𝑚 * 𝑣2 where 𝑚 = mass flux
- 9. But 𝑚= ρ* A * v Hence P = ½ * ρ * A * 𝑣3 So, Power cube of velocity Power air density Power rotor swept area A= π*𝒓 𝟐
- 10. Power Coefficient PowerCoefficient, Cp, is the ratio of power extracted by the turbine to the total contained in the wind resource Cp = PT/PW Turbine power output PT = ½ * ρ * A * 𝑣3 * Cp The Betz Limit is the maximal possible Cp = 16/27 59% efficiency is the BEST a conventional wind turbine can do in extracting power from the wind
- 11. Types Of WindTurbines A wind turbine is a machine for converting the kinetic energy in wind into mechanical energy. Wind turbines are classified into two general types: 1. Horizontal Axis and 2. Vertical Axis.
- 12. Horizontal Axis WindTurbine A horizontal axis machine has its blades rotating on an axis parallel to the ground. Due to this arrangement the generator and gearbox are located above the ground, making service and repair difficult. HAWTs are to be pointed into the wind, which makes wind-sensing and orientation mechanisms necessary.
- 14. Vertical Axis WindTurbine Vertical-axis wind turbines (VAWTs) are a type of wind turbine where the main rotor shaft is set traverse, not necessarily vertical, to the wind and the main components are located at the base of the turbine. This arrangement allows the generator and gearbox to be located close to the ground, facilitating service and repair. VAWTs do not need to be pointed into the wind, which removes the need for wind-sensing and orientation mechanisms.
- 15. Advantages of verticalaxis wind turbines They are Omni-directional and do not need to track the wind. This makes them much more reliable due to them not requiring a complex mechanism and motors to Yaw the rotor and pitch the blades. The gearbox of a VAWT take much less fatigue when compared to that of a HAWT, should they require it, replacement is less costly and logistically simpler as the gearbox is easily accessible at ground level. VAWTs do not need to track the wind to produce energy as they are omnidirectional, any reported inefficiencies are in fact cancelled out by the fact that a VAWT can take advantages of turbulent and gusty winds, these winds are not harvested by HAWTs, in fact this type of wind causes accelerated fatigue for HAWTs.
- 16. VAWTs wings(Darius type) have a constant chord and so easier to manufacture, when compared to the complex shape and structure of the blades of a HAWT. VAWTs can be packed much closer together in wind farms, meaning improved power per area of land used. VAWTs could be installed on existing wind farms below existing HAWTs, this would improve the efficiency of existing wind farms. Research at Caltech has also shown that carefully designing wind farms using VAWTs can result in power output ten times as great as a HAWT wind farm the same size. VAWTs can use a screw pile foundation, meaning a huge reduction in the carbon cost of an installation, a reduction in road transport (concrete) during installation, and are fully recyclable at the end of the installations life.
- 17. Disadvantages of verticalaxis wind turbines The blades of a VAWT were fatigue prone due to the wide variation in applied forces during each rotation. This has been overcome by the use of modern composite materials and improvements in design; the use of aerodynamic wing tips causes the spreader wing connections to have a static load. The vertically-oriented blades used in early models twisted and bent during each turn, causing them to crack . Over time, these blades broke apart, sometimes leading to catastrophic failure. VAWTs have proven less reliable than HAWTs.
- 18. Design Considerations Numberof Blades – One Rotor must move more rapidly to capture same amount of wind Gearbox ratio reduced Added weight of counterbalance negates some benefits of lighter design Higher speed means more noise, visual, and wildlife impacts Blades easier to install because entire rotor can be assembled on ground Captures 10% less energy than two blade design Ultimately provide no cost savings
- 19. Number of Blades- Two Advantages & disadvantages similar to one blade Need teetering hub and or shock absorbers because of gyroscopic imbalances Capture 5% less energy than three blade designs
- 20. Number of Blades- Three Balance of gyroscopic forces Slower rotation increases gearbox & transmission costs More aesthetic, less noise, fewer bird strikes
- 21. Blade Composition Wood Strong,light weight, cheap, abundant, flexible Popular on do-it yourself turbines Types-Solid plank Laminates Veneers Composites
- 22. Blade Composition Metal Steel Heavy & expensive Aluminum Lighter-weight and easy to work with Expensive Subject to metal fatigue
- 23. Blade Construction Fiberglass Lightweight,strong, inexpensive, good fatigue characteristics Variety of manufacturing processes Cloth over frame Pultrusion Filament winding to produce spars Most modern large turbines use fiberglass
- 24. Large Wind Turbines 450’ base to blade Each blade 112’ Span greater than 747 163+ tons total Foundation 20+ feet deep Rated at 1.5 – 5 megawatt Supply at least 350 homes
- 26. Lift & DragForces The Lift Force is perpendicular to the direction of motion. We want to make this force BIG. The Drag Force is parallel to the direction of motion. We want to make this force small. α = low α = medium <10 degrees α = High Stall!!
- 27. Airfoil Shape Just likethe wings of an airplane, wind turbine blades use the airfoil shape to create lift and maximize efficiency.
- 28. Twist & Taper Speed through the air of a point on the blade changes with distance from hub Therefore, tip speed ratio varies as well To optimize angle of attack all along blade, it must twist from root to tip Fast Faster Fastest
- 29. Tip-Speed Ratio Tip-speed ratiois the ratio of the speed of the rotating blade tip to the speed of the free stream wind. There is an optimum angle of attack which creates the highest lift to drag ratio. Because angle of attack is dependent on wind speed, there is an optimum tip-speed ratio ΩR V TSR = Where, Ω = rotational speed in radians /sec R = Rotor Radius V = Wind “Free Stream” Velocity ΩR R
- 30. Performance Over Rangeof Tip Speed Ratios • Power Coefficient Varies with Tip Speed Ratio • Characterized by Cp vs. Tip Speed Ratio Curve 0.4 0.3 0.2 0.1 0.0 Cp 121086420 Tip Speed Ratio
- 31. Betz Limit All windpower cannot be captured by rotor or air would be completely still behind rotor and not allow more wind to pass through. Theoretical limit of rotor efficiency is 59% Most modern wind turbines are in the 35 – 45% range
- 32. Rotor Solidity Solidity isthe ratio of total rotor planform area to total swept area Low solidity (0.10) = high speed, low torque High solidity (>0.80) = low speed, high torque A R a Solidity = 3a/A
- 33. References Wind EnergyConversion Systems, ENERGY SYSTEMS ENGINEERING,IIT BOMBAY. MIT Wind Energy Group & Renewable Energy Projects in Action. Wikipedia Wind Turbine Design Cost and Scaling Model, L. Fingersh, M. Hand, and A. Laxson. Guidelines for Design of Wind Turbines − DNV/Risø. Wind Turbine Power Calculations, RWE npower renewables, Mechanical and Electrical Engineering, Power Industry. Wind Turbine Blade Design, Classroom Activities for Wind Energy Science.