wind power generation

Wind Power and Wind Turbines: 

1 Wind Power and Wind Turbines ENGR 10 San Jose State University

Slide 2: 

Ken Youssefi 2 Alternative Sources of Energy Hydro Power Solar Power Wind Power

Slide 3: 

Ken Youssefi Engineering 10, SJSU 3 Wind Turbine Energy

Wind Turbine: 

4 Wind Turbine Wind energy is created when the atmosphere is heated unevenly by the Sun, some patches of air become warmer than others. These warm patches of air rise, other air rushes in to replace them – thus, wind blows. A wind turbine extracts energy from moving air by slowing the wind down, and transferring this energy into a spinning shaft, which usually turns a generator to produce electricity. The power in the wind that’s available for harvest depends on both the wind speed and the area that’s swept by the turbine blades.

Slide 5: 

Two types of turbine design are possible – Horizontal axis and Vertical axis. In horizontal axis turbine, it is possible to catch more wind and so the power output can be higher than that of vertical axis. But in horizontal axis design, the tower is higher and more blade design parameters have to be defined. In vertical axis turbine, no yaw system is required and there is no cyclic load on the blade, thus it is easier to design. Maintenance is easier in vertical axis turbine whereas horizontal axis turbine offers better performance. Wind Turbine Design Horizontal axis Turbine Vertical axis Turbine

Wind: 

Ken Youssefi / Hsu Engineering 10, SJSU 6 Wind Wind energy is created when: the atmosphere is heated unevenly by the Sun some patches of air become warmer than others the warm patches of air rise other air rushes in to fill the void thus, wind blows Source: www.physicalgeography.net/fundamentals/7n.html WIND

Main components of a Wind Turbine: 

Main components of a Wind Turbine Rotor The portion of the wind turbine that collects energy from the wind is called the rotor. The rotor usually consists of two or more wooden, fiberglass or metal blades which rotate about an axis (horizontal or vertical) at a rate determined by the wind speed and the shape of the blades. The blades are attached to the hub, which in turn is attached to the main shaft. Rotor

Wind Turbine – Blade Design: 

Ken Youssefi Engineering 10, SJSU 8 Wind Turbine – Blade Design The ideal wind turbine rotor has an infinite number of infinitely thin blades. In the real world, more blades give more torque, but slower speed, and most alternators need fairly good speed to cut in. Wind turbines are built to catch the wind's kinetic (motion) energy. You may therefore wonder why modern wind turbines are not built with a lot of rotor blades, like the old "American" windmills you have seen in the Western movies and still being used in many farms. Turbines with many blades or very wide blades will be subject to very large forces, when the wind blows at a hurricane speed. The ideal wind turbine design is not dictated by technology alone, but by a combination of technology and economics: Wind turbine manufacturers wish to optimize their machines, so that they deliver electricity at the lowest possible cost per kilowatt hour (kWh) of energy.

Wind Turbine – Blade Design: 

Ken Youssefi Engineering 10, SJSU 9 Wind Turbine – Blade Design A rotor with an even number of blades will cause stability problems for a wind turbine. The reason is that at the very moment when the uppermost blade bends backwards, because it gets the maximum power from the wind, the lowermost blade passes into the wind shade in front of the tower. This produces uneven forces on the rotor shaft and rotor blade. Even or Odd Number of Blades

Wind Turbine – Blade Design (Shape): 

Ken Youssefi Engineering 10, SJSU 10 Wind Turbine – Blade Design (Shape) To study how the wind moves relative to the rotor blades of a wind turbine, attach red ribbons to the tip of the rotor blades and yellow ribbons about 1/4 of the way out from the hub. Since most wind turbines have constant rotational speed, the speed with which the tip of the rotor blade moves through the air (the tip speed) is typically some 64 m/s, while at the centre of the hub it is zero. 1/4 out from the hub, the speed will then be some 16 m/s. The yellow ribbons close to the hub of the rotor will be blown more towards the back of the turbine than the red ribbons at the tips of the blades. This is because, at the tip of the blades, the speed is some 8 times higher than the speed of the wind hitting the front of the turbine.

Wind Turbine – Blade Design (Shape): 

Ken Youssefi Engineering 10, SJSU 11 Wind Turbine – Blade Design (Shape) Rotor blades for wind turbines are always twisted. Seen from the rotor blade, the wind will be coming from a much steeper angle (more from the general wind direction in the landscape), as you move towards the root of the blade, and the centre of the rotor. A rotor blade will stop giving lift (stall), if the blade is hit at an angle of attack which is too steep. Therefore, the rotor blade has to be twisted, so as to achieve an optimal angle of attack throughout the length of the blade.

Wind Turbine: 

Ken Youssefi Engineering 10, SJSU 12 The tip-speed ratio is the ratio of the rotational speed of the blade to the wind speed. The larger this ratio, the faster the rotation of the wind turbine rotor at a given wind speed. Electricity generation requires high rotational speeds. Lift-type wind turbines have maximum tip-speed ratios of around 10, while drag-type ratios are approximately 1. Given the high rotational speed requirements of electrical generators, it is clear that the lift-type wind turbine is the most practical for this application. The number of blades that make up a rotor and the total area they cover affect wind turbine performance. For a lift-type rotor to function effectively, the wind must flow smoothly over the blades. To avoid turbulence, spacing between blades should be great enough so that one blade will not encounter the disturbed, weaker air flow caused by the blade which passed before it. Wind Turbine Tip Speed Ratio

Wind Turbine: 

Ken Youssefi Engineering 10, SJSU 13 The generator converts the mechanical energy of the turbine to electrical energy (electricity). Inside this component, coils of wire are rotated in a magnetic field to produce electricity. Different generator designs produce either alternating current (AC) or direct current (DC), available in a large range of output power ratings. Most home and office appliances operate on 120 volt (or 240 volt), 60 cycle AC. Some appliances can operate on either AC or DC, such as light bulbs and resistance heaters, and many others can be adapted to run on DC. Storage systems using batteries store DC and usually are configured at voltages of between 12 volts and 120 volts. Generators that produce AC are generally equipped with features to produce the correct voltage (120 or 240 V) and constant frequency (60 cycles) of electricity, even when the wind speed is fluctuating. Wind Turbine Generators

Wind Turbine: 

Ken Youssefi Engineering 10, SJSU 14 Wind Turbine The number of revolutions per minute (rpm) of a wind turbine rotor can range between 40 rpm and 400 rpm, depending on the model and the wind speed. Generators typically require rpm's of 1,200 to 1,800. As a result, most wind turbines require a gear-box transmission to increase the rotation of the generator to the speeds necessary for efficient electricity production. Some DC-type wind turbines do not use transmissions. Instead, they have a direct link between the rotor and generator. These are known as direct drive systems. Without a transmission, wind turbine complexity and maintenance requirements are reduced, but a much larger generator is required to deliver the same power output as the AC-type wind turbines. Transmission

Slide 15: 

Ken Youssefi Engineering 10, SJSU 15 Cut-in speed is the minimum wind speed at which the wind turbine will generate usable power. This wind speed is typically between 7 and 15 mph. Wind Turbine Cut-in Speed Rated Speed The rated speed is the minimum wind speed at which the wind turbine will generate its designated rated power. For example, a "10 kilowatt" wind turbine may not generate 10 kilowatts until wind speeds reach 25 mph. Rated speed for most machines is in the range of 25 to 35 mph. At wind speeds between cut-in and rated, the power output from a wind turbine increases as the wind increases. The output of most machines levels off above the rated speed. Most manufacturers provide graphs, called "power curves," showing how their wind turbine output varies with wind speed.

Wind Turbine: 

Ken Youssefi Engineering 10, SJSU 16 Wind Turbine At very high wind speeds, typically between 45 and 80 mph, most wind turbines cease power generation and shut down. The wind speed at which shut down occurs is called the cut-out speed. Having a cut-out speed is a safety feature which protects the wind turbine from damage. Shut down may occur in one of several ways. In some machines an automatic brake is activated by a wind speed sensor. Some machines twist or "pitch" the blades to spill the wind. Still others use "spoilers," drag flaps mounted on the blades or the hub which are automatically activated by high rotor rpm's, or mechanically activated by a spring loaded device which turns the machine sideways to the wind stream. Normal wind turbine operation usually resumes when the wind drops back to a safe level. Cut-out Speed

Wind Turbine: 

Ken Youssefi Engineering 10, SJSU 17 Wind Turbine It is the flow of air over the blades and through the rotor area that makes a wind turbine function. The wind turbine extracts energy by slowing the wind down. The theoretical maximum amount of energy in the wind that can be collected by a wind turbine's rotor is approximately 59.3%. This value is known as the Betz limit. If the blades were 100% efficient, a wind turbine would not work because the air, having given up all its energy, would entirely stop. In practice, the collection efficiency of a rotor is not as high as 59%. A more typical efficiency is 35% to 45%. A complete wind energy system, including rotor, transmission, generator, storage and other devices, which all have less than perfect efficiencies, will deliver between 10% and 30% of the original energy available in the wind. Betz Limit

Power Generated by Wind Turbine: 

Ken Youssefi Engineering 10, SJSU 18 Power Generated by Wind Turbine California generates 11% of all commercial wind power generation in the world, Europe generates 70%. There are about 4,800 wind turbines in California at Altamont Pass (between Tracy and Livermore). The capacity is 580 MW, enough to serve 180,000 homes. In 2003, Altamont generated 822x10 6 kW hours, enough to provide power for 126,000 homes. In 2003, the California wind industry reported 3.7x10 9 kW hour of electricity output, enough to provide electricity for 570,000 homes (twice the size of San Jose). Average household uses 6,500 kW hour of electricity annually. PG&E reported, in 2006, out of all energy delivered, 12% was from renewable energy sources; 11% of this was from wind power.

Slide 19: 

Ken Youssefi Engineering 10, SJSU 19 Bergey wind turbines operate at variable speed to optimize performance and reduce structural loads. Power is generated in a direct drive, low speed, permanent magnet alternator. The output is a 3-phase power that varies in both voltage and frequency with wind speed. This variable power (wild AC) is not compatible with the utility grid. To make it compatible, the wind power is converted into grid-quality 240 VAC, single phase, 60 hertz power in an IGBT-type synchronous inverter, the GridTek Power Processor. The output from the GridTek can be directly connected to the home or business circuit breaker panel.  Operation of the system is fully automatic. It has a rotor diameter of 23 feet and is typically installed on 80 or 100 foot towers. 10kW Turbine $27,900 100 ft.Tower Kit $9,200 Tower Wiring Kit $1,000 Total Cost: $38,100 Example Residential Wind Turbine

Slide 20: 

Ken Youssefi Engineering 10, SJSU 20 Doubling the tower height increases the expected wind speeds by 10% and the expected power by 34%. Doubling the tower height generally requires doubling the diameter as well, increasing the amount of material by a factor of eight. At night time, or when the atmosphere becomes stable, wind speed close to the ground usually subsides whereas at turbine altitude, it does not decrease that much or may even increase. As a result, the wind speed is higher and a turbine will produce more power than expected - doubling the altitude may increase wind speed by 20% to 60%. Wind Turbine Tower heights approximately two to three times the blade length have been found to balance material costs of the tower against better utilization of the more expensive active components.

Energy Cost: 

Ken Youssefi Engineering 10, SJSU 21 Energy Cost Cost of Electricity Generation 1994 Compared to 2003 Technology [1] 1994 Cost of Electricity (rupees/kWh) Current Cost of Electricity (2003 data, rupees/kWh) Hydroelectric [2] 0.31 to 4.4 0.25 to 2.7 Nuclear [3] 2.5 1.4 to 1.9 Coal [4] 1.9 to 2.3 1.8 to 2.0 Natural Gas [5] 2.5 to 11.7 5.2 to 15.9 Solar [6] 16.4 to 30.5 13.5 to 42.7 Wind [7] 7.6 4.6

Wind Speed: 

Ken Youssefi Engineering 10, SJSU 22 Wind Speed Building wind facilities in the corridor that stretches from the Texas panhandle to North Dakota could produce 20% of the electricity for the United States at a cost of $1 trillion. It would take another $200 billion to build the capacity to transmit that energy to cities and towns. In 2007, the U.S. Gross Domestic Product (GDP, goods and services) was roughly 13.7 trillion and spending budget was 2.7