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Wind Energy

November 25, 2009 Leave a comment

Wind energy is the kinetic energy that is present in moving air; this kinetic energy in turn derives from the heating of the atmosphere, earth, and oceans by the sun. The amount of energy in the wind depends mainly on wind speed, but is also affected slightly by the density of the air, which is determined by the air temperature, barometric pressure, and altitude.

For any wind turbine, the power and energy output increases dramatically as the wind speed increases. Therefore, the most cost-effective wind turbines are located in the windiest areas. Wind speed is affected by the local terrain and increases with height above the ground, so wind turbines are usually mounted on tall towers.

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Building Offshore Wind Farms

November 20, 2009 Leave a comment

Most developments will be installed on either gravity foundations or sited on steel monopiles. Gravity foundations are concrete structures which settle and are stabilised by sand or water and the turbine tower fits into them. Monopiles are long, steel tubes which are hammered, drilled or vibrated into the sea bed until secure and then platforms and towers are installed on top.

Although it would be technically feasible to mount wind turbines on floating structures, studies have shown that it would be very expensive to do this. However, technical developments may make floating offshore wind farms economically feasible in the future.

Wind Turbine

November 20, 2009 1 comment

A wind turbine is a rotating machine which converts the kinetic energy of wind into mechanical energy. If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine is usually called a windmill. If the mechanical energy is instead converted to electricity, the machine is called a wind generator, wind turbine, wind power unit (WPU), wind energy converter (WEC), or aerogenerator.

Figure: Typical Horizontal Axis (left) and Vertical Axis (right) Wind Turbines.

A wind energy conversion device that produces electricity; it typically has one, two, or three blades. Wind turbines can be classified into the vertical axis type and the horizontal axis type. Most modern wind turbines use a horizontal axis configuration with two or three blades, operating either downwind or upwind.

A wind turbine can be designed for a constant speed or variable speed operation. Variable speed wind turbines can produce 8% to 15% more energy output as compared to their constant speed counterparts; however, they necessitate power electronic converters to provide a fixed frequency and fixed voltage power to their loads. Most turbine manufacturers have opted for reduction gears between the low speed turbine rotor and the high speed three-phase generators. Direct drive configuration, where a generator is coupled to the rotor of a wind turbine directly, offers high reliability, low maintenance, and possibly low cost for certain turbines.

Disadvantages of Offshore Wind Energy

November 17, 2009 Leave a comment

Wind power must compete with conventional generation sources on a cost basis. Depending on how energetic a wind site is, the wind farm may or may not be cost competitive. Even though the cost of wind power has decreased dramatically in the past 10 years, the technology requires a higher initial investment than fossil-fueled generators.

The major challenge to using wind as a source of power is that the wind is intermittent and it does not always blow when electricity is needed. Wind energy cannot be stored (unless batteries are used); and not all winds can be harnessed to meet the timing of electricity demands.

Although wind power plants have relatively little impact on the environment compared to other conventional power plants, there is some concern over the noise produced by the rotor blades, aesthetic (visual) impacts, and sometimes birds have been killed by flying into the rotors. Most of these problems have been resolved or greatly reduced through technological development or by properly siting wind plants.

The Environmental Impact of Offshore Wind Farms

November 14, 2009 Leave a comment

The environmental impact of offshore wind farms is considerably reduced compared with those onshore; both noise and visual impact are unlikely to be issues, but there are still some considerations. For example, there could be an environmental impact from carrying out work offshore, such as localised disturbance of the seabed.

Studies on existing projects have shown that some foundations can act as artificial reefs with a resultant increase in fish populations from the new food supply. It has been suggested that the noise from the turbine travel underwater and disturb sea life. Nonetheless ships, boats and engines have been a fact of life for over a hundred years.

Components of a Horizontal Axis Wind Turbine

November 14, 2009 1 comment

In our old post “Wind Turbines” we explained you about the basic horizontal and vertical axis wind turbines.

This post will explain in details the various parts in a Horizontal Axis Wind Turbine.

Parts:

Anemometer: Measures the wind speed and transmits wind speed data to the controller.

Blades: Most turbines have either two or three blades. Wind blowing over the blades causes the blades to “lift” and rotate.

Brake: A disc brake which can be applied mechanically, electrically, or hydraulically to stop the rotor in emergencies.

Controller: The controller starts up the machine at wind speeds of about 8 to 16 miles per hour (mph) and shuts off the machine at about 65 mph. Turbines cannot operate at wind speeds above about 65 mph because their generators could overheat.


Figure: Various parts in a Horizontal Axis Wind Turbine


Gear box: Gears connect the low-speed shaft to the high-speed shaft and increase the rotational speeds from about 30 to 60 rotations per minute (rpm) to about 1200 to 1500 rpm, the rotational speed required by most generators to produce electricity. The gear box is a costly (and heavy) part of the wind turbine and engineers are exploring “direct-drive” generators that operate at lower rotational speeds and don’t need gear boxes.

Generator: Usually an off-the-shelf induction generator that produces 60-cycle AC electricity.

High-speed shaft: Drives the generator.

Low-speed shaft: The rotor turns the low-speed shaft at about 30 to 60 rotations per minute.

Nacelle: The rotor attaches to the nacelle, which sits atop the tower and includes the gear box, low- and high-speed shafts, generator, controller, and brake. A cover protects the components inside the nacelle. Some nacelles are large enough for a technician to stand inside while working.

Pitch: Blades are turned, or pitched, out of the wind to keep the rotor from turning in winds that are too high or too low to produce electricity.

Rotor: The blades and the hub together are called the rotor.

Tower: Towers are made from tubular steel or steel lattice. Because wind speed increases with height, taller towers enable turbines to capture more energy and generate more electricity.

Wind vane: Measures wind direction and communicates with the yaw drive to orient the turbine properly with respect to the wind.

Yaw drive: Upwind turbines face into the wind; the yaw drive is used to keep the rotor facing into the wind as the wind direction changes. Downwind turbines don’t require a yaw drive, the wind blows the rotor downwind.

Yaw motor: Powers the yaw drive.

Offshore Wind Energy

November 10, 2009 Leave a comment

Wind energy is an indirect form of solar energy. It is estimated that 1-2% of the solar radiation that reaches the earth is converted to wind energy. In general, wind results from an unequal heating of different parts of the earth, causing cooler, dense air to circulate to replace warmer light air. While some of the sun’s energy is absorbed directly by the air, most of the energy in the wind is first absorbed by the surface of the earth and then transferred to the air by convection.

Offshore wind turbines are being used in a number of countries to harness the energy of the moving air over the oceans and convert it to electricity. Offshore winds tend to flow at higher speeds than onshore winds, thus allowing turbines to produce more electricity. Much of this potential energy is near major population (and energy load) centers where energy costs are high and land-based wind development opportunities are limited.

Because the potential energy produced from the wind is directly proportional to the cube of the wind speed, increased wind speeds of only a few miles per hour can produce a significantly larger amount of electricity. For instance, a turbine at a site with an average wind speed of 16 mph would produce 50% more electricity than at a site with the same turbine and average wind speeds of 14 mph.

 

Commercialscale offshore wind facilities are currently in operation in shallow waters off the coasts, but further technology development is needed for use in the deeper waters of the Outer Continental Shelf (OCS).

Wind is air in motion. Since the earth’s surface is made of various land and water formations, it absorbs the sun’s radiation unevenly. Wind is produced by the uneven heating of the earth’s surface by the sun.

Onshore, wind energy has been utilized for power generation for more than two thousand years. In modern times, wind energy is mainly used to generate electricity, primarily through the use of wind turbines. Wind flows over the airfoil-shaped blades of wind turbines, causing lift (similar to the lifting force on airplane wings), causing the turbine blades to turn. The blades are connected to a drive shaft that turns an electric generator to produce electricity.

Commercial-scale offshore wind facilities currently are similar to the onshore wind facilities, but with modifications to prevent corrosion and protect against wave and wind interactions. Because roughly 90% of the U.S. OCS resources are over waters that are much deeper than European waters where commercial wind facilities are currently sited, new technologies are being developed (e.g., for strengthened tower foundations) to harness the wind in the harsher conditions associated with deeper waters.