The Wind Turbine Can Generate Electricity For Every Home In A Country - Science/Technology - Nairaland
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| The Wind Turbine Can Generate Electricity For Every Home In A Country by cybelink(m): 6:22pm On Nov 30, 2012 |
Can you imagine the wind turbine generating electricity for every home in a country. According to the definition,a wind turbine, windmill or wind generator is a device for converting wind power to mechanical rotation with a low velocity turbine designed for compressible fluids (air). Most of this article covers the use of wind turbines to drive generators to produce electricity.Beginning in the 1980s, the falling cost of producing electricity from wind has made wind turbines an economically viable way to supply energy to the grid in more and more areas. But the economics are marginal, and wind farms must be huge to produce publicly interesting amounts of power. As a result, the installation of large wind farms is controversial.One 1.8 MW wind turbine at a reasonable site would produce over 4,700 000 kWh of electricity each year, enough to meet the annual needs of over 1,000 households." (the average household in the UK, with 2 parents and 2 children, uses approximately 5500 kWh of energy per year. -Strathclyde University statistic).The energy production of a wind turbine can be calculated using the wind resource, elevation, temperature range, and turbine power curve. The climatological factors vary day by day and season to season, whereas the power curve is product dependent. Wind resources are often expressed in annual average wind speed, but this method doesnt account for seasonal variation, and makes the incorrect assumption that wind speeds are normally distributed about the mean. A more accurate method for analyzing wind energy production is to use calculus and statistics to calculate the sum of the wind energy produced at every instant in the year, using specific resource data for that instant as the year progresses. This is very tedious to do by hand, and so is best done using software. A company called SunWind Solutions has a web-based software program that will calculate wind turbine (and solar panel) output at any site in the US using this method. It allows the comparison of different products to see how they will work at your home, and also does payback period analysis, incentives, etc. More general: This depends on the size of the turbine and the wind resource. A single 1MW turbine operating at a 45% production rate will generate about 3.9 milion kW of electricity in a year. This would be enough to meet the needs of about 500 households per year. The world largest turbines at 5 MW have been constructed at the DEWI-OCC test field in Cuxhaven, Germany. Typically, normal output of wind systems run between 8% and 10% of the rated power. It is not the fault of the system, but average winds. Wind Turbines are rated at between 25 and 28 MPH winds. If the wind goes over 31 MPH, most systems shut down. Power is cubed, so a wind of 14 MPH provides 100KWH from a 1 MWH system. Because of this variance, fossil fuel plants must run at near capacity speeds and producing no output. This makes wind seem to be far greener then they are. Mean time between failure is still very low.One persons experience is that "eight 1.2 KW generators in a Michigan harbor that I was involved with are able to produce about 2 KW a day. Almost enough to power a single family home for an hour. Cost: $100K.Another interesting point with wind systems is that fossil fuel plants normally run on standby to support the wind fluctuations that occur. So, not only do we see only 8 to 10% of a rated power output, but this is offset by the fossil fuel consumed an not delivered to the grid. There are two major types of wind turbine namely;the horizontal and the vertical. Horizontal-axis wind turbines (HAWT) have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.Since a tower produces turbulence behind it, the turbine is usually positioned upwind of its supporting tower. Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted forward into the wind a small amount.Downwind machines have been built, despite the problem of turbulence (mast wake), because they dont need an additional mechanism for keeping them in line with the wind, and because in high winds the blades can be allowed to bend which reduces their swept area and thus their wind resistance. Since cyclical (that is repetitive) turbulence may lead to fatigue failures, most HAWTs are of upwind design.Turbines used in wind farms for commercial production of electric power are usually three-bladed and pointed into the wind by computer-controlled motors. These have high tip speeds of over 320 km/h (200 mph), high efficiency, and low torque ripple, which contribute to good reliability. The blades are usually colored white for daytime visibility by aircraft and range in length from 20 to 40 metres (66 to 130 ft) or more. The tubular steel towers range from 60 to 90 metres (200 to 300 ft) tall. The blades rotate at 10 to 22 revolutions per minute. At 22 rotations per minute the tip speed exceeds 90 metres per second (300 ft/s). A gear box is commonly used for stepping up the speed of the generator, although designs may also use direct drive of an annular generator. Some models operate at constant speed, but more energy can be collected by variable-speed turbines which use a solid-state power converter to interface to the transmission system. All turbines are equipped with protective features to avoid damage at high wind speeds, by feathering the blades into the wind which ceases their rotation, supplemented by brakes. Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable, for example when integrated into buildings. The key disadvantages include the low rotational speed with the consequential higher torque and hence higher cost of the drive train, the inherently lower power coefficient, the 360 degree rotation of the aerofoil within the wind flow during each cycle and hence the highly dynamic loading on the blade, the pulsating torque generated by some rotor designs on the drive train, and the difficulty of modelling the wind flow accurately and hence the challenges of analysing and designing the rotor prior to fabricating a prototype.With a vertical axis, the generator and gearbox can be placed near the ground, using a direct drive from the rotor assembly to the ground-based gearbox, hence improving accessibility for maintenance.When a turbine is mounted on a rooftop, the building generally redirects wind over the roof and this can double the wind speed at the turbine. If the height of the rooftop mounted turbine tower is approximately 50% of the building height, this is near the optimum for maximum wind energy and minimum wind turbulence. It should be borne in mind that wind speeds within the built environment are generally much lower than at exposed rural sites, noise may be a concern and an existing house may not adequately resist the additional stress.Another type of vertical axis is the Parallel turbine similar to the crossflow fan or centrifugal fan it uses the ground effect. Vertical axis turbines of this type have been tried for many years: a large unit producing up to 10 kW was built by Israeli wind pioneer Bruce Brill in 1980s: the device is mentioned in Dr. Moshe Dan Hirsch 1990 report, which decided the Israeli energy department investments and support in the next 20 years.[citation needed] The Magenn WindKite blimp uses this configuration as well, chosen because of the ease of running.[color=#006600][/color] 2 Likes |
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