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Wind energy: Full speed ahead
The ADVISER to the chief minister on environment and alternate energy recently disclosed that a windmill power project would be launched in Gharo at an initial cost of $875 million, in collaboration with some foreign countries, to meet the electricity needs of Sindh. He also said the government had earmarked a piece of land measuring 19,700 acres for the project.
He added that for the project, professional or technical expertise could be obtained from both inside the country and outside. Letters of interest had been issued to 12 companies, including General Electric of the US and the Denmark-based Vestas, credited with establishing a majority of the windmills in Holland, said the adviser.
In Sindh, windmills were first installed near Gharo in the 1980s on an experimental basis for pumping sweet groundwater, which proved to be a successful venture.
In Sindh, windmills were first installed near Gharo in the 1980s on an experimental basis for pumping sweet groundwater, which proved to be a successful venture. In time, however, the wells started producing brackish water, resulting in a reduction in the demand for the technology.
However, the demand increased recently as a large number of wind turbines were installed at the coastline near Karachi to evaluate the true potential of the technology. The same turbines are now being used for providing power to parts of the Defence Housing Authority, besides a campus of Szabist and a model village set up by Karachi University, both in Gharo.
Wind energy has been in use for many centuries — in sailing, irrigation and grinding grains. Wind energy systems for irrigation and milling have been in use since ancient times, while in the twentieth century they were used for generating electrical energy.
The global installed capacity has increased from 2,500 megawatts (MW) in 1992 to just over 40,000MW at the end of 2003, that is, at an annual growth rate of about 30 per cent. Almost 75 per cent of this capacity has been installed in Europe.
The need to reduce the emission of greenhouse gases gives a special place to wind energy in energy planning strategies. Germany has the largest number of wind farms in the world, producing more energy than Denmark, Spain and the US put together. The country has set a target of producing 20 per cent of its electricity from renewable resources by the year 2015.
In the past 15 years Germany has set up more than 15,000 turbines, half of them in the last five years. Denmark, with over 2,000MW, has the highest per capita consumption, accounting for about 12 per cent of the electricity produced.
In the next seven years, more than 7,000MW of generating power will be installed on 73 new farms in Britain. In all, 9,000MW of capacity is proposed to be installed by 2010 in the UK.
With an installed capacity of 1,870MW, India is now the fifth largest user of wind energy after Germany, the US, Denmark and the UK. State-of-the-art wind power technologies are now available indigenously in India.
The terms “wind energy” or “wind power” describe the process by which wind is used to generate mechanical power or electricity. Wind turbines are moved by the wind, which convert its kinetic energy into mechanical power. This mechanical power can be used for specific tasks, such as pumping water, or a generator can convert this mechanical power into electricity. Utility-scale turbines range in size from 50 kilowatts to several megawatts. Larger turbines are grouped together in wind farms, which provide electricity in bulk to a grid.
Individual turbines, producing less than 50 kilowatts each, are used to generate energy for homes, telecommunications dishes, or for pumping water. Small turbines are sometimes used in connection with diesel generators, batteries, and photo-voltaic systems. These systems are called hybrid wind systems and are typically used in remote, off-grid locations, where a connection to the utility grid is not available.
It is important to note that the amount of wind power generated is proportional to the density of the air, area swept by the turbine’s rotor blades and the cube of wind speed. The faster the blades rotate, the more the energy produced.
As the kinetic energy of air is proportional to its mass, the energy in it depends on the density of air. The density of air decreases slightly with increasing humidity. And air is denser in winter than in the summer.
Therefore, a wind generator will produce more power in winter than in summer at the same wind speed. At high altitudes, air pressure is lower and the air is less dense. Therefore, at the same wind velocity, a windmill at a coastline will produce more power than the one at a hill station.
The rotor of the turbine captures the power in the mass of air that is passing through. It is clear that if a rotor covers a greater area, then it will produce more electricity.Since the rotor area increases with the square of the rotor diameter, doubling the size of a turbine means a four-fold increase in the energy produced. But by increasing the swept area, we also increase the stresses on the wind system at any given wind speed. In order to compensate for this change and to let the system survive the stresses generated, it is important to strengthen the mechanical components. Obviously, this approach is rather expensive.
Wind speed is the most important factor influencing the amount of energy a wind turbine can convert into electricity. Increasing the wind velocity increases the amount of air mass passing through the rotor, so increasing speed will also have an effect on the output of the system. The energy content of wind varies with the cube of the average wind speed. Thus, if the wind speed doubles, the kinetic power gained by the rotor increases eight times.
Although wind power plants have relatively little impact on the environment as compared to the conventional ones, concerns have been voiced over the noise produced by rotor blades, the visual impact of windmills and the dangers they pose to birds. Most of these problems have been resolved or greatly reduced through technological development, or by intelligently locating the plants.
Electricity produced from the relatively immature wind energy sector is more expensive than that from the fully entrenched and mature fossil fuel-based generation systems. This is because no value is ascribed to the inherent cleanliness of wind energy and no penalty is imposed on the use of resources, which pollute the environment. The cost of damage that burning of coal causes to the respiratory health of humans as well as animals and the bad effects it has on the environment is not reflected in the price of coal-based electricity. The society at large, rather than the producers, pick up these huge costs. Energy sources such as wind impose none of these burdens on society.
In terms of the development of wind power projects, a critical determinant vis-a-vis feasibility is the availability of adequate winds, especially the average speeds as well as daily and seasonal peaks.
Reliable data on meteorological conditions stretching over several years is ideally required to properly assess the harvest potential of a wind farm at a specific site. A wind speed of 15 to 25 miles per hour was necessary for the operation of a mill. Windmills are grouped together to form wind farms.
With the development of increasingly large turbines and improvements in power generation technology, besides advances in wind analysis methods, wind power plants are now designed very carefully to optimize their performance and returns on investment. Such sophistication places greater demands for reliable wind data, which are often seen as the weakest input in an otherwise robust design process.
Pakistan, too, has an abundance of wind, blowing in sufficiently high speeds in the coastal areas including Chor, Badin, Karachi and Hyderabad. Wind can be utilized to meet the future demands of electrical energy at low costs without the use of fossil fuels.
However, the absence of good quality data on wind regimes extending over the entire country is a serious deterrent to plans for establishing large-scale wind power production facilities. The only data available are with the meteorological department, which has developed wind maps for all the 12 months. But these data were recorded at a low height of about 12 feet and on the whole do not give a true picture regarding ready availability of wind energy.
The availability of reliable data cannot be over-emphasized, therefore. Also, if the authorities are serious about bringing about a sizeable national wind turbine capacity, a generous fixed price should be allowed for a limited period, coupled with large capital grants. International benchmarking can help ensure that prices are not set too high.
Wind energy can contribute a fairly large percentage of environmentally sustainable power, which is almost free from major recurring bills. But right government policies and timely support are a vital first step towards achieving this objective.
Wind-generated energy is more secure than the other sources of supply, such as nuclear or fossil fuel plants. Wind energy is indigenously available almost free of cost and offers regional economic benefits. It is less vulnerable to disruption. Good wind sites are often located in remote locations, far from cities where electricity is needed in bulk.
More than 60 per cent of the Pakistani population resides in the rural areas, where small wind machines should be promoted for private ownership and operated by each individual farmer or owner. It is less likely that these small generators would be connected to the national grid.
The writer, who holds a postgraduate degree in environmental engineering, works as an assistant professor for the Dawood College of Engineering and Technology, Karachi. Email: abdulwaheed27@hotmail.com
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