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Renewable options 1: Wind PowerPosted: 01 Nov 2000
Winds of change
by Leon Freris
The serious development of wind power in modern times began in 1973 after the oil crisis shook the confidence of the developed world that oil was there for the asking. Now, 18 years later, wind power is the fastest growing energy source in several regions of Europe, with the United States and India following behind in total installed capacity. And the potential is enormous.
The origins of this revolution go back a long way. The first recorded use of wind to provide mechanical power was for irrigation in Persia over 1000 years ago.
In the 12th century an amazing flowering of windmill technology took place in England with the development of the horizontal axis wind turbine. This English technology spread to Holland, France and Germany during the Middle Ages. Tens of thousands of windmills were used to grind corn, pump water and saw timber.
Another upsurge in the use of wind power took place in the United States during the last century. The multi-bladed American type windmill was used in hundreds of thousands to pump water in farms as the 'West' was being opened up.
Then, in the 1970s and early 1980s research and development programmes grew up in the United States, Sweden, the United Kingdom and Germany with the goal of developing large multi-megawatt wind turbines. These all ended in failure because of the superficial understanding of the technology at that time. In contrast to this pursuit of 'gigantism' the Danes began with the establishment of small-scale community-owned wind turbines and moved gradually to larger sizes on a learning curve. This policy paid off tremendously as Denmark now provides a large proportion of the world's wind turbines and employs 20,000 people in this industry.
Wind Park, Jutland, Denmark
© Jorgen Schytte/Still Pictures
Wind turbines for electricity generation are essentially simple devices, though their design requires deep understanding of the properties of wind, aerodynamics as well as mechanical and electrical engineering.
The kinetic energy in the wind is intercepted by three or two rotating, slender blades. The action of these blades is to extract energy from the wind by slowing it down. This extracted energy first appears as mechanical energy on the turbine shaft and then as electrical energy from a generator coupled to the shaft through a gearbox.
The power in the wind is proportional to the cube of the wind speed, hence doubling of the wind speed results in an eight-fold increase in electrical power generated. Wind turbines are designed to stop if the wind speed becomes excessive and do not rotate if the wind speed is too low for useful energy extraction.
Wind turbines are usually congregated in wind farms consisting of a few or as many as one hundred machines. By installing several machines on a site the costs of connection to the electricity grid and the operation and maintenance costs are reduced.
Modern wind turbines rated at around 1 to 2MW are large structures. Typically, a rotor of 60 metre diameter is attached to a nacelle at the top of a 60 metre tall tubular tower. Not surprisingly their environmental impact has not pleased everyone.
Controversy over their appearance is fuelled by the fact that wind farms are usually installed on tops of hills which make them prominent. In the past, wind turbines were also rather noisy. However, recent research has resulted in much quieter machines therefore noise is now not a major environmental issue.
Overall, major environmental bodies remain firmly in their favour. Opinion surveys carried out in areas where wind farms are installed consistently indicate a 70 to 75 per cent 'in favour' response with the approval rating increasing after the installation. The topic is an emotionally charged one. Some environmentalists see wind turbines as monstrous structures whilst others see them as elegant modern sculptures enhancing the landscape. The fact is that with wind turbines you get what you see. There are no insidious chemical or radiological emissions and their presence is a reminder of how natural forces can be benignly harnessed to provide us with energy.
Meanwhile, the cost of wind generated electricity continues to fall. In the United Kingdom in 1992 the average cost was around 7p/kWh whilst in 2001 it is 3.0 to 3.5p/kWh. This is lower than energy produced from oil, coal and nuclear power but higher than that from gas. This comparison does not take into account the environmental costs associated with fossil and nuclear fuels. Costs are likely to fall further as the technology matures and within a few years time it is predicted that wind will provide us with the cheapest electricity no matter what the source.
Today, wind power is growing fast in several European countries, with over 11,000 MW installed in the European Union by Autumn 2000. The United States and India follow with substantial installed capacities. The world potential of wind energy is enormous and capable of supplying the world needs several times over.
The feasibly exploitable potential is a lot less, but in many windy parts of the world it can easily provide 20 per cent of the energy needs: solar power, biofuels and water power together with wind energy are complementary and Shell predicts that by the middle of the next century they will be supplying half of our energy needs.
Almost every country in the European Union has plans for a substantial expansion over the next few years. The European White Paper on renewable energy published in November 1997 predicts that by the year 2010, 12 per cent of the energy in Europe will be supplied by renewables with wind energy contributing 40,000 MW. By the same year, Denmark is intending to supply 20 per cent of its electricity needs from wind. At the present rate of wind power expansion the 40 GW goal will be easily exceeded.
Because of the densely populated areas in Europe, offshore wind farms are now being planned. Although more expensive than onshore the price of this technology is falling. The great advantage of offshore exploitation is that it is not subject to the same environmental constraints as onshore.
The future of wind power is bright. It is a sobering thought that a technology invented one thousand years ago will make a marked impact on our energy needs at the turn of the second millennium.
Out of Germany's 16 states Schleswig-Holstein is the most northerly, right next to Denmark with the Baltic Sea to its east and the North Sea to its west. It is here, in this exposed landscape, that a considerable part of Germany's national wind potential is located.
The first step towards realising this potential occurred in 1988 when a change of the state government brought in a shift to energy policy. From an emphasis on nuclear there are in the region three plants of 2500 MW capacity the focus changed to renewables. Wind energy was seen as a local source of electricity which could cover a substantial proportion of the state's energy demand whilst simultaneously phasing out nuclear power and meeting ambitious goals for carbon dioxide reduction.
The new government set itself the goal of meeting 20-25 per cent of the electricity demand through wind by the year 2010. This could require 1200 MW of installed capacity consisting of about 2000 wind turbines. To launch this programme the state government offered investment grants of up to 30 per cent per plant initially, falling to 6 per cent during the last year of the programme which is now phased out. This initiative was supported by the national Electricity Feed Law which encouraged private generation. The result has been extraordinary. The wind power capacity of 2 MW in 1988 has now reached 600 MW in 1999.
Schleswig-Holstein's success has come about through a co-operative spirit amongst the state government, the regional utility, local manufacturers, planners, farmers and environmental groups.
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Dr Leon Freris is visiting Professor of Renewable Energy at the Centre for Renewable Energy Systems Technology, Loughborough University, England.