Reading Passage 1
A. Wind power refers to energy derived from wind, converted to a form, usually electricity, which can be used as a power source. This is most often achieved using wind turbines. Though this form of energy has enormous usage potential, by the end of 2006, wind power constituted less than 1% of global electricity used (although there are substantial differences between nations). This figure, despite its apparent insignificance, had in fact quadrupled between 2000 and 2006. Denmark’s consumption of electricity derived from wind power as a percentage of total consumption is the world’s most significant, this type of electricity constituting approximately 20% of total usage in that country. In contrast, no other country, at the time of writing, produces more than 10% of its electricity through wind power; most countries using less than 2%. Since there are numerous advantages to wind power, usage is anticipated to expand enormously over the next few years: it is readily available, clean (does not produce pollutants such as carbon dioxide, sulphur dioxide and mercury), it is renewable and can reduce pollution in the atmosphere, therefore benefiting the environment when used as an alternative to fossil fuel.
B. Windmills, which have been used for some time, involve the utilisation of wind energy to rotate mechanical machinery used for physical work such as the pumping of water. Modern day wind power, however, is more sophisticated, in that wind turbine blades and electrical generators convert wind power into electrical current. Wind power, generated and converted by wind turbines, can be on both a small and a large scale; the former commonly used by residents of rural areas unable to access electricity from regular sources, or large scale wind farms used to power national electrical grids. Wind as a source of energy is reasonably reliable, in that its availability is fairly constant; experts believe that wind generators are viable in areas where wind speed is anything above 16 kilometers per hour. Large scale wind turbine sites are strategically placed based on meteorological analysis; an ideal site is characterised by demonstrating a year round near constant flow of non-turbulent wind without patterns of intermittent powerful bursts.
C. The origin of wind itself is fairly intricate and it occurs due to the uneven manner in which the earth is heated by the sun. Areas around the equator receive more heat than areas near the poles; in addition, land heats and cools at a significantly faster rate than the oceans. These inconsistencies result in warmer and cooler air formations. Warmer air expands causing a build up of pressure, wind is, in essence, high pressure air moving towards a low pressure region. Wind moves in a convection current around the earth in the part of the atmosphere known as the troposphere. The troposphere, approximately 20 kilometres in depth around equator regions and 7 kilometres in depth around the poles, is the most turbulent part of the earth’s atmosphere; as a result, aircraft fly above it in the lower area of the stratosphere. This area of the atmosphere is, in contrast, stable; incorporating hotter air at the top which is heated by the suns rays and cooler air below. The stratosphere rises to approximately 50 kilometres regardless of whether it is above the equator or the poles, meaning that it varies in thickness from over 40 kilometres to 30 kilometres. The lower part of the stratosphere effectively acts as an invisible ceiling to wind currents.
D. Wind blows faster at higher altitudes and hilltop sites are consequently good spots for wind farm development. Likewise, coastal areas are also favourable as reliable sources of wind are generated due to the differing heating and cooling properties of land and sea; since air at sea level is denser than at higher altitudes, coastal winds are often also more powerful. Installation of wind farms, however, particularly in areas of scenic beauty, is often met with controversy and opposition from local residents and conservationalists. Many local residents often consider the mass of wind turbines to be an eye-sore and environmental protectors are often concerned about the potential dangers to wildlife; birds flying into the turbines and suchlike. In order to be effective, turbines are required to be placed a significant width apart, as neighbouring turbines reduce the energy of passing wind as their rotors turn, large wind farms can therefore have an enormous impact on the appearance of the landscape.
E. Offshore wind development sites, categorised as such by being at least 10 kilometeres from land, have proven in many countries to be the most suitable alternative and least likely to cause objections, since they cannot be easily seen or heard. Whilst wind conditions are optimum, the downside to offshore development is that construction is more costly than for land-based sites. Offshore towers need to be taller to compensate for the parts of the construction which need to be submerged in water; the logistics of building, then, are more complex and power needs to be transported via undersea cables which are more expensive to install. Salt from the sea can also lead to corrosion of the towers which is not a factor in onshore or freshwater lake locations, requiring ocean-bound turbines to be coated in special anti-corrosive substances. Maintenance is also often more complex and consequently more costly.
F. However, it seems that the negative aspects are outweighed by the positives, since offshore wind farms continue to grow and are currently the most common type of large-scale windfarm operation; this trend is expected to continue. Difficulties are considerably less significant in off-shore areas with shallow continental shelves which mean that construction does not need to be carried out in excessively deep bodies of water. Many of Denmark’s wind farms are situated in offshore locations and as the country aims to reach its goal of generating 50% of its electricity from wind power, it is likely that many more offshore sites will contribute towards this aim in the future.
G. Whilst it seems certain that wind power usage will continue to grow, arguments exist as to whether it has the capability to become an exclusive source of electricity; some believe that while it can effectively operate as a complement to other sources, such as fossil fuels or hydro-power, it would be too unreliable to become a large region’s only source of electricity. The main concern is that there are significant variations in quantity of electricity which can be produced from hour to hour or day to day; though overall annual output is fairly stable. In order to sustain industrial and domestic use, our power source needs to correlate with, and be able to meet, demand. Others hold that installation of wind farms on an enormous scale would ensure that our power needs could be fullfilled; though opposers say that the negative impact on the natural environment would be too high a price to pay as areas would need to be cleared of vegetation in order for wind farms to be built and that flora and fauna would suffer as a result.