ENVIRONMENTAL EFFECTS OF WIND POWER
The environmental impacts of wind power, with the exception of the aesthetic impact of a series of wind turbines being added to the landscape, are generally limited. Most of the problems that arise when attempting to gain permission to erect a wind turbine or build a wind farm are related to the siting of wind bines due to the visual impact. This has proved a major issue, particularly in densely populated countries such as the United Kingdom where wind farms are often subject to lengthy permitting procedures. It is partly for this reason that offshore construction is accelerating around European shores.
Of the other potential environmental effects, noise has been considered an issue in the past, but most modern wind turbines with their large, low-speed rotors have limited noise impact provided they are reasonably distant from habitations. Other areas of concern, such as the danger to birds from rotating turbine blades or impacts on marine life from construction offshore, have not generally proved serious and studies have suggested the impact is small, although anecdotal evidence sometimes contradicts this.
WIND INTERMITTENCY AND GRID ISSUES
Electricity generated from wind turbines suffers from two problems that make it difficult to accommodate on a conventional grid. First the wind is an intermit- tent source of energy so a single wind turbine cannot ever provide electric power continuously. Second, the wind is unpredictable so that it is impossible to know in advance when a wind turbine will supply power and when it will not. Together these make the management of wind energy more difficult than most other sources of power.
Intermittency on its own is not necessarily a problem. Tidal power is intermittent but the output can be predicted with great certainty so that the dis- patching of tidal power is relatively easy. Solar power is intermittent too and has a degree of unpredictability, but during daylight hours there will be generally some solar power available so the problem here is less severe. In addition, in regions where the sun shines often, power demand, particularly from air conditioning, will often follow solar output so that solar power can provide a reliable source of peak power that will coincide with rises in this type of demand. Wind power, on the other hand, cannot be relied on to coincide with anything. (However, the wind often blows more strongly in winter than in summer, so wind and solar can be complementary over a seasonal timescale.)
There are various ways of managing the intermittent and unpredictable out- put from wind power plants. The simplest solution, and the one often applied where wind is used for remote or small domestic supplies, is to store the wind energy—most frequently with a small battery storage system. So long as the wind power–generating capacity is sufficiently large enough compared to the demand, the wind power plant will be able to supply enough stored energy to provide a continuous supply of electricity. Such systems usually include some backup source of electricity too, for those rare periods when there is a lengthy calm period.
Energy storage is, in principle, the most robust solution for wind energy management on grid systems too. Unfortunately, energy storage capacity is generally expensive and very few grids have storage sufficient to manage the large amounts of wind power being introduced into grid systems across the world today. As the proportion of renewable energy grows, it may become economically expedient to expand storage capacity. Meanwhile, novel solutions to this problem for wind have been proposed, including the integration of wind generation with hydrogen production as a means of energy storage. It has yet to be established that this is an economically viable solution.
Where storage is not available, wind output variability is usually managed by maintaining a sufficiently large standby capacity to step in when wind output fails. The cheapest way of achieving this, but one that is not available every- where, is to use hydropower capacity as backup. Provided this capacity is based on dam and reservoir power plants, hydropower can be brought online or taken offline rapidly and at will. In a sense this is much like pumped storage hydro- power but without the full flexibility. Nevertheless, where hydropower capacity of this sort is available, the cost of grid integration of wind energy has been shown to be cheaper than where it is not available. When such hydropower capacity is not available the standby capacity will probably be based on natural gas–fired combined cycle power plants, which are more expensive to operate and therefore increase overall wind integration costs. Coal plant manufacturers are also trying to adapt their technologies to be able to provide the flexibility to provide grid support of this type too.
There are also other means of helping to integrate wind power. While wind unpredictability and intermittency cannot be avoided, there are ways of ameliorating the problems associated with them. One is to use sophisticated weather forecasting techniques. If wind output can be predicted with reasonable accuracy several hours or even a day ahead, dispatching of the power on the grid becomes much easier. Integrating weather forecasting into automated dispatching systems is already being used with advanced dispatching systems and the accuracy and applicability of such techniques can be expected to improve in the future.
A further factor that can help make wind output more predictable is geo- graphical averaging. An individual wind turbine will always have a varying and intermittent output. However, if the output of one turbine is combined with that of a second at a different location, the combined output will generally vary less because the wind level at one location will not be exactly correlated with that in another. This idea can be expanded so that the output from wind farms over a wide geographical area can be considered collectively as one source of power with much less variability than any one wind farm individually can pro- vide. Modern computerized grid management systems can treat groups of power plants such as wind farms as single, virtual power plants, creating more reliable and therefore more valuable wind energy power sources.