The current challenges to increased penetration of wind power are grid integration, forecasting of wind availability, public attitudes and visual impact. For offshore wind energy, a major challenge is cutting costs. The variable nature of wind electricity makes it difficult for wind to fully displace other electricity sources. When wind turbines constitute only a small fraction of generation capacity, their inter-mittency is hardly noticed by system operators, who are used to adjusting output to sudden changes in demand. At high penetrations, however, the marginal value of wind energy is equal only to the cost of the fuel and other marginal operating costs of power plants that are displaced. But if wind energy could be efficiently stored, wind power could compete economically with other types of electricity generation.
There is a wide range of technologies now available for storing wind energy, but choosing the appropriate one depends critically on the duration of storage required. For small turbines and at durations of only a few seconds to minutes, battery storage is a cheap option, along with flywheels and ultra capacitors. For longer durations, large-scale storage technologies such as pumped hydroelectric storage and compressed air energy storage are available at much lower costs per kWh of stored energy.
Another storage option is to combine back-up generation or integration with existing facilities such as gas turbines or hydro power. The back-up would be used when wind power generation is low. In extreme cases, wind turbines would simply be turned off when wind generation exceeds demand. More typically, the generator would try to maximize wind turbine output and shut off back-up sources of power. At least in the near term, this may be a more cost-effective strategy than large-scale energy storage.
Improved site assessment and identifying new locations, especially offshore, are important challenges. A 10% increase in wind speed will result in an energy gain of 33%. Improved assessment and siting require better models and measurements. Better measures are also needed to predict extreme wind, wave and ice situations. This may eventually make it possible to design site-specific systems that can utilize cheaper, lighter and more reliable turbines.
Several tools have been developed to overcome the aesthetic impacts of wind farms. Mapping of the zone of visual influence is used to show how many turbines will be visible from various locations. Photo-montage and animation techniques are employed to view potential wind parks from various angles. There has also been a great deal of research into the effect of wind turbines on the routes of migratory birds and on sites of special significance to bird populations. Sensitive siting has been found to avoid most of the problems.
Expensive undersea cabling and foundations have, until recently, limited the attractiveness of offshore wind energy. But new approaches in foundation technology, together with multi-megawatt-sized wind turbines, are at the point of making offshore wind energy competitive with onshore wind, at least at shallow water depths up to 15 m. Offshore wind turbines generally yield 50% higher output than turbines on nearby onshore sites because of more favorable and stable wind conditions.
Offshore wind turbines in deep water will become more economic with advances in floating platforms and continuing reductions in undersea cable costs. Recent studies have examined the technical feasibility of using floating platforms that are tethered to the ocean floor at depths of 180 m. Today, these installations are more expensive (USD 0.08 per kWh) relative to shallow installations (USD 0.05-USD 0.06 per kWh). Deep-water wind costs are projected to decrease to nearly the same level as shallow water costs by 2015 and to reach USD 0.04 per kWh by 2025 .
Although wind power is already competitive at many locations based on electricity production costs, the additional costs related to grid integration and back-up capacity must be considered as well. With government support for its development, wind power may become generally competitive with conventional technologies between 2015 and 2020. The deep-water offshore share in total wind power will increase, particularly if shallow sites in the United States and in Europe are exploited fairly quickly.
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