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More than four billion are sold each year for use in 'intelligent' electronic devices; ranging from smart egg-timer through to aircraft management systems. Most of Eyes on the Universe: The Story of the. The book examines the development of astronomical telescopes and provides a fascinating overview of the way astronomical telescopes and This book contains the eight invited papers presented at the workshop on Formal Aspects of A workshop to look at strategies, methods of implementation and evaluation of vocational training and A workshop to look at strategies, methods of implementation and evaluation of vocational training and Continuing Medical Education in General Practice was held in June in London.
This text represents papers written by contributors to the workshop and pre-circulated Lasers in Urology: Principles and Practice. Wind power is both old and new. From the sailing ships of the ancient Greeks, to the grain mills of pre-industrial Holland, to the latest high-tech wind turbines rising over the Minnesota prairie, humans have used the power of the wind for millennia.
In the United States, the original heyday of wind was between and , when thousands of farmers across the country used wind to pump water. Small electric wind turbines were used in rural areas as far back as the s, and prototypes of larger machines were built in the s. When the New Deal brought grid-connected electricity to the countryside, however, windmills lost out.
Interest in wind power was reborn during the energy crises of the s. Research by the USDepartment of Energy DOE in the s focused on large turbine designs, with funding going to major aerospace manufacturers. While these 2- and 3-MW machines proved mostly unsuccessful at the time, they did provide basic research on blade design and engineering principles. The modern wind era began in California in the s. Between and , small companies and entrepreneurs installed 15, medium-sized turbines, providing enough power for every resident of San Francisco.
Pushed by the high cost of fossil fuels, a moratorium on nuclear power, and concern about environmental degradation, the state provided tax incentives to promote wind power. These, combined with federal tax incentives, helped the wind industry take off. After the tax credits expired in , wind power continued to grow, although more slowly. Perhaps more important in slowing wind power's growth was the decline in fossil fuel prices that occurred in the mids.
In the early s, improvements in technology resulting in increased turbine reliability and lower costs of production provided another boost for wind development. In addition, concern about global warming and the first Gulf War lead Congress to pass the Energy Policy Act of — comprehensive energy legislation that included a new production tax credit for wind and biomass electricity.
However, shortly thereafter, the electric utility industry began to anticipate a massive restructuring, where power suppliers would become competitors rather than protected monopolies. Investment in new power plants of all kinds fell drastically, especially for capital-intensive renewable energy technologies like wind. America's largest wind company, Kenetech, declared bankruptcy in , a victim of the sudden slowdown. In , a period of uninterrupted federal support for wind began, which led to several years of record growth.
In other parts of the world, particularly in Europe, wind has had more consistent, long-term support. As a result, European countries are currently capable of meeting more of their electricity demands through wind power with much less land area and resource potential compared with the United States.
Denmark, for example, already meets about 30 percent of its electricity demand from wind power. Wind generation also accounts for about 17 percent of the national power needs in Portugal, 13 percent in Ireland, and 11 percent in Germany [ 4 ].
Small Wind Turbines: Specification, Design, and Economic Evaluation
Serious commitments to reducing global warming emissions, local development, and the determination to avoid fuel imports have been the primary drivers of wind power development in Europe. The power output from a wind turbine rises as a cube of wind speed. In other words, if wind speed doubles, the power output increases eight times. Therefore, higher-speed winds are more easily and inexpensively captured.
Wind speeds are divided into seven classes — with class one being the lowest and class seven being the highest. A wind resource assessment evaluates the average wind speeds above a section of land e. Wind turbines operate over a limited range of wind speeds. If the wind is too slow, they won't be able to turn, and if too fast, they shut down to avoid being damaged.
Wind speeds in classes three 6. Ideally, a wind turbine should be matched to the speed and frequency of the resource to maximize power production. Since the late s, the DOE National Renewable Energy Laboratory NREL has been working with state governments to produce and validate high-resolution wind resource potential assessments on a state-by-state basis. A assessment of the UStechnical potential for onshore wind found nearly 33, TWh of potential, which is equivalent to 8 times the total USpower use in [ 5 ]. Though no projects have yet been installed in the United States, the wind resources located offshore also offer great potential, with the additional advantage of being located close to highly dense coastal population centers.
The technical potential for offshore wind in the USis nearly 17, TW, four times the total USpower use in [ 6 ]. Several factors can affect wind speed and the ability of a turbine to generate more power. For example, wind speed increases as the height from the ground increases. In order to take advantage of this potential at higher elevations, the rotors of the newest wind turbines can now reach heights up to meters [ 8 ].
In addition to height, the power in the wind varies with temperature and altitude, both of which affect the air density. Winter winds in Minnesota will carry more power than summer winds of the same speed high in the passes of southern California.
The more the wind blows, the more power will be produced by wind turbines. But, of course, the wind does not blow consistently all the time. The term used to describe this is "capacity factor," which is simply the amount of power a turbine actually produces over a period of time divided by the amount of power it could have produced if it had run at its full rated capacity over that time period. A more precise measurement of output is the "specific yield.
Small Wind Turbine Program - NYSERDA
Overall, wind turbines capture between 20 and 40 percent of the energy in the wind. If the turbine has blades that are 40 meters long, for a total swept area of 5, square meters, the power output will be about 5. An increase in blade length, which in turn increases the swept area, can have a significant effect on the amount of power output from a wind turbine.
Another factor in the cost of wind power is the distance of the turbines from transmission lines. Some large windy areas, particularly in rural parts of the High Plains and Rocky Mountains, have enormous potential for energy production, although they have been out of reach for development because of their distance from load centers. A final consideration for a wind resource is the seasonal and daily variation in wind speed.
If the wind blows during periods of peak power demand, power from a wind farm will be valued more highly than if it blows in off-peak periods. In California, for example, high temperatures in the central valley and low coastal temperatures near San Francisco cause powerful winds to blow across the Altamont Pass in the summer, a period of high power demand. Dealing with the variability of wind on a large scale is by no means insurmountable for electric utilities. Grid operators must already adjust to constant changes in electricity demand, turning power plants on and off, and varying their output second-by-second as power use rises and falls.
Operators always need to keep power plants in reserve to meet unexpected surges or drops in demand, as well as power plant and transmission line outages. As a result, operators do not need to respond to changes in wind output at each wind facility. In addition, the wind is always blowing somewhere, so distributing wind turbines across a broad geographic area helps smooth out the variability of the resource.
In practice, many utilities are already demonstrating that wind can make a significant contribution to their electric supply without reliability problems. Xcel Energy, which serves nearly 3. In Colorado, Xcel recently relied on wind power to provide more than 50 percent of its electricity on several nights when winds were strong and power demand was low. Xcel has also produced 37 percent of its electricity from wind power in Minnesota under similar conditions [ 10 ].
There are also several areas in Europe where wind power already supplies more than 20 percent of the electricity with no adverse effects on system reliability. For instance, three states in Germany have wind electricity penetrations of at least 40 percent [ 11 ]. The challenge of integrating wind energy into the electric grid can increase costs, but not by much.
Extensive engineering studies by utilities in several USregions, as well as actual operating experience in Europe have found that even with up to 20 percent penetration, the grid integration costs add only up to about 10 percent of the wholesale cost of the wind generation. However, because wind has low variable costs, it can reduce overall system operating costs by displacing the output of units with higher operating costs e.
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Increasing our use of wind power can actually contribute to a more reliable electric system. This gives grid operators greater flexibility to respond to such events.