Wind energy

Wind first powered sailing ships in Egypt about 2500 B.C. and windmills in Persia about 650 a.d. The use of windmills for the grinding of grain was well established in the Low Countries (Holland and Belgium) by 1430 where they are still used to this day. 

The maximum power available from a horizontal axis windmill is given by 

However, to maintain a continuous air flow past the windmill implies that the extractable power, Pext niust be less than Pmax and it can be shown that Pext = (16/27)Pmax or 59.3% is the optimum extractable power available and usually 70% of this value is realized practically. The energy which is usually extracted by an electrical generator or turbine can be stored in a bank of batteries for future use. Several very large windmills have been built to generate electrical energy, but costs are still too high to make them commonplace. The vertical axis windmill is much simpler than the horizontal axis type, but large units have not as yet been tested. 

Fluid dynamics is based on Newton s axioms. It has been convenient to describe the action of a force on a body in the following forms of Newton s law (see also Chapter 4.1)  

Wind power is the conversion of wind energy into a useful form, such as electricity, using wind turbines. 

The most widely used form of renewable energy is hydroelectricity. As shown in Chapter 2.3.3, 27% of solar radiation (after solar absorption) is used for global evaporation of water and therefore transformed into latent heat in the atmosphere. Only a small percentage is usable as potential energy (uplift of surface water via evaporation and precipitation into river water above sea level) estimated to about 100 TW (corresponding to 0.1 % of solar absorption). 

The total power of latent heat, delivered first as kinetic energy (and finally dissipated in heat again) after water vapor condensation (cloud formation) amounts to 49 000 TW globally, 25 times more than the total wind power. 

400 to 700 nm (photosynthetical active radiation, PAR) can be utilized by plants, effectively allowing only 45 % of total solar energy to be utilized for photosynthesis. Furthermore, fixation of one CO2 molecule during photosynthesis necessitates a quantum requirement of ten (or more), which results in a maximum utilization of only 25% of the PAR absorbed by the photosynthetic system. On the basis of these limitations, the theoretical maximum efficiency of solar energy conversion is approximately 11%. In practice, however, the magnitude of photosynthetic efficiency observed in the field, is further decreased by factors such as poor absorption of sunlight due to its reflection, respiration requirements of photosynthesis and the need for optimal solar radiation levels. The net result is an overall photosynthetic efficiency of 3-6% of total solar radiation. 

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The issues of faciUtating options such as energy storage and transmission may prove to be important to the success of wind energy technology. Cost-effective storage coupled to wind systems would yield capacity credit benefits. In addition, because sites are often isolated, the value of wind energy would benefit from transmission/distribution access. 

The electricity generated depends primarily on the speed of the wind at the site of installation. A conventional formula to determine the wind energy, based on the design of the rotor (rotating blades) and the site conditions is given by... 

Wind Energy Technology. Kirloskar Electric Co., India. 

Wind turbines produce power by converting the force of the wind into torque. The power produced is a function of the wind energy flux (power), which, in turn, is a function of the air density multiplied by the wind velocity raised to the third power. Changes of air density with time at a particular site are negligible compared to the fluctuations in wind velocity. Meteorologists usually report wind speed as an average. To get the potential wind power, the average... 

During the late 1970s and early 1980s, there was considerable interest m harnessing wind energy m the... 

Gipe, P. (1995). Wind Energy Comes of Age. New York John Wiley Sons. 

Pacific Northwest Laboratories. (1991). Wind Energy Resource Atlas of the United States. Richland, WA Author. 

U.S. Environmental Protection Agency. (1997). EPA s Revised Particulate Matter Standards. Pact Sheet (July). Washington, DC U.S. Government Printing Office. Utility Data Institute. (1995). UDI Sees Electricity Demand Surging with Global Economy. Wind Energy Weekly o. 648 (May 29). 

Wave size is determined by wind speed and fetch, the distance over the oceans surface which the wind travels. Favorable wind energy sites are generally western coastlines facing the open ocean such as the Pacific Coast of North America and the Atlantic Coast of Northern Europe. Norway, Denmark, Japan, and the United Kingdom are the world leaders in wave energy technologies. 

Solar and wind energy account for less than 2 percent of the use of renewable energy (see Figure 2). Nevertheless, there are some important developments. The greatest increase in wind energy is outside the United States however, in 1997 the United States led the world for new wind generating systems by... 

Wind energy economics focuses on the fuel-saving aspects of this renewable resource, but capacity benefits and pollution reduction are important considerations as well. The capital costs are significant, hut there is no annual fuel cost as is associated with fossil fuel technologies. Thus, wind energy has been used... 

Billinton, R., and Chen, H. (1997). Determination of Load Cari ylng Capacity Benefits of Wind Energy Conversion Systems. Proceedings of the Probabilistic Methods Applied to Power Systems. Stli International Conference September 21-25, 1997. Vancouver, BC, Canada. 

HOE Wind Energy Program Home Page. U.S. Department of Energy, energy Efficiency and Renewable Energy Network. July 17, 2000. . 

Elliot D. L. Holladay, C. G. Barchet, W. R. Foote, H. P. and Sandusky, W. F. (1987). Wind Energy Resource Atlas of the United States, DOE/CH 10093—4, Golden, CO Solar Energy Research Institute . 

International Energy Agency. (1998). 1998 Wind Energy Annual Report. NREL/BR-500-26150. Golden, CO National Renewable Energy Lahoratoiy. 

National Wind Coordinating Committee Siting Subcommittee. (1998). Peniiitthig of Wind Energy Faci/iries. Washington, DC National Wind Coordinating Committee. 

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