Wind power generation

Various types of wind-driven turbines have been used for power generation. The efficiency of a rotor such as that shown in Fig. 12.6 e) is equal to the ratio of the energy developed to the energy content of the wind flowing across the projected area of the rotor (i.e., area M where I is the rotor height and d is the swept diameter). That is  

The munerator of Eq. (12.3) is the power delivered to the shaft per unit time while the denominator is the product of the specific energy of the wind (0.5pV ) and the volume rate of air flowing past the rotor (idV). The efficiency (e) is, of course, nondimensional. 

A dimensional analysis for the power (P) developed by any rotor of the S-type follows. Before dimensional analysis  

The quantity ndN)IV is the ratio of the tip speed to wind speed. Experimentally, it is found that maximum efficiency is obtained for a Savonius rotor when the gap (g) is about d 3 and (.Id is about 3. For a Savonius rotor of these proportions, the efficiency vs speed ratio curve shown in Fig. 12.10 (a) is obtained. The overall efficiency is seen to be a maximum (about 33%) when die shaft is loaded so that the speed ratio itdNyV is about unity. These results may be used to predict the behavior regardless of the fluid medium involved (air, water, etc). 

Also shown in Fig. 12.10 are efficiency vs speed ratio results for other types of wind devices. These fall into two categories—low-speed devices [ ndN)IV = 1] and high-speed devices [ ndN)IV 5]. The multiblade windmill is the usual horizontal-axis type found on farms across the USA, which have about 16 blades. This is seen to have a peak efficiency of about 27% at a speed ratio [ ndN)IV of about 0.9. The Dutch type four blade windmill is a horizontal-axis machine having a peak efficiency of about 20% at a speed ratio of about 2.2 [Fig. 12.10 (c)]. These machines have canvas sails lashed to the rotor blades. The high-speed two blade propeller is a horizontal-axis unit having a typical airfoil shaped cross 

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Zhou K Lu W. Self-sustainable off-grid wind power generation systems with hybrid energy storage. In 37th Annual Conference on IEEE Industrial Electronics Society (IECON 2011) 7-10 November 2011 Melbourne, VIC IEEE pp. 3198-3202. DOL10. 1109/IECON. 2011. 6119822. 

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