Answers to Energy Crisis Are Blowin' in the Wind

Sep 28, 2007 10:58 AM
By Lou Pechi, President, STRATA-Strategic Advisors, San Diego, Calif.

The title of this article, while recalling one of Bob Dylan’s famous antiwar and civil-rights anthems of the ‘60s, addresses another potential solution to our energy crisis. The energy crisis is not only a matter of energy shortage, but also of the pollution and global warming that the present sources of energy are causing.

In my last column, “Let the Sunshine In,” I addressed the issues of generating electric energy from the sun’s rays. Actually, the wind is a form of solar power that has been converted to mechanical energy. Moreover, just as the sunshine does not shine all the time, the wind does not blow all the time. The more the wind blows, the more power that can be produced by the wind turbines.

Most studies and predictions about world wind energy indicate that it can support the world’s energy needs several times over. The map below, compiled by researchers at Stanford University, shows wind speeds at many sites around the world. More than 13% of those sites experience winds fast enough to power modern wind turbines. Altogether, these energy-producing sites could generate 72 terawatts of electricity, or more than five times the roughly 14 terawatts used worldwide in 2002.

How fast the wind blows, how often and when — all these issues play a significant role in determining the cost of generating power from wind. A common term used to rate a wind-turbine output is the ”capacity factor,” or the ratio of power produced over a period to the amount of power a turbine could produce if it ran at full capacity over the same time. The power output from a wind turbine also 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 easier and less expensive to capture.

This global map of wind speeds compiled by researchers at Stanford University reveals that more than 13% of the sites surveyed experience winds fast enough to power modern wind turbines.

Just as the dc output of solar cells is unregulated, the ac coming from wind turbines is not regulated, since it depends on the wind, which is not a constant "fuel." The raw ac from the turbines is essentially unusable, since it varies both in frequency and in voltage. This is particularly true for small wind turbines (up to 10 kW). Large wind turbines (500 kW and up) are very similar even though some have a mechanical gear that orients the pitch of the blades so that the propeller always spins at the same speed. In that case, electronic inverters and regulators are unnecessary, but due to the change in pitch and mechanical gearing, the efficiency of the turbine is lowered.

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