Wind Power Has Great Potential
The letter by Frits de Wette (Claims for Wind Power Greatly Overblown, APS News May 2007
) makes a few good points but completely ignores the literature that evaluates the wind energy potential, grid integration, and technology in the US and in Europe. For example, the on-shore wind electric potential of the US has been analyzed in considerable detail. Taking into account restrictive land use constraints and economics, the potential is over 1200 GWavg, about 90 percent of which is located in the Great Plains. This potential is understated by about 30 percent since maximum wind turbine tower height was assumed to be 45 m, and towers as high as 100 m are currently being used. This also ignores the US offshore wind electric potential which is very conservatively estimated at about 100 GWavg. Compared to the total US generated electrical power of 440 GWavg (2005), there is clearly the possibility that wind generated electricity could make a substantial contribution to the power supply in the US, especially if energy efficiency and conservation were taken seriously.
Wind turbines are designed to produce power locally at the least possible cost for a given wind regime, which results in a capacity factor (the ratio of average power to maximum power) of about 30 percent. However, it is possible to design wind turbines  with a much higher capacity factor. For example, a capacity factor of about 50 percent is possible if the cost of electricity increases by about 10 percent, and even higher capacity factors are obtainable but at an ever-increasing cost. Moreover, if large premiums are paid for wind-generated electricity, as is the case in Germany, then capacity factors of 15-20 percent are tolerable. Since maximizing profitability is the only consideration for the wind turbine owner, low capacity factors are a perfectly reasonable choice.
Good wind resources are usually located far from consumers, and large amounts of intermittent energy are not easily handled by utilities, so that transmission and storage issues must be acknowledged and overcome if intermittent wind energy is ever to contribute significantly to demand. This analysis  has been done, and one can conclude that it is technically and economically feasible to transform intermittent wind energy to a reliable power source for distant consumers by combining large-scale wind turbine arrays with high voltage transmission lines and compressed air energy storage (CAES).
CAES is based on gas turbine technology and uses compressed air stored in underground structures (solution mined salt caverns or porous rock in a stratigraphic or structural trap) as the storage medium. This is a proven technology, with plants operating in the US and Germany, and is the lowest cost utility scale storage technology available.
Such an approach to wind energy integration has been taken by a group of Iowa utilities, who are building a 268 MW CAES plant with underground porous rock storage. More details are available at www.isepa.com
Current wind energy development relies on utilities to provide transmission and back-up for the intermittent power, often without compensation. This is the reason behind the hostility on the part of some utilities and system managers to intermittent renewable energy, and it is evident in the E.ON report cited by de Wette. Of course, demanding anything without compensation is a good way to make bitter enemies. While it may be justifiable for small numbers of wind turbines on a grid, this should not be expected to continue.
It is unfortunate that renewable energy advocates continue to use hand-waving arguments to justify, or simply ignore the difficulties with, integrating large amounts of intermittent renewable energy on the grid, and that skeptics refuse to examine the issues carefully. One can show  that it is possible to power a modern industrial economy using intermittent renewable energy, and that it is not technical or economic limitations, but our lack of imagination that prevents us from taking this approach. Alfred Cavallo New York, NY
1. Elliott, D.L. et al., 1991, An Assessment of the Available Windy Land Area and Wind Energy Potential in the Contiguous US, PNL-7789, Pacific Northwest Laboratories, Richland, WA.
2. Cavallo, A.J., 1997, Wind Turbine Cost of Electricity and Capacity Factor, J. Solar Energy Eng
, 119, 312-314.
3. Cavallo, A.J., 1995, High Capacity Factor Wind Energy Systems, J. Solar Energy Eng
, 117, 137-143.
4. Cavallo, A.J., 2007, Energy
, 32, 120-127.