Page 286 - Handbook of Energy Engineering Calculations

Designers today seek to have each wind turbine produce more power, so
fewer turbines are needed for a given installation. To achieve greater power
output, towers are built higher, blades are made longer, and turbine-
generating capacity is increased. With higher towers and longer blades,
logistical problems develop in delivering these parts by truck or rail. Some

parts are just too large to be transported conveniently.
One of the major problems with wind turbines is getting them to produce
power during periods of high demand. Often the time of highest power

demand coincides with time of weakest wind velocity. Conversely, wind
turbines may produce their highest output at times of weakest power demand.
To overcome these problems and store wind-generated power, a 268-mW
system in the midwestern area of the United States feeds excess power to an
air compressor that pumps air 3000 ft (914 m) down into porous sandstone.

This pressurized air displaces groundwater. When power is needed during
peak demand times, air is fed from the ground reservoir into a surface-
mounted gas turbine, increasing its efficiency by some 60 percent. Designers

hope that such subterranean storage can increase the power supplied by wind
turbines in the United States from its present 2 percent to 10 percent, or more.
Some subterranean projects can store as much as a 5-month supply of air.
The U.S. Department of Energy sees the possibility of wind turbines
generating some 20 percent of the electricity needed in the United States by

the year 2030. Wind power could even rival nuclear-power-generating
capacity if new nuclear stations are not approved, and built, by that time.
Reports say that wind-energy capacity is growing by almost one-third each

year. The only real competitor to wind power in the growth sector is natural
gas.
Wind farms containing 100, and more, wind turbines per farm are
becoming more popular in the United States. The reason for this is that large-
scale wind-turbine installations have a lower cost per unit of capacity than

isolated small-number sites. At this writing the usual cost in large sites of
wind turbines is $2-million per MW of nameplate capacity.
Again, at this writing, the first offshore wind-farm installation in the

United States has been approved. How long it will take to get final approval
of this first offshore installation is not known. The United States is far behind
Europe in offshore wind farms. The primary reason for this is the large land
areas available in the United States for wind farms. Europe, by comparison,