TWIRLING TURBINES

Humans have been using windmills for centuries, but machines for commercial energy-generation are a far cry from the square-sided towers with gracefully twirling sails still seen in parts of the Netherlands.

Typical wind turbines have a rotor diameter of from 75 to 105 feet. Instead of sails, they have two- or three-blade rotors. The larger the rotor, the more energy is produced. The largest wind turbine in Britain has a diameter of 180 feet and is located on the island of Orkney, off the coast of mainland Scotland. It generates 3 megawatts of electricity.

The rotors on large wind turbines turn slowly - under once every second - and do not appear to be a danger to birds, which soon get used to them. The land around the towers on which the rotors are placed can be used for farming, and there is no interference with television.

The electricity produced by the turbines can be fed directly into a national or regional power grid.

Manufacturers say the machines cost about 1,000 British pounds ($1,750) for each kilowatt of electricity produced. Over a 20-year life span, a wind turbine would produce electricity costing about the same to generate as that from fossil fuels, but for half the price of energy from nuclear-power stations.

In Denmark, some wind turbines are being placed on offshore sites or in shallow sea water, where winds are stronger. Construction costs for offshore turbines are roughly twice as high as costs on land.