London — Could one of the answers to Britain's future need for electric power be harnessing the wind with blades as tall as St. Paul's Cathedral? One of Britain's top experts on alternative energy believes that it could be so. But other sources warn that giant windmills have run into trouble in the United States and that they may be too difficult to build.
John Wright, director of the Technology and Planning Division of Britain's Central Electricity Generating Board (CEGB) sees ''good prospects'' in wind power.
Britain has plenty of wind, he points out. The CEGB has commissioned a 200 -kilowatt wind turbine at Camarthen Bay to launch a 10-year research project into wind potential.
The Scottish hydroelectric board is building a much bigger 3-megawatt windmill on Orkney Island. In theory, Mr. Wright says, wind turbines could generate 7 percent of current electricity consumption.
Yet other sources point to unhappy US experiences with giant windmills. Noted here is a report in the publication Energy Daily in Washington that all five of the US government's big windmills have been shut down.
A fail-safe device stopped a giant Boeing 2.5-megawatt windmill in Washington State, the Daily reported. An engineer climbed the 200-foot-high tower to find a big crack around the drive shaft holding the 100-ton rotor.
US officials are said to estimate that repair costs per windmill will be at least $500,000.
''These big windmills are uneconomic,'' a scientist here says. ''If you build them big to be efficient, the blades are too heavy and they crack. If you build them small, they are uneconomic. I'm not sure they can be built at all.''
But Mr. Wright sees possibilities. He sees wind power as more promising than solar in Britain, a country notoriously short of sun. Nor is he impressed with harnessing British waves or tides, or the heat from Britain's hot dry rocks.
Britain's Department of Energy has concluded that wave power was not promising enough to warrant expensive sea trials. An experiment with tides will probably not be built before the end of the century.
Critics of the CEGB say it deliberately downgrades alternative energy sources to push its own plans for nuclear power stations.