Pie in the sky

A 'POWER tower', 7,000 metres-high, which could produce pollution-free energy from the North Sea, is being proposed by researchers in the Netherlands.

Its proponents claim that the tower coUld gener- ate nearly twice as much electricity as Drax, Britain's largest power station, by harnessing the same natural ~ystem that cauSes water to evaporate from the oceans and fall as rain.

The four-mile-high structure woUld be only 1,848 m lower than the summit of the Mount Everest (8,848 m). But civil engineers doubt that it can be built, and renewable energy experts believe that there are better ways of generating non-polluting energy.

Details of this project, as published in The Independent, London, state that at the top of the 'Mega-Power Tower', ammonia or hydrogen gas would c~n- den~e in the cold upper atmosphere and then fall through a turbine to the bot- tom, where heat flowing from the warm sea wouid evaporate it and start the cycle all over again.

A year-long feasibility study carried out by Novem, the Netherlands energy and environmental agency on behalf of the Dutch government, concluded that such a vast structure should not be impossible to build.

However, since the tower would be more than 10 times taller than the high- estman-made structure -the 646 m- high Warsaw radio mast in Poland- this claim has been greeted with scepti - cism. The mast fell down in 1991, just 17 years after it had been erected. Even if the tower's construction was feasible, energy experts doubt if it would be of much use.

One of Britain's foremost advocates of renewable energies, John Twidell of De Montfort University in Leicester, pointed out 1hat conventional gas turbines generate electricity efficiently -, converting at least 50 per cent of the heat energy into electricity - because of the high temperatures of combustion. But the proposed tower would produce a temperature difference of only about 20c to 30c and so "in engineering terms, the thermodynamic efficiency would be very low. The tower would be very inefficient," he said.

According to Twidell, "It is a fallacy to believe that we are short of energy -there is an abundance, the challenge is to harn~ss that in a cost-effective way. It is clearly cheaper to have a wind turbine 50 m-high than a tower that is 7,000 m-high."

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