There's heat under them thar feet

Deep underneath the streets of Manhattan, deeper even than the sewers where the alligators lurk, something is stirring. An uptown apartment block being built on 64th Street is to have two holes, each 6in in diameter, sunk 1,500ft below the surface. That is a depth greater than the Canary Wharf tower in London is high, more than the 1,370ft of New York's own World Trade Towers.

The holes are being bored in order to tap the rocks below New York as a source of geothermal energy. Water will be pumped down one hole and drawn from the other. The resulting machine should be a perfect heat exchanger. The apartment building would be cooled in summer, warmed in winter. An external power source using a small amount of electricity will be needed to power the heat pumps. But in return rooms could be cooled and warmed ad lib.

No fussy, noisy and expensive air-conditioning, no bulky boilers, none of those huge whirling fans that seem to be obligatory on New York rooftops. The economics of the project look good, too. The extra cost of the drilling ($100,000) and pumps should be paid for within a few years by the savings that will come from not dispensing with conventional systems. Overall there will be less electricity consumed - which means less greenhouse gas, less global warming.

Geothermal energy is catching on in the United States, not in a dramatic way perhaps, but enough. Over the next five years the Americans are set to build as many as 400,000 geo-thermal systems; projects already running produce some 2,000 megawatts of power.

All of which prompts an obvious question: why aren't we trying similar schemes here in Britain? After all, geothermal power would be far less visible than wind farms (those semaphoring white giants that many detest). Geothermal power needs a lower technology level than solar panels (it's just pumps and holes). It doesn't need any long-distance transfer - you dig the hole where you need the cooling.

In fact geothermal energy systems have been investigated in the United Kingdom, where they are known by the vaguely disparaging term of "hot dry rocks", or HDRs. The energy potential is large - perhaps 10 per cent of the UK's electricity requirement could be provided by HDR systems. However, there are only three such projects up and running at present - in Cleethorpes, Southampton and Penryn. Development has been slow because the Department of Trade and Industry (which absorbed the Department of Energy) has never looked favourably on renewable energy.

"Everyone thought I was nuts," said John Barnes, who is sinking the two holes in New York. But it's really everyone else who, if not nuts, is missing a great chance.

There is an enormous reservoir of energy sitting there, leftover like a huge storage radiator from the time when the Earth coalesced from dust. Instead of reaching under our feet we use fuels that in the end are going to cost far, far more.