When is a British bore a splashy success? When it produces not hot air but hot water. That's what is at the bottom of the new Marchwood borehole at Southampton, according to Department of Energy Parliamentary Undersecretary John Moore. The test hole struck a hot water pond, or aquifer, about one mile underground. Mr. Moore recenlty reported that there is enough water at 70 degrees C. (158 degrees F.) to heat a thousand houses over a period of several decades.
The $:1.1.8 million ($4.1 million) experiment, jointly funded by Britain and the European Community (the Common Market), represents a sizable chunk of the Department of Energy's $:7 million research budget for renewable energy resources -- a budget which also covers energy extraction from waves, tides, winds, biomass (crops and organic waste), and the sun.
A recent Department of Energy study estimates that British geothermal reserves represent an energy resource amounting to hundreds of millions of tons of coal equivalent (MCTE). MCTE is a standard unit used in energy accounting. In a country now using about 330 MCTE, that is substantial. But problems in getting at geothermal heat -- and then in distributing it to nearby users of low-grade heat, such as greenhouses and residences -- make it unlike to contribute more than four MCTE by the year 2000.
Geothermal energy -- representing heat in Earth's crust and upper mantel -- is most readily available where the massive plates forming the crust join together.Thus, under Iceland, Italy, New Zealand, and Japan, for example, the water is hot enough to be used directly in generating electricity. Nevertheless , Hungary, farther from a plate boundary, has used geothermal waters to heat homes since the turn of the century. And water from the Paris basin now heats large apartment houses, with running costs already about 15 percent below those of conventional fuels. French authorities look forward to heating nearly half a million dwellings in this way by 1990.
It also looks to be useful in Britain until the problems of distribution are examined. Dr. F. P. J. Clarke, research director of renewable energy at the Energy Technology Support Unit (ETSU) at Harwell in Oxfordshire, is convinced that there is plenty of geothermal energy around. But, he asks, "At what cost can it be made available and useful to people?"
Valuable hot water, in particular, becomes worthless cold water over a relatively short distance. So geothermal experts are scouting around for places like Southampton, where major population centers are located atop hot aquifers. In fact, however, the heat from the Marchland borehole will probably be first used by the electricity station next door to preheat water for its boiler.
Another source of geothermal heat is called "dry hot rock" energy. It is extracted by pumping a fluid through formations devoid of natural ground water. Experiments by the Los Alamos Scientific Laboratories in New Mexico suggest that water can be pumped down onto dry underground rock, where temperatures range up to 200 degrees C. (392 degrees F.) to produce steam for generating electricity.
Britain's Department of Energy is also eyeing Cornwall and Durham as sites of such hot granite batholiths. But they admit that the technology is not yet ready to make the "dry hot rock" process economically feasible. However, as oil prices continue to rise expensive processes look less daunting.
Meanwhile, authorities here are almost literally looking backward and forward for potential geothermal sites. They have poked their test equipment into the hot springs at Bath, used since Roman times. And they are looking ahead to the time when North Sea oil and gas will run out. The left-overs holes, they think, might be useful for extracting the heat beneath the sea floor.