Getting Into Hot Water

The energy that heats the homes of the Paris suburb of Melun (pop. 42,000) comes from a highly unusual source: a natural underground reservoir of hot brackish water located more than a mile underneath the town. French engineers boast that the system for tapping geothermal energy is the first of its kind. What makes it unique, they say, is the fact that the water is piped back into the ground for reheating, which means that Melun's subterranean furnace could keep working almost indefinitely.

The use of geothermal energy is hardly new. Icelanders have used volcanic springs to heat their homes for generations. In Larderello, Italy, the earth's heat has been tapped to make electrical power since 1904. In the mountains north of San Francisco, a rich geothermal area called the Geysers produces about 40% of the city's electricity. In most of these applications, the geothermal energy is released as scalding steam. Unfortunately, reserves of accessible underground water hot enough to produce steam (above 212DEG F.) have been found only in scattered areas of the globe, which has until now hindered wider application of geothermal energy.

Melun's underground reservoir contains hot (about 160DEG F.) but not boiling water. To get at it, French Engineer Pierre Maugis, 65, drilled a 5,850-ft. hole, which allows the water to escape to the surface. There, it is passed through a radiator-like device called a heat exchanger, which heats water from the city's regular water supply. The temperature of the city water is raised from about 50DEG F. to 149DEG F., hot enough to use in bathtubs or sinks filled with dirty dishes. The water is also sent through floor pipes that act as radiators or used to provide heat for forced-air systems. Once it is cooled off, the salty water flows back into the ground at a point only 35 ft. from the original drill hole. None of the brine is allowed to pollute nearby lakes or streams--one of the major environmental hazards of geothermal energy.

Systems like Melun's are harder on the municipal pocketbook than the local ecology; they require a large initial investment. In addition to the high cost of the drilling, Melun's houses must be particularly well insulated to reduce heat losses. But Maugis's son Francois, 33, who has largely taken over the test project since his father suffered a stroke, is convinced that cost is not a serious obstacle. Depending on its location, he says, the system could be less expensive over the long haul than those based on other fuels.

The French government apparently agrees. Encouraged by the success of the Melun project, Industry and Research Minister Michel d'Ornano is now asking Parliament to allocate $1.5 million for more geothermal well-drilling. Says he: "The increase in the cost of oil and the birth of new techniques oblige us to consider the energy potential of our underground wealth."

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