Aquifers: nature's ready underground energy storehouses

The University of Minnesota at St. Paul may soon be getting some of its winter heating from hot water stored underground in a nearby aquifer. At the Stony Brook campus of the State University of New York, several campus buildings could get summer air conditioning from water stored underground.

Meanwhile, the remote community of Bethel, Alaska, plans to store waste heat from a city electric utility underground to heat a hospital and several other municipal buildings in winter.

These are three projects recently selected by the US Department of Energy in a program to turn the nation's underground water reservoirs into huge energy storage "batteries."

The program is similar to one tapping geothermal energy, but instead of tapping naturally hot water, "we're going to heat some up," said manager Ken Fox.

The idea is to pump hot or cold water into natural aquifers from which the heat or cold can later be retrieved for heating or cooling.

The Energy Department is planning to spend about $100 million on the program over the next five years, Mr. Fox said. It is being coordinated nationally by Battelle Northwest Laboratories here in Richland.

Compared to other energy technologies, aquifer storage is relatively simple. You take excess heat from a power plant or factory, pump it into the aquifer for storage, and then pump it back to the surface into a building's heating system.

Experiments in Alabama have shown that water injected into the ground at 170 degrees F. can be recovered months later at 120 degrees, still hot enough to be useful in a heating system, Mr. Fox said.

Conversely, it is also feasible to pump warm aquifer water to the surface in winter, run it through a chiller, and then pump it back into the ground for use in air-conditioning during summer.

In the Minnesota experiment, excess heat from a campus electrical power plant will be pumped into the ground in summer. In the winter the heated water will be pumped back to the surface and used to heat several buildings.

At Stony Brook, the task will be to inject chilled water into the ground and then withdraw it during summer months to cool campus buildings.

Mr. Fox estimates that about 60 percent of the US land mass has aquifers suitable for this kind of energy storage.

The aquifer storage program lends itself best to district heating, where a number of homes or buildings get heat from a single source.

District heating is rare in the United States but fairly common in Europe.

The current federal plan calls for funding of the initial design work and sharing of construction and operating costs with private contractors.