Economic competitiveness is the key to successfully developing alternative energies. Geothermal energy can generate electricity competitively where wellhead temperatures are at least 175 °C or where space heating needs can use the geothermal wells much of the year (as in Iceland). This paper describes the U.S. research and development program designed to make other, more common geothermal resources economically attractive. The colder Canadian climate makes geothermal energy even more attractive economically. It now appears that electricity can be generated competitively from 150 ° C geothermal waters by using the binary cycle. For direct heat uses, geothermal resources as cool as 50 ° C are very attractive if a large enough market is available within several kilometers of the resource.
∗ Dr. Kunze was the manager of the Moderate Temperature Geothermal Research and Development Program conducted by EG&G Idaho, Inc., at the U.S. Department of Energy's Idaho National Engineering Laboratory. His present affiliation is with Energy Services Division. Forsgren, Perkins, and Associates, Rexburg, ID 83440.
There are several places within the U.S. where underground geothermal reservoirs have been put to practical use economically. Though the total energy from these and future resources will never represent a large fraction of the U.S. 's total energy usage, the local importance of such resources can be tremendous. In this respect, geothermal energy is similar to hydroelectric power, which supplies less than 3% of the U.S. energy but is extremely important in many areas like the Northwest. By geologic extrapolation, the chances of finding useful geothermal energy are at least as good in Canada.
Except for the Geysers area near Santa Rosa, California, commercial uses of geothermal energy have been slow to develop in North America. If we contrast our experience with that of the rest of the world (See Table I), we realize that geothermal energy may be more effective when used directly than when converted to electricity. The direct use of geothermal heat worldwide is replacing the consumption of gas and oil more than the consumption of electricity. There has been little push in this direction in North America. Our space-heating and water-heating needs represent nearly one-fourth of our energy use, but until 1973 we had cheap gas and oil and little incentive to replace them with other fuels.
List of Table 1 (Worldwide Use Of Geothermal Energy) (Available in full paper)
We also observe that the distribution of groundwater above average ambient temperatures is likely to follow something similar to a Poisson distribution; the higher the temperature, the scarcer the water. The precise nature of the distribution is not known, but we can expect to find considerably more water (and more energy) at temperatures from 100 to 150 °C, for instance, than 150 to 200 °C. This not only affects the nature of the use, as discussed above, but focuses attention on the research program needed to generate more electricity from geothermal energy.
The dry-steam situations, as at the Geysers Field in California, will be rare.
