Evaluation and Ranking of Geothermal Resources for Electrical Generation or Electrical Offset in Idaho, Montana, Oregon and Washington. Executive Summary

In 1983, the Bonneville Power Administration contracted for an evaluation and ranking of all geothermal resource sites in the states of Idaho, Montana, Oregon, and Washington which have a potential for electrical generation and/or electrical offset through direct utilization of the resource. The objective of this program was to consolidate and evaluate all geologic, environmental, legal, and institutional information in existing records and files, and to apply a uniform methodology to the evaluation and ranking of all known geothermal sites. This data base would enhance the making of credible forecasts of the supply of geothermal energy which could be available in the region over a 20 year planning horizon. The four states, working together under a cooperative agreement, identified a total of 1,265 potential geothermal sites. The 1,265 sites were screened to eliminate those with little or no chance of providing either electrical generation and/or electrical offset. Two hundred and forty-five of the original 1,265 sites were determined to warrant further study. The Four-State team proceeded to develop a methodology which would rank the sites based upon an estimate of development potential and cost. Development potential was estimated through the use of weighted variables selected to approximate the attributes which a geothermal firm might consider in its selection of a site for exploration and possible development. Resource; engineering; and legal, institutional, and environmental factors were considered. Cost estimates for electrical generation and direct utilization sites were made using the computer programs CENTPLANT, WELLHEAD, and HEATPLAN. Finally, the sites were ranked utilizing a technique which allowed for the integration of development and cost information. On the basis of the developability index, 78 high temperature sites and 120 direct utilization sites were identified as having ''good'' or ''average'' potential for development and should be studied in detail. On the basis of cost, at least 29 of the high temperature sites appear to be technically capable of supporting a minimum total of at least 1,000 MW of electrical generation which could be competitive with the busbar cost of conventional thermal generating technologies. Sixty direct utilization sites have a minimum total energy potential of 900+ MW and can be expected to provide substantial amounts of electrical offset at or below present conventional energy prices. The combined development and economic rankings can be used to assist in determining sites with superior characteristics of both types. Five direct utilization sites and eight high temperature sites were identified with both high development and economic potential. An additional 27 sites were shown to have superior economic characteristics, but development problems. The procedure seems validated by the fact that two of the highest ranking direct utilization sites are ones that have already been developed--Boise, Idaho and Klamath Falls, Oregon. Most of the higher ranking high temperature sites have received serious examination in the past as likely power production candidates