Policy Analyses for an Infant Technology: Hot Dry Rock Geothermal Resources

This paper demonstrates the potential role of policy and management analyses at early stages of technology development as exemplified by the case of hot, dry rock (HDR) geothermal energy resources used for electricity generation. Management issues concerning initial drilling depths, power plant design, redrilling strategies and periodic choices for well-flow rates are analyzed as they relate to R and D policies concerning first, the staging of R and D within the HDR R and D program and, second, priorities for the HDR research program relative to other R and D programs. Results reported here suggest that commercially attractive HDR systems do not require the development of new, very high temperature drilling technology (>275°C). Priorities for research concerning reservoir renewal and completion methods and baseload dimensions of an HDR system are emphasized. The desirability of periodic variations in well-flow rates as a means to reduce reservoir cooling is shown to be questionable. The commercial potential of HDR-produced electricity is assessed using calculations of the busbar cost of electricity from optimally-managed HDR geothermal systems. Busbar costs for a plausible set of base case conditions were found to vary between 26--76 mills kWh (1978 dollars) as geothermal gradients varied between 30--60°C per kilometer of vertical depth. Commercial feasibility for HDR-produced electricity then involves a comparison of these costs with one's expectations for future busbar costs for electricity produced with other fuel sources.