An Assessment of Engineered Geothermal Systems for Water Management and Power Production

Abstract

This study presents a methodology to assess the economics of co-locating Engineered Geothermal Systems (EGS) with existing coal fired electrical plants to mitigate process water management and produce additional power. Fifteen coal plants in areas with geothermal gradients greater than 86 °F per 100 feet (30 °C/km) were identified and assessed based on resources and data quality. Five sites were further analyzed: Mountaineer Power Plant (West Virginia), North Valmey Generating Station (Nevada), Colstrip PPL (Montana), Cayuga Generating Station (Cayuga, New York) and Danskammer Generating Station (Newburgh, New York). Using the Geothermal Electricity Technology Evaluation Model (GETEM), site specific cost models were based on key constraints: temperature gradient, reservoir injectivity, and water availability. A detailed description of the geology, reservoir conditions, and power production system designs used to calculate the cost models is attached as an Appendix. These models were used to study improvement of the Levelized Costs of Electricity (LCOE) achieved both by reaching higher temperatures at greater depths and improving reservoir injectivity by stimulation. Project economics were best at coal plants in the western U.S. where higher geothermal gradients exist. However, these sites usually have limited water, which could limit the scale of geothermal developments possible. Sites in the eastern U.S. generally have larger amounts of process water and could support larger scale developments, but they also would have larger associated well field development costs. Technologies to improve binary plant efficiency and reduce drilling costs would make eastern U.S. sites more competitive within the current electricity market. The study illustrates that developing EGS to produce cost competitive electricity and mitigate process water effluence is feasible in most locations given favorable stimulation results.