The Impact of Changes in Water Availability on Geothermal Power Generation

Abstract:

The conventional geothermal electrical generation capacity potential in the United States is estimated to be as high as 90 GW (USGS, 2008). If Enhanced Geothermal Systems (EGS) are included, the estimated capacity soars beyond 800 GW. Current generation capacity in the U.S. is approximately 1,000 GW. With a capacity factor close to 0.9, these numbers suggest that geothermal energy has the potential to be the primary provider of electrical energy in the United States. Realizing that potential is important, since geothermal energy is renewable, has low to no emissions, involves no fuel cycle, has one of the lowest spatial footprints per MW, has one of the lowest levelized costs of energy and the highest energy returned on energy invested values.

However, access to water is an important prerequisite for geothermal power generation. It is required in drilling, heat transfer and power production. For EGS applications, water is also needed for stimulation. Much of the water currently utilized in these geothermal applications is groundwater.

The impact of climate change on geothermal power generation will be expressed primarily through water availability. The details of potential water change impacts on power generation in existing and future geothermal sites will be presented in three case studies. It will be shown that strategies for mitigating groundwater losses are available, and include: use of degraded water in geothermal systems; use of captured CO₂ for heat transfer; expanded use of dry cooling; improved resolution of subsurface permeability mapping; improved efficiencies in power generation; and expanded access to high enthalpy resources.

Achieving these benefits will require aggressive research programs. Developing model hybrid technologies that combine geothermal-solar-biomass-wind-small hydro should be part of this research effort. Coupling geothermal resource exploration and mapping with detailed analysis of groundwater resources (recharge sites; climate change impacts; budgets; evolution of competitive uses) must be more strenuously and rigorously pursued. Otherwise climate change effects on subsurface water budgets may, over the long term, negatively impact the ability to achieve the electrical generation potential of geothermal energy.