U.S. Department of Energy - Energy Efficiency and Renewable Energy
Geothermal Technologies Office
Geothermal energy is a clean, renewable energy. For example, this geothermal power plant in Mexico only emits steam. Nonetheless, GTO is analyzing the possible environmental impacts of geothermal energy associated with power plant life cycles, water use, and seismicity related to EGS.
The Geothermal Technologies Office (GTO) works to address the environmental impacts of geothermal technologies through research and analysis of geothermal project life cycles and water use, and seismicity issues related to enhanced geothermal systems (EGS).
Life Cycle Assessments
Life cycle analyses look at all aspects of a resource and the possible environmental impacts should the resource be tapped. The U.S. Department of Energy's national laboratories conduct various life cycle analyses for geothermal power plants including EGS. Currently, GTO is conducting research to address emissions and energy-use issues in an effort to reduce fossil energy use and greenhouse gas emissions.
Life-Cycle Analysis Results of Geothermal Systems in Comparison to Other Power Systems: Part I, a technical paper from Argonne National Laboratory, looks at life-cycle analyses from the modeling of EGS, hydrothermal binary, and hydrothermal flash geothermal plants. It summarizes the findings of an analysis using Argonne's GREET (Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation) model. Results indicate that fossil thermal plants have fossil energy use and greenhouse gas emissions per kWh of electricity output about one order of magnitude higher than renewable power systems, including geothermal power.
Life-Cycle Analysis Results of Geothermal Systems in Comparison to Other Power Systems: Part II expands the results of Part I to include life-cycle analyses on three additional power-generating technologies: i.e., geo-pressured gas and electric wells that produce both natural gas and electricity, integrated gasification combined cycle plants fired by coal and biomass, and concentrated solar power plants.
Water Use Assessments
As water becomes an ever more critical resource, its use in power production will be scrutinized to consider the quantity and type of water used, the quality of the resource, and potential effects of the fluid discharge. Currently, GTO is working with geothermal power plant operators to measure water consumption and the variability of use in cooling operations, field operations, and other power plant uses in an effort to identify opportunities to improve water use efficiency and reduce consumption.
Water Use in the Development and Operation of Geothermal Power Plants, a technical report from Argonne National Laboratory, summarizes what is currently known about the life cycle water requirements of geothermal electric power-generating systems and the water quality of geothermal waters.
Water Resource Assessment of Geothermal Resources and Water Use in Geopressured Geothermal Systems builds on the work in the previous Argonne report and presents an assessment of fresh water demand for future growth in utility-scale geothermal power generation and an analysis of fresh water use in low-temperature geopressured geothermal power generation systems.
Seismicity in EGS
Injection and extraction of water from the subsurface has the potential to create micro-seismicity. Through the Recovery Act, GTO has funded several projects to examine seismicity issues related to EGS development with AltaRock Energy, Array Information Technology, Lawrence Berkeley National Laboratory, and Pennsylvania State University.
Siting and Permitting
In an effort to streamline federal permitting while ensuring environmental safety, the GTO in collaboration with the National Renewable Laboratory developed a Geothermal Regulatory Roadmap (GRR) to help developers navigate the federal, state, and local regulatory requirements necessary to deploy geothermal energy projects. Nearly 300 flowcharts address all permitting issues, from land use and leasing plans, to drilling exploratory wells, to developing a utility-grade geothermal power plant. For more on GRR, see this GRR Fact Sheet.
In April 2012, NREL released the final transmission report, Geothermal Power and Interconnection: The Economics of Getting to Market.
This report provides a baseline description of the transmission issues affecting geothermal technologies. It is intended for geothermal experts in either the private or public sector who are less familiar with how the electricity system operates beyond the geothermal plant. The report begins with a comprehensive overview of the grid, how it is planned, how it is used, and how it is paid for. The report then overlays onto this "big picture" three types of geothermal technologies: conventional hydrothermal systems; emerging technologies such as enhanced engineered geothermal systems (EGS) and geopressured geothermal; and geothermal co-production with existing oil and gas wells. Each category of geothermal technology has its own set of interconnection issues, and these are examined separately for each. The report draws conclusions about each technology's market affinities as defined by factors related to transmission and distribution infrastructure. It finishes with an assessment of selected markets with known geothermal potential, identifying those that offer the best prospects for near-term commercial development and for demonstration projects.