In Jules Verne’s famous novel Journey to the Center of the Earth, a team of explorers descend into the Earth through a volcano and discover a prehistoric world. Subterranean exploration has been in the news recently for a different reason––because the ground beneath us stores a largely untapped source of renewable energy. In January 2023, the U.S. Department of Energy’s (DOE) Geothermal Technologies Office (GTO) published its Enhanced Geothermal Shot Analysis. The GTO’s recent report concluded that with improved technology, the United States could affordably utilize enough geothermal energy to power over 65 million homes. Through efforts such as The Heat Beneath Our Feet initiative from the Western Governors’ Association, geothermal energy is poised to become an integral component of a clean energy economy. This article will 1. provide an introduction to geothermal energy, 2. discuss the technical and nontechnical barriers currently hindering greater utilization, and 3. consider some of the environmental implications associated with its use.
Geothermal energy has been utilized in some form for decades in the United States. Yet although this country leads the world in the amount of geothermal energy harnessed (roughly 3.7 gigawatts), proportionally it still represents a tiny fraction of the energy sector here. By contrast, Iceland generates around 25 percent of its electricity through geothermal sources.
The word “geothermal” itself may intuitively conjure up visions of hot springs resorts. While perhaps hot springs are the most enjoyable way to experience the benefits of geothermal energy, they are only one of several means through which this heat source can be accessed. In fact, there are three main types of geothermal energy: 1. ground source heat pumps, 2. direct use, and 3. deep and enhanced geothermal systems (EGSs). Ground source heat pumps are most often used to heat or cool houses and small buildings, and this technology has been in use since the 1940s. Direct use geothermal power typically pipes water from hot springs or geothermal reservoirs close to the surface into pools and baths, greenhouses, or other small buildings. EGSs, however, have the most applicability for industrial uses and are at the center of efforts to harness more of this energy source.
EGSs are human-made underground reservoirs used to access geothermal energy. In short, they are created by drilling into an underground heat source and injecting fluid to increase the permeability of the rock, and then pumping that hot fluid back to the surface to generate electricity. These reservoirs can sit anywhere from three to ten kilometers underground. DOE has funded several successful demonstration projects using this technology.
The GTO’s Enhanced Geothermal Shot Analysis estimates that more than five terawatts of heat resources exist beneath the United States, or more than enough energy to meet the entire world’s electricity needs. At present, geothermal energy is most widely utilized in California, Hawaii, Nevada, and Utah, and the facilities in some of these states have existed for a surprisingly long time. But technical barriers have thus far prevented the more widespread use of geothermal energy. One set of barriers relate to where geothermal energy projects can be located and the associated infrastructure developments required to transmit the electricity generated to the power grid. Another barrier is that exploration and drilling costs are high; following in the footsteps of other successful DOE programs like the SunShot Initiative, however, the GTO aims to reduce the cost of EGS by 90 percent to $45 per megawatt hour by 2035 through improvements to the exploration and drilling process, as well as the creation of reservoirs and power plants.
Policy barriers exist as well. At the federal level, geothermal energy projects may be subject to the environmental review process under the National Environmental Policy Act, and can implicate the Endangered Species and Clean Water Acts. State environmental laws, such as the California Environmental Quality Act, may also apply. In some circumstances then, developers may need to obtain permits from both the relevant federal and state agencies. And even after successfully navigating these arduous permitting and regulatory processes, some permitted projects have encountered vocal resistance from local communities for various reasons, including concerns over potential effects on groundwater, and subsequently had those permits revoked.
Geothermal energy has many potential benefits as compared to fossil fuels. It does not require the use of additional fuels to operate, which in theory makes the cost more stable, and, importantly, the carbon emissions from geothermal power plants are far less than for fossil fuels. Geothermal energy also has potential benefits as compared to other renewable energy sources. It is not seasonally dependent, and based on current knowledge, adverse direct effects on wildlife are far fewer than with either other renewable energy sources or most fossil fuels.
That is not to say that there are no environmental issues with geothermal energy, and these considerations must be considered when developing geothermal projects. Geothermal power plants typically consume significant amounts of water, and therefore, may adversely affect groundwater systems. They also require disposal of hazardous waste, such as certain dissolved solids and other heavy metals, and geothermal developments have been linked to land subsidence and earthquakes.
Geothermal energy represents a promising option that for now, at least, appears to have modest environmental risks even as compared to other renewable energy sources.
It could also substantially increase the United States’ energy independence, and conveniently, many of the skills required for geothermal energy development are transferable from the oil and gas industries. But despite the overall environmental benefits, some proposed geothermal developments have encountered vocal resistance from local communities. Inconsistencies with federal and state permitting and regulatory processes can also significantly delay geothermal energy project development. Addressing these nontechnical barriers to geothermal energy may pose the biggest challenge to the wider utilization of this energy source. If addressed thoughtfully, however, geothermal energy could play a key role in a zero-carbon future.
