Is There A Greenhouse Effect With Geothermal Energy?

Table of Contents

What is geothermal energy?

Geothermal energy is thermal energy generated and stored in the Earth’s interior. The word “geothermal” comes from the Greek words “geo” meaning earth and “thermal” meaning heat. Geothermal energy originates from the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface (U.S. Energy Information Administration, 2023).

This heat energy can be harnessed to generate electricity, provide direct heating and cooling, or be used for a variety of other applications like agriculture and industry. There are three main types of geothermal energy systems: hydrothermal, enhanced geothermal systems (EGS), and direct use (Office of Energy Efficiency & Renewable Energy, 2023).

Hydrothermal systems utilize naturally occurring pockets of steam or hot water by drilling wells into geothermal reservoirs to bring the hot fluid to the surface. The steam can be used to spin turbines and generate electricity. EGS involves injecting fluid into hot rocks to create an artificial hydrothermal system. Direct use applications take advantage of geothermal reservoirs closer to the surface for direct heating purposes.

How geothermal energy works

Geothermal power plants use steam or hot water from deep underground reservoirs to spin turbines and generate electricity (https://www.energy.gov/eere/geothermal/electricity-generation). Wells are drilled 1-2 miles deep into underground reservoirs to tap into hot water or steam. The steam rotates a turbine which activates a generator, producing electricity. The steam is then condensed back into water and injected back into the reservoir to be reheated.

Geothermal heat pumps use pipes buried in the shallow ground as a heat exchanger to heat and cool spaces. The pipes circulate water or an anti-freeze solution through the ground, absorbing or relinquishing heat. In the winter, the heat pump takes heat from the ground and pumps it into the building. In the summer, it operates in reverse, taking heat from the building and transferring it into the ground (https://www.ucsusa.org/resources/how-geothermal-energy-works). This allows geothermal heat pumps to provide heating and air conditioning more efficiently.

Greenhouse gas emissions from geothermal

Geothermal energy has very low greenhouse gas emissions compared to fossil fuels. According to the U.S. Department of Energy, “Geothermal power plants largely release only excess steam, with most plants discharging no air or liquid. This makes geothermal a clean power source.”¹ However, geothermal energy is not completely emissions-free.

While geothermal plants do not burn fuel to generate electricity, some greenhouse gases are released in the process. Small amounts of carbon dioxide and sulfur dioxide can be released from geothermal reservoirs. According to the U.S. Energy Information Administration, “Constructing and operating geothermal power plants emits greenhouse gases, but at lower rates than burning fossil fuels to produce electricity. Geothermal plants emit 0.1 to 0.2 pounds of CO2 per kilowatt-hour of electricity, which is about 5% of the emissions from a natural gas plant.”²

So while geothermal has very low emissions compared to fossil fuels, it does result in some greenhouse gas emissions from construction, operation, and materials over the life cycle of a geothermal plant.

Water emissions from geothermal

Geothermal power plants produce significantly less emissions compared to fossil fuel plants. However, they can still release water vapor, carbon dioxide, and hydrogen sulfide into the atmosphere (UCSUSA). The main emissions from geothermal plants are:

Water vapor – Geothermal reservoirs contain hot water and steam which is tapped by geothermal power plants. This generates water vapor emissions as the steam rises from the geothermal fluid.
Carbon dioxide (CO2) – Geothermal fluid contains dissolved CO2 which can be released into the atmosphere. However, geothermal CO2 emissions are much lower compared to fossil fuel power plants.
Hydrogen sulfide (H2S) – Geothermal reservoirs sometimes contain H2S gas which can be emitted. High H2S emissions can be hazardous if not controlled.

These emissions can impact the local environment if not properly mitigated. Geothermal plants use cooling towers, condensers, and scrubbers to reduce emissions. Scrubbers help remove H2S and other gases from the geothermal steam. Condensers collect the steam condensate which reduces water vapor emissions significantly. Cooling towers eliminate 95% of thermal emissions. With proper mitigation methods, geothermal emissions have minimal environmental impact (EIA).

Land use impact of geothermal

Geothermal power plants require land for construction of the plant and drilling of wells to access the geothermal reservoir. Depending on the size of the plant, several acres may be required for the power plant facility and well pads. This can have a visual impact on the natural landscape. However, geothermal energy has one of the smallest land footprints per kilowatt-hour (kWh) compared to other energy sources like coal or nuclear. According to the think tank Energy Innovation, geothermal requires just 27 square meters per GWh, compared to wind power which requires 72 square meters per GWh and coal which requires 3,692 square meters per GWh (Think GeoEnergy, 2022).

There are ways to mitigate the land use impact of geothermal plants. Careful siting of facilities can reduce visual impacts, and using previously disturbed land when possible minimizes new land disturbance. Reinjecting geothermal fluids back into the reservoir instead of surface disposal also reduces surface infrastructure needs. With proper planning and site restoration, the land use impacts of geothermal energy can be minimized while providing a reliable source of renewable energy.

Induced seismicity

In rare cases, geothermal activities like drilling or water injection can trigger small earthquakes. According to the U.S. Department of Energy, “Induced seismicity refers to small earthquakes (typically between a magnitude of 1.0 and 3.5 on the Richter scale) that may occur as a result of injecting fluid into the subsurface during Enhanced Geothermal System development and operation” (source). These minor seismic events are usually not felt at the surface and do not pose a hazard to people or infrastructure.

However, there are monitoring techniques used at geothermal sites to detect any seismic activity. As the DOE’s Geothermal Induced Seismicity Protocol states, “It is important that protocols be established and utilized for seismic monitoring from the earliest stages of a project through the entire lifetime of the project” (source). This allows geothermal operators to modify operations if any concerning seismic activity is detected.

Sustainability of geothermal energy

One of the key benefits of geothermal energy is that it is considered a renewable resource, as it taps into the Earth’s internal heat which is continuously produced in the planet’s core. However, while the source itself is renewable, the reservoirs where geothermal resources are captured can become depleted over time with sustained use, typically over the span of decades

Currently, most geothermal energy projects rely on conventional hydrothermal resources where naturally occurring reservoirs of hot water and steam are tapped through wells drilled in geothermal hot spots. As these reservoirs are used, the pressures and temperatures can decline over time. However, new techniques called enhanced geothermal systems or EGS can be used to extend the lifespan of geothermal reservoirs. With EGS, water is injected back into underground rocks or reservoirs to restock them and prolong their productivity (U.S. Energy Information Administration).

By supplementing depleted reservoirs and unlocking geothermal potential in areas without natural hydrothermal activity, EGS can make geothermal energy more sustainable in the long-run. Additionally, because geothermal reservoirs replenish naturally over long timescales, geothermal energy can provide renewable baseload power for many generations if managed properly.

Cost of geothermal

Geothermal energy systems have high up-front costs for drilling and facility construction, but low operating costs over their lifespan. According to ClimateMaster, the average cost for a residential geothermal heating and cooling system ranges from $18,000 to $30,000. The majority of this cost is for installation, including drilling wells and installing the heat pump unit and ductwork. However, geothermal systems have an average lifespan of 25 years for the heat pump unit and 50+ years for the underground piping. They also have minimal fuel costs because they use the Earth’s natural heat rather than fossil fuels.

While geothermal systems have higher upfront costs compared to conventional HVAC systems, their low operating costs can make them more affordable long-term. According to Forbes, geothermal systems can save homeowners 20% to 60% on heating and cooling costs over their lifetimes. The fuel-free operation offsets much of the initial installation expense over time. Overall, geothermal systems provide a cost-effective heating and cooling option when factoring in their lifespan and minimal fuel usage.

Future of Geothermal

While geothermal energy currently provides only a small share of global energy production, the industry is poised for growth with new technologies that can unlock more of its potential. According to research from MIT, geothermal power capacity is projected to grow globally by 140-260% by 2050 [1]. However, it still faces limitations and geothermal satisfaction will likely continue providing just 1-3% of total global electricity generation by 2050.

Several key technologies and techniques aim to expand viable geothermal resources dramatically. Enhanced geothermal systems (EGS) inject fluid into hot rock formations to create new subsurface fracture networks, allowing more heat mining. Co-producing geothermal electricity alongside oil and gas extraction can also utilize untapped thermal resources. Research into advanced drilling techniques, improved reservoir modeling, and adopting hybrid geothermal systems can further aid growth [2]. However, these new approaches face uncertainties regarding cost-effectiveness and implementation at scale.

Summary

In summary, geothermal energy has minimal greenhouse gas emissions compared to fossil fuel-based energy sources. This is a major advantage as greenhouse gases contribute significantly to climate change. However, geothermal does have some other environmental impacts that should be considered, such as emissions of sulfur dioxide and hydrogen sulfide, impacts on land use and wildlife, and the potential for induced seismicity.

When weighing the pros and cons of geothermal energy, the benefits include its low carbon emissions, renewable nature, reliability, and ability to provide baseload power. The main downsides are its high upfront capital costs, limited suitable locations, and potential localized environmental impacts. Geothermal is a promising source of clean energy, but each potential site must be evaluated carefully to minimize risks. With continued innovation and appropriate siting, geothermal can play an increasing role in a diversified, low-carbon energy portfolio.