Why Is Geothermal Energy Renewable Energy?

Geothermal energy is heat from within the earth that can be harnessed to generate clean, renewable power. The word “geothermal” comes from the Greek words geo, meaning earth, and therme, meaning heat. Salah Abdelrahman – Procter & Gamble provides a brief definition of geothermal energy as heat derived from the earth. It is generated and stored in the earth’s core, mantle, and crust. Some of this heat constantly flows to the surface in the form of hot springs, hot pools, geysers, and steam vents. Geothermal energy utilizes this heat from below the earth’s surface for various direct-use and electricity generation applications.

Geothermal Energy is From the Earth’s Core

Geothermal energy taps into the Earth’s internal heat that comes from radioactive decay and residual heat from planetary accretion. The inner core of the Earth reaches temperatures of over 5,000°C due to the decay of radioactive isotopes like potassium-40, uranium-238, and thorium-232 over billions of years. Additionally, heat remains from the original formation of the planet over 4.5 billion years ago. This heat emanates outwards towards the crust and manifests in hot springs, geysers, and volcanic activity we can observe on the surface.

As explained by Universe Today, “The farther down you go, the hotter it gets…Temperatures hot enough to produce magma, which is molten (liquid) rock, exist between 50 to 100 km below the surface.” This intense subterranean heat generated in the core, mantle, and crust of the Earth provides an immense reserve of geothermal energy we can tap into for renewable power generation.1

Geothermal Energy is Constant and Reliable

Geothermal energy harness heat from the Earth’s core, which provides an endless and consistent supply. The Earth’s core temperature averages between 4,000 to 7,000 degrees Celsius, and this heat dissipates outwards through the planet’s crust [1]. This makes geothermal energy extremely reliable, as the heat within the Earth’s core is constantly replenished and will continue radiating outwards for billions of years to come. Geothermal power plants can operate at over 90% availability, comparable to fossil fuel plants but with far fewer interruptions in service. The baseload power supplied by geothermal energy ensures grid stability and helps balance variable renewable sources like solar and wind. Unlike wind and solar which rely on weather conditions, geothermal offers uninterrupted energy generation. The constant heat flow from the Earth’s interior provides a steady stream of renewable energy to tap into.

Geothermal Energy is Environmentally Sustainable

Geothermal energy is one of the most environmentally friendly and sustainable energy sources available. Geothermal power plants emit minimal greenhouse gases and air pollutants. According to the U.S. Environmental Protection Agency, geothermal power plants release less than 1/6th the carbon emissions of a natural gas power plant per kWh of electricity produced (see inhabitat.com). The emissions from geothermal power plants are nearly 100 times lower per kWh than fossil fuel plants.

This is because geothermal energy utilizes heat from the earth’s core and does not require the burning of fossil fuels. The steam and hot water used to turn the turbines in a geothermal power plant is derived directly from underground reservoirs in the earth’s crust. Unlike coal, oil, and natural gas power plants, little to no greenhouse gases are released in the geothermal electricity generation process.

Geothermal systems also emit minimal air pollution and do not contribute to acid rain or smog. The geothermal steam is returned to the reservoir after it has turned the plant’s turbines, keeping the process sustainable and emission-free over long periods of time. This makes geothermal energy one of the cleanest sources of baseload power available today.

Geothermal Energy has a Small Land Footprint

Compared to other renewable energy sources, geothermal power plants have a very small land footprint. According to a study, geothermal energy uses the least amount of land per kWh of electricity produced. Solar and wind farms can span hundreds or thousands of acres to generate substantial power. But the actual power plant and wellfield of a geothermal facility may occupy just a few acres. The reason is that geothermal plants tap into the Earth’s immense underground heat, so they don’t require large above-ground solar collectors or wind turbines to harvest diffuse energy flows.

geothermal power plants have a small land footprint compared to other renewables

This compact nature gives geothermal energy a land use advantage. More megawatts can be generated per acre compared to other renewables. Geothermal’s small land footprint means less overall environmental impact too. Drilling rigs and pipelines are temporary installations during plant construction. Once complete, the surface area can be fully restored.

Geothermal Reservoirs are Replenished Naturally

Water and steam removed during geothermal energy production is replenished by natural processes. The heat that fuels geothermal energy comes from the Earth’s core. This heat is constantly generated by the radioactive decay of elements like potassium, thorium and uranium in the Earth’s crust and mantle.

As a result, geothermal reservoirs are not depleted after being used for energy production. The underground heat continuously replaces and replenishes the water and steam in geothermal reservoirs over time. Studies show that geothermal fields can sustain energy production for decades with proper reservoir management.

For example, two of the oldest geothermal power plants in the world located at The Geysers in California have operated commercially since the 1960s. With improved technologies, The Geysers now generates around 725 megawatts of renewable baseload electricity.

Geothermal Energy Supplies Baseload Power

Geothermal energy is well-suited to provide baseload power, which is the minimum amount of energy needed to be supplied to an electrical grid at any given time. Geothermal plants can operate 24 hours a day, 7 days a week, regardless of weather conditions. The geothermal resource itself lies deep underground and is not impacted by above-ground weather. This means geothermal plants have very high capacity factors of 90-95%, compared to 30-35% for wind and solar. Geothermal energy can provide a consistent, reliable source of renewable energy to meet baseload demand.

Traditional baseload power sources like coal and nuclear plants suffer downtime from maintenance and refueling. But geothermal plants involve virtually no downtime and provide continuous operation. The geothermal reservoirs are essentially giant batteries storing thermal energy underground. This stored energy can be extracted and converted into electricity around the clock. Geothermal’s baseload capacity gives it an advantage over intermittent renewables like wind and solar that require backup generation or storage solutions.

With geothermal energy supplying baseload power, utilities can rely on steady geothermal generation and use other renewables, natural gas, hydro and energy storage to meet peaks in demand. Geothermal offers a renewable and sustainable solution for 24/7 reliable electricity to power homes and businesses.

Geothermal Energy is Versatile

Geothermal energy has a wide range of applications due to the versatility of harnessing heat from the earth. According to the U.S. Energy Information Administration, geothermal energy can be used for generating electricity, heating homes and buildings, food dehydration, gold mining, milk pasteurizing, and other industrial processes [1]. The three main uses of geothermal energy are:

Electricity Generation

Geothermal power plants use steam or hot water from geothermal reservoirs to spin turbines and generate electricity. According to Plug and Play’s report, geothermal power provided about 0.4% of total U.S. utility-scale electricity generation in 2020 [2]. Geothermal power can provide baseload electricity generation.

Direct Use Heating

Geothermal energy can directly heat buildings, greenhouses, fish farms and more through a distribution system of pipes. This direct use of geothermal heat does not require converting it to electricity first. According to the Geothermal Energy Association, geothermal heating and cooling is used in all 50 U.S. states today [3].

Geothermal Heat Pumps

Geothermal heat pumps use shallow ground or water as a heat source in winter and heat sink in summer. These systems transfer heat between the ground and buildings for space heating, cooling and hot water.

Significant Geothermal Resources Exist

Despite only accounting for a small percentage of total global energy production currently, there are substantial geothermal resources available across the planet to tap into. According to a World Bank report, the global geothermal power generation potential is estimated to be between 70 to 80 gigawatts (GW). However, only around 15% of the known geothermal reserves worldwide are actively utilized for energy production. This means the vast majority of geothermal potential remains untapped.

Countries like Iceland, New Zealand, Indonesia, and parts of the United States have some of the most abundant geothermal resources globally. But most regions worldwide have at least some accessible geothermal energy available. As technology improves to more efficiently harness geothermal resources, global capacity is expected to grow substantially in the coming decades.


Geothermal energy is considered a renewable energy source for several key reasons. Most importantly, geothermal energy comes from the Earth’s core, which means it is constantly replenished and will be available for the foreseeable future. The heat from the Earth’s interior is practically limitless and will continue radiating for billions of years to come.

Additionally, geothermal reservoirs are naturally replenished by rainfall and snow melt seeping deep underground. This makes geothermal power extremely reliable and resilient over long periods of time. Geothermal plants produce baseline power around the clock and have capacity factors of 90-95%.

Geothermal energy has a small land footprint, causes minimal emissions, requires no fuel source, and disturbs very little of the surrounding environment. The technology to capture geothermal energy is improving steadily, and significant global resources exist. With all of these renewable characteristics and advantages, geothermal power will be an important clean energy source for generations to come.

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