What Is Geothermal Simple Examples?

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What is Geothermal Energy?

Geothermal energy is a renewable energy source that generates electricity or provides heating and cooling by tapping into pockets of heat underneath the earth’s surface.[1] It utilizes the natural warmth within the upper 10 feet of the Earth’s crust to generate clean power and provide climate control.[2] The word geothermal comes from the Greek geo meaning Earth, and therme meaning heat.[3]

Geothermal energy relies on the constant temperature just below the Earth’s crust known as geothermal reservoirs. These reservoirs of hot water and steam are accessed by drilling wells into the reservoirs to bring the heated water to the surface. The steam from this superheated water can be used to turn turbines to generate clean electricity. The hot water itself can be used directly to provide heating and cooling for buildings, crops, aquaculture, and industrial processes.[1]

Because geothermal energy taps into the Earth’s continuous heat flow from its core outward, it provides a renewable and sustainable energy source. The heat in the Earth’s core powers geothermal energy due to radioactive decay and residual heat from the Earth’s formation.[3] This makes geothermal a clean energy source that does not require the burning of fossil fuels.

[1] https://www.energy.gov/eere/geothermal/geothermal-basics
[2] https://www.twi-global.com/technical-knowledge/faqs/geothermal-energy
[3] https://www.eia.gov/energyexplained/geothermal/

Types of Geothermal Energy Systems

There are three main types of geothermal energy systems that are utilized to harness the earth’s internal heat:

Geothermal Heat Pumps

Geothermal heat pumps use shallow ground warmth as an exchange medium for efficient heating and cooling. They transfer heat between the earth and a building by circulating fluid through pipes buried in the shallow ground or submerged in surface water. Geothermal heat pumps leverage the constant temperatures underground which can be warmer than the air in winter and cooler than the air in summer Electricity Generation.

Direct Use of Geothermal Energy

Some geothermal reservoirs produce hot water and steam at temperatures suitable for direct use. This includes heating homes, buildings, greenhouses, fish farms, and industrial processes. Geothermal district heating systems provide warmth to communities by distributing hot water through a network of pipes Types of Geothermal Power Plants.

Deep Geothermal Systems

Geothermal power plants drill wells into underground reservoirs to pump steam or hot water to the surface and convert it into electricity. There are three main types of geothermal power plant technologies: dry steam, flash steam, and binary cycle.

Benefits of Geothermal Energy

Geothermal energy provides many important benefits compared to traditional fossil fuel-based energy sources.

First and foremost, geothermal is a renewable and sustainable energy source. The heat from the Earth’s core is constantly being replenished and will remain available for billions of years to come. This sets geothermal apart from finite resources like oil, coal, and natural gas that will eventually be depleted (https://www.energy.gov/eere/geothermal/geothermal-faqs).

The renewable nature of geothermal energy means it can reduce reliance on fossil fuels and improve energy security and independence. Tapping into geothermal resources allows regions to generate their own local and stable supply of power without being as vulnerable to fuel price volatility or disruptions in the global energy market (https://www.enelgreenpower.com/learning-hub/renewable-energies/geothermal-energy/advantages).

Compared to traditional power plants, geothermal systems also have very low emissions. Geothermal plants emit on average 90-95% less greenhouse gases than natural gas plants, and close to zero emissions of major air pollutants like sulfur dioxide and particulates (https://www.energy.gov/eere/geothermal/geothermal-faqs). This makes geothermal a clean energy solution.

Geothermal Energy Applications

Geothermal energy has many applications that take advantage of its renewable and sustainable properties. Some of the main uses of geothermal energy are for heating and cooling, generating electricity, heating greenhouses, and aquaculture.

Geothermal heat pumps are used to provide heating and cooling for residential and commercial buildings. These systems circulate water through underground pipes to transfer heat between the earth and the building. This allows for heating in winter and cooling in summer without fossil fuels.

Electricity can be generated from geothermal energy by using the heat to produce steam which powers turbines connected to generators. Countries like the U.S., Philippines, and Iceland generate electricity from geothermal sources. The Geysers in California is the largest geothermal electricity plant in the world.¹

Greenhouses use geothermal heating to maintain optimal temperatures for plant growth during colder seasons. The heat extracted from shallow ground near the greenhouse is used to keep the air warm without external energy sources.

Fish farming and aquaculture facilities use geothermal reservoirs or heated groundwater to incubate fish eggs and accelerate growth. The steady water temperatures provided by geothermal sources are ideal for aquaculture processes.

Geothermal Energy Basics

Geothermal energy utilizes the heat generated and stored within the Earth to produce energy. The source of geothermal energy is the heat that exists in the Earth’s core due to radioactive decay and residual heat from the planet’s formation. This heat flows outward towards the Earth’s surface and heats underground reservoirs of water and steam. The temperature increases by about 15-25°C per kilometer of depth (Source 1). These geothermal reservoirs provide the energy that can be harnessed for geothermal power generation and other direct use applications.

There are three types of geothermal resources that can be utilized (Source 2):

Hydrothermal resources contain both hot water and rocks.

Geopressured resources contain hot water and methane gas.
Hot dry rock resources lack natural water but are good candidates for enhanced geothermal systems.

Enhanced Geothermal Systems (EGS) are engineered reservoirs created to produce energy from geothermal resources deficient in economical amounts of water and/or permeability. EGS expands the range and size of viable geothermal resources by injecting fluid into hot dry rocks to create geothermal reservoirs.

Geothermal Heat Pumps

Geothermal heat pumps are systems that leverage the relatively stable temperatures underground to provide heating and cooling for buildings. They are sometimes referred to as ground source or water source heat pumps. There are two main types of geothermal heat pump systems:

Ground-source heat pumps use underground loops of pipe buried in the ground near a building to transfer heat between the ground and the building. In winter, the system pulls heat from the ground into the building. In summer, it pulls heat from the building and transfers it into the ground. This leverages the fact that underground temperatures remain relatively stable throughout the year. According to the Department of Energy, ground temperatures range from 45°F to 75°F throughout much of the U.S. [1]

Water-source heat pumps work on a similar principle, but use bodies of water like ponds or lakes as the heat source and heat sink instead of the ground. They are less common than ground-source systems.

The key components of a geothermal heat pump system include ground loops, a heat pump unit, ductwork, and controls. They leverage principles of heat exchange and HVAC (heating, ventilation and air conditioning) to regulate indoor temperatures. While more expensive to install upfront, geothermal heat pumps can provide major cost savings on heating and cooling over time.

Direct Use of Geothermal Energy

One of the most common direct uses of geothermal energy is for heating swimming pools and spas. The warm water from geothermal reservoirs can be piped directly into pools and spas for heating. This provides a sustainable and inexpensive way to heat water for recreational purposes.

Geothermal energy can also be used to directly heat spaces like homes, offices, greenhouses, and aquaculture facilities. Hot water from geothermal wells can be piped through radiators or underfloor heating systems to provide space heating. Using geothermal heat directly for space heating eliminates the need to burn fossil fuels.

The direct use of geothermal energy is also quite common for agriculture and aquaculture. Greenhouses, fish farms, and livestock facilities often use warm geothermal water for heating and increasing growth rates. The direct heat allows plants and animals to thrive in colder environments.

On a larger scale, geothermal energy can be used to heat groups of buildings through district heating systems. District heating uses pipelines to distribute hot water from a centralized geothermal source to multiple buildings in a community. This allows many structures to take advantage of geothermal energy for heating.

Geothermal Power Generation

Geothermal power plants use geothermal resources to generate electricity. There are three main types of geothermal power plants:

Dry steam plants – which use steam from a geothermal reservoir to directly drive turbine generators. Steam coming from the ground is piped directly into the power plant where it spins turbines to generate electricity. According to the U.S. Department of Energy, the world’s first geothermal power plant was a dry steam plant built in Italy in 1904.
Flash steam plants – which pull deep, high-pressure hot water into lower pressure tanks and use the resulting flashed steam to drive turbines. The steam is separated from the water and used to power turbines while the remaining geothermal fluid is injected back into the reservoir.
Binary cycle power plants – which pass geofluid through a heat exchanger to heat a separate liquid with a lower boiling point that vaporizes and drives the turbines. The advantage of binary cycle plants is that they can operate with lower temperature geofluids than dry and flash steam plants.

As of 2021, geothermal power capacity worldwide amounted to around 17 gigawatts (GW), with the top countries being the United States, Indonesia, and the Philippines. The worldwide geothermal generating capacity has grown at a rate of 5% annually over the past decade.

Sources:

[Electricity Generation](https://www.energy.gov/eere/geothermal/electricity-generation), U.S. Department of Energy

[Geothermal Electricity Production Basics](https://www.nrel.gov/research/re-geo-elec-production.html), National Renewable Energy Laboratory

Geothermal Energy Costs

The costs of geothermal energy are dependent on the type of system being installed. Drilling and installation costs tend to be the most expensive components. According to Forbes, the average cost to drill a geothermal well is $10,000 to $30,000. The overall installation costs range from $8,000 to $24,000 for a standard residential geothermal system (Forbes). ClimateMaster estimates total geothermal installation expenses from $18,000 to $30,000 (ClimateMaster).

In comparison to traditional HVAC systems, geothermal energy costs more upfront but provides savings over time through lower energy bills. Geothermal systems have an estimated payback period of 3-10 years. The U.S. Department of Energy reports geothermal heat pump systems can reduce energy costs by 30-70% compared to conventional heating and cooling systems. Over a 30 year lifespan, geothermal systems can save over $5,000 in maintenance costs and $10,000-$12,000 in energy costs compared to conventional systems (Dandelion Energy).

Future of Geothermal Energy

The future looks bright for geothermal energy. As technology improves, geothermal capacity is expected to expand significantly in the coming years. According to a MIT study, the U.S. has the potential to generate 100 gigawatts of geothermal power by 2050 with improvements in technology. That’s enough to power 100 million homes and represents a huge growth opportunity.

New techniques like enhanced geothermal systems (EGS) could open up geothermal resources in areas that lack natural hydrothermal sites. EGS pumps water underground at high pressures to fracture hot dry rocks, creating an artificial geothermal reservoir. Experts believe EGS could expand geothermal capacity immensely in the coming decades.

Binary cycle power plants are another technology that can boost efficiency and enable lower temperature resources to be utilized. Binary plants use heat exchangers to transfer heat to a secondary fluid with a lower boiling point. The U.S. Department of Energy has set a goal to cut the cost of geothermal power by 50% by 2030 through research and development.

With geothermal able to provide constant baseload power, experts see it playing a key role in balancing intermittent renewables like wind and solar. The future of geothermal looks bright as a flexible, renewable resource that will be an important piece of the global energy transition.