What is Geothermal Energy and How Does It Work for Homes?
- rm3433
- Mar 26
- 14 min read
Geothermal energy is heat within the earth. The word geothermal comes from the Greek words geo (earth) and therme (heat). Geothermal energy is a renewable energy source because heat is continuously produced inside the earth. In Maryland, GRECs (Geothermal Renewable Energy Credits) help promote the adoption of geothermal systems, especially in areas like Prince George and Montgomery. People use geothermal heat for bathing, to heat buildings, and to generate electricity.
Geothermal Energy Comes from Deep Inside the Earth
Geothermal energy originates from the heat stored deep within the earth. The slow decay of radioactive particles in the earth's core, a process occurring in all rocks, continuously generates this renewable energy.
Earth’s Structure and Heat Generation
The earth has four major layers that contribute to geothermal energy production:
Inner Core – A solid iron core, about 1,500 miles in diameter, with extreme temperatures reaching 10,800°F, as hot as the sun’s surface.
Outer Core – A layer of hot molten rock (magma), approximately 1,500 miles thick.
Mantle – A mix of magma and rock, surrounding the outer core, about 1,800 miles thick, with temperatures ranging from 392°F near the crust to 7,230°F at the mantle-core boundary.
Crust – A solid rock layer forming the continents and ocean floors, ranging from 15 to 35 miles thick under land and 3 to 5 miles thick under the oceans.
Geothermal Activity and Heat Absorption
The earth's crust is divided into tectonic plates, and magma rises near the edges of these plates, forming volcanoes. The best geothermal Maryland locations are often near such geological activity, where magma heats underground water and rocks. The deeper these elements are found, the higher their temperature, making them ideal for geothermal energy systems.
Where Geothermal Energy is Found
Geothermal energy is sourced from naturally occurring hydrothermal reservoirs, which are deep underground and not easily detectable from the surface. These geothermal resources reach the Earth's surface in three primary ways:
Volcanoes and fumaroles (openings in the Earth that release volcanic gases)
Hot springs
Geysers
Most geothermal resources are found near the boundaries of the Earth’s tectonic plates, particularly along major tectonic plate boundaries where volcanic activity is most prevalent. One of the most active geothermal areas in the world is the Ring of Fire, a region that encircles the Pacific Ocean and is known for its high concentration of volcanic activity.
When magma rises near the Earth's surface, it heats groundwater trapped in porous rock or water flowing along fractured rock surfaces and faults. These hydrothermal features consist of two main elements: water (hydro) and heat (thermal).
Geologists typically use drilling methods to confirm the presence of geothermal reservoirs. Drilling wells and measuring the temperature deep underground remains the most reliable method for locating geothermal energy resources.
In the United States, most geothermal power plants are concentrated in the western states and Hawaii, where geothermal resources are closest to the surface. California is the leading state in geothermal electricity generation. The Geysers, located in Northern California, is the largest known dry steam field in the world and has been producing electricity since 1960.
How Geothermal Energy is Captured?
Geothermal springs for power plants. Currently, the most common way of capturing the energy from geothermal sources is to tap into naturally occurring "hydrothermal convection" systems, where cooler water seeps into Earth's crust, is heated up, and then rises to the surface. Once this heated water is forced to the surface, it is a relatively simple matter to capture that steam and use it to drive electric generators. Geothermal power plants drill their own holes into the rock to more effectively capture the steam.
There are three basic designs for geothermal power plants, all of which pull hot water and steam from the ground, use it, and then return it as warm water to prolong the life of the heat source. In the simplest design, known as dry steam, the steam goes directly through the turbine, then into a condenser where the steam is condensed into water. In a second approach, very hot water is depressurized or "flashed" into steam which can then be used to drive the turbine.
In the third approach, called a binary cycle system, the hot water is passed through a heat exchanger, where it heats a second liquid—such as isobutane—in a closed loop. Isobutane boils at a lower temperature than water, so it is more easily converted into steam to run the turbine. These three systems are shown in the diagrams below.
The choice of which design to use is determined by the resource. If the water comes out of the well as steam, it can be used directly, as in the first design. If it is hot water of a high enough temperature, a flash system can be used; otherwise it must go through a heat exchanger. Since there are more hot water resources than pure steam or high-temperature water sources, there is more growth potential in the binary cycle, heat exchanger design.
Uses of Geothermal Energy
Geothermal energy can be harnessed in a variety of ways, depending on the depth at which the heat is accessed. Some methods take advantage of the Earth's natural temperatures near the surface, while others involve drilling miles deep into the Earth. There are three main types of geothermal energy systems:
Direct use and district heating systems
Electricity generation power plants
Geothermal heat pumps
Direct Use and District Heating Systems
Direct use and district heating systems tap into hot water from natural springs or reservoirs located near the Earth’s surface. Ancient civilizations, such as the Romans, Chinese, and Native Americans, have long used hot mineral springs for bathing, cooking, and heating. Today, hot springs continue to be used for recreational bathing, with many people believing the mineral-rich waters possess natural healing properties.
In addition to recreational uses, geothermal energy is harnessed for district heating systems, where hot water is piped directly into buildings for warmth. Reykjavik, Iceland, is known for utilizing geothermal energy to provide heating to most of its buildings through a district heating system.
Industrial uses of geothermal energy include processes like food dehydration, gold mining, and milk pasteurizing. Among these, dehydration, which involves drying vegetables and fruit products, is the most common industrial application of geothermal energy.
Geothermal Electricity Generation
Generating electricity from geothermal energy typically requires water or steam heated to temperatures of at least 300°F (149°C). Geothermal power plants are generally located near geothermal reservoirs, which are often found within a mile or two of the Earth's surface (Energy.gov).
In 2023, geothermal power plants in seven U.S. states produced approximately 17 billion kilowatt-hours (kWh) of electricity, accounting for about 0.4% of total U.S. utility-scale electricity generation (EIA.gov). This makes geothermal energy a reliable and consistent source of clean energy.
Environmental Effects
Fluids drawn from underground during geothermal energy production can contain gases such as carbon dioxide (CO₂), hydrogen sulfide (H₂S), methane (CH₄), and ammonia (NH₃). If released, these pollutants can contribute to global warming, acid rain, and unpleasant odors (U.S. Geological Survey). However, geothermal power plants in the U.S. emit significantly lower CO₂ levels compared to fossil fuel power plants, averaging 122 kilograms (269 lb) of CO₂ per megawatt-hour (MWh) (Energy Information Administration).
To minimize emissions, modern geothermal plants use emission-control systems to capture and reduce harmful gases (Environmental Protection Agency). Additionally, new closed-loop geothermal technologies are being developed to eliminate emissions altogether, making geothermal energy an even cleaner alternative (Department of Energy).
Geothermal water may also contain trace elements like mercury, arsenic, boron, and antimony. If improperly managed, these elements can accumulate as the water cools, potentially harming the environment. To address this, most geothermal facilities in the U.S. reinject fluids back into the Earth, reducing environmental risks while helping sustain geothermal reservoirs for long-term energy production (National Renewable Energy Laboratory).
Benefits of Using Geothermal Energy
Several attributes make geothermal a beneficial source of energy, including:
Geothermal resources can be used in multiple ways, including to produce electricity, heat and cool homes and businesses, and provide energy storage.
Geothermal resources are “homegrown” and located in the subsurface, offering a domestic source of secure, reliable energy.
Geothermal energy is available 24 hours a day, 365 days a year, regardless of weather.
Geothermal power plants have a high-capacity factor—typically 90% or higher—meaning that they can operate at maximum capacity nearly all the time. These factors mean that geothermal can balance intermittent sources of energy like wind and solar, making it a critical part of the national renewable energy mix.
Some geothermal plants produce solid materials, or sludges, that require disposal in approved sites. Some of these solids are now being extracted for sale (zinc, silica, and sulfur, for example), making the resource even more valuable. In addition, lithium—a critical material—is present in high concentrations in some geothermal brines. Learning to cost effectively extract that lithium could provide the United States with a domestic source of this important material.
How Does Geothermal Energy Work for Homes?
Geothermal energy provides a highly efficient and sustainable way to heat and cool homes by taking advantage of the relatively constant temperature just a few feet below the Earth's surface. While many parts of the country experience extreme seasonal temperature fluctuations—scorching summers and freezing winters—the ground beneath our feet remains at a consistent temperature year-round. This underground temperature is warmer than the air above it in the winter and cooler in the summer, creating an ideal environment for heating and cooling systems.
Geothermal Heat Pumps (GHPs) work by exchanging heat between a home and the ground through a ground heat exchanger. This system taps into the natural thermal energy storage of the earth, which acts as both a heat sink and a heat source. During the summer, when the outside air is warmer, the GHP absorbs excess heat from the home and transfers it into the cooler ground. In the winter, when temperatures drop, the heat pump pulls warmth from the ground to heat the home, taking advantage of the stable, naturally warm temperature below the surface.
This cycle increases the system's efficiency and helps reduce the energy required to regulate the temperature of your home. By relying on the Earth’s constant underground temperatures, geothermal systems use significantly less energy than traditional HVAC systems, reducing both heating and cooling costs.
A geothermal system isn’t limited to just heating and cooling. Many geothermal heat pumps are equipped with the ability to supply hot water for a home as well, offering an all-in-one solution. Additionally, these systems often come with advanced features such as two-speed compressors and variable fans to enhance comfort while further reducing energy consumption. Compared to traditional air-source heat pumps, geothermal systems are known for being quieter, more efficient, and more durable, often lasting longer with minimal maintenance.
One of the major advantages of geothermal systems is their independence from the outside air temperature, making them more reliable and consistent than systems that rely on fluctuating outdoor conditions. In places with extreme weather patterns, where air-source systems can struggle, geothermal systems remain effective year-round.
Another interesting option is the dual-source heat pump, which combines the benefits of both an air-source heat pump and a geothermal heat pump. These hybrid systems can automatically switch between the two sources depending on which is more efficient at the time, ensuring that the system always operates at peak efficiency based on the home's heating or cooling needs.
Overall, geothermal energy for homes represents an eco-friendly, cost-effective, and efficient solution to climate control, offering long-term savings, a more comfortable living environment, and a sustainable way to reduce reliance on fossil fuels.
Geothermal heat pumps
Geothermal heat pumps use the earth's constant temperatures for heating and cooling
While air temperatures fluctuate throughout the day and with the changing seasons, temperatures just 10 feet below the Earth's surface remain relatively constant year-round. In most areas of the United States, the ground temperature stays between 50°F and 60°F, regardless of the weather above ground. This stable underground temperature is warmer than the winter air and cooler than the summer air, making it a perfect natural resource for heating and cooling. By tapping into this consistent thermal energy, geothermal heat pumps are able to efficiently regulate the temperature of buildings year-round.
Geothermal heat pumps work by transferring heat from the earth (or from groundwater) into a building during the colder months, effectively providing warmth. In contrast, during the summer, the process is reversed. Heat is drawn out from the building and transferred back into the cooler ground, providing effective cooling without the need for conventional air conditioning systems. This exchange of heat with the earth allows geothermal heat pumps to maintain a comfortable temperature inside a building while utilizing the Earth's natural energy.
One of the key benefits of geothermal heat pumps is their remarkable energy efficiency. The U.S. Environmental Protection Agency (EPA) has recognized geothermal heat pumps as the most energy-efficient and environmentally clean systems for both heating and cooling buildings. Unlike traditional HVAC systems that rely heavily on electricity to generate heat or cool air, geothermal systems move heat from the earth into the building or vice versa, using far less energy in the process.
In addition to their energy efficiency, geothermal heat pumps are also cost-effective in the long run. Though the initial installation costs can be higher than traditional heating and cooling systems, geothermal systems typically have a lower operating cost and are more durable, with a lifespan of 20 to 25 years for the heat pump itself and 25 to 50 years for the ground loop. Over time, the reduced energy bills result in substantial savings, making geothermal a great investment for homeowners and businesses alike.
Moreover, geothermal heat pumps are versatile and can be used in a wide range of buildings, from single-family homes and office buildings to schools and hospitals. Their ability to provide consistent heating and cooling, even in extreme weather conditions, makes them an ideal solution for both residential and commercial applications. As more people recognize the long-term cost savings and environmental benefits, the popularity of geothermal heat pumps continues to rise as an effective and sustainable alternative to conventional HVAC systems.
Types of Geothermal Heat Pump Systems
Geothermal heat pump (GHP) systems are typically divided into four main types of ground loop configurations. Three of these—horizontal, vertical, and pond/lake—are closed-loop systems, while the fourth option is an open-loop system. The choice of which system to install depends on a variety of factors, including local climate, soil conditions, available land, and installation costs.
Each of these systems is suitable for both residential and commercial applications, offering flexible solutions for various building types and environmental conditions.
Horizontal systems are often chosen when there is ample land space available. These systems involve trenches dug into the ground where the loop is placed horizontally, making it a cost-effective option in areas with sufficient land area.
Vertical systems are ideal for areas with limited space or where land is not suitable for horizontal loop installations. Vertical systems involve drilling deep vertical wells into the ground, providing a compact solution for smaller properties.
Pond/Lake systems are designed for properties with access to a large body of water. The loop is submerged in the water, offering an energy-efficient way to leverage the thermal properties of the water for heating and cooling.
Open-loop systems use groundwater from a well or other natural water source as the heat exchange fluid. This system is typically more common in areas with a consistent supply of clean groundwater.
To determine the most appropriate system for a specific location, it's important to have an accredited contractor or installer assess the site. They will evaluate the soil, ground conditions, and other factors and provide recommendations based on the intended use and environmental factors, ensuring the most efficient and cost-effective geothermal solution.
Residential Applications of Geothermal Heat Pumps (GHP)
A Geothermal Heat Pump (GHP) system can be installed in residential buildings of any size, whether it’s a single-family home or a multi-family unit. These systems are versatile and can be installed on nearly any size lot, including under lawns, landscaped areas, driveways, or even beneath the house itself. If you’re looking to retrofit an existing home with a GHP, it can often be integrated with the existing ductwork, minimizing the need for significant modifications. Your installer will assess the current system to determine if any adjustments to the ductwork are necessary to accommodate the new system.
Many homeowners and builders can also take advantage of special financing options available in many areas through utility companies or manufacturers, making the initial investment in a GHP more affordable.
Both the Department of Energy (DOE) and the Environmental Protection Agency (EPA) have endorsed Geothermal Heat Pump Systems as among the most energy-efficient, environmentally friendly, and cost-effective solutions for heating, cooling, and water heating (DOE | EPA). A 1993 report by the EPA highlighted geothermal technologies as a key opportunity to reduce energy use and pollution while providing homeowners with reliability, comfort, and long-term savings (EPA Archive).
Key Benefits of Residential GHPs:
Multi-functional: GHPs can serve as both a heating and cooling system, with many models also providing hot water heating, offering a comprehensive solution for year-round comfort.
Energy savings: They can help save up to 50% on water heating costs by preheating your tank water before it reaches the water heater, leading to substantial savings on energy bills.
Long-term reliability: GHP systems are built with durable mechanical components, most of which are either buried underground or housed inside the home, protecting them from outdoor elements. The piping in these systems typically carries a 50-year warranty, ensuring a long service life.
Significant energy efficiency: Geothermal systems can reduce energy consumption by 20-50%, making them one of the most efficient heating and cooling options available. They also cut down on maintenance costs due to their long-lasting design and low wear and tear.
Comfort and consistency: Unlike traditional systems, which can leave certain areas too hot or too cold, GHP systems provide even heating and cooling throughout the entire home, maintaining a consistent temperature year-round. This helps eliminate uncomfortable temperature fluctuations.
Quiet operation: Geothermal systems are designed to operate quietly, providing a peaceful indoor environment. There are no noisy outdoor units, making them ideal for homes with children or pets who may be disturbed by loud machinery.
Safety and aesthetics: With no exposed outdoor equipment or open flames, GHP systems eliminate the safety hazards often associated with traditional heating and cooling systems. They also help preserve the aesthetic appeal of your home’s exterior, as there are no bulky units or fuel storage tanks visible outside.
By making the switch to a geothermal heat pump, homeowners can enjoy significant savings, enhanced comfort, and the peace of mind that comes with a cleaner, more sustainable heating and cooling solution. Whether you're building a new home or retrofitting an existing one, a GHP system is a smart choice for both energy efficiency and long-term value.
The Future of Geothermal Energy in Maryland
Geothermal energy has the potential to play a pivotal role in transitioning Maryland—and other regions—toward a cleaner, more sustainable energy future. As one of the few renewable energy sources capable of providing continuous baseload power, geothermal energy stands out as a reliable, clean, and efficient option.
In Maryland, the cost of geothermal energy has become increasingly competitive, especially when considering the long-term savings on utility bills. Geothermal Maryland price is influenced by various factors such as installation size and type, but state and federal incentives, including the residential geothermal tax credit, are helping to offset these initial costs.
Unlike traditional power plants, binary geothermal plants offer a flexible energy solution that can adjust production based on the variable supply of wind and solar energy. These systems are capable of ramping production up or down multiple times throughout the day, from full capacity to a minimum of 10%, ensuring a stable energy supply.
Prince George's County and Montgomery County, two of Maryland's most populous counties, are also seeing increasing interest in geothermal energy. Residents and businesses in these areas are looking to take advantage of the energy-efficient benefits of geothermal systems, especially as local governments promote sustainability and energy savings initiatives. With strong incentives and an expanding network of geothermal installers in Prince George's County and Montgomery County, homeowners in these areas can make a significant impact on their energy consumption while lowering utility costs.
As the adoption of geothermal energy continues to rise, particularly in Maryland, including Prince George's County and Montgomery County, it will play a crucial role in reducing carbon footprints while providing homeowners with reliable and sustainable energy solutions. With these incentives and advanced technologies, the future of geothermal energy in Maryland looks incredibly promising.
Conclusion: Is Geothermal Right for You?
Geothermal energy is a smart investment for homeowners in Prince George’s County and Montgomery County, offering lower energy costs, eco-friendly benefits, and long-term savings. With available incentives, reduced maintenance, and increasing energy efficiency, installing a geothermal system is a step toward a sustainable future.
For expert guidance, cost estimates, and installation services, contact Maryland Geothermal today! Maryland Geothermal proudly serves communities across both counties, including Bowie, College Park, Greenbelt, Laurel, Hyattsville, Upper Marlboro, Glenarden, New Carrollton, District Heights, Mount Rainier, Riverdale Park, Seat Pleasant, Berwyn Heights, Bladensburg, Brentwood, Capitol Heights, Cheverly, Edmonston, Fairmount Heights, Forest Heights, Landover, Landover Hills, and North Brentwood.
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