Which Of The Following Describes Geothermal Energy?

What is Geothermal Energy?

Geothermal energy is a renewable energy source that utilizes the natural heat produced inside the earth (1). It is considered renewable because the heat is continuously produced in the earth’s core, replenishing the heat that is extracted (1). Geothermal energy is generated from geothermal reservoirs of hot water located below the earth’s surface. Wells can be drilled into these geothermal reservoirs to tap steam or hot water that can be brought to the surface for direct use or electricity generation (2). Unlike other renewables such as wind and solar which rely on weather conditions, geothermal energy offers a constant and steady flow of heat energy and is therefore considered a baseload renewable resource (3).

There are three main types of geothermal energy systems: hydrothermal, enhanced geothermal systems (EGS), and geothermal heat pumps. Hydrothermal systems utilize natural reservoirs of steam or hot water. EGS create artificial reservoirs by pumping water underground to be heated then brought back to the surface. Geothermal heat pumps use stable ground or water temperatures near the surface for heating and cooling (1).

How Geothermal Energy Works

Geothermal energy utilizes the heat contained below the earth’s surface to generate electricity and provide heating and cooling. The high temperatures below the surface are derived from a combination of radioactive decay in the Earth’s molten core, leftover heat from the planet’s formation, and absorption of sunlight. This geothermal energy manifests itself in the form of hot springs, geysers, and steam vents at various locations around the world. Geothermal power plants are built over these areas to harness the heat energy.

Geothermal power plants operate by drilling wells into underground reservoirs of steam or hot water called hydrothermal resources. The steam or hot water rises to the surface and powers a turbine, which activates a generator to produce electricity. The used geothermal fluid is then returned down an injection well into the reservoir to be reheated, continuing the process.

Geothermal heat pumps can also utilize shallow ground temperatures for space heating and cooling. These systems circulate water or an antifreeze solution through pipes buried just below the Earth’s surface to absorb heat in winter and dissipate heat in summer. The constant 50-60°F temperature of the shallow ground enables efficient heating and cooling.
geothermal energy uses heat from the earth's interior to generate power

So in summary, geothermal energy utilizes the constant heat from the Earth’s interior through steam or hot water reservoirs to generate power, or shallow ground temperatures for heating and cooling. This makes geothermal a stable, renewable energy source.

Types of Geothermal Energy Systems

There are three main types of geothermal energy systems:

Geothermal Heat Pumps

Geothermal heat pumps use the constant temperatures near the surface of the Earth to heat and cool buildings. According to the U.S. Department of Energy, these systems take advantage of the fact that the Earth (10 feet underground) remains at a relatively constant temperature throughout the year. Pipes buried underground can transfer heat between the Earth and a building. In winter, the relatively warm Earth heats the fluid, which is used to warm the air inside. In summer, the relatively cool Earth cools the fluid, which is used to cool the air inside.

Direct Use

Some geothermal reservoirs produce hot water and steam that can be used directly for heating buildings, greenhouses, fish farms and industrial processes. According to the California Energy Commission, hot geothermal fluids can be used directly to provide heat for many applications, from space heating to food preparation.

Deep Geothermal Systems

Deep geothermal resources exist at depths of one to two miles, with water/steam temperatures greater than 150°C. Deep geothermal systems require drilling into hot rock, fracturing the rock to improve permeability, and pumping water through the fractured rock to extract heat. The heated water is used to generate electricity in a power plant.

Advantages of Geothermal Energy

Geothermal energy has several key advantages that make it an attractive renewable energy source:

Renewable – Geothermal energy is considered renewable, as heat is continuously produced inside the earth. With proper reservoir management, geothermal energy can be sustained indefinitely.

Sustainable – Geothermal power plants produce very low emissions and have a small environmental footprint. The energy source itself does not get depleted or run out over time.

Reduces dependence on fossil fuels – Expanding geothermal energy production can help reduce reliance on coal, oil, and natural gas as energy sources. This enhances energy security and stability.

Low emission – Geothermal systems release negligible carbon emissions. They help lower the carbon footprint compared to conventional power generation.

Overall, geothermal energy delivers clean, renewable baseload power with minimal environmental impact.[1] Its advantages make it a key part of the global transition to a sustainable energy future.

Disadvantages of Geothermal Energy

While geothermal energy has many benefits, there are some drawbacks to consider as well. Some of the main disadvantages of geothermal energy include:

High upfront costs – Constructing a geothermal power plant requires significant upfront capital investment. Drilling geothermal wells thousands of feet deep and installing turbines and piping can be an expensive endeavor, often costing millions of dollars. The high initial costs mean geothermal energy may not be economically feasible in some locations.

Specific geographic requirements – Geothermal energy can only be harnessed in areas with adequate underground heat and water resources. This limits widespread adoption of geothermal energy. Favorable locations are often found along tectonic plate boundaries, volcanic hotspots or other areas with elevated subsurface temperatures. For example according to greenmatch.co.uk, only 10% of global electricity generation capacity is feasible using geothermal.

Potential emissions – While geothermal plants emit far fewer greenhouse gases than fossil fuel plants, some geothermal reservoirs contain gases like carbon dioxide, hydrogen sulfide and ammonia that can be released into the atmosphere. Proper well casing and plant design help minimize emissions.

Major Geothermal Energy Countries

Some of the top countries utilizing geothermal energy for power generation include: 1

  • United States – The US generates the most geothermal power in the world, with over 3,800 MW of installed capacity. Major geothermal plants are located in California, Nevada, Utah, Hawaii, Idaho and Oregon.2
  • Indonesia – Indonesia has over 2,400 MW of geothermal capacity and plans to expand further. The country has 40% of the world’s geothermal resources.2
  • Philippines – The Philippines generates almost 20% of its electricity from geothermal, with 1,900 MW of installed capacity.2
  • New Zealand – Around 17% of New Zealand’s electricity comes from geothermal power plants, with over 1,000 MW of capacity.3
  • Iceland – Geothermal supplies over 25% of Iceland’s energy needs. The country has nearly 700 MW of geothermal capacity.3

Geothermal Power Capacity

Geothermal energy currently accounts for a small but growing share of renewable energy capacity globally. According to the International Renewable Energy Agency (IRENA), global installed geothermal power capacity reached about 15 GW in 2022, representing around 0.3% of total global power capacity [1]. The top countries for installed geothermal capacity in 2022 were the United States, Indonesia, Turkey, New Zealand, and the Philippines [2].

Global geothermal power capacity has been gradually increasing over the past decade, rising from around 10 GW in 2009 to nearly 15 GW by 2022 [3]. IRENA projects global geothermal power capacity could reach 21 GW by 2025 and over 40 GW by 2030 under an optimistic scenario. This continued growth will depend on factors like policy support, project development costs, and technological innovation.

With its abundant geothermal resources, experts project countries such as Indonesia, Turkey, Kenya, and Chile will lead capacity growth in the coming decade. Realizing the full global potential for geothermal will require mobilizing investment, streamlining project development, and deploying new technologies like enhanced geothermal systems (EGS).

Geothermal Energy Costs

The cost of geothermal energy depends on the type of system and location. Geothermal power plants cost between $2,000 to $5,000 per installed kW in the U.S., making the levelized cost of electricity (LCOE) range between 4 to 10 cents per kWh[1]. Residential geothermal heat pump systems cost $2,500 to $5,000 per ton capacity, with an average installation cost of a 5-ton system being $15,000 to $30,000. Geothermal energy costs range on the lower end compared to fossil fuels and are competitive with other renewable energy sources.

The LCOE for geothermal power plants is comparable to wind (4 to 7 cents/kWh), hydroelectric (4 to 10 cents/kWh) and natural gas (4 to 8 cents/kWh), and less than solar (6 to 12 cents/kWh) or coal (6 to 14 cents/kWh)[2]. Geothermal’s capacity factor or uptime percentage is higher than wind or solar since it provides constant baseload power. While upfront installation costs for geothermal plants are higher, low maintenance and operating costs make geothermal cost-competitive in the long run.

For residential applications, geothermal heat pumps can reduce energy costs by 40-60% versus conventional HVAC systems. Though initial costs are higher, homeowners can achieve a return on investment in 3-5 years with energy savings[3]. Geothermal offers a clean, renewable energy source that is affordable compared to fossil fuels and competitive with other renewable options.

Environmental Impact

Geothermal energy has several environmental benefits compared to fossil fuels. Since geothermal plants do not burn fuel to generate electricity, they release very low emissions of greenhouse gases like carbon dioxide. The geothermal emissions that do occur come primarily from drill rigs, pumps, and generators at the plant. According to the Union of Concerned Scientists, geothermal plants release on average 97% less greenhouse gases per kilowatt hour than a coal-fired plant.

Geothermal energy also has minimal impacts on air and water quality. Geothermal plants release negligible emissions of pollutants like sulfur dioxide and nitrogen oxides that can contribute to acid rain. The geothermal water brought to the surface does pick up naturally occurring minerals that need to be disposed of properly to avoid contaminating water sources. Proper injection procedures are important for geothermal operations. Overall, the U.S. Energy Information Administration notes geothermal energy has lower emissions than even solar or wind.

However, geothermal sites can release measurable amounts of hydrogen sulfide, a toxic gas that smells like rotten eggs. Facilities need scrubber systems to filter hydrogen sulfide and prevent unsafe emissions. There are also concerns that pumping geothermal reservoir water could deplete the reservoirs over time. Ongoing monitoring helps determine sustainable extraction rates.

Future of Geothermal Energy

There is growth potential for geothermal energy due to recent developments in technology. The Department of Energy predicts that geothermal power capacity in the United States could increase more than 26-fold by 2050, reaching 60+ gigawatts, with growth aided by enhanced geothermal systems and co-produced fluids from existing oil and gas wells (MIT). Advances in deep drilling techniques, subsurface imaging, and controlled hydroshearing can access greater depths and hotter temperatures for enhanced geothermal systems (Yale). New binary cycle turbines can operate with lower temperature fluids, expanding opportunities for geothermal use, including using geothermal for heating and cooling (NREL). Geothermal is poised to help balance the grid as other renewables like solar scale up, providing consistent around-the-clock clean energy.

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