What is Geothermal energy?

What is Geothermal energy?

Geothermal energy is a renewable energy source from heat stored beneath the earth’s surface. This heat is derived from the planet’s core, where temperatures reach approximately 5,000°C due to the decay of radioactive materials and residual heat from earth’s formation. 

This intense heat can be harnessed for various applications, including electricity generation and direct heating for homes or businesses alike. Plus, geothermal energy is a renewable resource, unlike fossil fuels, meaning it can be sustainably used over long periods without diminishing its source.

The use of geothermal energy dates back thousands of years. Ancient civilizations, such as the Romans, Chinese, and Native Americans, utilised hot springs for bathing, cooking, and heating. The first geothermal power plant was built in Larderello, Italy, in 1904. Since then, geothermal technology has evolved significantly, becoming a viable alternative to fossil fuels in many parts of the world.

How does Geothermal energy work?

The earth's interior contains immense heat (up to 5,000°C/9,000°F), which creates convection currents in the mantle, causing magma to rise toward the planet's surface. The earth’s crust then acts as an insulator, trapping the heat and creating geothermal reservoirs. Drilling wells can access these reservoirs to tap into the hot water and steam beneath the surface. In certain areas, geothermal heat escapes through volcanic activity, hot springs, and geysers.

Geothermal power plants convert the heat from geothermal reservoirs into electricity by tapping into underground reservoirs of hot water and steam. There are three main types of geothermal power plants:

1. Dry steam plants: These plants directly utilise steam from geothermal reservoirs to drive turbines connected to generators.

2. Flash steam plants: These plants use high-pressure hot water from geothermal reservoirs, which is rapidly decompressed ("flashed") into steam to drive turbines.

3. Binary cycle power plants: These plants transfer heat from geothermal fluid to a secondary fluid with a lower boiling point, which vaporises and drives turbines.

Sources of Geothermal energy

Geothermal energy is primarily found in regions with significant tectonic activity. These areas include:

Tectonic plate boundaries and volcanic activity:

• The movement of Earth's plates creates fractures, allowing heat to escape. Due to the thinner crust and geological activity, heat from the Earth's core is more easily accessible in these regions. The Pacific Ring of Fire is a prime example of a region rich in geothermal resources.

Hot springs, geysers, and underground reservoirs:

• These natural features are visible indicators of geothermal activity. They occur when groundwater is heated by geothermal reservoirs and rises to the surface. A prime example is Yellowstone National Park’s geysers, which are located in the US. 

Enhanced Geothermal Systems (EGS):

• An advanced technology that enhances the permeability of geothermal reservoirs. This involves injecting water into hot rock formations to create or expand fractures, allowing for greater heat extraction. 

Types of geothermal energy systems

There are four main types of geothermal energy systems, three of which we discussed earlier. Let’s take a look:

1. Dry steam plants

Dry steam plants are the simplest and oldest type of geothermal power plant. They directly use steam from geothermal reservoirs to drive turbines connected to generators. Dry steam plants are most effective in areas with naturally occurring steam reservoirs.

2. Flash steam plants

Flash steam plants use high-pressure hot water from geothermal reservoirs. When the hot water reaches the surface, it is rapidly decompressed or "flashed" into steam, which then drives turbines connected to generators. These plants are the most common geothermal power plant, as they can operate in a broader range of geothermal conditions.

3. Binary cycle power plants

Binary cycle power plants transfer heat from geothermal fluid to a secondary fluid with a lower boiling point. The secondary fluid vaporises and drives turbines connected to generators. These plants are beneficial because they can operate with lower-temperature geothermal resources, making them more versatile and environmentally friendly.

4. Geothermal heat pumps for residential use

Geothermal heat pumps (GHPs) are a residential application of geothermal energy. They use the stable temperatures of the Earth's subsurface to heat and cool buildings. GHPs consist of a heat pump, an air delivery system, and a series of pipes buried in the ground (the ground loop). In the winter, the heat pump extracts heat from the ground and transfers it indoors. In the summer, the process is reversed, and heat is extracted from the building and transferred back into the ground.

Benefits of Geothermal energy

Harnessing geothermal energy has several benefits. Arguably, the most popular is that it is a renewable resource. The Earth's natural heat production processes continuously replenish it. Unlike fossil fuels, geothermal energy does not face depletion, making it a sustainable option for long-term energy needs.

Geothermal power plants also produce lower carbon emissions than coal or natural gas plants, which is a definite plus for the environment.

Unlike solar and wind energy, geothermal energy is not dependent on weather conditions and provides a stable power supply. Therefore, it is very reliable and consistent.

Harnessing geothermal energy is cost-effective financially. Although initial installation costs are high, geothermal systems have lower operational and maintenance costs, leading to long-term savings.

Environmental impact of Geothermal energy

Compared to fossil fuels, geothermal energy has a significantly lower environmental footprint. Key environmental considerations include:

• Land Use: Geothermal plants require less land compared to wind or solar farms.

• Water Usage: Some geothermal plants consume water for cooling, but closed-loop systems recycle fluids to minimise depletion.

• Potential Risks: Enhanced geothermal systems may induce minor seismic activity such as earthquakes due to fluid injection into rock formations. Drilling can also impact local ecosystems.

Applications of Geothermal Energy

Electricity generation in power plants

Geothermal energy is primarily used for electricity generation in power plants. These plants harness the heat from geothermal reservoirs to produce steam, which drives turbines connected to generators. Geothermal power plants provide a reliable source of renewable energy to the grid.

Residential and commercial heating and cooling

Geothermal heat pumps (GHPs) heat and cool buildings in residential and commercial settings. They use the stable temperatures of the Earth's subsurface to provide efficient and cost-effective climate control. This technology can significantly reduce energy consumption and greenhouse gas emissions compared to traditional heating and cooling systems.

Agricultural and industrial uses

Geothermal energy has various agricultural and industrial applications. In agriculture, geothermal heat can be used for greenhouse heating, soil warming, and drying crops. In industrial settings, geothermal energy can be used for processes like drying materials, pasteurising products, and heating water. These applications can improve efficiency and reduce reliance on fossil fuels.

Geothermal energy presents a sustainable and reliable alternative to fossil fuels. Its low environmental impact, consistent energy generation, and cost-effectiveness make it an attractive option for meeting global energy demands. By harnessing the Earth's natural heat, geothermal energy can play a significant role in the transition to a cleaner and more sustainable energy future. As technology advances, geothermal energy will play a crucial role in this transition.

Ultimately, geothermal energy offers a promising, eco-friendly solution for reliable and long-term power generation.