Geothermal energy is produced using the heat from the earth’s core. It is a renewable source of energy that can be used for heat or electricity. The majority of heat produced by the core is generated by the decay of radioactive isotopes which is a continuous process. Temperatures in the earth’s core can rise above 5000 degrees Celsius and the heat radiates out and warms water, rocks, gas and other geological material.

Magma is an example of heated material that heats nearby rocks and water. This water can be released through hot springs, steam vents, underwater hydrothermal vents, geysers, and mud pots. These are all sources of geothermal energy in which the heat or steam can be captured and used either for heat or electricity. However, most of the earth’s geothermal energy remains under the surface and is accessed by drilling.

Low Temperature Geothermal Energy

Geothermal energy can be accessed almost anywhere in the world, some areas such as Iceland have more natural supplies of geothermal energy which provides them with a safe and abundant source of energy. Low temperature geothermal energy refers to geothermal heat that can be accessed and used as an immediate source of heat. Most low temperature pockets are found just a couple of meters underground and are typically around 150 degrees Celsius. Low temperature energy is best used for heating spaces such as greenhouses, homes, and industrial processes.

Historically, geothermal energy has been used worldwide from as long as 10,000 years ago. The city of Bath in England is home to one of the most famous hot spring spas which was built by the Romans and utilises heat from low temperature geothermal energy.

Co-produced Geothermal Energy

This method of using geothermal energy relies on the water that has been heated as a byproduct of oil and gas wells. Previously, this was considered waste material and wasn’t utilised however it has been recognised as an alternative source of energy and the steam produced is used to generate electricity. Co-produced geothermal energy sources have the potential to supply significant amounts of electricity with minimal emissions and at a low cost. This method of using geothermal energy is very cost effective and a study from the University of North Dakota concluded that this process would pay for itself in around 7 years.

Geothermal Heat Pumps

Although many parts of the world experience extreme changes in temperature throughout the year, under the earth’s surface, the temperature remains fairly consistent all year round. This temperature is cooler than the air in the summer and warmer than the air in winter and geothermal heat pumps use this as an advantage by exchanging heat with the earth.

A geothermal heat pump is a pipework system that is usually around 100m long that is buried underground, they can be horizontal or vertical, depending on the available space. After installation, the land that was disturbed can be returned to its original purpose so there is no disturbance after installing the pipework. Liquid is pumped through the system and is heated up by the earth. A compressor raises the temperature of the fluid before a heat exchanger transfers the heat to a separate body of water. It then circulates around the central heating system and cools before being released back into the pipework, this cycle repeats to keep your home warm.

Geothermal heat pumps use electricity as its source of power however the emissions that are produced are still less than those from other conventional forms of heating. Connecting these systems to a renewable source of energy is also a possibility.

Harvesting Geothermal Energy

In some areas, heat can exist underground as hot water or steam however most of the time, areas need to be injected with water to create steam. The geothermal energy required to generate sufficient amounts of electricity is typically found a few kilometres underground.

• Dry steam power plants use natural sources of steam to generate electricity by pumping the steam into a power plant which turns turbines and generates energy.
• Flash steam power plants use sources of extremely hot water which is pumped into a low-pressure area. The water that evaporates into steam is used to propel a turbine and generate electricity and any remaining water is reused.
• Binary cycle power plants are a recent advancement in geothermal technology. They produce energy from geothermal sources of a temperature less than 150 degrees Celsius. The hot water is circulated in a pipe and heats a liquid with a lower boiling point than water, this liquid then creates steam which is then used to drive a turbine and generate electricity.

Advantages

• It is eco-friendly. Geothermal energy doesn’t involve any form of combustion meaning that it gives off very little, if any greenhouse gases. It also does not contribute to global warming or climate change and as it is underground, it is not visible.
• It is a renewable source of energy as the earth will continue to provide heat from its core for billions of years.
• Geothermal energy is reliable as it can be utilised all year round and in any weather conditions, thus making it a constant source of energy.
• It is widely available around the world.
• Geothermal energy creates many jobs for workers in areas where plants are built. These areas tend to be rural meaning that the employment opportunities that come with geothermal energy plants can be life changing for some.
• It is a more efficient source of energy than other renewables, the only energy lost is during the transport from the earth to the surface.

Disadvantages

• There is a high initial cost when installing systems and extracting energy. Drilling holes in the ground is costly and most of the time studies must be carried out before installation which are usually expensive.
• Geothermal power plants increase risk of earthquakes and movement in the earth. Although not severe, the risk is still there.
• Although internal heat is present everywhere under the earth’s surface, it cannot be used in all places.
• Geothermal energy can emit toxic emissions. Greenhouse gases are present under the earth’s surface, and these tend to be higher near geothermal power plants. If a leak occurred, there is a possibility that toxic substances such as hydrogen sulphide, arsenic or ammonia could be released.
• A source of power is required for geothermal heat pumps to function. These can be renewable energy sources but sometimes electricity is used.
• Geothermal heat may die down or run out after years of activity.
• Where geothermal energy sites are located far from the population, distribution systems are required which increases overall cost.