How Electricity is Generated from Geothermal Energy: A Sustainable and Efficient Solution

Geothermal energy is a renewable energy source that uses the natural heat stored beneath the Earth’s surface. While solar panels convert sunlight into electricity and wind turbines harness the movement of air, geothermal power plants use underground heat to produce electrical energy.

But how is electricity generated from geothermal energy?

In simple terms, wells access underground reservoirs containing hot water or steam. This geothermal resource transfers heat to a power-generation system, where steam or another working fluid drives a turbine connected to a generator. The resulting electricity can then be delivered to the grid.

Unlike solar and wind generation, geothermal energy is not directly dependent on sunshine or wind conditions. This ability to provide stable renewable power makes it an interesting part of the transition towards a more diversified, low-carbon electricity system.

In this guide, we’ll explain how geothermal energy generates electricity, the different types of geothermal power plants, its advantages and limitations, and the role this renewable resource can play in the future of electricity generation.

 

What Is Geothermal Energy?

 

Geothermal energy is thermal energy stored beneath the Earth’s surface. This heat originates from the Earth’s interior and can be found in underground rocks and fluids at different depths and temperatures. Depending on the characteristics of the resource, geothermal energy can be used for several purposes, including:

• Electricity generation
• District heating
• Domestic hot water
• Industrial processes
• Heating and cooling buildings through geothermal heat-pump systems

However, it is important to distinguish between geothermal electricity generation and geothermal heating and cooling. Producing electricity generally requires access to sufficiently hot geothermal resources, usually located deeper underground. Ground-source heat pumps, by contrast, can use relatively shallow ground temperatures to heat and cool individual buildings without generating electricity.

 

How Does Geothermal Energy Generate Electricity?

 

The process of generating electricity from geothermal energy begins underground. Natural geothermal systems generally require heat, fluid and sufficient permeability to allow the fluid to move through hot underground rocks.

Wells are drilled to access these geothermal resources and bring hot water or steam towards the surface. The exact process depends on the type of geothermal power plant, but electricity generation generally follows several stages.

1. Accessing Underground Geothermal Heat

Production wells are drilled into areas containing suitable geothermal resources. Hot water or steam travels through these wells towards the surface, carrying thermal energy stored underground.

The temperature and physical characteristics of the geothermal fluid determine which electricity-generation technology can be used.

2. Using Heat to Drive a Turbine

Once the geothermal resource reaches the surface, its energy is used to produce the vapour needed to rotate a turbine.

• In some geothermal plants, naturally occurring steam can be used directly.
• In others, high-pressure geothermal water is converted into steam by reducing its pressure.

Lower-temperature resources can also be used in binary-cycle systems, where geothermal heat is transferred to a separate fluid with a lower boiling point.

3. Converting Mechanical Energy into Electricity

The rotating turbine is connected to a generator. As the turbine turns, the generator converts mechanical energy into electrical energy through electromagnetic induction.

This is the fundamental step through which geothermal heat is converted into electricity.

4. Delivering Electricity to the Grid

The electricity generated at the power plant passes through electrical equipment and transformers so that it can be delivered efficiently to the electricity network. From there, geothermal electricity becomes part of the wider power supply available to homes, businesses and industry.

5. Returning Geothermal Fluids Underground

In many geothermal power plants, the cooled geothermal fluid is reinjected into the underground reservoir after its heat has been extracted. Reinjection helps manage the geothermal resource and can contribute to maintaining reservoir pressure and long-term operation.

The complete process therefore involves extracting underground heat, converting it into electricity and managing the geothermal resource so that it can continue providing energy.

 

Types of Geothermal Power Plants

 

There are three main types of geothermal power plants used to generate electricity: dry steam, flash steam and binary cycle. The most appropriate technology depends largely on the temperature and characteristics of the geothermal resource.

Dry Steam Power Plants

Dry steam plants use geothermal reservoirs that naturally produce steam. The steam travels directly from underground wells to a turbine. The turbine rotates a generator, which produces electricity.

Afterwards, the steam is condensed and the resulting fluid can be reinjected underground. Dry steam technology is the oldest type of geothermal electricity generation, although geothermal resources that naturally provide suitable steam are relatively uncommon.

Flash Steam Power Plants

Flash steam plants use very hot geothermal water stored underground under high pressure. When this fluid reaches a lower-pressure environment at the surface, part of the hot water rapidly turns — or “flashes” — into steam.

This steam drives a turbine connected to a generator. The remaining geothermal fluid can then be processed further or reinjected into the reservoir.

Flash steam is one of the established technologies used for geothermal electricity production where high-temperature resources are available.

Binary-Cycle Power Plants

Binary-cycle plants operate differently. Instead of sending geothermal steam directly through the turbine, geothermal water passes through a heat exchanger.

Its heat is transferred to a secondary working fluid that has a lower boiling point than water. This secondary fluid vaporises and drives the turbine, while the geothermal fluid remains within a separate closed system before being returned underground.

An important advantage of binary-cycle technology is that it can make electricity generation possible with lower-temperature geothermal resources than traditional dry steam or flash systems.

 

What Are the Benefits of Electricity Generation from Geothermal Energy?

 

Geothermal electricity has several characteristics that distinguish it from other forms of renewable generation.

Renewable Energy

Geothermal energy uses heat naturally present beneath the Earth’s surface. When geothermal reservoirs are properly managed, they can provide renewable energy over long operating periods.

Reliable Electricity Generation

One of geothermal energy’s most important advantages is its ability to generate electricity independently of short-term weather conditions. Solar electricity depends on available sunlight and wind generation varies according to wind conditions. Geothermal power plants with access to an appropriate resource can provide electricity much more continuously.

The U.S. Department of Energy notes that geothermal plants can achieve capacity factors of 90% or more, meaning they can generate electricity during a very high proportion of the year. This makes geothermal energy particularly interesting as a complement to variable renewable technologies.

Low-Carbon Electricity

Geothermal electricity generally produces substantially lower greenhouse gas emissions than electricity generated from fossil fuels. It is not completely impact-free: drilling, construction and plant operation have environmental effects, and some geothermal resources can release naturally occurring gases.

Nevertheless, geothermal energy is considered an important low-carbon renewable technology.

Small Surface Footprint

Geothermal power generation can produce substantial amounts of energy from installations with a relatively concentrated surface footprint. However, the actual environmental impact depends on the project, geological conditions and infrastructure required.

 

What Are the Challenges of Geothermal Electricity?

 

Although geothermal energy offers important advantages, it also has limitations. One of the biggest challenges is location. Electricity cannot be generated economically from geothermal energy everywhere because suitable underground temperatures, fluids and geological conditions are required.

Exploration and drilling can also involve significant upfront costs and geological uncertainty. Before developing a geothermal power plant, extensive geological studies are normally required to determine whether a commercially viable resource exists. Other challenges can include:

• High initial exploration and drilling costs
• Geological and financial risk
• Complex permitting requirements
• The need for specialised technical expertise
• Appropriate management of geothermal fluids
• Potential local environmental impacts

These factors help explain why geothermal electricity has expanded more slowly than technologies such as solar photovoltaic and wind power in many markets.

 

Geothermal Electricity vs Geothermal Heating: What’s the Difference?

 

This distinction is particularly important for homeowners. On one hand, geothermal electricity generation uses sufficiently hot underground resources to produce electricity at power-plant scale. On the other hand, geothermal heating and cooling can use ground-source heat pumps to exchange heat with the relatively stable temperature beneath the surface.

A ground-source heat pump does not generate electricity. It consumes electricity to transfer heat between a building and the ground. During winter, it can extract heat from the ground to help warm a property. During summer, the process can be reversed so that heat from the building is transferred into the ground.

This means that when homeowners hear about “geothermal energy”, the technology available for an individual property is usually very different from the deep geothermal systems used to generate electricity.

 

Geothermal Energy in Europe and Spain

 

Geothermal energy currently represents a relatively small part of Europe’s renewable electricity generation, but European institutions see potential for further development. According to the European Commission, geothermal energy can contribute both to renewable electricity generation and to the decarbonisation of heating and cooling.

At EU level, geothermal accounted for around 0.5% of renewable electricity generation, according to the Commission’s latest published figures, while approximately 1 GW of net geothermal electricity capacity was installed in the EU. The technology is receiving increasing attention because it can provide stable renewable energy and complement weather-dependent resources such as solar and wind.

In Spain, geothermal resources can also be used for different applications depending on temperature and geological characteristics. However, geothermal electricity is currently much less prominent in the Spanish electricity mix than solar, wind or hydropower.

For consumers and property owners in Spain, geothermal solutions are therefore more commonly discussed in relation to heating and cooling, while solar photovoltaic self-consumption is much more widely accessible for generating renewable electricity directly at homes and businesses.

 

The Future of Geothermal Electricity Generation

 

The future of geothermal energy is not limited to conventional natural reservoirs. New technologies are being developed to expand the number of locations where underground heat could potentially be used for electricity generation.

One important area is Enhanced Geothermal Systems (EGS). These technologies aim to access hot underground rock where natural permeability or fluid availability would otherwise be insufficient for conventional geothermal electricity generation.

Other developments include closed-loop geothermal systems, improved drilling techniques and technologies capable of using lower-temperature geothermal resources. At European level, geothermal energy is also receiving greater policy attention as governments look for renewable technologies capable of supplying both stable electricity and low-carbon heating.

Geothermal is therefore unlikely to replace solar or wind generation, but it could become an increasingly valuable complement within a diversified renewable energy system.

 

Frequently Asked Questions About Geothermal Electricity

 

How is electricity generated from geothermal energy?

Wells access hot underground fluids or steam. The geothermal heat is then used directly or indirectly to produce vapour that drives a turbine connected to an electrical generator. The electricity produced can then be supplied to the grid.

How does geothermal energy generate electricity?

Geothermal energy generates electricity by converting underground thermal energy into mechanical energy and then electrical energy. Heat from geothermal resources drives a turbine, and the turbine powers a generator.

What are the three types of geothermal power plants?

The three main technologies are dry steam, flash steam and binary-cycle power plants. The technology used depends mainly on the temperature and physical characteristics of the geothermal resource.

Is geothermal energy renewable?

Geothermal energy is classified as a renewable energy source. Sustainable operation depends on appropriate management of the underground geothermal resource.

Can geothermal energy generate electricity all day?

Geothermal power plants can generally operate independently of sunlight or wind conditions and can achieve very high capacity factors. This allows geothermal to provide more continuous renewable electricity than weather-dependent technologies.

Can a house generate electricity with geothermal energy?

Conventional geothermal electricity generation normally requires deep, high-temperature resources and specialised power-generation infrastructure. Residential geothermal installations are more commonly used for heating and cooling through ground-source heat pumps rather than electricity generation.

 

How Electricity Is Generated from Geothermal Energy: A Renewable Solution

 

Understanding how electricity is generated from geothermal energy shows how the Earth’s natural heat can become a useful source of renewable power. From drilling wells and accessing geothermal reservoirs to driving turbines and generators, geothermal electricity combines geology and engineering to produce energy that is renewable, low-carbon and capable of operating independently of short-term weather conditions.

Its potential is not unlimited. Suitable geological resources, substantial initial investment and careful reservoir management are essential. Nevertheless, geothermal energy can complement solar, wind and other renewable technologies as electricity systems continue their transition towards lower-carbon generation.

For homeowners and businesses in Spain, renewable energy can also be adopted directly through technologies such as solar self-consumption.

At Evergreen Eléctrica, we help homeowners, international property owners and businesses understand their energy consumption and explore renewable energy solutions adapted to their needs. From electricity optimisation to solar self-consumption, battery storage and EV charging, our team provides personalised advice to help you reduce long-term energy costs and make smarter energy decisions.

Request your personalised energy study and discover which renewable energy solutions are right for your property.