Where is Geothermal Energy stored and how is it used to generate electricity? Pros and Cons of Geothermal Energy

What’s the definition of geothermal energy?

The word “Geothermal” consists of two words: “Geo”, which means the Earth and “Thermal”, which stands for heat. Geothermal energy is stored in rocks beneath Earth’s surface, because enormous amounts of thermal energy are released due to radioactive decay in the inner layers of the Earth (the Inner and Outer Core, the Mantle and Crust).

This thermal energy heats up water (up to 300 degrees Celcius) in underground reservoirs, resulting in water breaking though the surface as steam / liquid, also known as Geyser.

The natural energy reserves in 10 km of Earth’s crust are equal to 10²⁷ joules. In comparison, the current global energy consumption is around 580 million terajoules (5,8 x 10²⁰ joules). According to theworldcounts.com .

Therefore, geothermal energy has a potential to last for several hundred million years! However, at the moment, it accounts for only 1% of the total energy capacity.

Let’s explore different ways of using geothermal energy and obstacles, which prevent us from fully extracting it.

Dry Steam Power Plant

In dry steam power plant wells are dug at a depth of 3-10 km, until the temperature reaches few hundreds degrees. The steam from underground reservoirs rises and spins turbines connected to electric generator.

Flash Steam Power Plant

In this power plant hot water is pumped up from underground and converted into steam to turn generator turbines. The steam then cools and condenses to water. It is piped back into the ground for reuse, making it a sustainable resource.

Binary Cycle Power Plant

In binary cycle power plant one fluid is pumped up from the underground, which then heats another liquid with lower boiling point. The latter “working fluid” spins the generator turbines. Binary cycle power plants operate on lower-temperature waters, that is, 74°–177°C. The “working fluid” is usually an organic compound with a low boiling point such as isobutene (e.g., isopentane, propane, freon, or ammonia). According to www.sciencedirect.com.

Enhanced Geothermal Systems (EGS)

Enhanced geothermal systems is a way to generate heat and electricity without the need for natural geothermal resources. Wells are drilled into a formation of hot rock, then fluid at high pressure is injected under precise conditions. This causes existing fractures to open wider. The heat can propagate further towards the surface, enabling to use the thermal energy to generate electricity.

Top Countries in terms of geothermal energy capacity

Energy capacity is the maximum level of electric power that a power plant can supply in certain time period under precise conditions. The total world geothermal energy capacity was equal to 14,075 MW in 2020.

Here is a list of countries, which have the greatest geothermal energy capacity in 2020:

1. USA: 2,587 MW
2. Indonesia: 2,131 MW
3. Philippines: 1,928 MW
4. Turkey: 1,613 MW
5. New Zealand: 984 MW
6. Mexico: 906 MW
7. Kenya: 824 MW
8. Italy: 797 MW
9. Iceland: 756 MW
10. Japan: 525 MW

The updated list of countries with greatest geothermal energy capacity in 2022:

Although Iceland does not have the greatest energy capacity, it has one of the highest energy capacity per capita, which is equal to around 2000 W per resident. Moreover, Geothermal sources account for 66% of Iceland’s primary energy use. The the biggest geothermal power plants in Iceland are: Nesjavellir (120 MW), Reykjanes (100 MW), Hellisheiði (303 MW), Krafla (60 MW), and Svartsengi (46.5 MW).

However the biggest power plant in the world, the Geysers Geothermal Complex, is located north of San Francisco, USA. It’s energy capacity is equal to 900 MW.

Advantages of geothermal energy

• Environmentally friendly. Firstly, at geothermal power plants no fossil fuels are burned. For example, Binary Cycle Power Plant is a closed loop system, thus the amount of greenhouse gases is at its minimum. Additionally, closed loop geothermal energy power plant release 80% less CO2 than natural gas power plants.

• Amount & Availability. Geothermal energy can last for for several hundred million years. Furthermore, it generates electricity 24/7, all year round. This is impressive, compared to solar and wind energies, which depend on weather conditions.
• Renewable. Geothermal energy is a renewable source of energy, because steam in Flash Steam Power Plant can be pumped back and reused.
• Small Land Footprint. Geothermal energy does not require large areas of installation. For instance, Climeon produces compact units, which are able to power houses.

Geothermal Energy compared to other energies

Around the world geothermal energy still accounts for only a small fraction of the total energy capacity. Why is this the case?

Disadvantages

• Pollution. Open cycle geothermal plants release far more greenhouse gases (Carbon dioxide, Methane, Sulfur dioxide) than the close cycle plants. Open cycle plant means the steam / liquid used to spin the turbines is dumped into the atmosphere or rivers, contaminating them. According to the diagram below, geothermal releases 3 times more CO2 per kWh than Solar, around 7 times more than Hydro and 14 times more than Wind!

• High Costs. Most geothermal power plants need high temperatures to produce steam, which in turn rotates turbines and generates electricity. There is a need of deep wells, which incurs huge costs. For example 4km well requires 5 million USD investment. The expense skyrockets with each additional km. So 10 km well costs 20 million USD.

According to the report by IEA (diagram above) the median cost of generating electricity using geothermal energy is 99 USD/MWh, while the median cost for wind energy (onshore) is 50 USD/MWh.

• Surface Instability / Earthquakes. Although very rare, drilling of wells can lead to instability underground, which can lead to earthquakes at the surface of the earth. Let’s look at two cases, where geothermal energy power plant construction was to blame for damages and injures.

First case: Pohang Earthquake.

“In March 2019, a government-commissioned research team in South Korea concluded after a year-long study that the 5.4-magnitude earthquake that rattled the city of Pohang in November 2017 was triggered by geothermal power generation.

A government-led renewable energy project was scheduled to build South Korea’s first geothermal power plant in Pohang’s Heunghae township by 2018. Different from a traditional geothermal system, which uses underground heat released naturally from the earth to generate electricity, Pohang’s enhanced geothermal system cracked open impermeable rocks to create conduits and infuse water with high pressure to bring the underground heat to the surface.

The government research team’s report concluded that the drilling and infusing process initially created microearthquakes around the facility, but the accumulated pressure from the water injections over time ultimately led to the Pohang earthquake, the second-largest earthquake in South Korean history. The quake left 1,800 people displaced and 135 injured as well as damaging 57,000 structures that cost around 144.5 billion won ($123 million) to repair.” – Juheon Lee, The Diplomat.

Second case: Staufen, Germany.

In 2007 the mayor of a small city called Staufen in Germany announced his will to heat houses using geothermal energy. The drilling project did not go as planned.

The drill went through a Keuper layer and into a reservoir that contained warm water under high pressure. The lower part of the Keuper layer has a fairly high content of clay and shale. It blocked water from upper Keuper layer. When drilled the water begun to rise and leaked into the upper part of the Keuper layer. The layer consists of calcium sulphate, which reacts with water to form gypsum. The gypsym has a higher volume, so the layer started to expand. This raised some parts of the city, leading to cracks in buildings.

As a result, people were evacuated from some parts of the city. However, some people chose to stay in Staufen, despite the problem. Currently, the rising of the ground has stopped and people are living in the city.