Geothermal Energy — Part 1
An introduction to the technology, its current state, and its future
Many of the traditional renewable energy technologies, such as solar and wind energy, are well known and receive lots of attention from the media and investors. Geothermal energy is less known, even though it has been around for decades. It is increasingly becoming more viable with new technological advancements and has a significant potential role to play in the energy transition. To help shed light on the technology, we are going to take a deep dive into what geothermal energy exactly is, the current state of the technology, and its potential.
Introduction to geothermal energy
A brief history of geothermal energy technology
Geothermal energy is energy contained as heat in the Earth’s surface. People have been making use of geothermal energy in the form of heat for hundreds of years, the Chinese used a hot spring to warm up a stone pool in the 3rd century BC, and the Romans utilized a hot spring for underfloor heating in the first century AD. It wasn’t until the very beginning of the 20th century that geothermal energy was actually used on a larger, industrial scale. In 1904, the first geothermal power generator was developed and tested in Larderello, Italy, generating just enough electricity to light four lightbulbs. This led to the development of the first commercial geothermal power plant in 1911. It took more than 50 years before the next geothermal power plant was developed, namely in 1958 in New Zealand. The first modern geothermal power plant that generated electricity in the U.S. started its operations in 1960 and ran for more than 30 years. Simultaneously to the development of geothermal power plants lies the development of geothermal heat pumps. Heat pumps were invented in the 19th century but were not commercially realized until the 1940s. They are systems that utilize the relatively constant temperature of the ground(water) at a depth of about 10–150 meters / 33–165 feet.
Geothermal energy for heating
Four types of geothermal systems are identified; hydrothermal, hot dry rock, geopressured and magmatic. Currently, only hydrothermal systems are exploited due to the technological advancements needed for the other three systems. Recent developments are made in hot dry rock geothermal systems, but these are not yet commercially utilized. Geothermal energy can be used in two distinct ways, for heating houses, buildings, and industries, or for creating electricity. Geothermal energy is available everywhere, however, it is easier to utilize in some geographical locations. Certain locations, such as Iceland, have the advantage that the earth’s heat is closer to the surface, which can be seen in the form of hot springs.
Depending on the size of the developed system (a few houses connected versus an industrial facility), a distinction is made between heat pumps and deep geothermal wells. Heat pump systems are usually closer to the surface, at a depth of 10–150 meters / 33–165 feet. Deep geothermal wells can be situated anywhere between 500 and 4000 meters (1640–13100 feet) and typically involve much higher temperatures and pressures. Heat pumps typically pump water through a closed underground system, which is being warmed up by the stable temperature of the subsurface. This warmed water is then used to heat houses and buildings.
At deep geothermal energy projects, a well is drilled into a hydrothermal reservoir. This reservoir then provides a steady stream of hot salt groundwater. The hot salt groundwater is pumped to the surface, where a heat exchanger extracts the heat from the salt groundwater. A heat exchanger is an installation that transfers the heat from the salt groundwater towards freshwater. This heated freshwater is then transferred to industries and/or city heating networks. A disposal system injects the cooled down salt groundwater back into the deep underground. The cooled groundwater will be released back into the ground at the same depth as where the water was initially extracted, but at a certain distance from the extraction point. This distance enables the cooled down groundwater to regain its original temperature so that it does not affect the temperature of the groundwater near the extraction point. This prevents the hydrothermal system from cooling down and becoming less efficient.
Geothermal energy for creating electricity
The cornerstone towards being able to create electricity using the earth’s heat, geothermal systems need to be able to reach high temperatures. These temperatures can only be reached in certain geographical locations with natural springs, or at extreme depths. Geothermal projects where electricity is created are thus often referred to as ‘ultra-deep geothermal’ projects.
A clear distinction between deep geothermal and ultra-deep geothermal energy does not exist, however, a general consensus of when one talks about ultra-deep geothermal projects is when the reservoirs are situated at a depth of minimal 4000 (13100 foot) meters and when a temperature of at least 120℃ (250 Fahrenheit) is reached. At these depths, water vapor is being pumped to the surface, which is used to drive a steam turbine, creating electricity. Just like in deep-geothermal heating projects, the cooled down water is being injected back into the ground at the same depth it was extracted, but at a certain distance from the extraction point. Creating efficient geothermal systems at these depths is technically complex and not everywhere possible. A solution for this is in Enhanced Geothermal Systems, which we will discuss later on.
Advantages of geothermal energy
Geothermal energy is seen as a form of renewable energy, with very low to negligible C02 emissions. Heating houses, office buildings and industry with heat from geothermal reservoirs significantly reduces CO2 emissions in comparison with heating these buildings by means of traditional fossil fuels. An average of 88 percent decrease in CO2 emissions, compared to natural gas, is obtained with current deep geothermal projects. Furthermore, geothermal energy can be produced independently from local weather circumstances and can thus provide energy (heating, electricity) every day throughout the entire year, whereas wind and solar energy show seasonal fluctuations. Additionally, geothermal energy plants can be used longer than most other renewable energy technologies. A geothermal reservoir can be used for minimally 30 years, compared to 20–25 years for solar panels and wind turbines. A last, and significant, benefit from geothermal energy is that there is no extraction from the ground; the net pressure stays the same. With gas and oil production the pressure in the reservoir changes significantly, resulting in soil subsidence.
Current state of geothermal energy
As countries and companies are increasingly trying to become more sustainable and less dependent on oil and natural gas, geothermal energy starts to get more attention. In 2015, the Dutch Ministry of Economic Affairs and Climate Policy stated that ‘geothermal energy can be seen as a promising technology to supply the country with a renewable form of heating and decrease its dependence on natural gas’. The top three global countries for geothermal energy production in the world are the U.S. with 3.4GW capacity, the Philippines with 1.8GW and Indonesia with 1.6GW. The EU has a combined capacity of just over 1GW, of which Italy is by far the largest player with a capacity of 915MW. There are some countries, such as Turkey, which are specifically pushing for geothermal energy development. Turkey has doubled its geothermal energy capacity between 2016 and 2018 to 1.3GW and targets to have more than 7GW of geothermal capacity by 2025, providing sustainable energy and heating for millions of households.
The International Energy Agency expects global geothermal power capacity to reach more than 17GW by 2023, at an average annual growth rate of 4.7%. As the technology advances and grows, prices for heating or electricity also decrease, making it potentially compatible compared to other renewable energy technologies.
Geothermal projects typically come with high upfront investment costs but have low recurring variable costs (fuel, maintenance, etc.). As there are no fuel costs, electricity prices by geothermal plants are very stable, compared to other renewable energy technologies. This means that the Levelized costs of electricity produced by geothermal electric plants are relatively low, ranging from US$ 0.05 to 0.095 cents per kWh. Based on data derived from IPCC and the IEA, there is a significant potential for geothermal applications worldwide. The most significant potential is for creating electricity through ultra-deep geothermal projects, which is seen as the future of geothermal energy.
Future of geothermal energy
Even though there is a significant worldwide potential for creating clean electricity through ultra-deep geothermal (UDG) projects, there are currently only a few UDG power plants. This is mainly due to technical barriers. At these depths, naturally occurring hydrothermal reservoirs are very rare due to the density of the rocks (the water cannot go through it). We have now entered the phase we called ‘dry rock geothermal systems’ in the introduction of this article. A solution for this is through Enhanced Geothermal Systems (EGS). Enhanced Geothermal Systems work, to a certain extent, the same as regular deep or ultra-deep geothermal systems, with the exceptions that the reservoirs are man-made. In an EGS, high-pressure water is injected deep into the subsurface rocks, causing it to fracture. Water can now get through these mini-fractures, and heat up due to the geothermal energy presents at these depths. There are no commercially running enhanced geothermal power plant systems at the moment, but the technology has been successfully tested on a pilot scale in Switzerland and is currently being tested on a handful of DOE-funded demonstration projects within the U.S. One of the most promising features of EGS is that it enables geothermal power plants to be constructed almost anywhere, without the constraints of surface heat or naturally occurring hydrothermal reservoirs. There are currently multiple consortiums being formed in different parts of the world, with the idea of exploring EGS on full-scale projects. It is certainly an exciting and promising time for the technology, and we will be sure to keep you updated.
About the author:
Andreas van Giezen is a NYC based environmental research analyst at Boundless Impact Investing, focusing on the climate impact of technologies from both an academic and commercial perspective.
