Warren C. Volles
Svartsengi Geothermal Power Station: Producing Reliable, Clean, and Renewable Energy in Iceland
Seeing the Svartsengi power station from the Blue Lagoon made me want to investigate how geothermal power is produced. Geothermal plants provide a reliable and renewable alternative to fossil fuels, solar, and wind energy.
The Svartsengi power station on the Reykjanes Peninsula in Iceland is a geothermal plant that has been supplying consumers with electricity and hot water for more than four decades. The Reykjanes Peninsula resides on the Mid-Atlantic Ridge, a tectonic plate boundary where the North American and Eurasian plates are moving away from each other. Due to this tectonic plate activity, the region has been shaped into a rift valley after millions of years of earthquakes and volcanic activity from the Eldvörp–Svartsengi volcanic system. The Svartsengi plant is located in a lava field above a geothermal reservoir created by these geological processes. Starting in 2023, a series of earthquakes and volcanic eruptions resulted in fissures and lava flows that eventually reached the town of Grindavík, which is about 6 kilometers (3.7 miles) south of the Svartsengi power station.
Mid-Atlantic ridge
The Mid-Atlantic Ridge is an underwater mountain range that lies in the center of the Atlantic Ocean. This ridge is one of the longest mountain ranges in the world, stretching about 16,000 kilometers (10,000 miles) in a north-south direction from the Arctic Ocean to the Southern Ocean near Antarctica. On average, it rises about 2,000 to 3,000 meters (6,600 to 9,800 feet) above the surrounding ocean floor. Ocean ridges are formed where tectonic plates move apart (diverge), allowing magma to rise from the mantle and create new oceanic crust. The Mid-Atlantic Ridge is where the Eurasian and North American tectonic plates are diverging by about 2.5 centimeters (1 inch) per year. This tectonic activity has created rift valleys along the ridge, characterized by fissures, faults, and volcanic activity. In Iceland, the Mid-Atlantic Ridge is tall enough to be exposed above sea level, making it one of the few places on Earth where this type of geological formation is visible on land.
Tectonic Plate Activity
Tectonic plates are large, rigid pieces of the Earth’s outer layer (lithosphere) that cover the Earth’s surface. Tectonic plate activity refers to the movement and interaction of these plates as they float on the semi-fluid layer (asthenosphere) beneath them. Tectonic plates can move apart (diverge), move toward each other (converge), or slide past each other (transform). Their movements shape the Earth’s landscape over millions of years by causing earthquakes, volcanoes, mountains, and ocean trenches. In Iceland, the separation of the Eurasian and North American tectonic plates has created a rift valley with significant volcanic and geothermal activity.
Geothermal reservoir
Geothermal reservoirs are hot water and steam reservoirs that are located beneath the Earth’s surface. They are formed when rainwater seeps into the Earth’s crust and is heated by the molten rock in the mantle. As the water flows through cracks in the rocks, it becomes trapped underground as pockets of hot water and steam. The formation of geothermal reservoirs often occurs near tectonic plate boundaries or areas with volcanic activity. These areas are ideal for geothermal reservoirs because they have high heat flow from the mantle, which raises the temperature of the underground water. Numerous fractures and faults allow water to penetrate deep into the Earth’s crust to reach the heated areas. In addition, the rocks are porous and have many interconnected spaces that facilitate the movement and storage of water.
Engineers from the Svartsengi power station drilled the first well into the geothermal reservoir in 1972. By 1976, Svartsengi became the world’s first geothermal plant to generate both electricity and hot water. Today, the Svartsengi plant has 13 wells. Five shallow wells produce only dry steam, and eight deep wells produce steam and salty water that has two-thirds the salinity of seawater. The depths of these wells range from 400 meters (1,312 feet) to over 2,000 meters (6,561 feet). The temperature in the reservoir is a relatively constant 240°C (464°F) at depths below 600 meters (1,968 feet).
The Svartsengi power station uses two processes to convert geothermal energy from the reservoir into electrical energy in the plant. The first, a dry steam process, extracts the dry steam that comes from the shallow wells. The dry steam is passed directly to a turbine, which is linked to an electrical generator that generates electricity through electromagnetic conduction for consumers.
Turbine
In a power plant, a turbine is a machine that converts internal kinetic energy of a fluid, such as steam, into mechanical energy. Steam enters the turbine and flows through a series of blades that are attached to shaft of a generator. The force of the steam on the blades rotates the shaft. This rotational energy can then drive the generator to produce electricity.
Generator
In a power plant, a generator is a machine that converts mechanical energy from a turbine into electrical power. It works according to the principle of electromagnetic induction, which states that an electric current will flow through a conductor, such as a coil of copper wire, when the conductor is subjected to a changing magnetic field. In a typical power generation setup, a turbine drives the rotation of the generator’s shaft. The shaft is connected to a magnet that is surrounded by a coil of wire. As the shaft spins, the magnetic field changes and produces an electric current in the wire. The electricity can then be used to power homes and businesses.
Faraday’s Law
In 1831, Michael Faraday described the principle of electromagnetic induction. Faraday’s Law states that the induced electromotive force in a copper coil is proportional to the rate of change in the magnetic flux through the coil. The equation is written as:
where E is the electromotive force induced in the coil, ΦB is the magnetic flux through the coil, and dΦB/dt is the rate of change in the magnetic flux. The negative sign shows that the induced current flows in the direction opposite to the change in the magnetic flux that created it.
The second process uses a binary cycle to generate electricity from the water and steam extracted from the deep wells. The water found deep within the geothermal reservoir is held under high pressure. It enters the wells through holes in a liner. Once the water rises in the well, it is no longer subjected to the high pressure of the reservoir. As a result of vaporization, some of the water transitions into steam due to the drop in pressure within the well.
When the water and steam mixture reaches the surface, it enters the primary loop in the binary cycle. While in the primary loop, the water and steam pass through a heat exchanger, where they transfer their heat to a secondary fluid. The heat transfer equation is used to calculate the amount of heat transferred in a heat exchanger. Once the heat transfer is completed, the water and steam mixture is reinjected back into the reservoir to be reheated and reused.
Vaporization
Water in the well undergoes a phase transition from a liquid to a gaseous state (steam) due to the drop in pressure from the reservoir to the well. In the high-pressure environment of the reservoir, water remains in a liquid state even at high temperatures because the molecules do not have enough energy to escape into the gaseous phase. However, as the water rises in the well and the pressure drops, the molecules in the water gain enough energy to overcome the forces holding them in the liquid state. When the pressure falls below the vapor pressure of the water at its current temperature in the well, the water rapidly vaporizes into steam.
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Heat Exchanger
A heat exchanger is a device that transfers heat among fluids without mixing them. It allows heat from a hot fluid to pass to a cooler fluid, according to the Second Law of Thermodynamics, which states that heat energy naturally moves from places of higher temperature to places of lower temperature until thermal equilibrium is achieved.
Heat exchangers are used to manage thermal energy in various applications, such as power plants, refrigerators, and air conditioners.
Heat Transfer Equation
The secondary loop in the binary cycle uses the secondary fluid isopentane because it vaporizes at a lower temperature than water. As the isopentane absorbs heat in the heat exchanger, it quickly vaporizes. The isopentane vapor is then directed to a turbine connected to an electrical generator. After passing through the turbine, the isopentane vapor is condensed into liquid isopentane and sent back to the heat exchanger to restart the cycle. This closed-loop system increases efficiency and minimizes the environmental impact by preventing the direct release of geothermal fluids into the air.
Diagram of binary cycle
by Warren Volles
To make hot water for consumers, the Svartsengi power station uses a portion of the water and steam mixture from the geothermal reservoir. This mixture is directed to a heat exchanger where it heats cold water coming from a freshwater tank. Interestingly, the runoff water from this process is used to fill the Blue Lagoon, a geothermal spa that is located near the power station.
Diagram of hot water production and runoff to the Blue Lagoon
by Warren Volles
66 MW
~200 MW
The total production capacity of the Svartsengi power station is 66 megawatts in electrical power and approximately 200 megawatts in thermal power. Geothermal energy is considered a reliable source of power because it is continuously available throughout the day. In contrast, solar and wind energy depend on weather conditions and the time of day. However, like other power plants, geothermal plants can be impacted by major events such as natural disasters. For example, the recent volcanic eruptions near the town of Grindavík released lava flow that destroyed roads and hot water pipes near the Svartsengi plant. As a solution, a large dyke was dug to prevent the lava from reaching the power plant and disrupting its supply.
Additional insights
Although geothermal plants produce one of the cleanest forms of power, they still emit some pollutants and greenhouse gases, including carbon dioxide and methane. To lessen their environmental impact, geothermal plants reinject unused water and gases back into the reservoir to reduce emissions. Additionally, the Svartsengi power station uses efficient methods to extend the life of its geothermal fields. For example, the plant extracts more energy from the same amount of geothermal fluid by using isopentane, which vaporizes at a lower temperature than water.
Geothermal reservoirs can become depleted over time if water and gases are extracted faster than they can be replaced. That’s why geothermal plants carefully plan and monitor their operations to balance extraction and reinjection rates. Moreover, when geothermal plants are located near tectonic plate boundaries, they must monitor, prepare for, and respond to geothermal activity to ensure safety and avoid disruptions in power supply.
References
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