Everything to Know About Geothermal Energy
The energy we need is right under our feet. Because, our earth is a giant, heat-producing machine. In fact, the earth's core is hotter than the sun's surface. The energy in the earth's core is far greater than we could ever hope to tap into.
If we can effectively tap even a small portion of it, it will be enough to power the entire world for many centuries. And, that's exactly what geothermal energy is. It's the heat from the earth that we can harness to produce electricity and to heat and cool our homes.
Geothermal energy is one of the most sustainable forms of energy. It's a renewable resource and has a very low carbon footprint. It doesn't produce greenhouse gases as burning fossil fuels do.
Because the heat from the earth's core is constantly being replenished, we'll never run out of geothermal energy. That's why geothermal energy is such an attractive option to explore.
What is geothermal energy?
Geothermal energy is thermal energy found in the Earth's crust. It is caused by many reasons including the radioactive decay of minerals, volcanic activity, and solar heat absorbed at the surface.
It can be used for a variety of purposes including space heating, cooling, and electricity generation.
In order to tap geothermal energy, we need to drill a hole deep into the Earth's surface.
We then pump water or steam through the hole which transfers the heat to a turbine. The turbine creates electricity which we can then use to power our homes and businesses.
That said, geothermal energy may not be equally available just anywhere. Certain areas of the world allow for easier access to geothermal energy due to their geological activity.
These areas are typically located near tectonic plate boundaries and volcanic hot spots.
Although it is typically necessary to drill a deep hole to access geothermal energy, it isn't always the case. In some cases, we can get geothermal energy from just a few feet below the ground.
For example, Iceland sits atop a geologically young volcanic island chain and as such, has an abundance of geothermal energy. In fact, geothermal energy supplies about 65% of the country's electricity needs.
The Philippines also has a high potential for geothermal energy due to its location in the “Ring of Fire“. The Ring of Fire is a zone of high seismic and volcanic activity that encircles the Pacific Ocean.
These examples show that the potential for geothermal energy is different in different parts of the world. That is why not every country is equally suited for harnessing this form of energy.
Certain countries or regions may not offer any geothermal energy potential at all. This is not because the geothermal energy isn't there, but because it is difficult and expensive to tap into.
In order to tap into geothermal energy, we need to drill deep wells. The average geothermal well is about 300 feet deep. Although not typical, some can go as deep as 600 feet or more.
The depth of the well depends on the proximity to the geothermal reservoir. The closer the well is to the reservoir, the shallower the well can be.
Whereas, if the reservoir is further away from the ground, the well will need to be deeper. That can quickly make tapping into geothermal energy a very expensive proposition.
The geothermal heat source can be either a dry steam field, where steam is brought to the surface; or a hot water field, where water is heated by rocks and then circulates through fractures and pores in the rock.
In either case, water or steam is used to spin a turbine which activates a generator to create electricity.
Also, the rate at which the temperature changes as one goes deeper into the Earth's interior is known as the geothermal gradient. The rate of increase is about 25–30 °C/km (72–87 °F/mi) as one goes from the Earth's surface to the mantle.
That's why the deeper our drilling, the more consistent and higher the temperature we can get.
How is geothermal energy generated?
Geothermal energy is generated from underground reservoirs of water or steam. In order to extract the energy, a well is drilled into the ground, and the water or steam is brought to the surface. The water or steam is then used to spin a turbine, which generates electricity.
There are three types of geothermal power plants in terms of how they utilize water or steam.
Dry steam plants
Dry steam plants are the oldest type of geothermal power plant. They use steam that is produced by the Earth's heat to spin a turbine.
The steam is then condensed back into water and injected back into the ground. The first dry steam plant was built in Italy in 1904, and it is still in operation today!
Dry steam plants use mostly steam-based hydrothermal fluids. The steam is routed directly to a turbine, which powers a generator, which generates electricity.
The steam eliminates the requirement for the turbine to be powered by fossil fuels (also eliminating the need to transport and store fuels). These plants simply release excess steam together with trace amounts of gas.
Flash steam plants
Flash steam plants convert high-pressure hot water from deep inside the earth to steam to power generator turbines.
When the steam cools, it condenses into water and is injected back into the earth, where it can be reused. The majority of geothermal power plants use flash steam.
The most prevalent type of geothermal power producing facility is the flash steam plant. Flashing occurs when high-pressure fluid is pushed into a lower-pressure tank at the surface, causing some of the fluid to rapidly evaporate, or “flash.”
Using the vapor as fuel, a turbine turns a generator. This process can be repeated as many times as necessary to extract as much energy as possible from any remaining liquid in the tank.
Binary cycle power plants
Binary cycle power plants transfer heat from underground hot water to a secondary fluid, which is then used to run generator turbines.
The secondary fluid has a lower boiling point than water, so it vaporizes at a lower temperature. This makes binary cycle power plants more efficient than dry steam or flash steam power plants.
Unlike Dry Steam and Flash Steam geothermal power plants, binary cycle geothermal power plants do not use water or steam from the geothermal reservoir to generate electricity.
A heat exchanger is used to transfer heat from a low to moderately heated geothermal fluid (below 400°F) to a secondary fluid (hence the term “binary”) with a much lower boiling point than water.
The vaporization of the secondary fluid, caused by the heat from the geothermal fluid, is what powers the turbines and, eventually, the generators.
Closed-loop systems, such as binary cycle power plants, emit almost nothing except water vapor into the atmosphere.
Binary-cycle plants could provide a significant portion of future geothermal power because the majority of geothermal resources are below 300°F.
How do geothermal energy projects proceed?
Every geothermal energy generation project is unique and as such, will have its own set of challenges. But in general, most projects goes through the eight major steps:
- Preliminary survey;
- Test drilling;
- Project review and planning;
- Field development and production drilling;
- Start-up and commissioning;
- Operation and maintenance.
Typically, a full-scale geothermal power plant project takes 5 to 10 years to complete. Due to its long cycle, geothermal power is not a quick fix for any country's power supply issues, but rather part of a long-term electricity strategy.
Many of the risks associated with geothermal development are the same as those associated with any other grid-connected power generation project: delay risk, pricing risk, operational risk, and regulatory risk.
However, there are additional concerns associated with geothermal energy.
The test-drilling phase is one of the riskiest in geothermal projects. Despite the fact that there is still a lot of uncertainty, the test drilling phase is much more capital intensive. Before understanding whether the geothermal resource has enough potential to return the expenses, significant investment is required.
1. Preliminary survey
The preliminary survey phase is the initial exploration of a geothermal area based on previous national or regional investigations.
If no geothermal studies are available, undertake your own research based on available literature and data, or conduct your own reconnaissance work to identify potential regions of interest.
This phase mainly consists of examinations of the geothermal activity discovered on the surface in the area under investigation. It often includes a reconnaissance tour to the area to investigate the scientific and environmental factors.
The reconnaissance would involve an evaluation of access roads, local communities, lodging, and security.
It is also crucial to investigate the feelings of the communities that surround geothermal sites. Visual inspection of activities, photogeological survey, aeromagnetic survey, and infrared survey are all conducted during this phase.
This phase's primary purpose is to investigate cracks, long lineaments, circular patterns, and other tectonic features, as well as subterranean geological formations and heat radiation from the ground surface.
Depending on the rules for this phase, the owner may already have the concession or is in the process of obtaining it. The costs for this first phase are commonly expected to be between $500,000 and $1,000,000, assuming that the essential information is available.
This figure can rise to $5 million depending on the information available and the condition of the sites. Because of these factors, preliminary surveys can take anywhere from a few months to a year to complete.
2. Exploration Phase
The exploration phase begins with the collection and examination of existing geological, geophysical, geochemical, heat flow measurements, hydrogeology, and baseline environmental data for the area.
During this phase, a detailed multidisciplinary exploration program has been designed and put into action to collect new data.
The exploration program will be based on the findings of the preliminary phase and will focus on a more in-depth study of the geothermal system.
During the exploration phase, surface surveys are carried out to confirm the preliminary resource estimation.
For this phase, the program frequently incorporates multiple surface exploration methods, which can include the following exploration approaches:
Geological surveys are the foundation of all surveys aimed at locating geothermal resources, and they are designed to investigate the distribution of geological formations, geological structures, and alterations.
Lithological mapping, structural geology, volcanism, hydrogeology, geo-hazards, and environmental geology are all part of the geological study.
There are three types of geophysical surveys: gravity surveys, seismic surveys, and magnetic surveys. For geothermal exploration, resistivity surveys are among the most important geophysical methods.
As a result, various methods of resistivity measurement are used including Schlumberger, transient electromagnetic, TDEM (Time Domain Electro-Magnetic), and MT (Magnetic Time Domain) (Magneto Telluric).
More than one km of the reservoir's uppermost layer can be seen by the TEM survey, and up to tens of kilometers of reservoir depth can be seen by the MT survey.
For example, resistivity anomalies can help define upflow and outflow zones in a geothermal field. The use of Bouguer gravity measurements in geophysical exploration complements the use of MT and TEM measurements.
In conjunction with geological information, geophysical survey results may point to a heat source and help determine where to drill for further exploration.
During a geochemical survey, surface water, underground water, hot water, natural steam, and gas are all sampled and analyzed in an effort to better understand the geothermal reservoir's basic environment.
Based on the chemical elements in the solution, we can estimate the speed at which hot water circulates, as well as learn about the fluid's origins and recharge history, and determine its temperature at the reservoir's depth. This information can be used to determine the permeability of the reservoir.
Seismic waves generated by earthquakes are used in a seismic survey to determine the condition of underground structures and bedrock. For the most part, the primary goal is to map fault lines and fractures, which are important conduits for hot geothermal fluid.
Temperature gradient hole and heat flow survey are examples of other surveys that may be conducted during the exploration phase.
The information gathered during the exploration phase is used to confirm or revise the preliminary resource assessment and define potential drilling sites for further investigation.
The results of all surveys are integrated to create a three-dimensional model of the geothermal system, which aids in well planning and development.
3. Test drilling
The primary objective of this phase is to confirm the existence and potential of the geothermal reservoir. Additionally, the borehole geology, thermodynamic properties, and the boundaries of the reservoir are established in this phase.
The conceptual model is used to design a drilling program, typically a set of three to five full-size, 2500 to 3000 meter deep, geothermal wells.
It's critical to note that test results necessitate frequent retooling of drilling plans, therefore it's vital to keep this in mind. Drilling pads will be placed depending on local environmental factors. The first well is essential because it captures the greatest amount of subsurface data possible.
If the first well fails to produce steam, the initial detailed geological, geochemical, and geophysical studies are analyzed along with the downhole data before deciding on the next target drill location.
A step-out well is drilled if the first exploration well is a success. There should not be too much distance between the subsequent step-out wells and their target fractures or geological structures.
Drilling is followed by well logging and discharge tests. It is possible that the results of the well surveys and tests will confirm the resource, which will allow for the development of a better conceptual model.
Even when the permeability and temperature are sufficiently high, wells don't immediately discharge after drilling. A high-pressure, high-volume air compressor used to induce well discharge is used as a last resort in such cases of well stimulation.
A Preliminary Study, which includes the collection of data and research on a certain topic, will be conducted during this phase.
An Environmental Impact Assessment (EIA) and the necessary permissions must be obtained during this phase, in addition to these activities.
A full-size well typically costs between $4 million and $6 million, depending on the location and depth of the drilling target. The cost of constructing new roads and well pads is generally estimated at between $1 million and $1.5 million.
Another option is to drill thin holes to confirm the reservoir's temperature and chemistry, which can be drilled to a depth of 1,500 meters for less money than a regular well of a similar depth.
4. Project review and planning
This phase determines the resource's exploitable size based on the conceptual model, geological structure, circulation fluids, and reservoir characteristics. The fluid collection and re-injection system must have a development strategy.
The power station's design, location, and grid connection are all established in this phase. The feasibility study will detail costs, timelines, and economic and financial analyses.
An EIA is being prepared in order to assess the potential environmental impacts of the project. The EIA will be used to develop an Environmental Management Plan (EMP), which will outline how the project will avoid, reduce, or offset any significant adverse environmental impacts.
Consultations with local residents, government, and other stakeholders are part of the approval process for the geothermal project. After this phase, you'll have a detailed technical and financial feasibility study to pitch to investors.
5. Field development and production drilling
The field development and production drilling phase involve drilling production and reinjection wells, constructing power plants and related infrastructure, and connecting to the grid.
The pipeline and separation station in the well pad to connect the production wells to the power plant and reinjection systems begin detailed design, procurement, and construction.
According to the drill plan and the well pad, one or more drilling rigs may be needed. A successful production well produces 5 MW of electrical power in the power plant.
Nowadays, well pad design allows drilling up to four directional wells with different bottom targets. This development scheme produces a small production field and is well suited to mountainous terrain.
As the production and reinjection wells are drilled, the geothermal power plant's detailed engineering, procurement, and construction take place simultaneously.
In most geothermal projects, the exploration and drilling phases account for well over half of the total cost. For field development and production, the number of wells to be drilled and their length are both important considerations.
The cost of a geothermal system ranges from $1.2 million to $2 million per installed megawatt, with the precise amount depending on the project's size and location.
Coordinating civil and infrastructure work, as well as finishing the steam collection system, is required in order to establish the power plant.
Substations are used to store and transmit the generated electricity. Engineering, Procurement, and Construction (EPC) contracts are commonly used to build power plants.
7. Start-up and commissioning
Prior to commercial operation, the power plant must be fully operational and ready for start-up and commissioning. Technical and contractual issues with the plant's supplier are often the focus of this phase.
The main objective is to optimize energy recovery and usage by optimizing the production and injection systems. It might take months for the power plant and all other equipment to reach their optimal performance levels.
8. Operation and maintenance
The operation and maintenance of the steam field (wells, pipelines, infrastructure, etc.) are distinct from that of the power plant (turbine, generator, heat exchanger, etc.).
Proper maintenance of all infrastructure assures a high availability factor and capacity factor for the power plant, as well as consistent steam output from the geothermal wells.
Power plant operations necessitate well-trained technical staff; for a fully automated 30 MW geothermal power station, roughly 20 technicians are required.
This does not apply in all nations since, for energy demand reasons, when a power plant trip occurs and geothermal involvement is critical, this power plant must be restored as quickly as possible, and this condition necessitates technicians being on-site.
What are the benefits of geothermal energy?
Geothermal energy has a number of benefits including:
Renewable & sustainable
Geothermal energy is renewable and sustainable. Once a geothermal plant is built, the heat energy it produces is almost free. The only costs are for running the pumps that circulate the water.
It does not produce greenhouse gases, and it can be used over and over again without damaging the environment.
Also, geothermal power plants have a very small footprint compared to other forms of energy generation, such as coal-fired power plants. Because they do not use fuel, they do not produce emissions and don't impact the environment negatively.
Doesn’t require large spaces
Geothermal energy installations are quite small in comparison to huge wind turbines and solar panels, taking up only a little amount of area. The majority of the components (including heat exchangers) are concealed beneath the ground, with only a little amount above ground.
For example, a geothermal plant requires a field of 1-8 acres per megawatt (MW), compared to 5-10 acres per MW for nuclear power plants and 19 acres per MW for coal power plants. This makes them better suited for installation in more built-up areas.
Reliable & consistent
Geothermal energy is a consistent and reliable source. It works in any weather and can run 24 hours a day, 365 days a year. Because it is so reliable, it can be used to supplement renewable energy sources like solar and wind.
Geothermal energy is always available and nearly limitless, as are many other renewables. It is not affected by day or night, as solar energy is, nor is it affected by season, climate, or weather conditions, as wind and solar power are.
Geothermal power plants typically operate for 8,600 hours per year on average, whereas solar power plants typically operate for 2,000 hours per year on average to produce energy.
As a result, the rate of geothermal energy generation can be described as constant, at least in the short or medium term. This makes it easier to predict and plan when integrating geothermal power into the grid.
Geothermal power plants, at least when operating at full capacity, make virtually no noise at all.
Even though some noise is expected throughout the initial drilling and construction process, once the plant is operational it is completely silent. This applies to both residential systems and larger power plants that have at most several turbines running.
According to the GSE study, geothermal energy creates more indirect jobs than any other renewable source for the same installed power.
This equates to 34 employment per megawatt installed, significantly greater than wind energy's 19 and photovoltaic energy's 12. In Italy alone, 2,000 gigawatts of installed power would provide employment for 4,000 people as well as 30,000 other jobs.
Provides more energy for the same nominal power
Because the supply is constant, geothermal energy may be utilized at maximum efficiency for an infinite period of time (excluding maintenance).
This indicates that the amount of energy produced will be equal to the power multiplied by the number of hours used.
This is in direct contrast to solar, hydropower, and wind turbines, which rarely produce their maximum capacity. As a consequence, for equal measured power, geothermal energy provides more actual energy than any other renewable source.
Allows for double recycling
Using geothermal energy conserves resources. Plants have components that can be salvaged and re-used at the end of the installation's lifecycle, which is one advantage of this design approach.
To offset this, the plant's steam pipes recycle any heat that isn't immediately needed back into the circuit, which allows for significant energy savings during operation.
Plants are durable, safe, and reliable.
The average lifetime of a domestic and large-scale geothermal power plant can be as long as 80 to 100 years. This is a significant improvement over the typical 15-year lifespan of a residential boiler.
With no fuels involved, there are no emissions, and very little maintenance is required.
As a result of the minimal environmental impact, geothermal energy is often referred to as a ‘green energy source.' Geothermal power plants have a very small carbon footprint and do not produce any greenhouse gases.
Geothermal plants require very little maintenance, particularly residential ones. Because they are closed systems, the fluid pressure in the piping self-regulates, and there are few electrical and mechanical components that can fail.
Can be used for cooling
We generally think of geothermal energy as a source of thermal energy and heating. Geothermal plants, on the other hand, are intended to heat and cool a building or facility.
As a result, aside from large power plants, geothermal power systems can be installed in almost any type of building, from homes to shopping malls, public buildings, and sports centers.
More advantages for the residential applications
In addition to cooling and heating, geothermal energy provides a host of other benefits when used in a residential setting. For example, it can be used for domestic hot water, swimming pool heating, and snow melting.
When many versatile uses are considered, geothermal energy can reduce overall energy consumption by 30% to 70% depending on the application.
Low operating costs
The initial investment in geothermal power may be high, but the operational expenses are low. This implies that over time, geothermal energy pays off and becomes increasingly cost-effective.
Once a geothermal power plant is built, the only major costs are associated with maintenance and operations. The cost of fuel is eliminated, which makes geothermal power plants very efficient.
Can be used for direct heating & cooling
Geothermal energy can be used for direct heating and cooling. This means that geothermal energy can be used to heat homes and businesses, as well as to cool them.
What are the drawbacks of geothermal energy?
There are a few drawbacks to geothermal energy, but they are by no means deal-breakers. The most common drawbacks are:
High initial investment costs
The high initial investment costs can be a barrier to entry for many people. However, the high initial cost can be offset by the long-term savings on energy costs. There are also a number of government incentives and programs that can help offset the initial investment costs.
Geothermal energy is not available everywhere. It is mostly found in areas with volcanic activity or hot springs.
The most significant drawback of geothermal energy is that it is dependent on location. Geothermal plants must be located in regions where geothermal resources are available. These resources are not evenly distributed around the world, which can limit the use of geothermal energy in some areas.
Can cause some environmental disruption
Geothermal energy can be disruptive to the environment to some extent. The drilling and construction of geothermal power plants can cause some environmental disruption, but this is typically temporary and localized.
Geothermal energy does not normally release greenhouse gases. But during the excavation, many of these gases that have been stored beneath the Earth's surface are released into the atmosphere.
These gases are naturally released into the atmosphere, but their concentrations rise near geothermal power plants. But still, the net impact of geothermal power plants is far less than that of fossil fuel power plants.
What are the Different Types of Geothermal Systems?
There are a variety of geothermal systems to choose from. The soil type, climate, local installation costs, and amount of available land all play a role in determining which system is best.
Many subgroups can be found within the two main ground loop systems. They are open-loop and closed-loop systems.
Each loop system has its own set of benefits and drawbacks that should be considered before installation.
Open Loop Geothermal Systems
Open-loop geothermal systems use groundwater from an aquifer as the heat-exchange fluid to transfer heat to or from the ground.
The water is then returned to the aquifer. Because this water is not recirculated, an open-loop system needs a large volume of groundwater available for continuous operation. The water table must also be close enough to the surface to allow for easy drilling of the well.
Open-loop geothermal systems have a few disadvantages.
First, they can lower the water table, which can lead to land subsidence. Second, they can pollute groundwater if the water is not properly treated before it is returned to the aquifer. Third, they can deplete groundwater resources if they are not managed properly.
Closed-Loop Geothermal Systems
A closed-loop geothermal system uses a heat-exchange fluid that is circulated through a loop of pipe buried in the ground. The fluid in the loop is typically a water and antifreeze mixture. Closed-loop systems can be installed in almost any location, regardless of the water table.
Closed-loop geothermal systems have a few disadvantages.
First, they require more initial investment than open-loop systems. Second, they require more maintenance than open-loop systems. Third, the heat-exchange fluid can leak thus it requires regular monitoring.
Closed-loop systems are classified as:
1. Horizontal systems
Horizontal closed-loop geothermal systems use piping that is laid horizontally in the ground. Because the loops are laid horizontally, this type of system is typically used in areas with a large amount of land available.
2. Vertical systems
Vertical closed-loop geothermal systems make use of vertically drilled piping in the ground.
The pipes are run vertically in several wells between 100 and 400 feet deep and connected at the bottom by a U-bend. The boreholes are then filled with grout, which provides good thermal conductivity to the vertical pipes.
3. Slinky Systems
Slinky closed-loop geothermal systems are a type of horizontal system. The piping is coiled in a helix shape and buried in the ground horizontally.
These systems shorten the trenches in which the pipes will be laid. They are particularly useful in areas with limited land availability.
Slinky systems have a few disadvantages.
First, they are more expensive to install than horizontal or vertical systems. Second, they are more difficult to maintain and repair due to their complex design. Third and final, they have a higher risk of failure than horizontal or vertical systems.
Does geothermal drilling cause earthquakes?
No, geothermal drilling does not cause earthquakes. Because earthquakes are caused by the movement of tectonic plates deep within the Earth. Geothermal drilling is done at much shallower depths. So it does not affect the Earth's crust in a way that could cause an earthquake.