Like coal, gas or nuclear power facilities, a geothermal power plant converts heat to electricity. It does this using high-temperature (300°F to 700°F) heat. Geothermal energy – from the Earth, accessed by drilling hot water or dry steam wells in a process similar to drilling for oil.
The hot water or steam is piped to the surface and used to power turbines that generate electricity.
In this blog, Pritish Kumar, discusses the Geothermal Energy source, through which it generates, its types, and its associated pros and cons.
According to the International Energy Agency (IEA), in 2017, global geothermal power generation was an estimated 84.8TW/h, while cumulative capacity reached 14GW.
Global geothermal power capacity is expected to rise to just over 17GW by 2023, with the biggest capacity additions expected in Indonesia, Kenya, Philippines and Turkey.
It is estimated that, as a source of renewable energy for both power and heating, geothermal has the potential to meet 3-5% of global demand by 2050.
Is geothermal a renewable energy source?
Unlike renewable energy sources such as wind and solar farms, geothermal power plants are unaffected by the weather. Meaning they can provide a stable supply of electricity (capacity factors range from 60% to 90%) and are therefore suitable for base load (continuous) electricity production.
Geothermal power plants have average availabilities of 90% or higher, compared with around 75% for coal plants.
Geothermal energy is considered to be a renewable resource since energy can be extracted without burning fossil fuels such as coal, gas or oil, resulting in less harmful emissions.
Also, geothermal power stations use the almost unlimited amount of heat generated by the Earth’s core. And even in areas dependent on a reservoir of hot water, the volume extracted can be re-injected, making it a sustainable energy source.
Types of geothermal power plants
Geothermal power plants, like their traditional counterparts, feature standard power-generating equipment including turbines, generators and transformers.
The first commercial geothermal station was built in Tuscany in 1911 and Italy was the world’s only industrial producer of geothermal electricity until 1958, when the Wairakei plant was commissioned in New Zealand.
There are three main types of geothermal power plants:
- Dry steam plants utilise steam directly from a geothermal reservoir in order to power turbines and generate electricity. The first geothermal power plant ever built was a dry steam plant.
- Flash steam plants are the most common type of geothermal power plants. They work by converting high-pressure hot water from deep inside the Earth into steam. When it cools, condenses to water and is injected back into the ground to be used again.
- Binary cycle power plants transfer the heat from geothermal hot water into another liquid. This then turns to steam used to drive a generator turbine.
Enhanced geothermal systems (EGS)
Until recently, geothermal power stations had to be built in areas with naturally occurring high-temperature heat and water sources, and where the rock was suitable for drilling.
However, enhanced geothermal systems (EGS) have the potential to extend use of geothermal resources. The technique works by injecting water into rock systems, creating cracks to increase the rock’s permeability.
This allows fluid to circulate in the fractured rock and transport heat to the surface, where electricity can be generated.
The US Government’s Office of Energy Efficiency & Renewable Energy estimates that more than 100GWe of economically viable capacity may be available in the US. A 40-fold increase over present geothermal power generating capacity and 10% of current overall US electric capacity.
What are the Advantages of Using Geothermal?
1. Environmentally Friendly
Geothermal energy is more environmentally friendly than conventional fuel sources such as coal and other fossil fuels. In addition, the carbon footprint of a geothermal power plant is low. While there is some pollution associated with geothermal energy. This is relatively minimal when compared to fossil fuels.
Geothermal energy is a source of renewable energy that will last until the Earth is destroyed by the sun in around 5 billion years. The hot reservoirs within the Earth are naturally replenished, making it both renewable and sustainable.
3. Huge Potential
Worldwide energy consumption is currently around 15 terawatts, which is far from the total potential energy available from geothermal sources. While we can’t currently use most reservoirs there is a hope that the number of exploitable geothermal resources will increase with ongoing research and development in the industry. It is currently estimated that geothermal power plants could provide between 0.0035 and 2 terawatts of power.
4. Sustainable / Stable
Geothermal provides a reliable source of energy as compared to other renewable resources such as wind and solar power. This is because the resource is always available to be tapped into, unlike with wind or solar energy.
5. Heating and Cooling
Effective use of geothermal for electricity generation requires water temperatures of over 150°C to drive turbines. Alternatively, the temperature difference between the surface and a ground source can be used. Due to the ground being more resistant to seasonal heat changes than the air, it can act as a heat sink/ source with a geothermal heat pump just two metres below the surface.
Energy generated from this resource is easy to calculate since it does not fluctuate in the same way as other energy sources, such as solar and wind. This means we can predict the power output from a geothermal plant with a high degree of accuracy.
7. No Fuel Required
Since geothermal energy is a naturally occurring resource there is no fuel required, such as with fossil fuels that are a finite resource which needs mining or otherwise extracting from the earth.
8. Rapid Evolution
There is a great deal of exploration into geothermal energy at the moment, meaning that new technologies are being created to improve the energy process. There are an increasing number of projects to improve and grow this area of industry. With this rapid evolution many of the current cons of geothermal energy will be mitigated against.
What are the Disadvantages of Geothermal Energy?
1. Location Restricted
The largest single disadvantage of geothermal energy is that it is location specific. Geothermal plants need to be built in places where the energy is accessible, which means that some areas are not able to exploit this resource. Of course, this is not a problem if you live in a place where geothermal energy is readily accessible, such as Iceland.
2. Environmental Side Effects
Although geothermal energy does not typically release greenhouse gases, there are many of these gases stored under the Earth’s surface which are released into the atmosphere during digging. While these gases are also released into the atmosphere naturally, the rate increases near geothermal plants. However, these gas emissions are still far lower than those associated with fossil fuels.
Geothermal energy also runs the risk of triggering earthquakes. This is due to alterations in the Earth’s structure as a result of digging. This problem is more prevalent with enhanced geothermal power plants, which force water into the Earth’s crust to open up fissures to greater exploitation of the resource. However, since most geothermal plants are away from population centres, the implications of these earthquakes are relatively minor.
4. High Costs
Geothermal energy is an expensive resource to tap into, with price tags ranging from around $2-$7 million for a plant with a 1 megawatt capacity. However, where the upfront costs are high, the outlay can be recouped as part of a long-term investment.
In order to maintain the sustainability of geothermal energy fluid needs to be pumped back into the underground reservoirs faster than it is depleted. This means that geothermal energy needs to be properly managed to maintain its sustainability.
It is important for industry to assess the geothermal energy pros and cons in order to take account of the advantages while mitigating against any potential problems.