Geothermal Power Generation: Sustainable Practices And Policies
Geothermal energy is thermal energy generated and stored in the Earth. It arises from the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface. Geothermal energy can be accessed by drilling water or steam wells in a process called geothermal power generation. It’s considered a renewable energy source because the heat emanating from the interior of the Earth is constantly being replenished.
The geothermal gradient, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat from the core to the surface. Geothermal power plants tap into this underground reservoir of heat to generate clean, renewable energy without burning fossil fuels. Water or steam carries the geothermal heat to the surface where its thermal energy powers a turbine generator to produce electricity.
Geothermal power offers a sustainable energy source that provides constant base-load power with high capacity factors and low carbon emissions. The ability to extract geothermal energy from enhanced geothermal systems could unlock a vast global energy resource. With the growth of geothermal power generation, this renewable energy source may play a key role in the transition to a cleaner energy future.
Geothermal Power Generation Methods
There are three main types of geothermal power plants used for electricity generation:
Dry Steam Plants
Dry steam plants utilize steam directly from a geothermal reservoir to turn the generator turbines. The first geothermal power plant was a dry steam plant built in Italy in 1904. This type of plant is only feasible where the geothermal reservoir produces steam at a temperature above 235°C. The steam is piped directly into the power plant and drives a turbine which is connected to a generator that produces electricity. The steam is condensed into water and re-injected into the reservoir to be heated again.
Flash Steam Plants
Flash steam plants are the most common type of geothermal power plant. They use water at temperatures above 180°C that is sprayed into a tank held at a much lower pressure, causing the water to vaporize into steam. The steam is then used to drive a turbine and generator. The condensed steam and remaining geothermal fluid are re-injected into the reservoir. Binary cycle power plants now generate most of the electricity from geothermal resources in the United States because reservoirs are mostly below 150°C.
Binary Cycle Plants
Binary cycle plants use lower temperature water from the geothermal reservoir (100-180°C) to heat a secondary fluid with a much lower boiling point that vaporizes and drives the turbine. The geothermal water and the secondary fluid are kept separated during the whole process, so the water is re-injected back into the reservoir for reuse. Binary cycle plants are the most efficient and now produce the majority of geothermal-based electricity worldwide.
Global Geothermal Power Generation Capacity
As of 2021, the installed global geothermal power generation capacity was just over 17 gigawatts (GW). While geothermal accounts for only about 0.4% of total global electricity production, capacity has been steadily growing over the past decade.
The countries with the largest installed geothermal capacity are the United States, Indonesia, and the Philippines. The United States leads with over 3.5 GW, predominantly located in California and Nevada. Indonesia comes in second with over 2 GW of capacity, and the Philippines third with almost 2 GW as well. Other top countries for geothermal power include New Zealand, Mexico, Italy, and Iceland.
Over the next five years, significant geothermal power growth is expected in Indonesia, Kenya, Ethiopia, the Philippines and Mexico. Indonesia aims to double its current capacity, while Kenya plans to add another 1 GW. Several European countries like Turkey, Germany and France also have plans to expand geothermal generation.
Overall, the global geothermal power market is projected to grow at a compound annual growth rate of over 5% through 2027 as countries increasingly turn to renewable baseload sources to reduce reliance on fossil fuels and meet climate goals.
Geothermal Power Generation Efficiency
Geothermal power plants operate with high capacity factors and efficiencies compared to most other forms of power generation. The capacity factor refers to the actual power output over time compared to the maximum possible output. Geothermal plants typically have capacity factors above 90%, meaning they generate over 90% of their maximum potential output over a year. This compares favorably to capacity factors around 35% for wind and solar power.
The thermal efficiency of geothermal power plants describes how much of the heat energy from geothermal fluids gets converted into electricity. Modern geothermal plants can achieve thermal efficiencies over 10%, with some facilities reaching above 15%. By comparison, the average efficiency of coal plants is around 33%. This makes geothermal reasonably efficient at converting heat into power.
Energy return on investment (EROI) ratios indicate how much energy is gained compared to the amount of energy required to build and operate a power plant. Geothermal energy has an EROI ratio estimated between 15-40. This means for every unit of energy used to construct and run a geothermal plant, it generates 15-40 times that amount of electricity. This EROI ratio is better than solar, wind, and biofuels. It demonstrates that geothermal can provide a substantial net energy gain.
Environmental Benefits
Geothermal power generation has significant environmental benefits compared to conventional fossil fuel power plants. The most notable benefits are:
Low Emissions
Geothermal plants release very little emissions into the atmosphere. Unlike coal, natural gas, and oil plants, geothermal energy does not burn any fossil fuels to generate electricity. This results in near-zero emissions of greenhouse gases like carbon dioxide, methane, and nitrous oxide. The emissions from geothermal plants are typically at least 90-95% lower per kWh than conventional thermal power plants.
Small Land Footprint
Geothermal plants require a small land footprint compared to other renewable energy sources. While solar or wind farms can cover hundreds or thousands of acres, a geothermal plant uses about 1/2000th the land area per kWh generated. The actual facility size is comparable to a small fossil fuel plant.
Sustainability
Geothermal energy is considered renewable and sustainable. The heat from the Earth’s interior is constantly being replenished and will be available for billions of years to come. Once a geothermal reservoir is tapped, the energy can be extracted sustainably if the rate of fluid extraction does not exceed the rate of natural recharge.
Economic Benefits of Geothermal Power Generation
Geothermal power provides significant economic benefits compared to conventional fossil fuel power plants. The most notable economic advantage is the levelized cost of geothermal power, which measures the overall cost of building and operating a power plant over its lifetime.
According to the U.S. Department of Energy, the estimated levelized cost of geothermal power ranges from $0.047 to $0.111 per kWh, making it highly competitive with conventional coal ($0.095/kWh) and natural gas ($0.049/kWh) power generation. Geothermal’s levelized costs are not subject to fuel price volatility, providing a reliable and predictable electricity price over decades of operation.
Geothermal plants also have high capacity factors of over 90% compared to the average capacity factors of 56% for coal plants and 34% for solar PV. This near constant operation reduces the levelized cost and provides baseload power production. In addition, geothermal power production from hydrothermal resources uses a free domestic energy source, enhancing energy security and stability.
Challenges and Limitations
While geothermal power offers many benefits, it also comes with some challenges and limitations that have prevented more widespread adoption globally. Some of the main challenges and limitations include:
High upfront costs – Drilling geothermal wells and building power plants requires significant upfront capital investment, which can deter investors and project developers. Geothermal power plants cost about $2-5 million per installed megawatt, which is higher than traditional fossil fuel plants.
Specific geological requirements – Geothermal reservoirs require specific geological conditions to produce viable amounts of heat and fluid flow. Reservoirs need to be relatively shallow, porous, permeable, and saturated with water. As a result, geothermal power is only feasible in tectonically active regions.
Induced seismicity – Injecting water into geothermal reservoirs can sometimes cause induced seismic events or minor earthquakes. While rare, induced seismicity has hampered geothermal development at certain sites like Basel, Switzerland.
While geothermal power has excellent potential as a renewable baseload resource, these limitations need to be addressed through technological innovations, policy support, and public engagement for the industry to reach its full potential.
Policies and Incentives
Governments around the world have implemented various policies and incentives to support the growth of geothermal power generation. These include:
Renewable Portfolio Standards
Renewable portfolio standards (RPS) require utilities to source a certain percentage of their electricity from renewable sources like geothermal. For example, California’s RPS program requires utilities to increase their renewable share to 60% by 2030. This creates guaranteed demand and motivates investment in geothermal plants.
Tax Credits
Tax credits reduce the tax liability of geothermal developers and lower the cost of projects. The U.S. provides tax credits such as the Production Tax Credit (PTC) and Investment Tax Credit (ITC) for geothermal. The ITC offers credits equal to 26% of expenditures.
Loan Guarantees
Loan guarantee programs provided by the government cover potential losses, encouraging financing of geothermal projects by mitigating risks. The U.S. Department of Energy has provided billions in loan guarantees for innovative geothermal systems.
Future Outlook
The future looks bright for geothermal power generation as governments and companies continue to invest in and expand their use of this renewable energy source. Here are some key trends that point to strong growth ahead:
Projected Growth: According to the International Energy Agency (IEA), global geothermal power capacity is expected to grow by over 50% from 2020 to 2025. Growth is being driven by countries like Indonesia, Turkey and Kenya rapidly developing new geothermal resources. The IEA projects the Asia Pacific region will add the most new geothermal capacity going forward.
Technology Improvements: Advances in deep drilling, well design and reservoir modeling are making previously unreachable geothermal resources accessible. Enhanced geothermal systems (EGS) are being developed to extract heat from areas without naturally occurring hydrothermal resources. These technologies could vastly expand viable geothermal sites.
Emerging Markets: Countries such as Chile, Ethiopia and Costa Rica have significant untapped geothermal potential and are working to grow development and attract investment. Europe is also expected to substantially increase geothermal power use for heating and electricity in the coming decade. More broadly, over 70 countries have geothermal power resources that remain largely unutilized.
Conclusion
In conclusion, geothermal power generation offers a sustainable and renewable alternative to fossil fuels. Key points covered in this article include:
- Geothermal plants use heat from the Earth’s interior to produce steam and generate electricity.
- Leading geothermal countries include the U.S., Philippines, and Indonesia, but potential exists worldwide.
- Geothermal has a small land footprint, emits little to no greenhouse gases, and provides reliable baseload power.
- While capital costs are high, geothermal offers low operating costs and pays back its carbon footprint quickly.
- Barriers include location-dependence, high upfront costs, and management of brine wastewater.
- Supportive policies, tax incentives, feed-in tariffs, and renewable mandates can aid geothermal growth.
Moving forward, enhancing technologies, exploring new sites, and implementing favorable policies can help unlock geothermal’s full potential as a clean, renewable electricity source. Readers are encouraged to support further geothermal development in suitable locations.
