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examBoard: Cambridge
examType: IGCSE
lessonTitle: Geothermal Energy Resources
Geothermal energy is heat derived from the Earth's interior. The word "geothermal" comes from the Greek words "geo" (earth) and "therme" (heat). This natural heat energy can be harnessed from hot water or steam reservoirs deep beneath the Earth's surface, or from shallow ground near the surface. Unlike fossil fuels, geothermal energy is a renewable resource that provides clean, reliable power with minimal environmental impact.
Key Definitions:
The Earth's core is incredibly hot about 5,500°C similar to the surface of the sun! This heat comes from the original formation of the planet and from the decay of radioactive elements. The heat flows continuously from the core to the cooler surface. In some places, this heat reaches close to the surface, creating hot spots that can be tapped for energy.
Geothermal resources are typically found along tectonic plate boundaries where volcanic activity brings heat close to the surface. The "Ring of Fire" around the Pacific Ocean is particularly rich in geothermal resources. Countries like Iceland, New Zealand, Japan, the Philippines and parts of the United States have significant geothermal potential due to their geological settings.
There are three main types of geothermal power plants, each suited to different resource temperatures and characteristics:
These use steam directly from a geothermal reservoir to turn generator turbines. The steam then condenses to water and is injected back into the ground. The Geysers in California is the world's largest dry steam field.
These pull deep, high-pressure hot water into lower-pressure tanks, causing the water to rapidly vaporize or "flash" into steam to drive turbines. Most geothermal power plants are flash steam plants.
These transfer heat from geothermal hot water to another liquid with a lower boiling point. This second liquid turns to vapor, which drives a turbine. The geothermal water is never exposed to the air and is reinjected into the ground.
Geothermal energy isn't just for electricity generation. It has many direct applications that have been used for thousands of years:
Hot springs have been used for bathing since prehistoric times. Today, many buildings and districts use geothermal water directly for heating. In Iceland, about 90% of homes are heated with geothermal energy, saving the country millions in imported fuel costs.
Farmers use geothermal water to heat greenhouses, allowing them to grow crops year-round in cold climates. The warm water is also used in fish farming to speed growth of species like tilapia and tropical fish, even in cold regions.
Geothermal energy offers several significant environmental advantages compared to fossil fuels:
Iceland sits on the Mid-Atlantic Ridge where the North American and Eurasian tectonic plates are pulling apart. This geological setting provides Iceland with abundant geothermal resources. Before the 1970s, Iceland relied heavily on imported coal and oil. Following the oil crisis, Iceland invested in developing its geothermal resources.
Today, geothermal energy provides about 25% of Iceland's electricity and 90% of its heating needs. The Blue Lagoon, a popular tourist attraction, is actually a byproduct of the Svartsengi geothermal power plant. The warm, mineral-rich water that would otherwise be waste is used for a spa that attracts visitors from around the world.
Iceland's success demonstrates how geothermal energy can transform an economy, reduce carbon emissions and create new opportunities from what was once considered waste.
Despite its many benefits, geothermal energy faces several challenges:
Drilling deep wells is expensive and risky. The corrosive nature of geothermal fluids can damage equipment. Some geothermal reservoirs contain harmful gases like hydrogen sulfide, which must be carefully managed. Enhanced Geothermal Systems (EGS) that create artificial reservoirs are still developing technology.
High upfront costs for exploration and drilling can make geothermal projects expensive to start. The long development time (3-5 years) before energy production begins can deter investors. However, once operational, geothermal plants have low maintenance costs and long lifespans.
New technologies are expanding the potential of geothermal energy:
Kenya is leading Africa in geothermal energy development. The Great Rift Valley provides ideal conditions for geothermal resources. The Olkaria Geothermal Field, near Lake Naivasha, hosts several power plants with a combined capacity of over 860 MW.
Geothermal now provides about 45% of Kenya's electricity, reducing dependence on hydropower (which is vulnerable to drought) and expensive imported fossil fuels. The reliable power supply has supported economic growth and industrial development.
Kenya's success shows how developing countries can use geothermal energy to achieve energy security, reduce carbon emissions and support sustainable development. The country aims to have 5,000 MW of geothermal capacity by 2030.
The future of geothermal energy looks promising. As technology improves and costs decrease, more countries are likely to develop their geothermal resources. Enhanced Geothermal Systems could potentially unlock enormous amounts of energy by tapping into hot dry rock that exists everywhere beneath the Earth's surface.
With growing concerns about climate change and the need for clean, reliable energy sources, geothermal energy is likely to play an increasingly important role in the global energy mix. The International Renewable Energy Agency (IRENA) estimates that geothermal electricity generation could reach 200 GW by 2050, providing about 3.5% of global electricity with continuous, reliable clean power.
For students interested in sustainable energy careers, geothermal energy offers opportunities in geology, engineering, environmental science and policy development. As we transition to a low-carbon future, the heat beneath our feet may become one of our most valuable resources.
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