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examBoard: Cambridge
examType: IGCSE
lessonTitle: Geothermal Power Generation
Geothermal power generation harnesses heat energy from beneath the Earth's surface to produce electricity. This renewable energy source taps into the natural heat of the Earth's core, which maintains a temperature of about 5,500°C. The word "geothermal" comes from the Greek words "geo" (earth) and "therme" (heat), literally meaning "earth heat".
Key Definitions:
The Earth's core heats surrounding rock, which in turn heats groundwater. This hot water and steam can be accessed by drilling wells into geothermal reservoirs. The steam or hot water is then brought to the surface and used to drive turbines connected to electricity generators. After use, the cooled water is returned to the reservoir through injection wells to be reheated, making this a sustainable cycle.
Geothermal resources are most accessible in regions with active or geologically young volcanoes. These areas, often found along tectonic plate boundaries, have higher geothermal gradients. Countries with significant geothermal resources include Iceland, New Zealand, the United States, Indonesia, the Philippines, Kenya and Italy. However, with advanced technology, geothermal energy can be harnessed in many more locations.
There are three main types of geothermal power plants, each suited to different resource temperatures and conditions:
The oldest type of geothermal power plant. They use steam directly from a geothermal reservoir to turn generator turbines. The steam then condenses to water and is injected back into the ground. These plants work best with resources above 235°C. The Geysers in California is the world's largest dry steam field.
The most common type today. They use high-pressure hot water from deep inside the earth (above 175°C). When brought to the surface, the pressure drops and the water "flashes" into steam to drive turbines. The remaining water and condensed steam are injected back into the reservoir.
These operate with lower temperature water (125-175°C). The hot water is passed through a heat exchanger, where it heats a secondary fluid with a much lower boiling point (like butane). This secondary fluid vaporises to drive the turbines. These plants are closed-loop systems with minimal emissions.
While geothermal energy is considered environmentally friendly, it's important to understand its potential impacts:
Modern geothermal plants are designed to minimise these impacts through closed-loop systems, proper waste management and careful site selection.
Iceland sits on the Mid-Atlantic Ridge, a boundary between tectonic plates with intense volcanic activity. This makes it ideal for geothermal energy production. Today, geothermal power provides about 25% of Iceland's total electricity generation and heats about 90% of homes.
The Hellisheiði Power Station, Iceland's largest geothermal plant, produces 303 MW of electricity and 133 MW of thermal energy for district heating. Beyond electricity, Iceland uses its geothermal resources for:
Iceland's success demonstrates how geothermal energy can transform a nation's energy security and economy while reducing carbon emissions.
Enhanced Geothermal Systems represent the future of geothermal power, potentially making it available almost anywhere. EGS involves creating artificial geothermal reservoirs by:
While still developing, EGS could dramatically expand geothermal energy's potential beyond traditional geothermal areas.
As of 2021, the global installed capacity for geothermal power was approximately 15.4 gigawatts (GW). The top producers include:
Many countries are rapidly expanding their geothermal capacity as part of their renewable energy strategies.
The future of geothermal energy looks promising with technological advances making deeper resources accessible and EGS potentially opening up new regions. The International Renewable Energy Agency (IRENA) projects global geothermal power capacity could reach 40 GW by 2050. Beyond electricity, direct use applications like district heating, greenhouse heating and industrial processes are expanding rapidly.
Geothermal energy offers a reliable, renewable source of electricity with minimal carbon emissions. While currently limited by geography, technological advances are expanding its potential. With proper management, geothermal resources can provide sustainable energy for centuries. As we transition to cleaner energy sources, geothermal power will likely play an increasingly important role in our global energy mix, especially in countries with favourable geological conditions.
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