Geothermal Energy: A Comprehensive Guide

Posted on Sep 12, 2024 in Geology

Geothermal Energy

Introduction

Definition: Geothermal energy is a renewable energy source derived from the Earth’s internal heat. This heat originates from two primary sources:

  • The decay of radioactive elements within the Earth’s core.
  • Residual heat from the planet’s formation.

History

Geothermal energy has a long history, dating back centuries for direct heating applications. However, electricity generation from geothermal heat is a relatively recent development.

  • 1904: Piero Ginori Conti pioneered the first geothermal power plant in Larderello, Italy.
  • 1930: Iceland established the first large-scale geothermal district heating system.
  • Early 20th Century: New Zealand saw the first industrial application of geothermal heat.
  • 1975-1995: The geothermal energy sector experienced significant growth.
  • Present: Geothermal heat pumps are driving further advancements and adoption of this technology.

Theoretical Bases

Geothermal Deposits

A geothermal deposit is a subsurface area where geothermal resources can be economically extracted. These deposits are classified based on temperature:

  • Very Low Temperature Deposits: Temperatures below 30°C, found at shallow depths or in aquifers. Used for heating homes and buildings with heat pumps.
  • Low-Temperature Deposits: Temperatures between 30°C and 90°C, found at depths of 1,500 to 2,500 meters. Suitable for direct heating applications.
  • Medium-Temperature Deposits: Temperatures between 90°C and 150°C, found at depths of 2,000 to 4,000 meters. Can be used for electricity generation.
  • High-Temperature Deposits: Temperatures above 150°C, found in areas with high geothermal gradients. Ideal for electricity generation.

Harnessing Geothermal Energy

To harness geothermal energy, a well is drilled into a geothermal deposit to extract the heated fluid (water or steam). High-temperature fluids can directly drive turbines connected to generators, producing electricity. The used fluid is then reinjected into the reservoir to maintain pressure and sustainability.

Utilizing Very Low-Temperature Geothermal Energy

Geothermal heat pumps leverage the relatively constant temperature of the shallow subsurface to heat and cool buildings. In winter, heat is extracted from the ground, and in summer, excess heat from the building is transferred to the ground. This heat exchange is facilitated by a geothermal heat pump and a heat exchanger.

  • Geothermal Heat Pump (GHP): An electrical device designed to exchange heat with the ground.
  • Heat Exchanger: A network of pipes that circulate water to facilitate heat exchange with the ground.

Geothermal installations can be configured vertically or horizontally, depending on site conditions.

Advantages of Geothermal Energy

  1. Reduces reliance on foreign energy sources.
  2. Minimal waste generation and lower environmental impact compared to fossil fuels.
  3. Cost-effective and energy-efficient.
  4. Quiet operation.
  5. Abundant geothermal resources compared to fossil fuels and uranium.
  6. Stable energy prices, independent of international fluctuations.
  7. Smaller land footprint per megawatt compared to other power plants.

Disadvantages of Geothermal Energy

  1. Potential emission of hydrogen sulfide (H2S), which can be toxic in high concentrations.
  2. Possible contamination of nearby water sources with toxic substances.
  3. Thermal pollution.
  4. Potential landscape alterations.
  5. Limited transportability of geothermal energy as a primary energy source.
  6. Geographic limitations on resource availability.

Environmental Impact

  • Resource Depletion: Extracting geothermal fluids can gradually cool down natural deposits.
  • Damage to Geothermal Features: Geothermal development can negatively impact natural features like hot springs and geysers.
  • Subsidence: Fluid extraction can cause land subsidence due to reduced underground pressure.
  • Water Pollution: Geothermal fluids may contain elevated levels of pollutants, potentially harming aquatic life.
  • Air Emissions: Released gases from geothermal fluids can contribute to air pollution.

Cost of Geothermal Energy

  • Geothermal power plants typically cost between $1,150 and $3,000 per kilowatt installed, depending on factors like temperature, geology, and technology.
  • Costs are decreasing with technological advancements.
  • Geothermal power plants have a lifespan of 30 to 45 years.