Geothermal Energy: Sources, Fields and Practical Uses
Geothermal Energy: Heat Within the Earth
Geothermal energy is the heat energy stored within the Earth. This heat originates mainly from:
- Residual heat from the Earth’s formation
- Heat generated by radioactive decay of elements like uranium, thorium, and potassium
Geothermal energy can be harnessed for electricity generation, space heating, industrial processes, and direct heating applications. It is considered a renewable, reliable, and environmentally friendly energy source.
2. Nature of Geothermal Fields
A geothermal field is a region where heat from the Earth’s interior is close enough to the surface to be economically exploited.
Characteristics of Geothermal Fields
- High underground temperatures (150°C–350°C or more)
- Presence of hot water or steam reservoirs
- Permeable rocks to allow fluid movement
- Impermeable cap rock to trap heat
- Associated with volcanic activity, tectonic plate boundaries, or hot spots
Components of a Geothermal Field
- Heat source – magma or hot rocks
- Reservoir – porous and permeable rocks
- Fluid – water or steam
- Cap rock – prevents heat loss
3. Geothermal Sources
Geothermal sources are broadly classified into:
- Hydrothermal sources
- Hot Dry Rock (HDR) or Enhanced Geothermal Systems (EGS)
- Geopressured resources
- Magma resources
Among these, hydrothermal sources are the most commercially exploited.
4. Hydrothermal Sources
Hydrothermal sources contain hot water and/or steam trapped underground. They are divided into two major types:
4.1 Vapour-Dominated Systems (Dry Steam Systems)
Description
- Reservoir contains dry steam with little or no liquid water
- Steam is directly used to rotate turbines
Characteristics
- Reservoir temperature: >240°C
- Low water content
- High-quality steam
Power Generation
- Steam from wells → turbine → generator → condenser.
Examples
The Geysers, California (USA); Larderello, Italy
Advantages
- Simple plant design
- High efficiency
Disadvantages
- Rare in nature
- Reservoir pressure declines rapidly
4.2 Liquid-Dominated Systems (Wet Steam Systems)
Description
- Reservoir mainly contains hot water
- Steam is produced by flashing hot water at lower pressure
Characteristics
- Temperature range: 150°C–300°C
- Most common geothermal resource
Power Generation Methods
- Single flash system
- Double flash system
- Binary cycle system (for low-temperature sources)
Examples
Wairakei (New Zealand); Cerro Prieto (Mexico)
Advantages
- Widely available
- Suitable for multiple power plant designs
Disadvantages
- Scaling and corrosion problems
- Lower efficiency than dry steam systems
5. Applications of Geothermal Energy
5.1 Power Generation
- Electricity generation using steam turbines
- Base-load power supply
5.2 Direct Heating Applications
- District heating
- Space heating
- Greenhouse heating
- Aquaculture
5.3 Ground Source Heat Pumps
- Heating and cooling buildings
- Very high efficiency
5.4 Agricultural Uses
- Crop drying
- Soil warming
6. Advantages of Geothermal Energy
- Renewable and sustainable
- Low greenhouse gas emissions
- Reliable 24/7 base-load power
- Small land footprint
- Low operating costs after installation
7. Disadvantages of Geothermal Energy
- High initial capital cost
- Location-specific availability
- Risk of induced seismicity
- Corrosion and scaling issues
- Possible release of harmful gases (H₂S)