Geo Thermal Energy
Geothermal energy is the powerful heat that is generated and stored within the Earth. The word originates from Greek, where “geo” means earth and “thermal” means heat. It is a highly reliable renewable resource that can be harvested for human use, primarily for heating buildings and generating electricity.
The Origin of Earth's Heat
To understand geothermal energy, we must look deep inside the planet. About 2,900 kilometers below Earth’s crust lies the hottest part of our planet: the core. Temperatures in the core rise to more than 5,000°C.
The heat from the core comes from two main sources:
- Original Heat: A small portion comes from the friction and gravitational pull formed when Earth was created over four billion years ago.
- Radioactive Decay: The vast majority of Earth’s heat is constantly generated by the natural decay of radioactive isotopes, such as potassium-40 and thorium-232. As these isotopes break down in the core, they continuously emit enormous amounts of energy (radiation).
This heat constantly radiates outward, warming rocks, water, and gas. Earth’s temperature naturally rises with depth, a steady change known as the geothermal gradient. On average, the temperature increases by about 25°C per 1 kilometer of depth. When underground rock formations are heated to extreme temperatures (700-1,300°C), they melt into magma. This magma heats nearby underground aquifers, creating natural sources of geothermal energy like geysers, hot springs, steam vents, and mud pots.
Harvesting Geothermal Energy: Heating and Cooling
Geothermal energy can be harvested directly from the ground to heat and cool structures without needing to convert it to electricity first.
1. Low-Temperature Geothermal Energy
- This energy is obtained from shallow pockets of heat at about 150°C.
- It is directly used for heating greenhouses, homes, fisheries, and industrial processes.
- Historical Use: People have used natural hot springs for centuries for comfort and healing (balneotherapy), such as the ancient Roman spas in Bath, England.
2. Co-Produced Geothermal Energy
- This energy is obtained from shallow pockets of heat at about 150°C.
- It is directly used for heating greenhouses, homes, fisheries, and industrial processes.
- Historical Use: People have used natural hot springs for centuries for comfort and healing (balneotherapy), such as the ancient Roman spas in Bath, England.
3. Geothermal Heat Pumps (GHPs)
- GHPs are drilled relatively shallowly (about 3 to 90 meters deep) and can be used almost anywhere in the world.
- They use a continuous pipe system (called a “slinky loop”) filled with water or antifreeze.
- In Winter: The liquid absorbs natural underground heat and carries it into the building.
- In Summer: The system reverses. It pulls heat out of the building and pumps it underground to cool the structure. GHPs are highly energy-efficient and environmentally safe.
Harvesting Geothermal Energy: Electricity Generation
To generate electricity, power plants require intense heat found a few kilometers below the surface. There are three main types of geothermal power plants:
1. Dry-Steam Power Plants
- The oldest type of geothermal plant. It pipes natural, underground dry steam directly into a power plant to turn turbines and generate electricity.
- The world’s first dry-steam plant was built in Larderello, Italy (1911). Another famous example is The Geysers in California.
2. Flash-Steam Power Plants
- The most common type of geothermal plant globally.
- Extremely hot underground water (above 182°C) is pumped into a low-pressure tank. This sudden drop in pressure causes the water to rapidly “flash” or evaporate into steam, which then powers the turbine.
- Iceland and the Philippines rely heavily on flash-steam plants for their national electricity grids.
3. Binary Cycle Power Plants
- These plants use hot water (107°-182°C) to heat a secondary organic fluid (like a refrigerant) that has a much lower boiling point than water.
- The heat causes the secondary fluid to flash into steam and turn the turbine. The underground water never touches the turbine; it is simply recycled back into the Earth in a closed-loop system.
4. Enhanced Geothermal Systems (EGS)
- Many underground areas possess hot, dry rock but lack the water or permeability to create steam.
- In an EGS, high-pressure cold water is injected deep into the rock to purposely create fractures. As the water flows through these new cracks, it absorbs the rock’s heat, creating an artificial underground reservoir of hot brine that is then pumped back up to generate power
Advantages and Disadvantages of Geothermal Energy
Advantages (Pros):
- Renewable and Baseload: Earth will radiate heat for billions of years. Unlike wind or solar, geothermal plants provide baseload power—they operate 24 hours a day, 7 days a week, regardless of the weather.
- Compact Footprint: Geothermal facilities require significantly less land space than sprawling wind farms or massive solar parks.
- Clean Energy: Most modern systems (like Binary cycle) operate in closed loops and only emit safe water vapor, making them incredibly clean.
- Longevity: Properly managed geothermal reservoirs and power plants can reliably operate for many decades.
Disadvantages (Cons):
- High Initial Costs: The expensive drilling equipment and infrastructure make the start-up costs extremely high, often requiring government assistance in developing nations.
- Induced Seismicity: Pumping high-pressure water into the ground (especially in EGS) can cause minor seismic activity, or small earthquakes.
- Land Subsidence: In some cases, extracting deep fluids can lead to subsidence, which is the slow, dangerous sinking of the land above the reservoir.
- Toxic Emissions: If not properly contained in pipes, geothermal fluids can carry trace amounts of harmful underground elements to the surface, such as hydrogen sulfide, arsenic, and mercury.
India’s Geothermal Energy Developments
- Dirang, Arunachal Pradesh became the site of Northeast India’s first geothermal production well, drilled by CESHS (Centre for Earth Sciences and Himalayan Studies) with support from the Ministry of Earth Sciences and ₹2.42 crore funding from the Ministry of Coal, using a closed-loop binary organic Rankine cycle.
- The site is a medium to high-temperature reservoir (~115°C) located near a fault between quartzite and schist rocks, enabling direct-use applications like agricultural drying, space heating, and cold storage in Himalayan conditions.
- Dirang may become India’s first geothermal-powered town, following two years of structural and chemical surveys; drilling was carried out with precision to minimize environmental impact.
- International collaboration includes Norway’s Geotechnical Institute (NGI) and Icelandic firm Geotropy ehf, along with the Guwahati Boring Service for drilling support.
- Other geothermal projects in India:
- Manuguru, Telangana: India’s first operational geothermal power plant (20 kW) by SCCL.
- Khammam, Telangana: A 25 MW project by Geosyndicate Power stalled due to tariff disputes.
- Puga Valley, Ladakh: 1 MW ONGC pilot project, halted in 2022 due to hot water leakage, resumed in 2024.
- Dholera, Gujarat: Demonstration use in cooking and air conditioning by PDEU and Amani Group.
- The Geothermal Atlas of India (2022) by GSI identified 381 thermally anomalous sites; India’s estimated geothermal potential is 10,600 MW, capable of base-load power generation (unlike solar/wind).
- International cooperation: MoUs with Iceland (2007), Saudi Arabia (2019), and inclusion under RETAP with the US (2023) for geothermal R&D and deployment.
Experts emphasize geothermal as a clean, reliable energy source for sustainable development in remote and mountainous regions, while cautioning about fluid leaks and ecological risks if not monitored properly.
