Heat of the moment

GEOTHERMAL ENERGY SHOULD BE TREATED AS SPECIALISED INFRASTRUCTURE, NOT A NATIONWIDE BACKBONE

- AASHEERWAD DWIVEDI ADITYA SINHA

INDIA'S FIRST NATIONAL Policy on Geothermal Energy, released in September, promises to tap the vast stores of heat beneath the earth’s surface to power homes, factories, and farms. It is a bold move.

Geothermal is renewable, stable, and free from the intermittency of solar and wind. But a closer look at both the science and the numbers suggests that India’s hopes must be tempered by geological reality and economic risk.

“Geothermal” is not one thing; there are layers to the resource which can be categorised as follows:

Shallow heat (a few metres deep) can be tapped by ground-source heat pumps, which heat buildings in winter and cool them in summer by exploiting the relatively stable underground temperature. These systems are mature, widely used in parts of Europe, China, and the US.

Medium-depth heat (hundreds of metres down, 40-60°C) can supply district heating, greenhouses, aquaculture, and industrial drying. Iceland and Turkey have built thriving direct-use industries on such resources.

Deep, high-enthalpy heat (kilometres underground, >100°C) is what powers turbines to make electricity. But this is geologically rare, mostly along tectonic plate edges like the “Ring of Fire”.

Globally, the split is stark: Despite abundant subsurface heat, geothermal electricity constitutes just 0.3% of the world’s power; even in the US, which leads with a 3.7-gigawatt installed capacity, geothermal supplies less than 1% of national electricity.

Here is where caution enters. The Geological Survey of India has mapped 381 hot springs and 10 “geothermal provinces”, but these are mostly lowto medium-enthalpy surface temperatures, often under 90°C. That is fine for bathing and direct heating but nowhere near the >150°C needed for cost-effective power generation.