Which of the following sources of energy has the maximum potential in India?

Concept

The potential of an energy source means the assessed resource — the energy that could in principle be harnessed within the country — and not the capacity already installed or the electricity actually generated today. Two factors fix it: the size of the primary energy flux that reaches the country, and the share of the national territory over which that flux can be tapped.

These sources also sit in a physical hierarchy. Solar radiation is the parent flux: atmospheric circulation is a small secondary conversion of the solar energy the earth absorbs, and the ocean’s surface-to-deep temperature difference is solar heat stored in seawater. Only the tidal flux has a different origin — lunar and solar gravitation — and it is orders of magnitude smaller than the radiation budget.

Application

1. India lies roughly between 8°N and 37°N, so almost the whole land mass sits in the tropical and sub-tropical solar belt, with about 300 clear sunny days a year and 4–7 kWh per square metre per day of global horizontal irradiance. That is of the order of 5,000 trillion kWh of solar energy falling on the country every year, and the National Institute of Solar Energy assesses the usable solar power potential at about 748 GW using only a small share of wasteland.

2. Wind is a secondary conversion of that same solar input and is commercially usable only where the resource is strong — mainly Gujarat, Tamil Nadu, Karnataka, Maharashtra, Rajasthan and Andhra Pradesh. The National Institute of Wind Energy assesses about 302 GW at a 100 m hub height (about 695 GW at 120 m); the contemporaneous 2011 assessment at 50 m hub height was only about 49 GW.

3. Ocean thermal conversion needs a temperature difference of roughly 20°C between warm surface seawater and cold water drawn from about 1,000 m depth, which confines it to deep water off the southern peninsula and around the Lakshadweep and Andaman islands. Its Indian theoretical potential is put at about 180 GW, and no commercial plant operates.

4. Tidal power needs a large tidal range and an estuary that can be barraged. India’s identified sites are the Gulf of Khambhat (about 7,000 MW), the Gulf of Kutch (about 1,200 MW) and the Sundarbans delta (about 100 MW), which come to about 8.3 GW between them; the widest theoretical estimate for Indian tidal power is about 12 GW.

Cross-check

The ranking is the same whether it is read off the modern assessed figures or off the physical hierarchy, because wind and the ocean thermal gradient are both derived from the solar flux and can capture only a small part of it.

Result

Solar energy has the maximum potential in India. Note that potential is not the same as present output: India’s electricity today still comes mainly from coal-fired thermal stations, while the solar resource remains the largest that is available to be developed.