Stepping up from its ongoing initiative of providing potable water on six islands of Lakshadweep using low temperature thermal desalination (LTTD) technology, the Chennai-based National Institute of Ocean Technology (NIOT) is working at making this process free of emissions.

Currently, the desalination plants, each of which provides at least 1,00,000 litres of potable water every day, are powered by diesel generator sets — there being no other source of power on the islands. The LTTD exploits the difference in temperature (nearly 15 degrees Celsius) in ocean water at the surface and at depths of about 600 feet. This cold water condenses water at the surface, which is warmer but whose pressure has been lowered using vacuum pumps. Such depressurised water can evaporate even at ambient temperatures, this resulting vapour when condensed is free of salts and contaminants and fit to consume.

However, the need for diesel power to reduce the water pressure means that the process is not fossil-fuel free and also consumes diesel, a precious commodity on the islands that has to be shipped from the mainland, critical for powering the electric grid.

“For the first time in the world, probably, we are setting up a [desalination] plant that will also supply power to the plant,” said G.A. Ramadoss, Director, NIOT, Chennai.

Currently, there are five desalination plants in operation on the Lakshadweep islands. Four more were expected to be functioning in the coming months. The proposed self-sustaining plant — the 10th plant — is expected to be ready later this year, he added.

The NIOT, an institute under the aegis of the Ministry of Earth Sciences (MoES), has worked for years on harnessing energy from the ocean. However, ocean thermal technology, while plausible for islands, was unlikely to be useful for supplying power onshore. “For such plants to work, we need a large gradient [difference in temperature between the surface and the ocean depths]. In Lakshadweep, these depths can be achieved fairly easily unlike, say, off the coast of Chennai. It will make the power produced this way extremely expensive,” M. Ravichandran, Secretary, MoES, told The Hindu.

While demonstration plants were funded by the MoES, the existing desalination plants were funded by the Lakshadweep administration. The Ministry provided technical assistance and the plants were commissioned via private industry, Mr. Ravichandran added.