The future of green may be blue, too

Edged out of business by wind and solar for long, ‘ocean energy’ is making a comeback. While tens of designs and prototypes are being developed, and are at various distances to commercialisation, at least half-a-dozen commercial-scale plants are being built the world over.

Last month, a British company called Atlantis Resources signed up with an Indonesian utility to build a 150 MW tidal energy plant. Atlantis is building a 298 MW tidal energy plant near Scotland, the first phase of which is almost ready to generate power. In Wales, UK, a 320 MW Swansea Lagoon Tidal Power project is cruising towards completion. In South Korea, the 254 MW Sihwa Lake project has been in operation since 2011. There are many others too, but of smaller capacity.

Clearly, ocean energy is beginning to turn viable. Importantly, unlike wind and solar, ocean energy is available 24x7 – no intermittency issues.

India, with a 7,500-km coastline, has a huge potential to tap into but ocean energy is not even a footnote in any cleantech discourse. After a few tentative, failed attempts, India has practically ignored this resource.

In the early 1980s, two engineers from IIT-Madras developed a design and set up an experimental project at Vizhinjam, Kerala. According to CRISIL, the project failed and was formally decommissioned in 2011. In the meantime, Gujarat Petroleum Corporation Ltd tied up with Atlantis Resources for a 50 MW tidal energy component of a much bigger project, the ₹60,000-crore Kalpsar project. The tidal energy component has since been dropped on technical grounds. The 3.75 MW Durgaduani project in the Sundarbans, West Bengal, met with the same fate — it was approved in December 2011 by the Union Cabinet, but was discontinued in two years, because the cost had gone up from ₹48 crore to ₹238 crore.

However, globally technology has evolved, particularly in the last decade. Today, there are at least 50 different designs.

Basically, ocean energy technologies fall into four broad categories — those for wave energy, tides, underwater currents and ocean thermal.

Wave energy technologies typically have buoys that bob up and down with the waves or ocean swells, and the movement is converted into electricity. Some designs let the waves crash into a closed chamber; the air pushed out of the other end of the chamber drives the turbines. The Vizhinjam project was based on this technology.

Technologies for tapping tides typically create a lagoon, across the mouth of which they build a barrage holding a series of turbines. When the tide rises, the waters rush in through the barrage, turning the turbines on the way. When the tide ebbs, the waters flow in the reverse direction, back into the sea, and again turn the turbines. The Swansea Lagoon and Sihwa Lake projects are based on this technology.

 Tidal current projects have an array of turbines sitting on the sea bed. The deep water currents turn the turbines. Atlantis’ MeyGen project is based on this technology. Sea water is 832 times denser than air, so a 5-knot flow has the same energy as a 10 metres-per-second gust of wind.

Ocean thermal technologies make use of the temperature difference between the surface and deep waters, but are somewhat behind the other three. Here again, India started early— in 2000, the government of India and IIT-Madras attempted to put up a 1 MW plant near Tuticorin, but the project failed. In 2008, the Comptroller and Auditor General observed that “poor planning and deficient project management rendered the entire expenditure of ₹60.82 crore unfruitful.”

In January, India joined International Energy Agency – Ocean Energy Systems, by virtue of which India will partner in developing test protocols with other countries and participate in joint programmes.

“That is a good first step, but India should pay more attention to ocean energy,” says Malolan Cadambi, Founder and Managing Director of Greenshore Energy, who has studied ocean energy for a decade.

As for costs, the Atlantis-GPCL venture had asked for a tariff of ₹13 a kWhr of the Gujarat State Electricity Regulator – exactly where solar energy was five years ago. With improvements in technology and scale-effect, ocean energy can get a lot cheaper, says Cadambi.

“Wave, tidal and marine current devices could be integrated into a composite offshore platform housing wind turbines as well. This will help reduce per-MW capital cost,” he says.

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