Oceans are throbbing, which means they are full of energy that can be tapped. There are many ways of tapping this energy for commercial use, but all are still in the works. But broadly, the methods are of three kinds — making use of the up-down movement of the oceans; harnessing underwater currents; and harvesting energy from tidal movement.
Of these, the up-down movement of water is the lowest hanging fruit, perhaps because it calls for the least investment in equipment.
The ‘ocean wave energy converter’ that IIT-Madras unveiled last week has been tailored for Indian waters. Prof Abdus Samad of IIT-Madras, who has established a Wave Energy and Fluids Engineering Laboratory, tells Quantum that Indian seas are characterised by waves that are not tall, but have a high variation — they come in quick succession. This is a useful feature.
Prof Samad and his team tested the small 85 kW machine in the Bay of Bengal, 6 km off the coast of Tuticorin, at a water depth of 20 m. The device chiefly consists of a buoy (a hollow drum of less than 1 m diameter and one foot tall), a flat plate, and a 10 m rod, called spar, connecting the plate and the buoy. Notably, the plate does not rest on the sea floor — it just hovers inside the water. This makes it deployable anywhere, including in seas with slopy, uneven floors. Atop the buoy is a rack-and-pinion arrangement — a gear wheel that can run up and down a pair of toothed guidelines. The wheel is connected to a small generator.
As the buoy bobs up and down in the seawater, the underwater plate remains stable. In tandem with the buoy’s movement, the gear wheel runs up and down, and the generator produces electricity.
Samad’s team wants to build a bigger device, with a buoy of 15 m diameter and larger plate. Samad’s PhD student Prashant Kumar, who is part of the project, told Quantum that with 20 15-m buoys, you can produce electricity for ₹9 a kWhr.
Costs will reduce with scale and alternative materials. Samad reckons that Indian seas pack at least 54 GW of energy, of which 40 GW could come from waves.
Desalination
Samad’s team is working on repurposing the same machine to produce drinking water from seawater. After all, reverse osmosis is about pushing saltwater through a membrane — drinking water accumulates on the other side. When the energy for the ‘push’ is available in the seas, why not use it? The Department of Science and Technology has given IIT-M a grant of ₹1 crore for this purpose.