Tidal Wave Energy Generation Is Key For India's Sustainable Energy Future

The rise of spring tide in Gulf of Khambat is over 10 meters. Few other locations in the world have such large tidal ranges. This is nature¡¯s way of providing us a large amount of ¡®power¡¯ every few hours and taking it back, since we have not learnt to harness it.

The ocean provides us ¡®power¡¯ to harness in a few forms. Waves on the surface, ocean currents, tidal streams, rise of tide and of course, the thermal inversion.

Many attempts have been made to harness ocean wave energy. If you search for images of ¡®Wave energy harvester¡¯ on the net, there are dozens of images. But most of them are illustrations of ideas, untested by prototyping.

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Promise of tidal wave energy generation

The photographs of a few that have been prototyped, are those that have made the technical cut, but are struggling to make a good commercial case in order to inch towards economy of scale. This is common at the infancy of any technology.

There are dozens of ways to convert the energy on the surface waves to useful forms. This can be done by rotating a shaft of a generator or by pumping air or hydraulics. ¡®Wave energy converters¡¯ is a generic term given to various plant designs that can harness or convert the energy on the surface waves to usable forms like electricity or usable potential energy. This may be converted to electricity locally or at the landfall point.

Wave Energy Converters (WEC), where part of system is seated on the seabed have logistical challenges of deployment and siting*. Floating versions of the same can be assembled in port, wet towed to location and anchored.

Sekhar DC

Most countries with a coast have a large fetch and waves bring a lot of energy to the coast. It is not the breaking waves on the beach, but the unbroken waves about a hundred odd meters away that represents this energy.

Tidal energy is a very reliable source of power. Unlike the wind and wave with their seasonal and unseasonal variations, tides are very predictable years ahead. That will make the production predictable and plan the consumption cycles. Since tides predominantly follow the moon, there is a time lag every day and not the easiest to sync the power production and the human consumption cycles. Storage of energy becomes absolutely necessary to smoothen the power yield and demand curves.

While rise of tides is the potential energy, the tidal streams are very interesting aspect of this tidal movement, representing the kinetic energy of the tidal action. The movement of water in one or opposite direction brings about the rise and fall of tide. A turbine kept on the path of this stream will generate power.

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It has to be able to pivot around or generate power in both directions since that is the nature of tidal streams. There is one snag. The tidal stream weakens during change of tide and a part of the cycle around the change of tide is below the threshold of generation. The production is interrupted every change of tide and once again the capacity to store energy becomes absolutely necessary.

A lot of wind farms have moved to the sea in some geographies. This is mainly where land is scarce, better yield of wind power is available over the sea, and where the uninterrupted view of the horizon is a sensitive issue.

Most offshore installations currently are fixed turbines in shallow waters. But recent trends are to deploy huge floating wind turbines in deeper waters. The size of recent floating turbine deployments are large. Hywind Scotland operates five floating wind turbines of 6MW each, totaling to 30 MW. Of course the wind resource availability is higher in those latitudes.

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Tidal wave energy potential for India

The SW monsoon along the entire west coast brings a large wave energy resource, notwithstanding its seasonality. If this seasonality of resource can be factored in the project feasibilities with a design that has a low minimum threshold of wave height for generation, there is a good possibility for a wave energy plant along the entire west coast. For the record, various studies available in public domain have put the energy potential ranging from 10kW/M of wave crest to 30 kW/M.

With minimal 1 Meter tides is the Southern Kerala coast, the maximum tide amplitude reaches around 6 Meters in Mumbai and 10 Meters when we go further north to the Gulf of Kutch. Stored energy becomes a good option in larger tidal ranges.

It is to be borne in mind that generally tidal streams are equally strong where tidal ranges are large and therefore Gujarat coast becomes a natural choice for these tidal energy plants. Pelamis, a Scottish company made a working wave energy harvester of 750kW capacity. But the device failed to raise investor interest, and the company later shut down.

A wave energy project was developed in India in 1991 near Vizinjam in Kerala, but was also closed down later. There has been other prototypes that have seen technical successes in harnessing wave energy, though financial success has eluded most of them.

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Islands have logistical issues with connecting fuel for running generators due to monsoon and rough seas. Converting a problem to an opportunity would involve deploying wave energy generators that generate good power when fuel logistics become difficult in rough seas.

A lot of hybrid models are being assessed, be it wind and solar or waves. The net search will throw up many such attempts. There are contradicting resource and environment requirement for each of these models. There needs to be a clear synergy if two resources were to be harnessed by the co-located system. Else the attempt will fizzle out after the media hype dies down.

It may be noted that since input energy is free, energy efficiency of these machines need not be directly compared with other forms of harnessing. The feasibility is a factor of project capex, besides the lifecycle and plant maintenance costs. If the project is designed well, with lower fabrication and operating costs, as can be expected in this part of the world, a project unviable in another part of the world can be viable here.

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The energy is definitely out there in abundance. Those who go out to sea, know the power of the waves. It can bend steel pipes and break up a ¡®non-seaworthy¡¯ vessel.

We have to think beyond solar and wind now, to cost effectively harness ocean energy in ten years¡¯ time. If we can achieve the economy of scale in solar, it is time to start the ocean energy journey now. In short, the energy is out there. What are we waiting for? If we are not smart enough to harness it in our lifetime, of course the next generation will.

AlphaMERS has prototyped and tested a wave energy harvester with a seabed component and floats. This design allows customisation for various locations with varying wave heights, tidal ranges and depths. Now it is developing a floating version of the same system. AlphaMERS is designing a wave powered boat as a small unmanned floating platform for payloads of surveillance and security equipment. This is designed as a small boat with extraordinary cruising range.

About the author: D C Sekhar is the founder of AlphaMERS. He has carried out various techno commercial feasibility studies ranging from cruise tourism to yacht marinas and inland waterways for the Indian government. His company¡¯s flagship innovation is floating barriers for river clean up that has stopped tens of thousands of tons of trash and a few thousand tons of plastics from reaching the seas, using only natural river flow. Opinion expressed here is author's alone.