Keeping in view the commitment for a healthy planet and as per India’s Nationally Determined Contributions made in the Paris Accord on Climate Change, India has made a pledge that by 2030, 40 per cent of installed power generation capacity shall be based on clean energy sources. Accordingly, an ambitious target has been set of installing 175 GW of renewable energy capacity by 2022. This includes 100 GW from solar, 60 GW from wind, 10 GW from bio- power and 5 GW from small hydro power. The possibility of venturing into new emerging renewable energy technologies, such as Floating Solar, Offshore wind, solar wind hybrid, energy storage, etc is also being explored. However, renewable energy technologies such as geo-thermal and ocean energy still remain at a nascent stage in India.

Ocean Energy:

• Oceans occupy more than 70 per cent of Earth’s surface and are an inexhaustible source of renewable energy.
• Ocean energy is the energy harnessed from ocean waves, tidal range (rise and fall) & tidal streams, temperature gradients and salinity gradients.
• Only few commercial ocean energy power plants have been commissioned till date.
• Apart from tidal barrage plants which use established tidal turbine technology, other ocean energy technologies are still largely in pre-commercial development stages.

Indian Scenario:

• As per study conducted by IIT Madras, Theoretical Potential for tidal Energy in India is 12500 MW.
• Promising locations are Gulf of Khambhat & Gulf of Kutch (GJ), Sunderbans (WB), Western Ghats etc.
• Theoretical Potential for Wave Energy in India is 41,000 M W, Promising locations are Western Coast of Maharashtra, Goa, Karnataka, Kerala, Kanyakumari, Southern tip of India. etc.
• However, resource survey at target locations i.e. Western Ghats, Eastern Ghats, etc may be undertaken to assess/ validate actual potential.
• These technologies are more Suitable for Off grid electricity generation in remote coastal areas’ mangroves/ islands where Tariff is very high @ Rs 25/Kwh for diesel based captive power generation.

Technology:

1. Tidal Energy:

• The tidal cycle occurs every 12 hours due to the gravitational pull of the moon.
• The difference in water level from low tide and high tide is potential energy that can be harnessed.
• Similar to hydropower generated from dams, tidal water captured in a barrage across an estuary during high tide and forced through a turbine during Iow tide.
• The capital cost for tidal energy power plants is very high due to high civil construction that results in high power tariff.
• In order to harness power from the tidal energy, the height of high tide must be at least five meters (16 feet) greater than low tide.

1. Wave Energy:
   • Wave energy is generated by the movement of a device either floating on the surface of the ocean or moored to the ocean floor by the force generated by the ocean waves.
   • Many different techniques for converting wave energy to electric power have been developed.
   • Wave conversion devices floats on the surface have joints hinged together that moves with the waves.
   • The kinetic energy pumps fluid through turbines and generates electric power.
   • Moored wave energy conversion devices use pressure fluctuations produced in long tubes from the waves moving up and down.
   • This wave motion drives a turbine.
2. Current Energy:
   • Ocean current is ocean water moving in one direction.
   • This ocean current is also known as the Gulf Stream.
   • Kinetic energy can be captured from the Gulf Stream and other tidal currents with submerged turbines that are very similar in appearance to miniature wind turbines.
   • Similar to wind turbines, the movement of the marine current moves the rotor blades to generate electric power.
3. Ocean Thermal Energy Conversion (OTEC):

• Ocean thermal energy conversion, or OTEC, uses ocean temperature differences from the surface to depths lower than 1,000 meters to harness energy.
• A temperature difference of even 20 degree Celsius can yield energy efficiently.
• Research focuses are on two types of OTEC technologies to extract thermal energy and convert it to electric power: closed cycle and open cycle.
• In the closed cycle method a working fluid such as ammonia is pumped through a heat exchanger and vaporized. This vaporized steam runs a turbine. The cold water found at the depths of the ocean condenses the vapor back to a fluid where it returns to the heat exchanger.
• In the open cycle system, the warm surface water is pressurized in a vacuum chamber and converted to steam to run the turbine. The steam is then condensed using cold ocean water from lower depths.

Future Road Map:

• Most Ocean Technologies are still at Pre R&D/commercialization stage worldwide.
• Therefore, technologies need validation from leading research institutes before demonstration.
• It is necessary to plan to develop Demonstration projects initially for each ocean energy technology at feasible sites before going for commercial plants as also to undertake resource assessment with support from leading countries as ocean energy expert.

Geothermal Energy:

• Geothermal Energy is a mature renewable energy technology that has a potential to provide clean and reliable energy for power generation and direct heating/cooling.
• Geothermal Energy can be utilized for both electric power production and direct heat applications including Ground Source Heat pump (GSHP) for space or district heating, generating hot water for domestic/ industrial use, running cold storages and greenhouse, horticulture, etc.
• However, Geothermal Energy has experienced modest growth worldwide in recent times as compared to other RE sources especially wind or solar due to its site specific nature, risk/uncertainty involved with resource exploration and high capital cost.

Indian Scenario:

• The promising geothermal sites for electric power generation are Puga Valley & Chummathang in Jammu & Kashmir, Cambay in Gujarat, Tattapani in Chattisgarh, Khammam in Telangana & Ratnagiri in Maharasthra.
• The promising geothermal sites for direct heat use applications are Rajgir in Bihar, Manikaran in Himachal Pradesh, Surajkund in Jharkhand, Tapoban in Uttarakhand & Sohana region in Haryana.

Power Generation:

• Hot water and steam from deep underground can be piped up through underground wells and used to generate electricity in a power plant.
• There are three types of geothermal power plants:

1. Dry Steam Plants which use geothermal steam directly.

2. Flash Steam Plants which use high pressure hot water to produce Steam.

3. Binary Cycle Plants which use moderate-temperature water (107 to 182 degree Celsius) from the geothermal reservoir.

Future Roadmap:

• Industry led, applied R&D proposals to harness geothermal energy under Research, Design, Development & Demonstration (RDD&D) policy are necessary for this renewable energy source to become operational.
• Plans should be made to develop Demonstration projects initially each for geothermal electricity production & direct heat use applications.
• PSUs may undertake resource assessment with support from leading countries as geothermal expert.
• Projects for space cooling and industrial process heating using GSHP technology may be supported through subsidy, preferential tariff from power companies as technology is energy/ water efficient.