Current Energy

Can Trinidad & Tobago Harness Ocean Energy?

As seen in recent times, the ocean contains massive amounts of energy. Tropical storm Sandy which devastated portions of the Caribbean and Northeastern United States during late October 2012 was able to harness just a fraction of the ocean’s energy to produce strong winds and a massive storm surge, securing its place in history as one of the most unique storms recorded. Many clean energy enthusiasts believe that the ocean as an energy source is often over looked.

Water covers approximately three quarters of the earth’s surface. The World Energy Council estimates that the energy that can be harvested from the world’s ocean is twice the amount of electricity that the world now produces. Trinidad and Tobago is still heavily dependent on non-renewable resources such as oil and gas for the generation of electricity. The largest percentage of electricity generated from oil and gas in Trinidad over the past 38 years was 99.81% in 2003, while the lowest value was 96.47% in 1971. Although the use of energy generated by the ocean is increasing across the globe, Trinidad and Tobago and other islands of the Caribbean have not as yet exploited this potential source of clean energy.

Renewable energy resources are the future as they are available in significant amounts and are by far the cleanest sources of energy available on planet earth. These alternative sources of energy generally require startup capital which is a challenge for many Caribbean islands. Tidal, wave and ocean thermal energies are all within the realm of reality. The ocean can produce two types of energy: thermal energy from the sun’s heat, and mechanical energy from the tides, waves and ocean currents. It is important that we understand some of the technologies that can produce ocean energy and what it could mean for us in Trinidad and Tobago.

Tidal energy is generated from the power of changing tides caused by the magnetic pull of the moon. This may be achieved by building a dam across a bay or an estuary where there is a significant difference between high and low tide. The high tides allow immense amounts of water to rush into the bay. The gates of the dam then shut when the water level is at its maximum height. When the tides fall the gates open and the water flows out and spins a turbine which creates electrical energy.

The world’s first Tidal Power Station, Rance opened on the 26th November 1966 in France and takes advantage of tidal water flow to produce electricity. A major drawback to tidal energy is that it is not a constant source of electricity as it relies on the rise and fall of tides to work and there are only two tides per day. For tidal energy to be considered economical a range of at least seven metres at high tide is needed. Unfortunately in Trinidad waters, the highest tides reach only two metres. So what does that mean for our future with tidal energy? Rather than using a change in water height, offshore turbines are made to work just like wind turbines but underwater, harnessing water currents to turn the turbines and produce electricity. These Tidal Current technologies extract energy from the high tide bulge created by the gravitational pull of the Moon and Sun moving horizontally around the Earth’s surface.  Unless taken to extremes, it does not require blocking of any waterways, and hence does not have the adverse environmental effects associated with Tidal Barrages. Trinidad’s east coast is close to the Guiana Current the second largest ocean current in the world, which has speeds between 0.2 and 4.2 knot that is sufficient to produce electricity using submarine turbines. Currently the Institute of Marine Affairs (IMA) recognizes the potential for these ocean currents to power submarine turbines and as such has embarked on a project that entails a detailed study of ocean currents around Trinidad and Tobago especially in the Columbus Channel and the Galleons Passage.

Submarine turbines can produce clean renewable energy. However, a disadvantage of underwater turbines is that they require additional maintenance as the salt water corrodes mechanical parts, also moving the electricity generated back to land is always a challenge once implemented. In 2008, the tidal current power plant SeaGen began operating off the Irish Coast using offshore turbines which produce 1.2 megawatts of clean electricity. This is enough to supply a town of 1,500 households, solely from the power of the tides.

One of the possible means provided by the sea for generating electricity is to make use of the force produced by waves.  The Northeast Trade Winds which contribute to the abundance of waves around Trinidad and Tobago increases the possibility of having large scale wave energy farms in our waters.  So how do we harvest wave energy? Most of the wave energy technologies rely on the up-and-down motion of waves to generate electricity. In Portugal, the world’s first wave farm consists of Pelamis’ wave energy devices. This device, which resembles a large segmented sea snake, consists of four big cylinders strung together by hydraulic joints. As the tubes bob up and down on the waves, their movements lob the joints, moving oil through hydraulic motors. These motors drive generators to produce electricity. The Pelamis snake is 600 feet long and 13 feet wide and generates up to 0.75 megawatts, that’s enough to power about 500 households for a year. It is estimated that with just 15 of these devices around our coast it is possible to generate enough electricity to power the entire Borough of Arima. However, the amount of electricity that can be generated depends largely on the frequency and height of ocean waves, also once implemented Pelamis poses a possible threat to navigation from collisions due to the low profile of the wave energy device.

The ocean offers the single largest opportunity for meeting our energy needs. It acts as the world’s largest solar panel collecting 80% of energy the earth receives from the sun or enough to offset 250 billion barrels of oil every day.  While the ocean’s surface water heats up, the depths of the ocean remain cold.  Ocean Thermal Energy Conversion (OTEC) turns this difference in temperature into power. The process begins when the warm surface water is used to boil a fluid producing steam. The steam turns a turbine and generates electricity; cold water in the ocean depths is used to condense the steam and turn it back into water thus completing the cycle.

The Atlantic Ocean on the eastern side of Trinidad is both warm at the surface and cold enough at depths to sustain an OTEC plant. OTEC can provide a responsible way to meet growing power needs and in Trinidad and Tobago reduce the amount of electricity generated from oil and gas. For OTEC to be viable as a power source, the technology must have tax and subsidy treatment similar to competing energy sources. Because OTEC systems have not yet been widely deployed, cost estimates are uncertain. One study estimates power generation costs as low as US $0.07 per kilowatt-hour, compared with $0.05 – $0.07 for subsidized wind systems.

The vast ocean is full of energy potential.  The Pelamis, Tidal offshore turbines submarine turbines and OTEC are just a few mechanisms used to tap into the oceans energy reserve. Through their continued research and projections, scientists believe that in order to have clean energy the world’s power may need to come from the ocean. With energy security concerns on the rise the ocean is an energy source which Trinidad and Tobago can explore as we look to new ways of powering our nation with a sustainable energy source.

 

Credit: Glendon Glasgow at the Institute of Marine Affairs. Article first published in the Trinidad Express

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