Water makes up seventy-one percent of the planet earth and ninety-eight percent of it makes up the ocean. It is a single source of water for all forms of life on earth and it also plays an important role in climate changes in the atmosphere. Ocean is the biggest heat sink and absorbs sun’s heat and also a carbon sink absorbing excess carbon dioxide from atmosphere. The surface temperature of seawater is warmer than the temperature at the bottom of the ocean. Sun supplies solar energy to the ocean. In fact the water temperature in Deep Ocean is about 15-20C less than the surface temperature, and it is used as a working fluid to cool buildings by evaporative cooling without using any electricity like commercial air-conditioning.
OTEC (ocean thermal energy conversion) system is a potential method of generating power using the temperature gradient between ocean’s surface water and ocean’s deep water. A temperature difference, as small as 15 -20C is enough to generate power using Kalina cycle, like geothermal energy systems. Commercial plants using this technology are already in operation in few countries. The biggest advantage with open cycle ocean thermal energy conversion system is the fresh water (desalinated ocean water) as a by-product. This technology is unique because it can generate not only power but also drinking water from sea without polluting the air with greenhouse gas emissions. In fact this technology should be deployed commercially is many islands around the world, where there is always a demand for power and drinking water.
“Water, water, everywhere but not a drop to drink”. It is the situation in many islands and many parts of the world. Islands like Maldives and Mauritius should adopt this technology to generate power and supply drinking water without burning fossil fuels like diesel or setting up desalination plants. Of course, the economy of scale and finance is an issue in many islands.
PNG (Papua New Guinea) is one of the biggest islands in Pacific Ocean where there is s severe shortage of power and water. The country is endowed with rich minerals, oil and gas but the basic necessity like power and water are in short supply. OTEC will be an ideal solution for such islands. Fresh water supply is going to be a major issue in parts of the world due to global warming and climate changes. In countries like India, drinking water is in short supply and a number of seawater desalination plants are coming up. Bottled waters are expensive and unaffordable to a common man. This will only increase the power requirements in the country when there is already a massive shortage of power. OTEC is an ideal solution for India with its long coastal line.
One of the major issues with current power generation technologies is the pollution. In any combustion process involving fossil fuel the combustion products like carbon dioxide, carbon monoxide and Oxides of Nitrogen (the greenhouse gases) will contribute global warming. What is the level of such emission and how fast the globe is warming is a futile argument. The pollution can be small in term of PPM (parts per million) but the cumulative effects over several decades is a major issue and that cannot be simply dismissed. There are many places where the Arsenic content in drinking water is above certain acceptable levels (only in ppms) but such small excess cause debilitating health conditions. This is the same argument with greenhouse emission and global warming. It can be gradual and insignificant but it will reach a tipping point and dramatic changes can happen all of a sudden. Nature has got its own mechanism to adjust any imbalances and keep up certain equilibrium. But humans cannot take them for granted and pollute the air and water indiscriminately. There will be a price to pay.
Ocean is the largest and inexhaustible source of Hydrogen. Currently Caustic soda plants use sodium chloride (salt) brine as the raw material for conversion into Caustic soda; the by-products are Hydrogen and Chlorine. Caustic soda plants are currently using Hydrogen as a fuel or use to manufacture Hydrochloric acid. They can generate on site power using Hydrogen to offset their energy cost. In both water electrolysis as well as brine electrolysis, Hydrogen is a product and Ocean water is the largest source of such Hydrogen. In fact countries should generate Hydrogen using desalinated water and OTEC power. The stored Hydrogen is a stored energy that can be used as and when required. That is why we believe ‘water and energy are two sides of the same coin’.