OCEAN THERMAL ENERGY CONVERSION
A method of converting part of the heat from the Sun which is stored in the surface layers of a body of water into electrical energy or energy product equivalent.
ENERGY PRODUCT EQUIVALENT
An energy carrier including, but not limited to, ammonia, hydrogen, or molten salts or an energy-intensive commodity, including, but not limited to, electrometals, fresh water, or nutrients for a aquaculture.
Schematic of OTEC system (Source: www.lockheadmartin.com/us/products/otec.html)
Ocean thermal energy conversion relies on the fact that water near the surface is heated by sunlight while seawater deep in the dark is much colder. OTEC plants work by using warm surface water to heat ammonia or some other fluid that boils at a low temperature to produce gas used to drive the turbines needed to produce electricity. The gas is then cooled by cold water pumped up from the ocean depths and the resulting fluid is recycled to help generate power.
The oceans cover more than 70% of Earth’s surface and capture a large part of the sun’s heat in the upper layers, making them the world’s largest solar collectors and energy storage system. Utilizing just a small portion of this energy, can cover the global energy need.
The energy source of OTEC is free, available abundantly and is continually being replenished as long as the sun shines and the natural ocean currents exist. Various renowned parties estimate the amount of energy that can be practically harvested to be in the order of 3 to 5 terawatts (1 terawatt is 112 watts) of baseload power generation, without affecting the temperature of the ocean or the world’s environment. That’s about twice the global electricity demand. The oceans are thus a vast renewable resource, with the potential to contribute to the future energy mix offering a sustainable electricity production method (otecfoundation, Published October 25, 2012).
The technology is viable primarily in equatorial areas where the year-round temperature differential is at least 20°C (36°F).
The distinctive feature of OTEC is the potential to provide baseload electricity, which means day and night (24/7) and year-round. This is a big advantage for for instance tropical islands that typically has a small electricity network, not capable of handling a lot of intermittent power.
Next to producing electricity, OTEC also offers the possibility of co-generating other synergistic products, like fresh water, nutrients for enhanced fish farming and seawater cooled greenhouses enabling food production in arid regions. Last but not least, the cold water can be used in building air-conditioning systems. Energy savings of up to 90% can be realized.
The vast baseload OTEC resource could help many tropical and subtropical (remote) regions to become more energy self-sufficient.
- Fresh Water: The first by-product is fresh water. A small hybrid 1 MW OTEC is capable of producing some 4,500 cubic meters of fresh water per day, enough to supply a population of 20,000 with fresh water. OTEC-produced fresh water compares very favourably with standard desalination plants, in terms of both quality and production costs.
- Food: A further by-product is nutrient rich cold water from the deep ocean. The cold “waste” water from the OTEC is utilised in two ways. Primarily the cold water is discharged into large contained ponds, near shore or on land, where the water can be used for multi-species mariculture producing harvest yields which far surpass naturally occurring cold water upwelling zones, just like agriculture on land.
- Cooling: The cold water is also available as chilled water for cooling greenhouses, such as the Seawater Greenhouse or for cold bed agriculture. The cold water can also be used for air conditioning systems or more importantly for refrigeration systems, most likely linked with creating cold storage facilities for preserving food. When the cold water has been used it is released to the deep ocean.