The Power of the Oceans is Electrifying!
The main body of the conference featured prominent speakers every half hour, the topics covering every facet of ocean energy recovery, including Ocean Thermal Energy Conversion (OTEC), offshore wind projects, onshore wave installations and wave energy conversion technology. Environmental concerns, financial strategies on taxes, and the all-crucial fund- raising aspects of this technology were other important issues that were addressed with aplomb.
Why ocean energy as a source of electricity?
During an average day, an area covering 23 million square miles of tropical seas can store the solar radiation in heat content equal to 250 billion barrels of oil, according to the National Renewable Energy Laboratory (NREL). Between the thermal energy stored in the ocean, the powerful, eternally crashing motion of the waves, and the wind blowing over the oceans, the sea offers the largest clean energy generator on the planet.
We begin a series of three articles covering the subject, briefly describing the workings of various types of technology available and its current applications. The problems are also discussed, from the unwieldy financing and permitting processes to the various environmental issues surrounding this critical energy source.
Ocean Thermal Energy Conversion (OTEC), is the process whereby electricity is made utilizing the thermal gradient between the cold and warm ocean waters, which has to have a 20-degree differential. In open cycle technology, the warm waters from the ocean’s surface (26 degrees centigrade) are pumped into a vacuum chamber causing the seawater to boil in a flash-evaporative process. The seawater, cooled by evaporation, is returned to the ocean. The resultant steam flows into a low-pressure turbine connected to a generator, which creates the electricity. The steam is then funneled into a condenser using cold seawater (6 degrees centigrade), which is pumped from 1000-meter depth, to condense the turbines exhaust steam and cool it producing clean, desalinated water.
In the closed cycle technology the same process described above is used on a working fluid, such as liquid propane or ammonia, which in turn drives the turbine-generator in a closed loop.
Luis Vega, PH.D, a well known author/researcher on OTEC, discussed projects in Hawaii, a 50 kW mini-OTEC plant established since 1979, one in Nauru, Japan a 100 kW OTEC plant, and a 210 kW OTEC Plant in Hawaii that has been operating from 1993 to 1998. He said that the main problem with these energy projects is the huge annual maintenance, repair and replacement costs. Some of the equipment needed for these projects are: heat exchangers, turbines, submergible equipment, and the massive submarine cables that are required to transport the electrical energy (sometimes up to 1,000 meters) to shore.
The obvious added benefits of the open-cycle technology are the fresh water and mariculture produced, as described by Dr. Jacqui Hoover, Natural Energy Laboratory of Hawaii Authority (NELHA) Gateway Manager. She began by explaining how the bathymetric offshore slopes of Hawaii favor OTEC technology because within one-eighth of a mile from the shoreline the water drops off to 1,000 meters. Their OTEC plant in Keahole Bay, Hawaii was established in 1974 and produces 50,000 liters of fresh desalinated water per day, as well as providing nutrient rich, pathogen free water that creates a wonderful environment for marine aquaculture. Their technical problem with the plant is the transmission of power from the origin to the end user on shore.
Another interesting application of OTEC is the floating plantship, introduced to us by Mr. Robert Nicholson, M.D., of Sea Solar Power. His current company is in the business of marketing ocean technology, and their partner company built the first commercial OTEC plant. He pointed out that the ocean as the largest solar collector in the world, and that the advantages of using OTEC to generate electricity include fresh desalinized water and mariculture parks. A 10 mW floating plantship can create three million gallons of fresh water a day; a 100-mW plantship creates 32 million gallons of fresh water a day. The 100-mW plantship is 780 feet long and weighs 25,000 tons. He reverently mentioned one of the earliest OTEC pioneers, James Hilbert Anderson, who invented the reverse refrigeration cycle (a key component in the OTEC cycle) in 1962.
Here are three of the environmental considerations regarding OTEC:
#1. There is possible long term significance to the marine environment caused by the massive amounts of sea water required to operate OTEC plants, but this is easily resolved by using plantships (referred to in the article) of appropriate size. By moving through the oceans, they wouldn’t be displacing an inordinate amount of these waters in any one place.
#2. In closed cycle technology, the hazardous substances are contained (e.g., ammonia) and no toxic byproducts are generated. The carbon dioxide out-gassing generated by OTEC plants is less than one percent of the 700 grams per kWh released by fuel oil plants.
#3. As with other under water construction (as in oil drilling), there are concerns over commercial and recreational fishing having a negative effect of inshore fish populations, but adequate siting of the plants could actually enhance the productivity due to increased nutrients from the deep sea water being redistributed to the surface waters.
The general consensus among the scientists who have been working with these technologies over a sustained period of time, is that with proper design, construction, siting and maintenance, these plants are not only environmentally friendly they are productive sources of power, clean water and food.
