Wind and Solar
Wind and solar energy generation are of course not unique to oceans. Yet oceans provide not only vast amounts of space and sufficient sunlight and wind – but also provide these as a commons property that can in theory be more easily accessed than private property to meet the public good.
Offshore windfarms are common in some parts of the world, such as Northern Europe. Oceanic wind is a preferred alternative to other forms of energy generation in areas where land is in short supply, and where coastal winds are sustained and strong. Denmark has led the effort in harnessing sea wind, and constructed the first offshore wind farm in 1991 off the Port of Vineby. According to the Financial Times, wind farms are expected to supply 8% of Denmark’s electricity by 20087. The UK opened its first offshore wind farm in 2000 in Northumberland, and is following Denmark’s lead with expanded wind farms and feasibility studies for siting in new areas.
The oceans are also the world’s largest solar collector: one square mile contains more energy potential than 7,000 barrels of oil.8 Solar arrays with unfettered access to sunlight can be installed in virtually any coastal area sheltered from excessive wind or waves. Currently most offshore solar plants are used to power oil platforms and in situ research equipment.
Thermal
The oceans can also be harnessed for energy by using the temperature differential of surface and deep waters to drive energy generation The differential exists because the sun warms the surface layers of the ocean, especially in the tropics, while deep waters stay cool. In order for the technology to be able to capture the thermal energy, this temperature differential must be more than 25 degrees Celsius.
Using the temperature of water to make energy actually dates back to 1881, when a French Engineer by the name of Jacques D'Arsonval first thought of using ocean thermal energy gradients. His student, Georges Claude, built the first OTEC plant in Cuba in 1930, producing 22 kilowatts of electricity with a low-pressure turbine. OTEC (Ocean Thermal Energy Conversion) is shorthand for all such thermal energy technologies, but it also refers specifically to the best known and largest scale pilot effort to harness ocean thermal energy, initiated in Hawaii in 1974.
Three types of systems are used to convert ocean thermal energy to electrical energy. Closed cycle systems use the warm surface water to vaporize a low-boiling point fluid such as ammonia. As the vapor boils and expands, it drives a turbine, which then activates a generator to produce electricity. Open cycle systems operate at low pressure and actually boil the seawater, which produces steam to drive the turbine/generator. Hybrid systems use elements of each, in an attempt to improve conversion efficiencies.
Although the temperature differential between surface waters and the deep ocean is significant in almost all parts of the globe, there are constraints to being able to harness this potential energy. Main among them is having deep cold water in close proximity to warm surface waters. Tropical island nations in the Pacific Ocean that have narrow continental shelves are particularly suited. According to NASA, some 98 tropical countries could benefit from the technology.9
OTEC also has spin-off benefits, including air conditioning, chilled-soil agriculture, aquaculture, and desalination10. And OTEC also may one day provide a means to mine ocean water for 57 trace elements, many of which are very valuable.
Thermal energy conversion has great potential, but enormous challenges remain. The technology is still very inefficient and piping large volumes across great depths of ocean (a kilometer or more) is a major engineering feat. Yet some energy experts believe OTEC could produce billions of watts of electrical power if it could be made cost-competitive with conventional power technologies.
Marine biofuels
At the moment there is a flurry of interest in alternative fuels, especially biofuels. Biofuels can be derived from agricultural and forestry residues, energy crops, landfill gas, and the biodegradable components of municipal and industrial wastes. Such fuels can be used for transportation fuel, to provide heat, or to generate electricity. Biomass residues have been burned to create power since at least the middle of the 19th Century, but inefficiencies tended to be extremely high until R&D became focused on making biofuels economically viable.
Corn and switchgrass have received most of the attention as biofuel sources, but there is no reason why marine plants cannot provide the same cellulose for fuel conversion. This emerging technology is being tested in various venues.
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