How Renewable Energy from the Ocean Could Transform the Caribbean
Caribbean islands surrounded by deep water are perfect candidates for technologies that can produce renewable energy from temperature differences in the ocean layers.
The problem with the two most widely implemented types of renewable energy is that they are intermittent: a solar power system doesn’t work at night, and wind turbines don’t work if there’s no wind. To address these problems, you need to have a method of storing surplus energy in some sort of battery that can be discharged when the generating source is not available.
Other renewable sources, such as hydroelectric dams, geothermal energy, or energy from biomass, rely on specific local resources, such as rivers, volcanic vents, or readily available and cheap material for burning to create steam to spin a turbine or decomposition for gas production.
But what if you are trying to generate reliable and affordable electricity on an island in the middle of the ocean with few natural resources? What if you have no rivers, no volcanoes, insufficient biomass, and you are looking for a solution that produces electricity cheaper than wind/sun power and is always available?
There is one potential solution that could overcome at least some of the problems in finding an energy generation model that is clean, green, sustainable, and cheap. Ocean Thermal Energy Conversion (OTEC), a technology conceptualized in the 1880s, has proven promising in laboratory conditions since the 1970s but is only recently proving itself as having large-scale commercial possibilities.
Some of us are already familiar with a form of OTEC technology called Seawater Air Conditioning (SWAC), used by commercial developers and governments for district cooling and heating of buildings, offices, hotels, and apartments. These systems extract deep, cold water from a nearby ocean or lake to produce air-conditioning using just 10% of the electricity used by traditional air conditioning systems.
An OTEC system does a lot more. Not only can it generate electricity, but it can also provide other major benefits that include desalinated water for drinking and agriculture as well as fish farm nutrients and climate-controlled greenhouses cooled by seawater, enabling more and diverse food production. It is even possible to produce commercial quantities of hydrogen by electrolysis using OTEC.
Three things are needed in order to make a renewable energy OTEC system attractive — warm surface water, easy access to deep, cold water, and high energy costs due to importing diesel for electricity generation. On the face of it, OTEC is the ideal Caribbean renewable energy solution, where low-lying islands are surrounded by a coral reef and a deep drop-off to the ocean floor close to shore. They also have to import a lot of expensive diesel to run the generators for their electricity.
OTEC technology uses the temperature difference between the warm surface water and deep cold water to spin a turbine and produce electricity. It requires a minimum temperature differential of 17–20°C between the surface waters and those at a depth of 1km. This condition is met year-round in Caribbean waters.
In 2015 Hawaii became the first US state to produce commercial quantities of electricity using this method via a 105-kilowatt plant on Big Island. As of 2021, a 1-megawatt OTEC plant is nearing completion in the Pacific island nation of Kiribati, while a further 1-megawatt facility in Japan is on the drawing board.
The current development of OTEC renewable energy programs is mostly concentrated in the Far East and Pacific, with a half dozen operational and at least eight more proposed systems on the drawing board, most with a modest output. In the Caribbean, there are proposals for operating OTEC power plants in Barbados, the Bahamas, the US Virgin Islands, and Martinique, some with an output capacity between 10 and 15 — megawatts.
For remote islands and coastal villages that have no power grids, OTEC can provide clean, self-reliant, sustainable energy and, when ramped up to commercial scale, has the potential to produce electricity at less than 20 US cents per kilowatt-hour. An OTEC system provides this energy in a steady stream that can be ramped up or scaled down quickly in response to demand as a constant and clean energy source.
An OTEC investment could be a boon for Caribbean nations such as the Cayman Islands, with few land-based natural water resources and no rivers. Many islands have a busy tourism industry heavy with visiting cruise liners and suffer from a shortage of fresh water and fresh local produce.
The attraction of an OTEC system should be immediately apparent to anyone familiar with the energy demands of small, often remote tropical island nations throughout the Caribbean and the western edge of the North Atlantic. According to its proponents, OTEC has the potential to offer global amounts of energy up to 100 times greater than other ocean energy options such as wave, tide, or current power.
Industry insiders say the biggest obstacle to the development and implementation of OTEC technology is not technical but financial. Large amounts of investment capital need to be secured in order to scale up from small test plants to large-scale commercial operations.
