How to bring electrical power to a tropical island?
Providing electrical power to coastal and island communities in the tropics can be fraught with problems. Now some specific solutions are being developed.
- Wave power leaves tropical islands high and dry
- France picks up the baton
- The problems faced in providing power to coastal and island communities
- Harnessing the ocean’s thermal differential
- Historical developments of OTEC technology
- Current developments
- A radical adaptation of existing technology
Wave power leaves tropical islands high and dry
The wave power systems in operation at present, such as the Limpet and the Oyster, are most effective in the temperate regions between the 40th and 60 parallels where prevailing winds strongly drive waves onshore. At present, wave power leaves island and coastal communities in the tropics figuratively ‘high and dry’. So how do you power your tropical island paradise if you are remote from major power generation centres on the mainland or even in an idyllic setting in the middle of the ocean, such as many of the islands in Oceania enjoy?
France picks up the baton
The French islands in the Pacific and Indian oceans and the Caribbean are not colonies but integral parts of French national territory. Politicians tend to be mostly interested in their own back yard and most French deputies come from Metropolitan France but, nevertheless, there is an obligation to provide the same freedoms and benefits as are enjoyed by European French citizens. Now, the DCNS Group, in which the French government holds a 74% stake, is addressing the problem of supplying power to the these remote French outposts. The group has long been a supplier of naval vessels and equipment and is expanding into new markets in civil nuclear engineering and marine renewable energy. Early in 2011, DCNS acquired a €14-million stake in OpenHydro, a leading company in the growing marine turbines market.
The problems faced in providing power to coastal and island communities
Island and coastal communities are frequently small and remote from the main commercial power plants. Power lines must be run over long distances, either on pylons or underground in order to provide electricity. Small-scale conventional power plants are uneconomic to operate and difficult to supply with the relevant fuel; on small islands and broken shorelines, suitable locations for such a plant may also be unavailable. The more remote the location of the community, the greater the problems faced in supplying the community with power. The ideal solution would be a scalable power plant capable of producing low carbon footprint power from on-the-spot resources and requiring little or no space on land. DCNS has now developed two solutions to these problems, one ambitious and the other a radical adaptation of existing technology.
Harnessing the ocean’s thermal differential
In the tropics, the sun’s heat maintains the surface water of the sea at around 25°C (77°F), whereas the ocean depths below 1000m (3300ft) remain at around 5°C (41°F). This temperature differential can be harnessed all year round by means of a heat engine. Outside the tropics, the temperature differential is too low to be utilizable.
Plants utilizing this heat differential are termed ocean thermal energy conversion (OTEC) plants. Because of the small heat differential, the overall efficiency of the generating process is low but is capable of producing power 24/7. The plants can be designed in three different configurations, open loop, closed loop and hybrid. The water used by the plant can also subsequently be utilized in a variety of ways, including air conditioning and aquaculture and, in some configurations, also for desalination and hydrogen production (see “How an OTEC marine energy plant works”).
Historical developments of OTEC technology
The USA maintains an operating plant and research laboratory at Keahole Point in Hawaii, Japan is contributing heavily to development of OTEC technology and India has built a 1 MW floating pilot plant near Tamil Nadu.
DCNS has signed agreements for OTEC plant feasibility studies with three French islands
In April 2009, the group signed an initial agreement with the Regional Council on Réunion Island for a feasibility study on an initial 1.5 MW demonstration plant.
This has been followed, in February 2010, by an agreement with the local government for French Polynesia for a feasibility study for a plant in Tahiti.
Most recently, the Caribbean island of Martinique responded to an invitation for tenders from the European Commission with a proposal for a 10 MW OTEC pilot plant. Under the preliminary sizing agreement signed between DCNS and the local authority for Martinique, the plant could be on-stream as early as 2015. DCNS expects that in addition to providing useful power, this pilot power will be the forerunner of a series of similar OTEC plants that DCNS hopes to install throughout the Tropical zone.
All these projects are for a closed loop plant utilizing a low-boiling-point fluid (for instance, ammonia) as the fluid operating the turbo-generator.
A radical adaptation of existing technology
DCNS’s second solution is radical but based on their long experience with naval vessels and systems and in particular their nuclear submarine programme.
Termed the ‘Flexblue’ system, the solution consists of a nuclear reactor, a steam turbine-generator and associated electrical equipment, all securely housed in a watertight hull anchored to the seabed. The reactor is based on a well-proven design of submarine propulsion unit but adapted instead for continuous power generation. Undersea cables will carry electricity from the plant to the coast for distribution via the local network. Flexblue is of modular design so as to be compatible with future developments in small and medium-sized reactors. Flexblue plants have output ratings from 50 to 250MW and should be able to meet the electricity demands of communities or regions with populations of 100,000 to 1000,000 people, depending on the reactor rating and the demand from local industries.
A self-contained Flexblue unit is housed in a cylindrical hull 100m (330 ft) long by 12-15m (40-50 ft) in diameter and weighs, in total, around 12,000 tons. The units must be transported by a purpose-built vessel. Each unit is designed to be moored a few kilometres offshore, on an extremely stable area of the seafloor, at a depth of 60-100m (200-330 ft). It is lowered to the seafloor using ballast tanks that will subsequently be used to raise the unit for major maintenance, refuelling or dismantling.
Given France’s ardent love affair with nuclear power, reiterated as a committed marriage in the wake of the Fukushima disaster, it is perhaps not surprising that a French company, majority owned by the French government should design a nuclear solution to the power problems faced by many tropical island communities but, to date, no idyllic island paradise appears interested in taking up the idea. A pilot plant is therefore being proposed off France’s Nuclear Coast, which already accommodates the two existing nuclear reactors and the enormous flagship EPR Generation 3+ reactor under construction, all on the Flamanville site, plus the nuclear waste reprocessing plant at La Hague. The unit will be serviced from the nearby naval yard at Cherbourg. This will locate the unit in one of the world’s busiest shipping lanes, the English Channel. The proposal is currently generating intense debate, although this is unlikely to affect any governmental decision to go ahead.
DCNS has also released a video demonstrating a prototype of the Flexblue unit.