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August 27, 2015 – ClimateWire (via Scientific American), By Makavike Vyawahare

A new power plant offshore converts the temperature difference between sea surface and deep waters into electricity.

A small but operational ocean thermal energy conversion (OTEC) plant was inaugurated in Hawaii last week, making it the first in the world. The opening of the 100-kilowatt facility marked the first time a closed-cycle OTEC plant will be connected to the U.S. grid. But that amount of energy production can power only 120 Hawaiian homes for a year, a tiny drop in the ocean for the island state’s own energy needs. What promise OTEC holds for other regions is even less certain.

The United States entered OTEC research in 1974 with the establishment of the Natural Energy Laboratory of Hawaii Authority (NELHA). But after decades of investment in the development of OTEC, this new Navy-bankrolled project is still seen by many as only a way to test the process rather than secure the place of OTEC as a viable renewable technology.

aerial view of the Natural Energy Laboratory
An aerial view of the Natural Energy Laboratory of Hawaii Authority. (United States Department of Energy/Wikipedia)

The company that developed the facility, Makai Ocean Engineering, is named for the Hawaiian word “makai,” which means “toward the ocean.” Hawaii, which is heavily dependent on imported fossil fuels to meet its energy demand, might indeed have to look toward the ocean to meet its ambitious target of having 100 percent renewable energy by 2045. “This plant provides a much-needed test bed to commercialize ocean thermal energy conversion technology and bolster innovation,” Hawaii Gov. David Ige said in a statement.

Robert Freeman, a spokesman at the Office of Naval Research, described the project that is partly funded by the ONR as a “prototype.” Through this plant, the office is trying to understand what the challenges to developing OTEC are, he said. The revenues generated from the plant, which will supply the NELHA facility where it is located, will be plowed back to fund more research and development in OTEC technology.

“Since not much is going on OTEC-wise, having anything that is functioning, visible, however small, is great,” said Gérard C. Nihous, an OTEC expert at the University of Hawaii. “You are looking at tiny, tiny systems that by themselves are not significant,” he said. “Their significance lies in their ability to demonstrate the process.”

The Makai plant is designed to draw in warmer ocean surface waters to vaporize ammonia, which boils and creates steam at a relatively low temperature. The steam spins a turbine and generates electricity. Cold water extracted from the ocean depths is then used to cool and condense the ammonia back into a liquid, which is then recycled in the system, known as a closed-loop system. The other commonly used OTEC technology, called the open system, does not rely on a medium, but uses the vaporized ocean water itself to run the turbine.

Diagram showing how an ocean thermal energy conversion system works
A little engine that could transform seacoast power: Ocean thermal energy conversion uses the temperature difference between warm surface water and the much cooler depths to boil ammonia, using the resulting steam to generate electricity (Graphic courtesy of Makai Ocean Engineering).

Chinese system in the works

Currently, there are no operational OTEC plants that produce power at a commercial scale. About a dozen exist across the world, but they have limited capacity, and most of them produce less than 1 megawatt of power. In contrast, the United States at present has 20 gigawatts of installed solar capacity.

Lockheed Martin, a major defense manufacturer, which has been involved in the development of the technology for decades now, recently announced a new OTEC project in China. The company entered into a memorandum of understanding with a Chinese real estate developer, Reignwood Group, for a 10-MW offshore plant that will supply a green resort. “Initial system engineering, concept design, site evaluation and supply base identification work is complete. We are working toward finalizing a site so that detailed design, pre-construction and permitting activities can begin,” Lockheed Martin said in an email.

The company has in the past worked closely with the Navy on OTEC research and development. It submitted a “completed concept design contract” for a 10-MW OTEC plant in Hawaii to the Naval Facilities Engineering Command (NAVFAC) in 2011. “There was no follow on work with NAVFAC to develop an OTEC plant in Hawaii,” it said.

“The technology is simple to understand but very difficult to implement in the field,” Nihous said of OTEC. “There are engineering challenges, but most of the reasons for its incomplete development are economic.”

Most developers have to contend with prohibitive upfront capital costs, even for small-scale projects. For completed projects and those in the pipeline today, a large chunk of the funding is coming from governments and technology developers. However, to scale up would require private-sector funding, which is currently not forthcoming.

Navy hopes to cut shore-based energy

The Makai project that came with a price tag of about $5 million was funded by the ONR and NAVFAC. “An OTEC facility of this size costs approximately $3M to build. Outfitting the plant for R&D [research and development] bumped the costs up to [more than] $5M,” a Makai company representative said in an email.

The project fits well with the Navy’s ambition of being an early adopter of clean energy technologies and to help it achieve its own clean energy targets. The Navy currently meets about 12 percent of its total energy needs through renewable sources. Its goal is to source 50 percent of its shore-based energy from alternative sources by 2020, Freeman said.

While its development has been stunted, nobody denies that OTEC is an attractive renewable energy source, for more than one reason. The potential for the technology, which channels solar energy, is undeniably huge. Oceans cover 71 percent of the Earth’s surface, and 1 square meter of ocean surface area on average receives about 175 watts of solar irradiation. The total amount of globally received solar power is thus approximately 90 petawatts; harnessing even a fraction of that energy would be enough to meet the entire world’s energy demand.

But to generate power using existing OTEC technologies, the difference in temperature between deep cold and warm surface waters has to be at least 20 degrees Celsius (36 degrees Fahrenheit), which means that the plants must have access to water from the deep ocean. The number of sites across the world where OTEC power generation is feasible is only a few hundred. “It is really a tropical technology only,” Nihous said. “If you look at it from the perspective of Western Europe, Japan, North America and other rich developed countries, the impact is really limited to outlying areas like Hawaii, Guam and American Samoa.”

There is also the question of how OTEC compares with other renewable resources that have managed to hit commercial maturity. One key advantage that OTEC has over other renewables, such as wind and solar energy, is the fact that OTEC is a baseload source, which means that it is a constant and stable source of power, unlike solar and wind, which are intermittent sources prone to weather-related fluctuations. This makes OTEC-generated power three times more valuable than other sources, according to some estimates.

“ONR intends to continue funding research at Makai on OTEC technologies, contingent on the availability of money in future years,” Freeman said.


The information above is for general awareness only and does not necessarily reflect the views of the Office of Economic Adjustment or the Department of Defense as a whole.

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