First U.S. Grid-Connected OTEC Plant Goes Live on Hawaii

Hawaii Governor David Ige on Aug. 21 joined executives from the Office of Ocean Naval Research (ONR), Makai Ocean Engineering and other organizations on-site at the Natural Energy Laboratory of Hawaii Authority (NELHA) in cutting the ribbon and commissioning the first U.S., and world's largest, grid-connected ocean thermal energy conversion (OTEC) power plant.

Employing a closed-loop operating cycle, Makai's 105 kW OTEC plant would be able to meet the year-round power needs of 120 Hawaiian homes 24x7 with zero emissions, according to a Makai statement.

The electricity Makai's OTEC power plant produces will supply power to organizations, including Makai, based on the grounds of NELHA's campus outside of Kona on the “Big Island” of Hawaii. It will also pump in the seawater used for a variety of purposes by NELHA's resident organizations, Makai's VP of business development Duke Hartman said in an interview.

Commemorating the event, Gov. Ige said: “Today marks the launch of the world’s largest operational ocean thermal power plant. This plant provides a much-needed test-bed to commercialize ocean thermal energy conversion technology and bolster innovation, and it serves as a stepping stone to larger plants that will provide meaningful amounts of stable, clean power to Hawaii and other locations in Asia-Pacific, such as Okinawa, in the near future.”

Complementing Solar and Wind

Using OTEC to generate electricity involves taking in warm seawater from surface layers and using it to evaporate a liquid with a low boiling point, such as ammonia. The resulting vapor and pressure is used to drive a turbine that generates electricity. Cold water pumped up from deeper ocean layers is then used to condense the ammonia, initiating restart of the closed-loop power generation cycle.

For a variety of reasons, Makai and other OTEC specialists believe that OTEC can be a cost-effective source of emissions-free, renewable 24x7 baseload power, as well as a key aspect in coordinated, policy-driven shifts away from fossil fuels towards a diversified mix of renewable energy generation sources. Leading examples include Hawaii, which has the highest per-capita base of installed solar power capacity of any U.S. state, and which has set a 2045 target of relying on clean renewable energy sources to meet all its power needs.

Hartman pointed out that OTEC power plants can ramp up and down very rapidly, in a matter of seconds, in response to changing power supply and demand conditions, an additional benefit OTEC offers to grid operators and power generation companies.

Cost-competitive with Grid Power

Hartman believes that a large-scale OTEC power plant, one of 100 MW for example, would be commercially viable and produce baseload electrical power that would be cost-competitive with grid power in Hawaii and other areas where imported fossil fuels are used to produce electricity.

Today, such a plant could generate clean, renewable, 24x7 baseload power at around $0.20 per kWh, possibly less, he estimated. Moreover, that would be for the first several plants; costs would decline as more plants are ordered. By way of comparison, power usage rates in Hawaii can run as as $0.35 per kWh.

“You could have OTEC plants off the coasts of each [Hawaiian] island with a combined capacity that meets or exceeds the 12,000 or so megawatts of power currently used across the entire state,” Hartman said.

By doing so, he added, government leaders would address reservations and resistance that residents of Maui, Molokai, Kaui and the Big Island have expressed in response to developers' proposals to build solar, wind or any large-scale power plants on their home islands that would serve mainly, if not solely, to supply power to Oahu.

The U.S. Navy, for its part, is keen to further develop and fully assess OTEC's potential to serve as a clean, renewable power source for fleet operations in U.S. and other waters.

Hartman also noted that project planning aimed at bringing larger scale OTEC power plants online is already underway.

“An exciting next step was just announced at NELHA, where a memorandum of understanding was signed with a consortium of Japanese companies to build a 1 MW OTEC power plant on Okinawa,” he said.

Lead image credit: Makai Engineering

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