OTEC, a Long-Stalled Baseload Ocean Power Technology, Is Seeing a Swell

A undertaking to deploy a 1.5-MW commercial-scale ocean thermal power conversion (OTEC) platform within the African island nation of São Tomé and Príncipe by 2025 has gained a key design certification. The essential milestone immediately addresses technical dangers which have hampered OTEC, a long-pursued baseload offshore renewable expertise.

UK-based agency International OTEC Sources in April acquired its first certificates of approval for the methodology of set up of a cold-water riser—a pipe used to move seawater from the ocean to the seawater tank and vice versa from an offshore OTEC platform (see sidebar beneath). The certificates was granted by marine warranty surveyor ABL Group, which offers unbiased third-party technical opinions for high-risk marine development and transportation initiatives. The milestone “is especially necessary given the technical challenges confronted by OTEC installations, and the lengthy historical past of OTEC’s unsuccessful implementations,” famous International OTEC.

“Historical past is a crucial trainer, and we’re dedicated to studying from it,” stated International OTEC Founder and CEO Dan Grech. “Failure of earlier OTEC initiatives highlights the place we should always train warning, so third-party technical due diligence from the earliest stage is necessary for our success,” he stated.

1. International OTEC has designed what it says would be the first commercial-scale ocean thermal power conversion system. The 1.5-MW floating platform named Dominique is about to be put in in São Tomé and Príncipe in 2025. Courtesy: International OTEC

Poised to Develop into the First Industrial-Scale OTEC System

International OTEC’s flagship undertaking is the “Dominque,” a floating 1.5-MW OTEC platform set to be put in in São Tomé and Príncipe in 2025 (Determine 1). The corporate says the platform “would be the first commercial-scale OTEC system.”

That’s vital as a result of OTEC is a expertise that was proposed way back to 1881 by French physicist Jacques Arsene d’Arsonval for changing photo voltaic radiation absorbed into the ocean to electrical energy. OTEC has been confirmed to offer steady energy in addition to contemporary ingesting water and chilly water for refrigeration. However whereas more than a dozen prototypes have been examined intermittently for the reason that first experimental 22-kW low-pressure turbine was deployed in 1930, no commercial-scale vegetation exist.

OTEC primarily seeks to take advantage of the ocean’s thermal gradients—temperature variations of 36F or extra between heat floor water and chilly deep seawater—to drive a power-producing cycle. “Because the ocean contains round 70% of the earth’s floor it’s a huge receiver and repository of photo voltaic power. Whereas waves, winds, tides, and currents are all types of ocean renewable power, which fluctuate with time and season, conversely, an OTEC system permits the technology of fixed energy 24 hours a day, twelve months a yr,” defined the Worldwide Vitality Company’s (IEA’s) Ocean Vitality Programs (OES) expertise collaboration program in an October 2021 white paper.

The Swell of Curiosity and Exercise in OTEC

Present prototypes have usually conformed to 3 primary configurations relying on their location: on land, comparatively a brief distance from the coast; mounted on the sting of a continental shelf; or on a floating platform or ship, the place deep chilly water might be accessed immediately beneath the hull.

As well as, OTEC usually leverages three major forms of energy technology methods: a closed cycle, an open cycle, or a hybrid of the closed and open cycles. In a closed OTEC cycle system, ammonia—as a liquid with a low boiling level—is pumped into an evaporator (warmth exchanger) that’s heated by heat seawater, inflicting the working fluid to develop in a generator-driving turbine. The expanded vapor is then condensed again to a liquid utilizing chilly seawater in one other warmth exchanger. In an open cycle, the seawater itself features because the thermodynamic fluid after it’s “flashed” into steam in {a partially} evacuated chamber. The steam is then used to drive a steam turbine, and exhausted vapor is condensed utilizing chilly seawater.

Based on the IEA’s OES, one of many world’s most vital assessments was the U.S. Division of Vitality’s floating OTEC-1 project, a 1-MW closed cycle test loop that ran between 1980 and 1981. The undertaking proved the feasibility of horizontal launching, towing, and efficiently mating to the underside of a transformed U.S. Navy tanker a bundle of three high-density polyethylene (HDPE) chilly water pipes (CWPs), plus later disconnection, utilizing a particular movement decoupling gimbal. It “offers confidence that if, particularly, the abilities of the oil business are utilized, it’s attainable to design and set up efficiently bigger CWPs,” which have posed a “key uncertainty for OTEC,” OES stated.

What Is a Riser Pipe?

“A riser pipe is a vertical pipe that strikes fluid from one location to a different, in our case, that is from beneath the ocean’s floor, to the floor,” explains International OTEC Sources. “OTEC risers can are available many varieties, they are often made out of a versatile tube, seawater-resistant steel alloys, or concrete, and a few testing has even been carried out on composite supplies similar to glass fiber.”

In a floating barge configuration, ocean thermal power expertise (OTEC) primarily works by drawing heat floor seawater (of round 26C) which has been heated by the solar. The nice and cozy water is then used to evaporate a working fluid with a low boiling level, producing a vapor that spins a turbine. On the similar time, chilly water (of round 4C) is drawn via a riser pipe from the ocean’s depths. That chilly water cools the vapor, condensing it again right into a liquid that may be reused. Courtesy: Global OTEC

The cold-water risers for a large-scale OTEC technology want massive diameters to permit sufficient water stream fee for the warmth exchangers, the corporate famous. “These risers might be a number of meters (m) in diameter and exceed 750 m in size. Some areas require as excessive as 1,400 m.”  The risers additionally “want to resist the vessel motions because the boat strikes with the wind and waves, whereas the pipe tries to stay static; lateral forces of the ocean present which might lengthen far down in the direction of the seabed; and long-term cyclic masses attributable to the problems above.”

Designing resilient risers has posed a permanent problem that has long-hampered OTEC’s industrial feasibility. “These installations have deliberate set up lifetimes of tens of years, so designing the riser to resist all these forces for that lengthy might be very difficult,” famous International OTEC. “Failure of the cold-water pipe would stop the OTEC cycle from working, inflicting lack of energy and, relying on the situation of the break, might pose a hazard to the vessel itself.”

More moderen notable initiatives embrace Makai Ocean Engineering’s land-based 105-kW OTEC plant at a research center in Hawaii, and a 20-kW OTEC floating pilot plant spearheaded by the Korean Analysis Institute of Ships and Ocean Engineering (KRISO) that started working in 2012. KRISO is now creating a 1-MW OTEC demonstration within the small Pacific Island of Kiribati primarily based on a trial operation of a system examined in South Korea’s East Sea (close to Pohang, Determine 2).

The Korean Analysis Institute of Ships and Ocean Engineering (KRISO) plans to relocate its 1-MW Ok-OTEC 1000 barge OTEC energy cycle gear, examined close to Pohang, South Korea, to Kiribati Island. Courtesy: KRISO

“The 1-MW OTEC demonstration was designed for 24-degree-C seawater temperature distinction and has efficiently carried out in a trial operation (output of 338 kW beneath working situation of 18.7-degree-C temperature distinction) in Korea,” Dr. Hyeon-Ju Kim, a KRISO principal researcher, instructed OES in a July 2022–published interview. “If the demonstration of the 1-MW OTEC plant close to the equator is efficiently carried out sooner or later, competent professionals can draw a optimistic outlook on the dimensions of 10-, 100-, and 400-MW OTEC vegetation regularly.”

OTEC growth can also be making headway in Japan, the place in 2016, a 100-kW OTEC demonstration on Kume Island, Okinawa Prefecture, was linked to the grid. OTEC energy generator Xenesys, which runs and maintains the undertaking for Okinawa Prefecture (Kumejima City), alongside undertaking companions Japanese transportation agency Mitsui O.S.Ok. Traces (MOL) and Saga College, confirmed the demonstration (Determine 3) remains to be working.

In March 2023, the companions gained the backing of Japan’s Ministry of the Surroundings beneath a expertise growth program for “regional symbiosis and cross-sectoral carbon neutrality” to develop the OTEC undertaking to a commercial-scale 1 MW “by round 2026.” The trouble will entail manufacturing massive, parallel-type titanium warmth exchangers equal to 200 kW of energy technology and verifying their efficiency from fiscal yr 2022 to 2024, aiming to determine large-scale warmth restoration expertise from seawater for the commercialization of OTEC, the businesses instructed POWER.

3. An ongoing 100-kW ocean thermal power conversion (OTEC) demonstration facility owned by Japan’s Okinawa Prefecture is slated to be expanded right into a commercial-scale 1-MW facility. Courtesy: Mitsui O.S.Ok. Traces

The Quest: Offshore Renewable Baseload Energy

MOL lauded OTEC’s potential as a baseload energy useful resource that’s “not tremendously affected by climate situations.” One other famous profit is that “even after deep ocean water is used for energy technology, the water high quality is unchanged, and the temperature remains to be low sufficient for use for secondary functions similar to fisheries, agriculture, and air-con.” Whereas MOL acknowledged unsuccessful makes an attempt globally to commercialize the long-latent expertise, it stated that its efforts “to rapidly commercialize OTEC in Japan and abroad,” could be bolstered by a undertaking to confirm its analysis from the Okinawa demonstration at a undertaking in Mauritius.

“Mauritius established a highway map to boost its proportion of renewable power to 60% by 2030,” the corporate famous. “OTEC, which might reliably generate energy 24 hours a day no matter climate situations, has nice potential in Mauritius, because of the island’s advantageous geographical location within the Indian Ocean. Secondary use of seawater after energy technology may assist different industries on the island.” MOL stated it additionally plans to make use of the “data and experience it has gathered via its offshore enterprise and provide chain community,” to spice up OTEC commercialization.

International OTEC additionally lauds OTEC’s potential for small island creating states (SIDS). SIDS typically endure excessive power costs, owing to a reliance on diesel and different gas imports, and face house constraints to put in enough quantities of wind and photo voltaic. Together with baseload energy, “OTEC can provide portions of chilly water as a by-product. This can be utilized for air-con and the nutrient-rich deep water can be utilized for aquaculture and the creation of a sustainable native economic system,” stated Neil Reynolds, International OTEC board director, who can also be a particular advisor to the worldwide group SIDS DOCK. “OTEC may also be coupled with desalination for ingesting water and the manufacturing of ammonia and inexperienced hydrogen,” Reynolds added.

Together with its first closed-loop barge deliberate for São Tomé and Príncipe, off the western equatorial coast of Central Africa, International OTEC is exploring OTEC websites within the Turks and Caicos Islands (TCI), an archipelago of 40 low-lying coral islands within the Atlantic Ocean. “Having an unlimited unique financial zone of ocean house many multiples the world of their land waters and being within the tropics, TCI is effectively fitted to OTEC,” the corporate stated. International OTEC’s desktop research have proven TCI possesses the best mixture of heat seawater all yr spherical and easy accessibility to chilly deep water with continental cabinets rapidly falling to 1,000 meters (3,281 toes) inside 4 kilometers of the shore.

Addressing a Essential Problem: Chilly-Water Riser Pipes

International OTEC acknowledged, nevertheless, that launching its first industrial undertaking, the Dominique, would require trailblazing a deployment pathway that immediately addresses dangers which have lengthy hampered OTEC. Essentially the most outstanding one pertains to chilly water riser pipes (see sidebar above, “What Is a Riser Pipe?”), which furnish OTEC installations with the numerous quantity of chilly water they require.

International OTEC says it selected a floating barge design as a result of onshore OTEC vegetation “require a number of multi-kilometer pipes fastened to the seabed” to facilitate the acquisition and protected discharge of water. Water pipes, it famous, “signify one of many largest price facilities of an OTEC plant.” Onshore OTEC, which successfully centralizes energy manufacturing, additionally limits the areas the place the method might be economical, and it presents a single level of failure within the occasion of a pure catastrophe.

Together with totally vetting its dangers associated to OTEC riser pipes—via third-party technical opinions—the corporate says it has pursued a rigorously detailed design part for the cold-water pipe “in collaboration with suppliers and scientists on the cutting-edge of subsea riser pipe designs.” To additional curb dangers, it is going to deploy its first industrial methods “in a market the place a lot smaller distances between heat floor seawater and chilly deep water are current,” it stated.

Given economies of scale, smaller fledgling methods will probably be expensive, International OTEC acknowledges. Citing literature opinions of earlier OTEC plant designs, the corporate factors to a levelized price of power (LCOE) for large-scale vegetation of $0.05/kWh. “Our procurement research and engagement with suppliers present a variety between $0.30 and $0.15 per kWh is practical for early generations of OTEC barges,” it stated.

Nevertheless, current modifications within the international economics of power and developments within the effectivity of OTEC parts might enhance price, it famous. “Traditionally, the effectivity of the cycles and parts proved tough for early initiatives to make a industrial case. All through many years of very low-cost oil, gasoline, and coal, it was thought that OTEC initiatives wanted to be 50 MW and even 100 MW scale to be aggressive,” it famous. Whereas the corporate predicts that early industrial OTEC methods should want “progressive funding fashions to succeed,” it seems assured that situations imposed on international energy methods by the power transition might current the “excellent storm” to start commercialization of OTEC.

Sonal Patel is a POWER senior affiliate editor (@sonalcpatel@POWERmagazine).

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