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The United Nations Development Program is seeking consultants to build a 2 MW solar project and three hydropower plants ranging in generation capacity from 1.15-2 MW.
The troubles afflicting utility EMAE are dragging down the economy of the island nation.
Image: David Stanley, Flickr
The United Nations Development Program is seeking consultants to conduct feasibility studies for a 2 MW solar project and three mini hydropower plants ranging in size from 1.15-2 MW in São Tomé and Principe.
The facilities, which will be a mix of grid connected and off-grid assets, are intended to improve power supply in the West African island nation.
The $1 million studies will be financed by the UN''s Green Climate Fund. Consultants have until Wednesday to offer their services for the tender.
The African Development Bank says São Tomé & Príncipe has an electricity access rate of around 70% and installed power generation capacity of 35 MW, some 95% of which comes from thermal power. Of that theoretical capacity, however, only 58% is available, due to ageing generation assets and lack of maintenance.
The Macauhub website which reports on relations between China and Portuguese-speaking countries quoted Celestino Andrade, MD of São Tomé & Príncipe state-owned utility EMAE as describing his electric company as "technically insolvent and [in] need [of] urgent restructuring."
Macauhub reported the monopoly-holding utility owes around $140 million to national fuel and oil company ENCO and $80 million to other suppliers and spends $2 million per month on 2.2 million liters of fuel for its interconnected and isolated power plants.
More articles from Emiliano Bellini
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A project to deploy a 1.5-MW commercial-scale ocean thermal energy conversion (OTEC) platform in the African island nation of São Tomé and Príncipe by 2025 has gained a key design certification. The crucial milestone directly addresses technical risks that have hampered OTEC, a long-pursued baseload offshore renewable technology.
UK-based firm Global OTEC Resources in April received its first certificate of approval for the methodology of installation of a cold-water riser—a pipe used to transport seawater from the ocean to the seawater tank and vice versa from an offshore OTEC platform (see sidebar below). The certificate was granted by marine warranty surveyor ABL Group, which provides independent third-party technical reviews for high-risk marine construction and transportation projects. The milestone “is particularly important given the technical challenges faced by OTEC installations, and the long history of OTEC’s unsuccessful implementations,” noted Global OTEC.
“History is an important teacher, and we are committed to learning from it,” said Global OTEC Founder and CEO Dan Grech. “Failure of previous OTEC projects highlights where we should exercise caution, so third-party technical due diligence from the earliest stage is important for our success,” he said.
Global OTEC’s flagship project is the “Dominque,” a floating 1.5-MW OTEC platform set to be installed in São Tomé and Príncipe in 2025 (Figure 1). The company says the platform “will be the first commercial-scale OTEC system.”
That’s significant because OTEC is a technology that was proposed as far back as 1881 by French physicist Jacques Arsened’Arsonval for converting solar radiation absorbed into the ocean to electrical power. OTEC has been proven to provide continuous power as well as fresh drinking water and cold water for refrigeration. But while more than a dozen prototypes have been tested intermittently since the first experimental 22-kW low-pressure turbine was deployed in 1930, no commercial-scale plants exist.
OTEC essentially seeks to exploit the ocean’s thermal gradients—temperature differences of 36F or more between warm surface water and cold deep seawater—to drive a power-producing cycle. “Since the ocean comprises around 70% of the earth’s surface it is a vast receiver and repository of solar energy. While waves, winds, tides, and currents are all forms of ocean renewable energy, which vary with time and season, conversely, an OTEC system permits the generation of constant power 24 hours a day, 365 days a year,” explained the International Energy Agency’s (IEA’s) Ocean Energy Systems (OES) technology collaboration program in an October 2021 white paper.
Existing prototypes have typically conformed to three basic configurations depending on their location: on land, relatively a short distance from the coast; mounted on the edge of a continental shelf; or on a floating platform or ship, where deep cold water can be accessed directly underneath the hull.
In addition, OTEC typically leverages three main types of power generation systems: 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 point—is pumped into an evaporator (heat exchanger) that is heated by warm seawater, causing the working fluid to expand in a generator-driving turbine. The expanded vapor is then condensed back to a liquid using cold seawater in another heat exchanger. In an open cycle, the seawater itself functions as the thermodynamic fluid after it is “flashed” into steam in a partially evacuated chamber. The steam is then used to drive a steam turbine, and exhausted vapor is condensed using cold seawater.
According to the IEA’s OES, one of the world’s most significant tests was the U.S. Department of Energy’s floating OTEC-1 project, a 1-MW closed cycle test loop that ran between 1980 and 1981. The project proved the feasibility of horizontal launching, towing, and successfully mating to the underside of a converted U.S. Navy tanker a bundle of three high-density polyethylene (HDPE) cold water pipes (CWPs), plus later disconnection, using a special motion decoupling gimbal. It “provides confidence that if, in particular, the skills of the oil industry are utilized, it is possible to design and install successfully larger CWPs,” which have posed a “key uncertainty for OTEC,” OES said.
In a floating barge configuration, ocean thermal energy technology (OTEC) essentially works by drawing warm surface seawater (of around 26C) which has been heated by the sun. The warm water is then used to evaporate a working fluid with a low boiling point, producing a vapor that spins a turbine. At the same time, cold water (of around 4C) is drawn through a riser pipe from the ocean’s depths. That cold water cools the vapor, condensing it back into a liquid that can be reused. Courtesy: Global OTEC
More recent notable projects include 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 Research Institute of Ships and Ocean Engineering (KRISO) that began operating in 2012. KRISO is now developing a 1-MW OTEC demonstration in the small Pacific Island of Kiribati based on a trial operation of a system tested in South Korea’s East Sea (near Pohang, Figure 2).
The Korean Research Institute of Ships and Ocean Engineering (KRISO) plans to relocate its 1-MW K-OTEC 1000 barge OTEC power cycle equipment, tested near Pohang, South Korea, to Kiribati Island. Courtesy: KRISO
“The 1-MW OTEC demonstration was designed for 24-degree-C seawater temperature difference and has successfully carried out in a trial operation (output of 338 kW under operating condition of 18.7-degree-C temperature difference) in Korea,” Dr. Hyeon-Ju Kim, a KRISO principal researcher, told OES in a July 2022–published interview. “If the demonstration of the 1-MW OTEC plant near the equator is successfully carried out in the future, competent professionals can draw a positive outlook on the scale of 10-, 100-, and 400-MW OTEC plants gradually.”
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