Ocean Thermal Energy Conversion - The Cost Challenge

The limited petroleum resources available for mankind have led to the exploration and development of oil fields in the offshore deep-sea regions, especially in light of the rising oil prices. Different studies and projects on the ocean thermal energy conversion (OTEC) technology, which operates the power generation facilities using the temperature difference between the deep-sea water and the sea surface water, are currently being undertaken. In this study, various methods of applying the OTEC technology to a floating production storage and offloading (FPSO) facility installed in a deep-sea area were simulated and analyzed. In the closed cycle, a 1595.5 kW net power generation capacity was obtained. In the open cycle, a 863.5 kW generating capacity and 54.4 m3/h fresh water were obtained. In the hybrid cycle, a 643 kW generating capacity and 55.1 m3/h fresh water were obtained. In addition, the cooling water of the heating, ventilation, and air-conditioning systems (HVACs) obtained using deep-sea water cooling was also investigated. Ultimately, a 100 MW OTEC power plant was designed, and the required seawater amount and operating fluid capacity were confirmed. Considering the similarity of OTEC power generation facilities and FPSOs, the conversion of an FPSO in the deep-sea region to an OTEC power generation facility after the end of the life of the FPSO was proposed. It will be an alternative way of addressing two important issues: the need for petroleum resource development considering the limited petroleum resources that are currently available, and the need to ensure the sustainable development of countries.

The following discussion presents a status of the technology, market, industry, and economic viability of Ocean Thermal Energy Conversion (OTEC) systems. The main focus is on the Open-Cycle OTEC (OC-OTEC) investigations being conducted primarily under the auspices of the Department of Energy (DOE) Ocean Energy Program (OEP). A summary of technology advances which have enhanced the economic prospects for both open- and closed-cycle OTEC are presented. Of key importance was the demonstration of the technical feasibility of using the OTEC flashevaporation of seawater process to produce fresh water. The production of such “by-products” as fresh water from the OTEC cycle significantly improves its cost effectiveness in producing electrical energy. A synopsis of planned activities which will culminate in a test facility designed to establish the technical feasibility of producing net power from the OC-OTEC system is presented. The facility will be used to conduct the Net Power-Producing Experiment (NPPE).

Ocean Thermal Energy Conversion (OTEC) is the principal ocean energy source under development by the U. S. Department of Energy (DOE) because of its potential, state of development, and availability and access of the resource to the U. S. The major features of OTEC are that the source is renewable with minimum impact on the environment, and the constant availability of the resource enhances OTEC acceptability as a power baseload option, with no requirement for additional storage. DOE has delegated the National Oceanic and Atmospheric Administration (NOAA) to carry out its OTEC Ocean Engineering Technology Development program. This program involves conducting research in critical, high technical risk areas in order to demonstrate technical and economical feasibility and develop a technical information base which can be used by industry to develop commercially viable systems. This program established preliminary baseline designs for floating and fixed systems; developed analytical computer models; conducted laboratory tests of scale models to calibrate analytical models; and is now preparing for sea tests of larger scale models for further validation of analytical models and improvement of baseline designs. This paper summarizes the technical accomplishments and major findings, mainly reported over the last year, and describes some of the remaining critical needs and the projects underway or planned to minimize the problems and associated risks. This paper covers the ocean engineering technology, viz., platforms, cold water pipe and sea water system, mooring and foundation systems and other areas related to the overall system integration aspects. The development of the electrical umbilical cable and bottom-mounted transmission cable has been managed directly by DOE and is integrated into the ocean engineering system.

The study explores the feasibility of utilizing Ocean Thermal Energy Conversion (OTEC) systems collocated with deepwater oil and gas facilities to power monitoring activities for plugged and permanently abandoned (PA) offshore oil and gas wells in the Gulf of Mexico (GOM). As offshore oil and gas operations expand, the need for sustainable monitoring solutions for PA wells, which may release hydrocarbons, may become critical. Current regulations do not mandate long-term ongoing monitoring post-PA, presenting an opportunity for innovative approaches. This research evaluates the potential of OTEC, a renewable marine energy technology, to provide continuous, dispatchable power for such monitoring systems. The study models an OTEC system collocated with an oil and gas platform, assessing its capability to power long-range autonomous underwater vehicles (AUVs) shuttled to the relevant locations for periodic surveys of PA wells. The findings suggest that while OTEC can technically support PA well monitoring, logistical challenges such as and economic viability remain. The study underscores the need for further research and investment in OTEC technology to enhance its economic competitiveness and integration with offshore operations. This approach not only aids in addressing potential PA well hydrocarbon release concerns but also offers a model for other offshore monitoring applications, including subsea geologic carbon dioxide (CO2) storage projects.

Heat exchangers comprise one of the largest cost drivers for Ocean Thermal Energy Conversion (OTEC) systems. Reductions in fabrication costs and improvements in performance are critical to successfully commercialize sustainable energy power plants using this low (∼20°C) ΔT resource. Heat exchanger (HX) units should maximize heat transfer per unit area (U value) while minimizing pressure losses, corrosion and cost. Current OTEC research is focused on heat exchanger configuration design, materials, and fabrication techniques. This paper summarizes the OTEC heat exchanger test programs underway and describes the heat exchanger development goals, the heat exchanger performance test facilities being used, and the corrosion testing being performed.

Microalgae cultivation in offshore floating photobioreactor: State-of-the-art, opportunities and challenges

Ultrasonic radiation is being investigated as a way to remove biofouling from Ocean Thermal Energy Conversion (OTEC) heat exchangers. Experiments conducted in Hawaii, in the Gulf of Mexico, and at the Applied Physics Laboratory have shown that ultrasonic cleaning devices can remove fouling from aluminum tubes exposed to ocean water for periods of up to 13 weeks without damage to the metal surface. Data were gathered on exposure levels, times, and cleaning effectiveness. Results have indicated that a 15-sec exposure once every two weeks at a surface intensity of 1 W/cm2 would maintain a thermal resistance factor of less than 0.000035 W−1-m2-K. The cleaning does not interrupt heat exchanger operation and would require < 0.5% of the OTEC plant's gross power output.

Experimental study of an absorption-based refrigeration driven by ocean thermal energy

P+E wins Navy contract for water recovery

The U.S. Department of Energy (DOE) invites small businesses, or those with 500 employees or less, to write for a copy of its Small Business Innovation Research (SBIR) program solicitation, to be issued January 2, 1985. To receive a copy, contact the SBIR Program Manager, U.S. Department of Energy, Washington, DC 20545; telephone 301‐353‐5707. The closing date for this solicitation is March 15, 1985.

Previous studies focus mainly on the inherent properties of the catalysts such as the metal-hydrogen binding energy (EM-H) to rationalize their catalytic activities toward the hydrogen evolution and oxidation reactions (HER/HOR) in aqueous solutions, as well as the HER/HOR kinetics. While this strategy proves effective in rationalizing and predicting the HER/HOR activity trend across a wide range of elements in dilute acidic solutions as per the Sabatier Principle, it is inapplicable to account for the sluggish HER/HOR kinetics of many transition metals in alkaline solutions. Recent works suggest that interfacial water plays critical roles in affecting the HER/HOR kinetics of Pt-based surfaces in alkaline solutions.1-4 However, the specific roles of interfacial water for the HER/HOR kinetics remain elusive, partly because of the lack of methods to explore the surface-electrolyte interface.Herein, we probe the Pt electrode/electrolyte interface by depositing a variety of transition metals (TMs) onto Pt surfaces and monitoring their redox-controlled interactions with the HOR/HER intermediates and interfacial water via in situ x-ray absorption spectroscopy. Carbon monoxide stripping experiments with varied alkaline metal cations (AM+) concentrations are conducted to facilitate correlating the redox-controlled interactions to the TM-induced changes of the HOR/HER kinetics of Pt. We found that the TM-induced changes of the HOR/HER kinetics of Pt in alkaline are governed by the TM0/TM(OH)x redox potential or the metal-oxygen binding energy (ETM-O). The TMs with too strong ETM-O or too low redox potentials such as Mn or Co are dominated by TM(OH)x within the HOR potential region and can only improve the HER kinetics of Pt but not the HOR. The TMs with moderate ETM-O or redox potentials located within the HOR kinetic potential region of Pt (0-0.25 V) such as Ni and Ru can simultaneously improve the HOR/HER of Pt in alkaline, but the HOR improvement vanishes as the TM0 transforms to TM(OH)x with increasing potentials. The TMs with too high redox potentials or weak ETM-O(s) such as Cu improve neither. According to these results, we propose that the TM in either the form of TM0 or TM(OH)x can improve the HER of Pt in alkaline by hosting the OHad generated from water dissociation that is subsequently removed by the interfacial water coordinated to AM+ via the HSAB interaction: TM0/TM(OH)x-OHad-[AM(H2O)x]+ + e- ↔ TM0/TM(OH)x + OH--[AM(H2O)x]+;1 whereas only the form of TM0 can improve the HOR by hosting the water molecule with the oxygen facing-down orientation (H2O↓ad) that removes Had from the Pt atoms nearby via the L-H mechanism: Pt-Had + TM0-H2O↓ad ↔ Pt + TM0 + H3O+ + e-. By this new notion, the surface TM promotes the HOR/HER kinetics of Pt by facilitating interfacial water shuffling reaction intermediates against the electric field, rather than by weakening the electric field by negatively shifting the potential of zero free charge (pzfc)2, or by weakening the (apparent) EPt-H,5 or by facilitating the dissociation and formation of water molecules.6,7 The participation of interfacial water in the HOR/HER of Pt is further verified by kinetic isotope effect studies in both acidic and alkaline solutions. Acknowledgements.This work was supported by the Office of Naval Research (ONR) under award number N00014-18-1-2155. The authors declare no competing financial interests. This research used beamline 6-BM, 7-BM, and 8-ID (ISS) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. References (1) Liu, E.; Li, J.; Jiao, L.; Doan, H. T. T.; Liu, Z.; Zhao, Z.; Huang, Y.; Abraham, K. M.; Mukerjee, S.; Jia, Q. J. Am. Chem. Soc. 2019, 141, 3232-3239.(2) Ledezma-Yanez, I.; Wallace, W. D. Z.; Sebastián-Pascual, P.; Climent, V.; Feliu, J. M.; Koper, M. T. M. Nat. Energy 2017, 2, 17031.(3) Herranz, J.; Durst, J.; Fabbri, E.; Patru, A.; Cheng, X.; Permyakova, A. A.; Schmidt, T. J.Nano Energy 2016, 29, 4-28.(4) Rebollar, L.; Intikhab, S.; Snyder, J. D.; Tang, M. H. J. Phys. Chem. Lett. 2020, 11, 2308-2313.(5) Schwämmlein, J. N.; Stühmeier, B. M.; Wagenbauer, K.; Dietz, H.; Tileli, V.; Gasteiger, H. A.; El-Sayed, H. A. J. Electrochem. Soc. 2018, 165, H229-H239.(6) Li, J.; Ghoshal, S.; Bates, M. K.; Miller, T. E.; Davies, V.; Stavitski, E.; Attenkofer, K.; Mukerjee, S.; Ma, Z.-F.; Jia, Q. Angew. Chem. Int. Ed. 2017, 56, 15594-15598.(7) Strmcnik, D.; Uchimura, M.; Wang, C.; Subbaraman, R.; Danilovic, N.; Van Der Vliet, D.; Paulikas, A. P.; Stamenkovic, V. R.; Markovic, N. M. Nat. Chem. 2013, 5, 300-306.

: The 1991 SSSC Forum was conducted under the auspices of the Board on Physics and Astronomy's Solid State Sciences Committee (SSSC) and cosponsored with the National Materials Advisory Board (NMAB). The Forum was the culmination of a year-long dissemination effort following up the NCR study Materials Science and Engineering for the 1990s that was released in September of 1989 and successfully brought together experts and policy makers in the field of advanced materials processing to discuss issues pertinent to the field. Support for the Forum was provided by the Air Force office of Scientific Research (AFOSR), the Department of Energy (DOE), the National Science Foundation (NSF), and the office of Naval Research (ONR).

Low-cost solar hydrogen production through water splitting using photo-electrochemical (PEC) cell offers a clean and renewable source of energy. However, its low performance remains a primary concern. Solar hydrogen production of TiO2 supported copper and nickel oxides photoanod (Cu–Ni/TiO2) was significantly influenced by photoanode fabrication and reaction parameters. To maintain the optimum operating conditions of PEC cell for practical application, we systematically investigated the effect of sintering temperature, photoanode thickness, electrolyte concentration, and applied voltage on hydrogen production over 5 mol% Cu–Ni/TiO2 and PEC characteristics, including charge carrier transfer resistance, photocurrent density, and flat band potential. Findings reveal that the optimized sintering temperature for hydrogen production was 400 °C due to low charge transfer resistance and more excited electrons at the electrode/electrolyte interface. The photocatalyst with the four layers of printed 5 mol% Cu–Ni/TiO2 (thickness ~ 24.8 µm) improved the photocatalytic performance, highlighting the importance of the number of excited electrons and the surface area of the photocatalyst. Furthermore, applied voltage exerted the most significant effect on hydrogen production up to 24.9 mL at the optimum level of 3.4 V by minimizing the recombination rate of electron–hole pairs. The stability of the photoanode was tested under the optimum conditions for 4 days and the maximum accumulative hydrogen of 443.4 mL was produced over this highly stable photoanode.

Coordinated scheduling of wind-solar-hydrogen-battery storage system for techno-economic-environmental optimization of hydrogen production

This report documents a detailed study to determine the expected efficiency and product costs for producing hydrogen via water-splitting using energy from an advanced nuclear reactor. It was determined that the overall efficiency from nuclear heat to hydrogen is high, and the cost of hydrogen is competitive under a high energy cost scenario. It would require over 40% more nuclear energy to generate an equivalent amount of hydrogen using conventional water-cooled nuclear reactors combined with water electrolysis compared to the proposed plant design described herein. There is a great deal of interest worldwide in reducing dependence on fossil fuels, while also minimizing the impact of the energy sector on global climate change. One potential opportunity to contribute to this effort is to replace the use of fossil fuels for hydrogen production by the use of water-splitting powered by nuclear energy. Hydrogen production is required for fertilizer (e.g. ammonia) production, oil refining, synfuels production, and other important industrial applications. It is typically produced by reacting natural gas, naphtha or coal with steam, which consumes significant amounts of energy and produces carbon dioxide as a byproduct. In the future, hydrogen could also be used as a transportation fuel, replacing petroleum. New processes are being developed that would permit hydrogen to be produced from water using only heat or a combination of heat and electricity produced by advanced, high temperature nuclear reactors. The U.S. Department of Energy (DOE) is developing these processes under a program known as the Nuclear Hydrogen Initiative (NHI). The Republic of South Africa (RSA) also is interested in developing advanced high temperature nuclear reactors and related chemical processes that could produce hydrogen fuel via water-splitting. This report focuses on the analysis of a nuclear hydrogen production system that combines the Pebble Bed Modular Reactor (PBMR), under development by PBMR (Pty.) Ltd. in the RSA, with the Hybrid Sulfur (HyS) Process, under development by the Savannah River National Laboratory (SRNL) in the US as part of the NHI. This work was performed by SRNL, Westinghouse Electric Company, Shaw, PBMR (Pty) Ltd., and Technology Insights under a Technical Consulting Agreement (TCA). Westinghouse Electric, serving as the lead for the PBMR process heat application team, established a cost-shared TCA with SRNL to prepare an updated HyS thermochemical water-splitting process flowsheet, a nuclear hydrogen plant preconceptual design and a cost estimate, including the cost of hydrogen production. SRNL was funded by DOE under the NHI program, and the Westinghouse team was self-funded. The results of this work are presented in this Final Report. Appendices have been attached to provide a detailed source of information in order to document the work under the TCA contract.