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Ocean Thermal Energy Conversion
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Ocean Thermal Energy Conversion

A special issue of Journal of Marine Science and Engineering (ISSN 2077-1312).

Deadline for manuscript submissions: closed (31 December 2017) | Viewed by 43559

Special Issue Editor

Dr. Luis A. Vega

E-Mail Website
Guest Editor
Hawaii National Marine Renewable Energy Center, University of Hawaii, Honolulu, HI, USA
Interests: marine renewable energy; development and commercialization of OTEC

Special Issue Information

Dear Colleagues,

Given that world oil reserves can only satisfy current demand for about 60 years, and that close to one hundred nations have been identified with appropriate Ocean Thermal Energy Conversion (OTEC) resources within their 200-nautical-mile Exclusive-Economic-Zone (EEZ), it would make sense to continue the process required to deploy the first generation of OTEC plantships, which would supply electricity to shore stations via submarine power cables. These would be followed, in about 30 years, with grazing OTEC systems operating as self-contained factory ships that would produce energy-intensive fuels like ammonia or hydrogen. This latter design is essentially decoupled from land and would potentially give access to OTEC resources, spread over more than 100 million square kilometers across tropical oceans.

The technical demonstration of the OTEC process has already been accomplished with relatively small experimental plants (<0.25 MW) and it has been determined that to achieve current cost competitiveness, an OTEC plant must be sized at about 50 MW. To proceed to commercialization, however, it is necessary to operate an appropriately scaled version of a commercially viable plant. Such a pilot plant is required to establish the life cycle of major components, the environmental impact baseline and annual production rates. Considering modular designs, a 5 MW plant is an ideal stepping stone for the OTEC technology. This size is believed to represent the lower, more affordable end of the range for meaningful scaling.

We are seeking contributions for this Special Issue on the following subjects:

  • Ocean thermal resources
  • OTEC experimental plants
  • OTEC potential environmental impact
  • OTEC Economics
  • OTEC Plant Design

Dr. Luis A. Vega
Guest Editor

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Published Papers (6 papers)

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Research

12 pages, 2668 KiB  
Article
Basic Heat Exchanger Performance Evaluation Method on OTEC
by Takeshi Yasunaga, Takafumi Noguchi, Takafumi Morisaki and Yasuyuki Ikegami
J. Mar. Sci. Eng. 2018, 6(2), 32; https://doi.org/10.3390/jmse6020032 - 3 Apr 2018
Cited by 21 | Viewed by 7014
Abstract
Ocean thermal energy conversion (OTEC) harvests the power from the thermal energy in the ocean, which is reserved in the ocean as the temperature difference between warm surface and cold deep seawaters. In the energy conversion, the heat exchangers transfer the thermal energy [...] Read more.
Ocean thermal energy conversion (OTEC) harvests the power from the thermal energy in the ocean, which is reserved in the ocean as the temperature difference between warm surface and cold deep seawaters. In the energy conversion, the heat exchangers transfer the thermal energy to the heat engine, which converts it into power. The pressure drops yielded by piping, valve and heat exchangers cause pump loads, which show significant negative power with respect to net power in OTEC. The heat transfer performance and the pressure drop in heat exchanger depend on the types and shapes of each heat transfer area. Generally, heat exchangers with higher friction factors yield higher heat transfer performance and vice versa. However, heat transfer performance and pressure drop are separately evaluated and there is no comprehensive performance evaluation index for OTEC power take-off. Therefore, this research proposes a new simplified overall performance evaluation method for heat exchangers, which can be comprehensively and easily applied and takes into consideration the heat transfer performance and the pressure drop. The evaluation results on plate-type heat exchangers show that the overall performance in each heat exchanger are elucidated and are quantitatively compared. Full article
(This article belongs to the Special Issue Ocean Thermal Energy Conversion)
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10 pages, 1172 KiB  
Communication
A Preliminary Investigation of the Effect of Ocean Thermal Energy Conversion (OTEC) Effluent Discharge Options on Global OTEC Resources
by Gérard Nihous
J. Mar. Sci. Eng. 2018, 6(1), 25; https://doi.org/10.3390/jmse6010025 - 12 Mar 2018
Cited by 13 | Viewed by 6591
Abstract
A simple algorithm previously used to evaluate steady-state global Ocean Thermal Energy Conversion (OTEC) resources is extended to probe the effect of various effluent discharge methodologies. It is found that separate evaporator and condenser discharges potentially increase OTEC net power limits by about [...] Read more.
A simple algorithm previously used to evaluate steady-state global Ocean Thermal Energy Conversion (OTEC) resources is extended to probe the effect of various effluent discharge methodologies. It is found that separate evaporator and condenser discharges potentially increase OTEC net power limits by about 60% over a comparable mixed discharge scenario. This stems from a relatively less severe degradation of the thermal resource at given OTEC seawater flow rates, which corresponds to a smaller heat input into the ocean. Next, the most practical case of a mixed discharge into the mixed layer is found to correspond to only 80% of the so-called baseline case (mixed discharge at a water depth of initial neutral buoyancy). In general, locating effluent discharges at initial neutral-buoyancy depths appears to be nearly optimal in terms of OTEC net power production limits. The depth selected for the OTEC condenser effluent discharge, however, has by far the greatest impact. Clearly, these results are preliminary and should be investigated in more complex ocean general circulation models. Full article
(This article belongs to the Special Issue Ocean Thermal Energy Conversion)
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18 pages, 4677 KiB  
Article
Ocean Thermal Energy Conversion Using Double-Stage Rankine Cycle
by Yasuyuki Ikegami, Takeshi Yasunaga and Takafumi Morisaki
J. Mar. Sci. Eng. 2018, 6(1), 21; https://doi.org/10.3390/jmse6010021 - 1 Mar 2018
Cited by 39 | Viewed by 9469
Abstract
Ocean Thermal Energy Conversion (OTEC) using non-azeotropic mixtures such as ammonia/water as working fluid and the multistage cycle has been investigated in order to improve the thermal efficiency of the cycle because of small ocean temperature differences. The performance and effectiveness of the [...] Read more.
Ocean Thermal Energy Conversion (OTEC) using non-azeotropic mixtures such as ammonia/water as working fluid and the multistage cycle has been investigated in order to improve the thermal efficiency of the cycle because of small ocean temperature differences. The performance and effectiveness of the multistage cycle are barely understood. In addition, previous evaluation methods of heat exchange process cannot clearly indicate the influence of the thermophysical characteristics of the working fluid on the power output. Consequently, this study investigated the influence of reduction of the irreversible losses in the heat exchange process on the system performance in double-stage Rankine cycle using pure working fluid. Single Rankine, double-stage Rankine and Kalina cycles were analyzed to ascertain the system characteristics. The simple evaluation method of the temperature difference between the working fluid and the seawater is applied to this analysis. From the results of the parametric performance analysis it can be considered that double-stage Rankine cycle using pure working fluid can reduce the irreversible losses in the heat exchange process as with the Kalina cycle using an ammonia/water mixture. Considering the maximum power efficiency obtained in the study, double-stage Rankine and Kalina cycles can improve the power output by reducing the irreversible losses in the cycle. Full article
(This article belongs to the Special Issue Ocean Thermal Energy Conversion)
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11 pages, 3683 KiB  
Article
Determination of the Potential Thermal Gradient for the Mexican Pacific Ocean
by Alejandro García Huante, Yandy Rodríguez Cueto, Rodolfo Silva, Edgar Mendoza and Luis A. Vega
J. Mar. Sci. Eng. 2018, 6(1), 20; https://doi.org/10.3390/jmse6010020 - 21 Feb 2018
Cited by 13 | Viewed by 4739
Abstract
The energy potential of the oceanic thermal gradients of the Mexican Pacific Ocean was valued theoretically, using seasonal oceanographic data on surface and 1000 m depth ocean temperatures from 1955 to 2013, taken from the World Ocean Database (WOD). The study was carried [...] Read more.
The energy potential of the oceanic thermal gradients of the Mexican Pacific Ocean was valued theoretically, using seasonal oceanographic data on surface and 1000 m depth ocean temperatures from 1955 to 2013, taken from the World Ocean Database (WOD). The study was carried out to determine possible sites for Ocean Thermal Energy Conversion (OTEC), assuming that the minimum usable gradient is 20 °C and the maximum profitable distance from the extraction site to the shore is 10 km. Geographic Information System tools were used to compute thermal gradients and distances to shore all along the Mexican coast. Then, the optimal sites were identified. The results show that the best sites for OTEC exploitation are found in the southern Pacific coast on the littoral of the states of Guerrero and Oaxaca. Full article
(This article belongs to the Special Issue Ocean Thermal Energy Conversion)
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14 pages, 1068 KiB  
Article
Construction of a Static Model for Power Generation of OTEC Plant Using Uehara Cycle Based on Experimental Data
by Yoshitaka Matsuda, Takuma Yoshitake, Takenao Sugi, Satoru Goto, Takafumi Morisaki, Takeshi Yasunaga and Yasuyuki Ikegami
J. Mar. Sci. Eng. 2018, 6(1), 18; https://doi.org/10.3390/jmse6010018 - 15 Feb 2018
Cited by 9 | Viewed by 4586
Abstract
This paper considers the construction of a static model for the power generation of an ocean thermal energy conversion (OTEC) plant using Uehara cycle. The model is constructed based on experimental data obtained from an actual experimental OTEC plant. In this paper, two [...] Read more.
This paper considers the construction of a static model for the power generation of an ocean thermal energy conversion (OTEC) plant using Uehara cycle. The model is constructed based on experimental data obtained from an actual experimental OTEC plant. In this paper, two kinds of static models are proposed. In both models, the relations among significant quantities are represented by polynomials. The polynomials are determined via least squares for experimental data, and the orders of polynomial which minimize the integral of absolute error between experimental data and simulation results of power generation are adopted. The usefulness and limitations of the proposed models are evaluated by simulation results. Full article
(This article belongs to the Special Issue Ocean Thermal Energy Conversion)
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28 pages, 18424 KiB  
Article
An Evaluation of the Large-Scale Implementation of Ocean Thermal Energy Conversion (OTEC) Using an Ocean General Circulation Model with Low-Complexity Atmospheric Feedback Effects
by Yanli Jia, Gérard C. Nihous and Krishnakumar Rajagopalan
J. Mar. Sci. Eng. 2018, 6(1), 12; https://doi.org/10.3390/jmse6010012 - 22 Jan 2018
Cited by 22 | Viewed by 9125
Abstract
Previous investigations of the large-scale deployment of Ocean Thermal Energy Conversions (OTEC) systems are extended by allowing some atmospheric feedback in an ocean general circulation model. A modified ocean-atmosphere thermal boundary condition is used where relaxation corresponds to atmospheric longwave radiation to space, [...] Read more.
Previous investigations of the large-scale deployment of Ocean Thermal Energy Conversions (OTEC) systems are extended by allowing some atmospheric feedback in an ocean general circulation model. A modified ocean-atmosphere thermal boundary condition is used where relaxation corresponds to atmospheric longwave radiation to space, and an additional term expresses horizontal atmospheric transport. This produces lower steady-state OTEC power maxima (8 to 10.2 TW instead of 14.1 TW for global OTEC scenarios, and 7.2 to 9.3 TW instead of 11.9 TW for OTEC implementation within 100 km of coastlines). When power production peaks, power intensity remains practically unchanged, at 0.2 TW per Sverdrup of OTEC deep cold seawater, suggesting a similar degradation of the OTEC thermal resource. Large-scale environmental effects include surface cooling in low latitudes and warming elsewhere, with a net heat intake within the water column. These changes develop rapidly from the propagation of Kelvin and Rossby waves, and ocean current advection. Two deep circulation cells are generated in the Atlantic and Indo-Pacific basins. The Atlantic Meridional Overturning Circulation (AMOC) is reinforced while an AMOC-like feature appears in the North Pacific, with deep convective winter events at high latitudes. Transport between the Indo-Pacific and the Southern Ocean is strengthened, with impacts on the Atlantic via the Antarctic Circumpolar Current (ACC). Full article
(This article belongs to the Special Issue Ocean Thermal Energy Conversion)
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