Performance Evaluation Concept for Ocean Thermal Energy Conversion toward Standardization and Intelligent Design

Takeshi Yasunaga, Kevin Fontaine and Yasuyuki Ikegami
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Takeshi Yasunaga: Institute of Ocean Energy, Saga University, 1 Honjo-Machi, Saga 840-8502, Japan
Kevin Fontaine: Graduate School of Science and Engineering, Saga University, 1 Honjo-Machi, Saga 840-8502, Japan
Yasuyuki Ikegami: Institute of Ocean Energy, Saga University, 1 Honjo-Machi, Saga 840-8502, Japan

Energies, 2021, vol. 14, issue 8, 1-12

Abstract: Ocean thermal energy conversion (OTEC) uses a very simple process to convert the thermal energy stored mainly in tropical oceans into electricity. In designs, operations, and evaluations, we need to consider the unique characteristics of OTEC to achieve the best performance or lower the electricity cost of projects. The concept and design constraints of OTEC power generation differ from those of conventional thermal power plants due to the utilization of a low temperature difference. This research theoretically recognizes the unique characteristics of the energy conversion system and summarizes the appropriate performance evaluation methods for OTEC based on finite-time thermodynamics and the equilibrium condition of the heat source. In addition, it presents the concept of normalization of thermal efficiency for OTEC and exergy efficiency based on the available thermal energy in the ocean defined as the transferable thermal energy from the ocean and the equilibrium condition as the dead state for exergy. The differences between conventional thermal efficiency and the effectiveness of the evaluation methods are visualized using the various reference design data, and it is ascertained that there is no clear relation between the conventional thermal efficiency and exergy efficiency, whereas the normalized thermal efficiency is definitely proportional to the exergy efficiency. Moreover, the exergy efficiency shows the effectiveness of the staging Rankine, Kalina, and Uehara cycles. Therefore, the normalized thermal efficiency and the exergy efficiency are important to analyze the heat and mass balance as well as improvement of the system.

Keywords: OTEC; normalized efficiency; exergy; finite-time thermodynamics; transferable energy (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (3)

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