Ocean Thermal Energy Conversion (OTEC) is a foundation for an appealing renewable energy technology owing to its vast and inexhaustible resources of energy, stability, and sustainable output. Development of OTEC power plant is to exploit the energy accumulated in between the top layer of warm surface seawater (heat source), and the cold layer of deep seawater (heat sink). It operates based on Rankine cycle to produce electricity between the source and the sink at the smallest temperature difference of approximately 20 K. OTEC power plant commonly utilized ammonia as working fluid. Nevertheless, ammonia poses potential lethal health risks and hazardous fluid. Hence, the effect of the working fluid types and the subsequent operation conditions may be critical and therefore become the subject of this study. In addition to OTEC power plant’s thermodynamic efficiencies study, this research also explores the economic efficiencies in term of capital cost per net power output ($/kW) and environmental criteria of different working fluids including that of ammonia, ammonia-water mixture (0.9), propane, and refrigerants (R22, R32, R134a, R143a, and R410a). The results showed that ammonia-water mixture gave the excellent performance with regard to the characteristics of heat transfer with the best thermodynamic efficiency of 4.04% compared to pure ammonia with 3.21%, propane with 3.09%, followed by refrigerants from 3.03% to 3.13%. Capital cost of using propane was economically efficient with 15730 $/kW compared to ammonia-water mixture at 16201$/kW, refrigerants from 16990 $/kW to 21400 $/kW, and pure ammonia being the costliest at 21700 $/kW. Despite being lower in its thermodynamic efficiency, propane gave the lowest capital cost and had the lowest toxicity in contrast to all other working fluids. Therefore, propane has the potential to be used as a clean and safe working fluid that would further enhance the OTEC technology.

Ocean Thermal Energy Conversion (OTEC) is a promising renewable energy technology with the concept to harness the energy stored at the surface seawater (SSW) and the cold deep seawater (DSW). The operation is based on the Rankine cycle, and involves at a minimum temperature difference of 20 K of the SSW and DSW to generate electricity. This research focuses on the economic efficiency of different working fluids used in the OTEC Rankine cycle. The various working fluids include ammonia, ammonia-water mixture (0.9), propane, R22, R32, R134a, R143a, and R410a. Most of the existing commercial OTEC systems use ammonia as the working medium despite its toxic nature. This study shows that the ammonia-water mixture still gives the best results in terms of heat transfer characteristics because of its greater transport properties and stability compared to other fluids. However, fluids such as propane and R32 can also be used as a substitute for ammonia-water mixture despite having slightly lower efficiency, because they are non-toxic and safer towards the environment. The same developmental model was used to present the proposed modified OTEC Rankine cycle, which shows a 4% increase in thermal cycle efficiency. This study reveals economically efficient and environmentally friendly working fluids.

Ocean Thermal Energy Conversion (OTEC) is a foundation for an appealing renewable energy technology with regards to its vast and inexhaustible resources of energy, renewability, stability, and sustainable output. The principle of an OTEC power plant is to exploit the energy stored in between the upper layer of warm surface seawater (heat source), and the cold layer of deep seawater (heat sink). The plant operates based on a Rankine cycle to produce electricity between the source and the sink at the minimum temperature difference of approximately 20 K. The main objective of this study is to evaluate the performance of the proposed OTEC closed Rankine cycle using ammonia as the working fluid, to be paralleled with basic OTEC Rankine cycle. Preliminary simulation was performed at the initial stage of the study to validate the simulation model by referring to previous OTEC studies. The same developed model was deployed to test the efficiency of the proposed modified OTEC Rankine cycle, resulting in an enhancement in terms of thermal cycle performance from 3.43% to 7.98%. This study has revealed that the proposed OTEC closed Rankine cycle which introduced an interstage superheating as well as an improved condenser cooling system, augmented the system competence of an OTEC power cycle.

Ocean Thermal Energy Conversion (OTEC) is a foundation for an appealing renewable energy technology regarding its vast and inexhaustible resources of energy, renewability, stability, and sustainable output. The principle of an OTEC power plant is to exploit the energy accumulated in between the top layer of warm surface seawater (heat source), and the cold layer of deep seawater (heat sink). The plant operates based on a Rankine cycle to produce electricity between the source and the sink at the smallest temperature difference of approximately 20 K. In an OTEC power plant, a commonly utilized working fluid is ammonia since its qualities are suitable for the OTEC cycle. Nevertheless, ammonia poses certain potentially lethal health risks and hazardous fluid. Hence, the effect of the working fluid types, and the subsequent operation conditions may be critical and therefore become the subject of this study. The analysed working fluids, including that of ammonia, are ammonia-water mixture (0.9), propane, and refrigerants (R22, R32, R134a, R143a, and R410a). The results revealed that ammonia-water mixture showed the highest network performance and reliability. Even so, it is essential to continue seeking the suitable working fluids which are safe and economically effective to replace ammonia.