OTEC Supported Energy System for Offshore Fish Farming: A Bi-Level Optimization Approach for Sizing and Operation

Blue economy industries like aquaculture are expanding further offshore to leverage the ocean’s vast scale. However, this shift demands reliable, regular power independent of land-based grids. This study introduces a bi-level optimization framework for the design and operation of a hybrid OTEC-diesel system equipped with battery energy storage to power offshore fish farms. The upper-level optimization aims to minimize the levelized cost of energy (LCOE) and ensure continuous operation by optimizing the battery size within the constraints of energy storage. The objective of the lower-level optimization is to minimize energy waste while also addressing an environmental goal, which is to decrease the unnecessary mixing of cold and warm water in the Rankine cycle of the ocean thermal energy conversion (OTEC) system. In our study, we investigated two system configurations: first, a traditional setup using only a diesel generator; second, an OTEC/Diesel/BESS hybrid configuration was evaluated under two scenarios for different fish farm sizes. The results show that scaling up the fish farm and hybrid OTEC-diesel system with energy storage significantly lowers the LCOE. Furthermore, regulating the working fluid’s mass flow rate cuts energy waste by nearly 20% compared to single-level optimization, which reduces environmental impact, and positions this hybrid system as a sustainable and cost-effective alternative to diesel-powered fish farms.