Zero-carbon energy system for offshore Islands: integrating freeze desalination, hydrogen storage, and fuel cells

Energy supply challenges hinder the economic development of remote offshore islands, which traditionally rely on diesel generators, causing pollution, shortages, and high costs. Wind power and photovoltaics, promising renewable sources, offer solutions when integrated with technologies such as desalination, refrigeration, and power generation, tailored to local conditions. However, their fluctuating nature leads to system instability. Additionally, while freshwater and cooling energy are vital for island residents, traditional desalination is costly, and refrigeration systems often fail to meet comprehensive needs. The pursuit of low-cost desalination and effective low-temperature refrigeration is still needed. This research proposes an integral renewable energy system for islands, combining ocean thermal, wind, and solar energy, with ocean thermal energy conversion system as the stabilizer. By employing freeze desalination technology, the system achieves a joint supply of low-cost seawater desalination and low-temperature refrigeration. Additionally, the integration of freshwater, hydrogen storage, and fuel cell technology facilitates the storage and reconversion of surplus electricity, addressing temporal and spatial energy mismatches while lowering power consumption costs. This study employs multi-objective optimization to refine the configuration of the multi-energy complementary supply system, concentrating on thermodynamic and economic performance objectives. Findings show that for user electrical loads fluctuating between 2 MW and 4.5 MW, with theoretical design capacities of 2 MW for ocean thermal energy conversion system, 2.2 MW for photovoltaic, and 1.7 MW for wind turbines. Its exergy efficiency is 34.63 % with a levelized cost of power at 0.084$/kWh. Furthermore, the system can potentially reduce CO₂ emissions by approximately 2.16 × 10⁴ tons annually, demonstrating significant environmental benefits. This research offers a solution with enhanced stability and lower energy supply costs for offshore islands, contributing to the advancement of zero-carbon offshore integrated energy technologies.