Exploiting the Ocean Thermal Energy Conversion (OTEC) technology for green hydrogen production and storage: Exergo-economic analysis
Lorenzo Ciappi, Luca Socci, Mattia Calabrese, Chiara Di Francesco, Fabio Savelli, Giampaolo Manfrida, Andrea Rocchetti, Lorenzo Talluri, Daniele Fiaschi
Abstract
This study presents and analyses three plant configurations of the Ocean Thermal Energy Conversion (OTEC) technology. All the solutions are based on using the OTEC system to obtain hydrogen through an electrolyzer. The hydrogen is then compressed and stored. In the first and second layouts, a Rankine cycle with ammonia and a mixture of water and ethanol is utilised respectively; in the third layout, a Kalina cycle is considered. In each configuration, the OTEC cycle is coupled with a polymer electrolyte membrane (PEM) electrolyzer and the compression and storage system. The water entering the electrolyzer is pre-heated to 80 °C by a solar collector. Energy, exergy, and exergo-economic studies were conducted to evaluate the cost of producing, compressing, and storing hydrogen. A parametric analysis examining the main design constraints was performed based on the temperature range of the condenser, the mass flow ratio of hot and cold resource flows, and the mass fraction. The maximum value of the overall exergy efficiency calculated is equal to 93.5% for the Kalina cycle, and 0.524 €/kWh is the minimum cost of hydrogen production achieved. The results were compared with typical data from other hydrogen production systems. • An OTEC based offshore hydrogen production system is analysed by exergo-economics. • Three different OTEC cycles are compared: two Rankine and Kalina. • System includes OTEC, electrolyzer, H 2 compression, water desalination and heating. • Kalina cycle is the best performing, with 93.5 %, 83–87% for Rankine. • The cost of H 2 from Kalina OTEC is estimated at 17.3 €/kg (0.52 €/kWh).