Extracting Energy from Ocean Thermal and Salinity Gradients to Power Unmanned Underwater Vehicles: State of the Art, Current Limitations, and Future Outlook

Hyunjun Jung, Chinmayee Subban, Joshua Dominic McTigue, Jayson Martinez, Andrea Copping, Julian Osorio, Jian Liu, Daniel Deng

Research output: Contribution to journalArticlepeer-review

17 Scopus Citations


Thermal gradient energy-generation technologies for powering unmanned underwater vehicles (UUVs) or autonomous sensing systems in the ocean are mainly in the research development phase or commercially available at a limited scale, and salinity-gradient energy-generation technologies have not been adequately researched yet. The demand for self-powered UUVs suitable for long-term deployments has been growing, and further research related to small-scale ocean gradient energy systems is needed. In this study, we conducted a comprehensive review about harvesting energy from ocean thermal or salinity gradients for powering UUVs, focusing on gliders and profiling floats. Thermal gradient energy systems for UUVs based on phase change materials (PCM) cannot provide the energy required for powering autonomous sensing systems because of the systems’ low energy conversion efficiency. Besides reducing energy consumption by developing more efficient electrical-mechanical systems, enhancing the thermal conductivity of the PCMs may help address this challenge by increasing the power generation rate of the UUVs. Several other emerging technologies, such as thermoelectric generators, shape memory alloys, and small-scale thermodynamic cycle systems, have shown potential for powering UUVs, but they are still only at the laboratory testing or conceptual design phase. The most advanced power generation technologies based on salinity gradients, reverse electrodialysis and pressure-retarded osmosis, are still not economically viable for large-scale deployment, mainly because of the high cost of the components required to operate in harsh saline environments. Our feasibility evaluation showed that existing salinity gradient power generation technologies are not directly feasible for powering UUVs in the open ocean.

Original languageAmerican English
Article number112283
Number of pages21
JournalRenewable and Sustainable Energy Reviews
StatePublished - May 2022

Bibliographical note

Publisher Copyright:
© The Authors

NREL Publication Number

  • NREL/JA-5700-80980


  • Energy harvesting
  • Phase change material
  • Salinity gradient
  • Thermal gradient
  • Unmanned underwater vehicle


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