Hot air recirculation enlarges efficient operating window of reversible solid oxide cell systems: A thermodynamic study of energy storage using ammonia

Amogh Amladi*, Vikrant Venkataraman, Theo Woudstra, P. V. Aravind

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

Energy storage is vital for the energy transition, enabling reliable power grids based on intermittent renewables. Reversible solid oxide cell (rSOC) technology is promising for seasonal energy storage. The novel finding from this work is that optimised air recirculation for rSOC in endothermic electrolyser mode leads to efficiency being nearly independent of current density. Thereby the operating region of highest efficiency is expanded from the thermoneutral point to the entire endothermic region, leading to highly efficient part-load operation. Air recirculation increases fuel cell mode efficiency too, particularly at higher loads. This widens the efficient operating window in both modes. These findings emerge from a thermodynamic study of an rSOC-based energy storage system with ammonia as fuel. A process design is developed and optimised for efficiency, supported with detailed exergy analysis. First, ammonia synthesis subsystem integrated with the rSOC system in electrolyser mode is optimised. Second, rSOC outlet air recirculation is optimised for high system efficiency. Finally, rSOC operating points are optimised for highest round-trip efficiency. We find the least exergy destruction for the ammonia synthesis subsystem at 170 bar synthesis pressure and 30 °C condensation temperature (without needing refrigeration). The overall system achieves round-trip efficiencies up to 60.3%.

Original languageEnglish
Article number122276
Number of pages29
JournalApplied Energy
Volume355
DOIs
Publication statusPublished - 2024

Funding

Funding Information:
This work was a part of the BALANCE project, which received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 731224.

Funding Information:
This work was a part of the BALANCE project, which received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 731224 .

Keywords

  • Air recirculation
  • Ammonia
  • Energy storage
  • Exergy
  • Fuel cell
  • Reversible solid oxide cell

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