Adiabatic compressed air energy storage technology

[Formula presented]Edward Barbour obtained his bachelor's degree in Physics from Oxford University and his PhD in Mechanical Engineering from the University of Edinburgh in 2013. His doctoral thesis focused on the development of ACAES and the economics of energy storage within the UK market framework. He held subsequent postdoc positions at the University of Birmingham and Massachusetts Institute of Technology. As of 2019, he is a lecturer at Loughborough University in the Centre for Renewable Energy Systems Technology (CREST), where his research is focused on thermomechanical energy storage and the future role of energy storage in the UK. [Formula presented]Daniel L. Pottie obtained his bachelor's in Mechanical Engineering from Universidade Federal de Minas Gerais (UFMG), Brazil in 2016. In the same year, he started as a research assistant at UFMG, developing hydraulic compressed air energy storage technology. He started his MSc degree in the subject in 2018, and his thesis detailed the thermodynamic performance of a novel pumped hydraulic compressed air energy storage (PHCAES) system. He was awarded the degree in September 2019. Currently, he is a PhD candidate at Loughborough University where his research is focused on the development of competitive, efficient, and innovative adiabatic compressed air energy storage. For decades, technical literature has appraised adiabatic compressed air energy storage (ACAES) as a potential long-duration energy storage solution. However, it has not reached the expected performance indicators and widespread implementation. Here, we reflect on the design requirements and specific challenges for each ACAES component. We use evidence from recent numerical, theoretical, and experimental studies to define the technology-readiness level (TRL). Lastly, we discuss promising new directions for future technology development.