Carnot Batteries for Grid-Scale Energy Storage: Technologies and the Potential Valorization of Biomass Ash as Thermal Storage Media

Leonel J. R. Nunes ()
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Leonel J. R. Nunes: PROMETHEUS, Unidade de Investigação em Materiais, Energia, Ambiente para a Sustentabilidade, Instituto Politécnico de Viana do Castelo, Rua da Escola Industrial e Comercial de Nun’Alvares, 4900-347 Viana do Castelo, Portugal

Energies, 2025, vol. 18, issue 16, 1-32

Abstract: The transition towards renewable energy necessitates large-scale, cost-effective energy storage solutions. Carnot Batteries (CBs), which store electricity as thermal energy, offer potential advantages for medium-to-long-duration storage, including geographical flexibility and lower energy capacity costs compared to electrochemical batteries. This article examines the evolution and current state-of-the-art of CB technologies, including Pumped Thermal Energy Storage (PTES) and Liquid Air Energy Storage (LAES), discussing their performance metrics, techno-economics, and development challenges. Concurrently, the increasing generation of biomass ash (BA) from bioenergy production presents a waste valorization challenge. This article critically evaluates the potential of using BA, particularly from woody biomass, as an ultra-low-cost thermal energy storage (TES) medium within CBs systems. We analyze BA’s typical composition (SiO 2 , CaO, K 2 O, etc.) and relevant thermal properties, highlighting significant variability. Key challenges identified include BA’s likely low thermal conductivity, which impedes heat transfer, and poor thermal stability (low ash fusion temperatures, sintering, corrosion) due to alkali and chlorine content, especially problematic for high-temperature CBs. While the low cost is attractive, these technical hurdles suggest direct use of raw BA is challenging. Potential niches in lower-temperature systems or as part of composite materials warrant further investigation, requiring detailed experimental characterization of specific ash types.

Keywords: Carnot Batteries; Thermal Energy Storage (TES); biomass ash; grid stability; renewable energy integration (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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