Material Insights · Understanding the Material World

Carnot batteries: Impact and additionality

A second life for coal plants as clean power stores

What this tab covers The impact and additionality lens: what it displaces on the grid, who gains and who bears the burden along the supply chain, and what happens at end of life.

At 10 hours or more, a Carnot battery could firm wind and solar overnight and replace gas peakers, and it offers a second life for coal sites. The claim rests on technology not yet operating at grid scale.

Grid decarbonisation versus fossil displacement

Mixed

Durations of 10 to 100 hours or more go beyond shifting solar into the evening; they can cover windless nights and replace gas plants that provide firm capacity. Malta says it is pursuing 10 to 12 hour projects and that its design can reach 200 hours; in Germany it is testing full-scale heat exchangers with DLR, Alfa Laval and Siemens Energy (Store2REPower). Estimated costs for coal-plant conversions, USD 80 to 100 per MWh, are still above coal and gas in the Chilean case studied.1610

Malta duration (company claim) 10-12 h focus; up to 200 h6 Coal-plant conversion energy cost (Chile) USD 80-100 per MWh vs coal 63-76 and gas 65-911

Just transition and local community impact

Favourable

Converting coal plants could keep turbine halls, grid connections and some skilled jobs in coal communities. Supply chains use steel, salt and turbomachinery, which are manufactured in many countries. The risk is developer failure: Isentropic went into administration in 2016.12

Circular economy and end of life

Favourable

Steel, salt, gravel and sand can be recycled or reused, and there are no hazardous electrode materials. No end-of-life studies specific to Carnot batteries were found. A 2024 comparative life-cycle study of home-scale Carnot batteries found no clear winner against lithium-ion on most impact categories, with impacts dominated by the solar panels and grid power used rather than the storage, and an 18% lower mineral depletion for a heat-store-and-engine design than for heat storage paired with lithium-ion.28

Mineral resource depletion, thermal store plus heat engine vs thermal store plus Li-ion (home scale) 18% lower8

Sources

  1. Carnot Battery development: A review on system performance, applications and commercial state-of-the-art (Vecchi et al., Journal of Energy Storage 55, 105782) University of Birmingham repository, 2022
  2. Review of Carnot Battery Technology Commercial Development (Novotny et al., Energies 15(2), 647) MDPI, 2022
  3. Long-duration 'pumped heat energy storage' startup Malta raises US$50 million in Series B round (news report of company claims) Energy-Storage.news, 2021
  4. Comparative and prospective life cycle assessment of residential Carnot batteries (Laterre, Coppitters, Lemort and Contino, 4th International Workshop on Carnot Batteries) UCLouvain DIAL repository, 2024
  5. Malta Inc. Store2REPower project breaks ground for full-scale heat exchanger qualifications Energy Storage Europe, 2024