King's College London

Popular permissionless distributed ledger technology (DLT) systems using proof-of-work (PoW) for Sybil attack resistance have extreme energy requirements, drawing stern criticism from academia, business and the media. DLT systems building on alternative consensus mechanisms, particularly proof-of-stake (PoS), aim to address this downside. In this paper, we take an initial step towards comparing the energy requirements of such systems to understand whether they achieve this goal equally well. While multiple studies have analysed the energy demands of individual blockchains, little comparative work has been done. We approach this research gap by formalising a basic consumption model for PoS blockchains. Applying this model to six archetypal blockchains generates three main findings. First, we confirm the concerns around the energy footprint of PoW by showing that Bitcoin's energy consumption exceeds the energy consumption of all PoS-based systems analysed by at least three orders of magnitude. Second, we illustrate that there are significant differences in energy consumption among the PoS-based systems analysed, with permissionless systems having a larger energy footprint overall owing to their higher replication factor. Third, we point out that the type of hardware that validators use has a considerable impact on whether the energy consumption of PoS blockchains is comparable with or considerably larger than that of centralised systems.