Renewable gas production costs in 2018 and projections for 2030 and 2050. Note: SMR — steam-reformed methane; ATR — auto-reformed methane; AD — anaerobic digestion; P2GPEM — power to hydrogen using polymer electrolyte membrane electrolyser; CCS — carbon capture and storage. Source: Lambert and Oluleye (2019, p. 17, Fig. 12).