Sunshine-to-fuel: Demonstration of coupled photovoltaic-driven biomethanation operation, process, and techno-economical evaluation.

[Display omitted] • Successful biomethanation in trickle bed reactors following a solar energy pattern. • Ramp-up times of < 16 min was achieved at a rate of 40.65 ± 0.11 NL H 2 L−1 d−1. • Standby periods function as a natural clean-in-place to convert accumulated acids. • Producing grid injected CH 4 retained 50.70 % of the photovoltaic power input. • Levelised cost of production of CH 4 was demonstrated to be 147.84 $ (MWh)−1. The accelerating green transition envisions large shares of renewable intermittent power supplies, which challenges the balancing of the grid. A promising approach to long-term storage is the power-to-X technology of biomethanation. This study developed an operating model for ex situ biomethanation in a trickle bed reactor (TBR) based on daily photovoltaic (PV) solar generation profiles from the California Flats solar cell park and demonstrated long-term discontinuous biomethanation of raw biogas. The TBR was operated discontinuously for 29 days, where biomethane admissible for natural gas grid injection could be achieved within a ramp-up time of < 16 min after an adaptation period of 6 days with a purity of < 2 % hydrogen and > 97.5 % biomethane. The shutdown periods demonstrated a continuous digestion of accumulated acids and biomass. Therefore, shutting off the hydrogen addition could synergistically be employed as a clean-in-place procedure, where ∼60 % of the accumulated volatile fatty acids were converted during 12 h of standby. The TBR performance was subsequently used to evaluate the economic feasibility of integrating biomethanation to convert and store solar PV energy. The levelized cost of production of grid-quality biomethane by a small commercial biomethanation system, subject to solar PV energy (28 MWh e d−1), was found to be 147.84 $ (MWh CH4 HHV)−1 in a 2030 scenario. [ABSTRACT FROM AUTHOR]