Sunshine-to-fuel: Demonstration of coupled photovoltaic-driven biomethanation operation, process, and techno-economical evaluation
Mads Ujarak Sieborg, Nicolaas Engelbrecht, Lars Ditlev Mørck Ottosen, Michael Vedel Wegener Kofoed
Abstract
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 MWhe d−1), was found to be 147.84 $ (MWhCH4 HHV)−1 in a 2030 scenario.