| Work Detail |
Danish researchers have studied the technical and economic feasibility of biomethanization through large-scale photovoltaic energy generation. They stated that the intermittent biomethanation process powered by photovoltaics equals the efficiency of continuous processes after several days.
Scientists from the Danish University of Aarhus have demonstrated the possibility of producing biomethane using photovoltaic energy. They have studied how to apply the biomethanation process in photovoltaic installations, where activity is interrupted due to lack of solar radiation.
Biomethanization consists of transforming organic materials into biogas, composed mainly of methane (CH4) and carbon dioxide (CO2). In this process, hydrogen gas (H2) plays an important role as a substrate for microbial reactions and as part of the final product.
“As an alternative to energy storage in batteries, the use of photovoltaic solar energy has been proposed to produce H2 through the process of water electrolysis,” the scientists explained. “H2 can be used as a building block to produce other fuels and chemicals, [such as biomethane]. Biomethane, with typical concentrations greater than 98 vol% CH4, is very suitable for injection into natural gas networks.”
To demonstrate the feasibility of producing biomethane on batch PV terms, the academics first collected solar data from the California Flats Solar Park, a 280 MW PV plant located in Monterey County, California.
With a stable nine-hour power supply, the California Flats Solar Park operates on a 1.5-hour ramp-up and ramp-down ramp, spending the remaining 12 hours in standby mode. The research group studied the use of a trickling bed reactor (TBR), a catalytic system that transforms organic matter into biomethane by converting sulfur, nitrogen and aromatic compounds from hydrocarbon fuels.
They also considered a period of continuous operation of 20 days as a reference and compared it with 29 days of discontinuous operation based on the production profile of the aforementioned plant. The scientists defined the desired fraction of H2 in biomethane as less than 2%, as it adjusts to grid injection of natural gas.
“By starting the PV-based batch mode of operation, it became evident that the TBR did not achieve the same biomethanation conversion efficiency as the previous continuous mode of operation,” the academics explained. “However, after six days of following this discontinuous operating strategy, the reactor recovered its baseline performance on the seventh day.”
According to academics, in the first four days of discontinuous operation, H2 concentrations ranged between 10% and 40% in the biomethane product gas. However, on the sixth day, the H2 content in the biomethane was less than 2%, as desired. Furthermore, on days 7 to 12, this quality was achieved within 16 minutes after start-up; on days 13 to 21, it was achieved instantly; and in recent days, it was completed within 20 minutes from the start of the operation.
“During the 12-hour waiting periods, the acids accumulated during the operating period degraded by 58.44% to biogas,” the scientists explained. “Thus, waiting periods could be used synergistically as an in-situ cleaning technique to eliminate accumulated acids and biomass.”
To demonstrate that the discontinuous process is viable, scientists propose a techno-economic evaluation. They calculated that the photovoltaic biomethanization plant used a daily average of 28 MWh of photovoltaic solar energy. The electrical load of the process was calculated at 2,675.59 kW, of which 2,423.07 kW (or 90.56%) is used for H2 production through electrolysis.
“If a pre-commercial TBR biomethanization plant is installed at an existing biogas facility, the levelized cost of biomethane production (LCOP) in a 2030 scenario is $147.84, with electrolysis being the largest cost contributor. ", they conclude. “Although this LCOP is higher than that of conventional biogas upgrading, biomethanization offers the possibility of capturing and using CO2.”
They presented the novel system configuration in “ Sunshine-to-fuel: Demonstration of coupled photovoltaic-driven biomethanation operation, process, and techno-economical evaluation ” ), recently published in Energy Conversion and Management. |
