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The integration of renewable electricity generation poses challenges for today's energy system. Since renewable potentials are geographically unevenly distributed, solutions to overcome bottlenecks such as grid congestion are necessary to raise as much renewable potentials as possible. In specific, a part of Austria is characterised with high photovoltaic installation inquiries and low electricity demand. Electricity grids are designed to cope with today's loads, therefore the integration of inquired photovoltaic would overstrain the built infrastructure. In this paper we investigate how power-to-gas can ease this photovoltaic related grid strain. The feed-in of hydrogen into natural gas transmission pipelines and the usage of hydrogen and biogas from local fermentation plants for methanation feeding synthetic natural gas (SNG) into local distribution grid is assessed in various scenarios. Based on the technical assessment results, an economic evaluation of each scenario is performed to determine generation costs of hydrogen or SNG. Depending on the electrolysers location in the electricity grid, the installable photovoltaic power can be increased significantly without causing electricity grid congestion. Costs for hydrogen and SNG vary across each scenario, mainly influenced by CapEx for electrolyser and methanation as well as electricity purchasing costs. • Increasing installed renewable energies power through power-to-gas. • Implementing renewable energy sources. • Power-to-gas as grid relief measure. • Hydrogen and SNG generation costs. [ABSTRACT FROM AUTHOR]

Biological methanation as a method of sector coupling between electric and gas grids is expected to be an integral part of the green energy change. Wastewater treatment plants (WWTPs) involving anaerobic digestion (AD) allow existing infrastructure to operate as energy conversion plants, to close carbon cycles and to generate long-term storable energy in the form of biomethane. Therefore, municipal raw sludge and additional organic residuals (co-substrates) are converted into biogas. Hydrogen is added to convert the carbon dioxide in the biogas into methane via biological methanation (BM). In this study, the energy amount that is convertible via BM in municipal digesters in Austria was calculated. The amount of energy, which can be transformed from electric surplus energy into biomethane, was assessed. Operational data from lab-scale digesters were combined with data from 28 Austrian full-scale wastewater treatment plants with AD. They represent 9.2 Mio population equivalents (PE), or 68% of Austria's municipal AD capacity for WWTPs > 50,000 PE (in sum, 13.6 Mio PE). Energy flows for BM including water electrolysis and anaerobic digestion were created on a countrywide basis. It was found that 2.9–4.4% (220–327 GWh·y−1) of Austria's yearly renewable electricity production (7470 GWh·y−1) can be transformed into biomethane via BM in municipal digesters. [ABSTRACT FROM AUTHOR]

The energy supply in Austria is significantly based on fossil natural gas. Due to the necessary decarbonization of the heat and energy sector, a switch to a green substitute is necessary to limit CO2 emissions. Especially innovative concepts such as power-to-gas establish the connection between the storage of volatile renewable energy and its conversion into green gases. In this paper, different methanation strategies are applied on syngas from biomass gasification. The investigated syngas compositions range from traditional steam gasification, sorption-enhanced reforming to the innovative CO2 gasification. As the producer gases show different compositions regarding the H2/COx ratio, three possible methanation strategies (direct, sub-stoichiometric and over-stoichiometric methanation) are defined and assessed with technological evaluation tools for possible future large-scale set-ups consisting of a gasification, an electrolysis and a methanation unit. Due to its relative high share of hydrogen and the high technical maturity of this gasification mode, syngas from steam gasification represents the most promising gas composition for downstream methanation. Sub-stoichiometric operation of this syngas with limited H2 dosage represents an attractive methanation strategy since the hydrogen utilization is optimized. The overall efficiency of the sub-stoichiometric methanation lies at 59.9%. Determined by laboratory methanation experiments, a share of nearly 17 mol.% of CO2 needs to be separated to make injection into the natural gas grid possible. A technical feasible alternative, avoiding possible carbon formation in the methanation reactor, is the direct methanation of sorption-enhanced reforming syngas, with an overall process efficiency in large-scale applications of 55.9%. [ABSTRACT FROM AUTHOR]