Synthetic Power-to-Gas Methane as Fuel for Transportation - Life Cycle Environmental Impacts of the PtG Methane Supply Chain Powered by Renewable Electricity
Wettstein, Sarah; Stucki, Matthias (2017). Synthetic Power-to-Gas Methane as Fuel for Transportation - Life Cycle Environmental Impacts of the PtG Methane Supply Chain Powered by Renewable Electricity: Oral presentation. In: Life Cycle Management 2017. Konferenz. (4. September 2017). Luxemburg: Luxembourg Institute of Science and Technology LIST.
Natural gas plays an increasingly important role as a fuel for the transport sector. With the power-to-gas (PTG) technology, synthetic methane (CH4) is produced from carbon dioxide (CO2) and hydrogen (H2). Methane can be stored in the already existing natural gas grid until it is used as fuel for vehicles. Synthetic PTG natural gas made of hydrogen produced by hydrogen electrolysis (HE) and powered by electricity from renewables is an important alternative for reducing the dependency from fossil fuels in the transport sector.
The goal of this study is to analyse the environmental sustainability of mobility fuelled by synthetic PTG methane. We performed a prospective LCA with time horizon 2020 to identify greenhouse gas (GHG) emissions of mobility fuelled by synthetic PTG methane from CO2 methanation, considering the whole value chain from CO2 capture and H2 production to methanation of CO2 and H2 to synthetic PTG CH4, which is used as fuel in the transport sector. The study included different scenarios as CO2 capture from industrial waste gases or atmosphere and H2 production through HE with efficiencies of 62%, 70% and 80%, respectively. For CO2 capture, methanation and HE various power sources including Swiss grid mix, hydropower, photovoltaics (multi-crystalline solar cells (Multi-Si), cadmium telluride (CdTe) solar cells), electricity from waste incineration plants and excess power were considered.
The carbon footprint of driving with natural gas cars fuelled with synthetic PTG methane corresponds to 141 g CO2‑eq./km if HE, CO2 capture and methanation are supplied by Swiss electricity mix (HE efficiency: 80%, CO2 source: waste gases from industrial plant) with synthetic PTG methane production (50%) and vehicles and road (49%) as main contributors to the carbon footprint. Synthetic PTG methane production is dominated by H2 production (94%), whereas distribution (3%), methanation (2%) and CO2 production (1%) only have a minor contribution. GHG emissions can be reduced if HE is powered by photovoltaics (Multi-Si: 138 g CO2‑eq./km; CdTe: 105 g CO2‑eq./km), hydropower (92 g CO2‑eq./km), electricity from waste incineration plants (87 g CO2‑eq./km) or excess power (85 g CO2‑eq./km). In comparison, the same vehicle type fuelled with petrol or diesel causes life cycle GHG emissions of 269 g CO2‑eq./km and 237 g CO2‑eq./km, respectively.
Synthetic PTG methane is a promising approach to mitigate GHG emissions of transportation and individual mobility, if the electricity used in the synthetic PTG methane value chain is produced by renewable energy technologies with low greenhouse gas intensity. The mitigation potential is highest when using excess power or power from waste incineration plants to supply HE, industrial waste gases as CO2 source in combination with a high hydrogen production efficiency. A reduction of 68% of GHG emissions is achievable with vehicles fuelled by synthetic PTG methane when compared to conventional petrol vehicles. If CO2 capturing and methanation are supplied by renewable energy or excess electricity too, a reduction of GHG emissions of additionally 4% can be reached.