Moving towards economical decarbonization in transport

Berlin, Germany (SPX) Dec 04, 2024
The Paul Scherrer Institute (PSI) has unveiled a concept designed to decarbonize road transport while maintaining economic viability. Central to this approach is the increased use of carbon dioxide from biogas plants to produce and store renewable energy for transport.

In 2022, transport in Switzerland accounted for 13.6 million tonnes of CO2 emissions, representing 41% of the nation's total emissions, excluding international aviation. While electric vehicles dominate passenger car decarbonization, hydrogen propulsion offers technical advantages for heavy commercial vehicles due to superior weight efficiency, load capacity, refueling speed, and range. However, both technologies require renewable electricity to ensure true decarbonization.

A key challenge is balancing renewable energy supply and demand, particularly in seasons with limited solar energy. PSI researchers Emanuele Moioli, Tilman Schildhauer, and Hossein Madi propose an innovative solution that integrates electricity generation with biogas production to provide consistent, low-carbon energy for transport year-round.

A Two-Step Storage Process

The PSI concept involves capturing surplus renewable electricity - generated in seasons of abundance - and converting it into storable energy forms for use during electricity-scarce periods. This is achieved through multiple steps of energy conversion and storage.

Initially, surplus electricity powers water electrolysis, splitting it into hydrogen and oxygen. The hydrogen is then converted into two synthetic fuels: methane (CH4) and methanol (CH3OH). "These molecules are critical for storing energy," said Emanuele Moioli of PSI's Laboratory for Sustainable Energy Carriers and Processes. Compared to hydrogen, methane and methanol offer higher energy densities, simplifying storage and transport.

Leveraging Biogas Plants

Biogas plants provide a cost-effective source of carbon dioxide needed to produce methane and methanol. Captured CO2, a byproduct of biogas production, is combined with stored hydrogen at the biogas plant site. Additional infrastructure at these facilities would include tanks for CO2 and hydrogen processing into synthetic fuels.

When renewable electricity is scarce in winter, the stored methane and methanol are transported to centralized refueling stations. Methanol, transported by truck, and methane, delivered via pipelines or gas cylinders, are converted back into hydrogen or electricity for refueling vehicles. Methanol, which performs efficiently during steam reforming, is prioritized for hydrogen production, while methane is used for electricity generation due to its high combustion efficiency.

Cost Considerations and Environmental Benefits

The PSI study evaluated the economic feasibility of this concept using data from Zurich's Werdholzi biogas plant. The analysis revealed that energy derived from stored synthetic fuels is more expensive than conventional gasoline. However, combining renewable electricity, biogas, and infrastructure can reduce costs, making decarbonized transport competitive with fossil fuels when supported by moderate incentives, such as CO2 certificates.

Additionally, this model enhances greenhouse gas reductions and can even achieve negative carbon emissions through effective carbon capture and storage.

Scaling Renewable Energy Storage

A successful transition to low-carbon mobility depends on dramatically increasing renewable electricity supplies, which remain insufficient today. Moioli noted that the seasonal mismatch between renewable energy supply and demand poses a challenge: "Installing more photovoltaic systems without additional storage limits direct use of solar power. This discourages PV expansion."

Enhancing storage capacity would enable greater renewable electricity utilization, creating a robust foundation for climate-friendly transport. "Significant energy storage increases are essential to accelerate photovoltaic system deployment and support sustainable mobility," Moioli emphasized.

Research Report:Comprehensive analysis of renewable energy integration in decarbonised mobility: Leveraging power-to-X storage with biogenic carbon sources