On the road to achieving climate neutral road traffic

Researchers in Switzerland have made significant progress towards achieving climate neutral road traffic with novel study.

At present, road traffic is accountable for over 30% of Switzerland’s greenhouse gas emissions. The journey to lowering these emissions is a difficult one as the transition from fossil-based mobility to electricity-based mobility will only result in a significant reduction in greenhouse gas emissions if more renewable energy is simultaneously incorporated into the energy system.

Towards climate neutral road traffic

In a novel study funded by the Competence Center for Energy and Mobility of the ETH Domain (CCEM), a team of scientists from Empa, the Paul Scherrer Institute (PSI), ETH Zurich and EPFL cooperatively explored the possibility of electricity-based mobility in mitigating climate change impact.

This research was carried out in the background of the shifting Swiss energy system, considering direct domestic greenhouse gas emissions and the indirect greenhouse gas emissions that are globally produced. Indirect emissions occur, for example, in the manufacture of vehicles and fuels or in the exploration of critical raw materials for batteries.

The team utilised a model based on CO2 legislation for new vehicle registration, to evaluate the total Swiss vehicle fleet. While the researchers assumed for the new car fleet, that 60% of the gas-powered passenger cars will be substituted by electricity-based vehicles by 2040, the effect on the overall fleet will only be gradual.

This means that a fleet ratio of 60/40 between electricity-based and fossil-based passenger cars will only be achieved in 2050. The energy demand from this prospective model of future electricity-based mobility in Switzerland was established on the basis of the anticipated technological development, then incorporated into a model of projected future electricity demand.

Twelve energy system scenarios

The team designed 12 different scenarios that investigate the variation in different core characteristics. Three different photovoltaic development paths of 13, 32, and 52 terawatt hours (TWh) were under review for the revolution of the electricity market.

Two different electricity import scenarios were investigated for winter supply: Import of largely renewable electricity or electricity from fossil gas-fired combined cycle power plants. Lastly, the team explored the potential of utilising surplus electricity. The high domestic photovoltaic development paths demonstrated large temporary electricity surpluses in summer. In the simulation models, these were either employed for the manufacture of synthetic methane, which can be applied in the gas market, or they were ‘curtailed’, which is where solar power generation is separated from the network to prevent overloads.

Efficiency or flexibility?

Electricity-based vehicles fluctuate significantly in their energy impacts: While electric vehicles are incredibly energy efficient, they have short-term flexibility to use electricity in their batteries and currently, they can only be charged if electricity is being simultaneously fed into the grid. The possibility of synthetic fuels offers an inverse solution that shows low efficiency and long-term flexibility, implying that temporary electricity surpluses can be stored for months and utilised for mobility when required. Meanwhile, hydrogen-powered vehicles lie somewhere between the two in terms of efficiency and flexibility.

Research findings

The findings of the simulations indicate that for three quarters of the scenarios, the variations for greenhouse gas decline between battery-powered vehicles, hydrogen-powered fuel cell vehicles and synthetic fuel-powered vehicles are small. This is largely because efficiency and flexibility cancel each other out over the year. This was demonstrated in the six scenarios that presume imported electricity from gas combined cycle power plants when there is not enough production in Switzerland, as well as in two scenarios that are based on largely importing renewable electricity.

In the last four scenarios, the utilisation of battery vehicles results in a substantial reduction in greenhouse gas emissions when contrasted with the other electricity-based options. This is due to the fact that efficiency is more advantageous when a large amount of renewable energy is accessible at any time of the year. This applies to the three scenarios whereby surplus electricity can be converted as synthetic methane and employed in other sectors and the scenario with the lowest PV addition and the possibility of importing renewable electricity.


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