Trucks on the grid

A recent report by the German Advisory Council on the Environment (SRU) envisions freight trucks powered electrically by overhead cables as a way to reduce climate damaging CO2 emissions from freight transport. A field test with electric-powered trolley trucks is currently being conducted in Brandenburg – but the city of Solingen is Germany's secret capital of trolley-buses.

Visitors walking through the streets of Solingen can't help but notice cables running overhead. They provide electricity to the city's small fleet of trolleybuses carrying passengers on six different routes.

Although still popular in Switzerland and Eastern Europe, trolleybuses have nearly disappeared in Germany, with the exception of Solingen, Eberswalde and Esslingen. Most of them were replaced in the 1950s and 1960s with diesel-powered vehicles.

But trolleybuses could return, according to Bert Leerkamp, a traffic engineer at the Bergischen University in Wuppertal. "Freight trucks with electric motors connected to an overhead cable have more traction," he said. "They also have no direct emission and don't have to carry the energy along with them."

Siemens is participating in the trial north of Berlin in the state of Brandenburg , where the company is testing its own electrically powered trucks with overhead cables.

"The challenge is to make freight trucks not only more low-emission and efficient but also safer," said Roland Edel, technical director of the transport division at Siemens.

The efficiency factor of biofuel is between 7 and 10 percent. The electricity saved in batteries is around 65 percent and the directly converted electricity around 80 percent.

Electricity is only CO² free if generated from renewable energy sources, according to Holger Sommer. He is the director of the Siemens project 'Electro-Mobility for Heavy-Utility Vehicles for the Environmental Protection of Urban Areas.'

"In the development process, it was especially important to integrate the concept into existing transport solutions so that both the technical and economic viability remains intact," he said. "It must be possible for conventional freight trucks to safely use the electric lines, just as hybrid freight trucks must be able to function remotely from the electric lines."

Siemens has developed a new current collector that can be automatically docked on the overhead cables.

Even the disconnection occurs automatically, for example when overtaking, following sudden swerves or turning-off from the highway, according to Sommer. Sideways movement of the trucks inside of their traffic lanes, he says, is equalized through the steering system. It ensures the safe and reliable transfer of electricity.

"The electric system makes practically no additional demands of drivers," Sommer said.

But transport expert Leerkamp expects trolley trucks to meet resistance from transportation companies.

They will need hybrid vehicles that can connect to the overhead cables, and these come with a cost, he notes.

"But the big advantage could come someday when normal fuel becomes so expensive that they need to find an alternative," he said. "We're thinking well into the future here."

There are other challenges, too. Traffic lanes on the right-hand side of highways will have to be equipped with overhead cables. The Environmental Advisory Council suggests limiting cables to the most important 5,700 kilometers of highway. That would cost about 12 billion euros. But Leerkamp is convinced it's worth it.

Because electric powered vehicles have more traction and a higher tractive output, their speed will hardly differ between heavily loaded freight trucks and those that drive empty up into the mountains, according to Leerkamp.

Trolleybuses have brought Solingen's transportation costs down dramatically. That fact is sure to get the attention of local governments in other regions. In Germany, the trolley truck concept has gone from a relic of the past to a vision for the future.

Author: Antje Dechert / jrb
Editor: Saroja Coelho