Electric vehicles make for cleaner transport. However, they’re hung up by the limited range available from batteries. Long recharge times further compound the issue.
These issues are exacerbated when it comes to trucks hauling heavy goods. More payload means more weight, which means less range, or more batteries, which means less payload. Electric highways promise to solve this issue with the magic of overhead wires.
The formula for combustion-engined trucks is simple. Simply throw a good-sized engine up front, and add a few big fuel tanks to keep it running. When you run out of fuel, it takes maybe ten minutes to top off and get rolling again.
Electric trucks don’t have this luxury. They need gigantic, heavy battery packs to give them decent usable range. To recharge these packs in a reasonable time, they then need chargers that deliver hundreds of kilowatts of power. It’s all very expensive, and all that battery weight cuts in on payload and adds to wear on things like tires and brakes.
The electric highway concept solves this problem in a remarkably simple way. It uses the same concept as the trolleybus of the 19th century. Overhead wires are strung over one lane of the highway, and provide high-voltage power from the grid. The truck receives power from the overhead wires via a pantograph, much the same as those seen on electric trains and trams.
While the truck is on the highway, it can drive solely using grid power thanks to the overhead wires. The truck then only needs a comparatively smaller battery of a nominal 50-100 km range, allowing it to get on and off the highway. This also allows the truck to change lanes on the highway where needed and operate seamlessly when overhead lines aren’t available.
Having batteries onboard the truck brings other benefits too. It means that the overhead wires don’t need to be continuous across complex traffic junctions. This greatly simplifies their installation and cuts costs. The batteries can also be charged while the truck is driving along under overhead power.
The idea is to electrify key highway routes linking up major freight depots. Suitably equipped trucks could then deliver goods from depot to depot, running on grid power. This promises to reduce emissions, even where grid power is derived from dirty sources like coal and gas. This is because generating electricity in a giant power plant is far more efficient than running a diesel engine in a truck. Plus, switching to renewable energy sources further cleans up the systemwide emissions.
It’s a plan that allows trucks to be electrified in a straightforward manner. It reduces reliance on big battery packs and high-power chargers. It also eliminates the trouble of building hydrogen refuelling infrastructure for fuel-cell trucks, as well as the issues around producing hydrogen fuel in a clean manner.
It’s expected that overhead power would even be more efficient than solely running battery electric trucks. This is because the electricity from the grid is sent straight to the wheels, eliminating efficiency losses in the charging process. Battery powered trucks score an overall well-to-wheel efficiency of around 62%, and fuel cell trucks come off worse at 29%. In comparison, electric highway trucks are expected to be around 77% efficient based on modelling by the German Ministry of Environment.
It’s a Real Thing
It might sound like a high-strung idea, but working prototypes are already in testing. Siemens Mobility is working on a project it calls the “eHighway,” with overhead wires strung over small sections of highway. Testing is being run with hybrid Scania trucks outfitted to work with the overhead power system.
The key to the project is the special active pantograph, which is capable of dealing with road travel at highway speeds. Sensors and active control of the pantograph ensure it remains in good contact with the wires as the truck moves within the lane. The pantograph can raise and lower from the wires on demand, allowing the truck to pull away and change lanes as needed without disrupting the flow of traffic.
Thus far, the trucks have performed well and in line with expectations. Since 2016, Siemens has tested eHighway trucks in Sweden, Germany, and the US. The project has won the concept fans, too. The Federation of German Industries is recommending that 4,000 km of Autobahn roads are equipped with overhead wires in this way. This figure was chosen because over two-thirds of fuel used by German trucking occurs on just 4,000 km of the 13,000 km highway network.
(Editor’s note: Hackaday’s parent company, Supplyframe, is part of Siemens. Neither of them have any editorial input whatsoever, but the name showed in the article up so we thought we should say something for transparency’s sake.)