Electric Trucks: Reliable on Roads, Profitable as Storage

The researchers tested the underlying technology at a freight forwarding company in Regensburg. They used an electric truck with a usable battery capacity of 480 kilowatt-hours. Using a bidirectional DC charging station, the truck fed electricity back at a power output of up to 350 kilowatts.

Three applications were tested: The truck supplied electricity to other vehicles (vehicle-to-vehicle), supported the power supply at the company's premises (vehicle-to-site), and fed electricity into the public grid (vehicle-to-grid). Communication between the vehicle and the charging infrastructure was based on the international standard ISO 15118-20.

In addition to the joint project results, the TUM Chair of Automotive Technology conducted accompanying research to determine whether and how freight carriers can reliably operate electric fleets and how the transition can be made economically viable. The research drew, among other sources, on real-world driving data from six German heavy-duty vehicle fleets covering a total of 2.15 million recorded kilometers. The key findings:

• Reserving charging points: If electric trucks can reserve public charging points in advance on long-haul routes, planning reliability improves. Depending on the scenario, the median additional time required compared with diesel trucks falls to around 1 to 4 percent.
• Plan the fleet and depot together: With dedicated charging infrastructure at the depot, a significantly larger share of the fleet can be reliably operated on electricity than with public charging alone. Companies that also include solar power and battery storage in their planning can save 25 to 44 percent more than by converting the trucks alone.
• Rethinking dispatch planning: If route planning takes charging flexibility into account, charging can be deliberately scheduled for periods when electricity is less expensive. Depending on the mix of transportation orders, this reduces the fleet's total costs.
• Integrate the depot intelligently into the energy system: Smart integration with the power grid and electricity market reduced the total costs of the fleets studied by an average of 1.7 cents per kilometer. With bidirectional charging, the reduction reached 6.1 cents per kilometer.

Using the stored electricity at the depot is particularly promising. For example, electric trucks can charge using surplus electricity from a photovoltaic system during the day and supply that electricity again later. This can increase the amount of a company's electricity demand that it meets from its own generation. The vehicles can also cover short-term spikes in electricity demand, helping to avoid costly peak loads.

The project team estimates that this could reduce energy costs by around 10 percent. For a truck traveling 100,000 kilometers a year, that is equivalent to the energy cost of driving 10,000 kilometers. How much a freight carrier can save depends primarily on annual mileage, vehicle downtime, and electricity prices. Vehicles used for regional transportation and returning regularly to the depot are particularly well suited to this approach.

The project results show that the biggest hurdles now lie less in technical implementation than in grid integration and the economic framework. At many depots, for example, the existing grid connection capacity is insufficient to charge larger fleets of electric trucks. Flexible grid connection agreements, battery storage, or shared charging infrastructure can help overcome these constraints.

There are also currently no uniform standards for marketing the electricity stored in truck batteries. Many providers use proprietary technical solutions that are incompatible with one another. It also remains to be determined how responsibilities and revenues should be divided among freight carriers, vehicle manufacturers, and electricity marketers.

"SPIRIT-E has shown that heavy-duty electric trucks can be much more than just new electricity consumers. Technically, they can be integrated into the energy system as flexible storage systems. The task now is to standardize and scale the solutions that have been tested and turn them into viable business models. This will require researchers, grid operators, industry, the logistics sector, and policymakers to work together," says Prof. Markus Lienkamp, holder of the Chair of Automotive Technology at the TUM School of Engineering and Design.