So far, electric cars with solar cells on the body have been seen as a gimmick. But with trucks, thanks to the large area, photovoltaics can certainly make a contribution to the power supply. How well this succeeds is now to be demonstrated by an 18-tonne electric truck that is now on the road on Germany’s roads. It carries a particularly light and flat high-voltage photovoltaic system on the roof and can cover five to ten percent of its energy requirements with it.
Freight transport by truck makes a particularly large contribution to greenhouse gas emissions in the transport sector. Scientists have therefore been working on concepts for a long time, primarily to make trucks more climate-friendly. The approaches that have already been tested include alternative drives such as liquefied gas or hydrogen, but also electric vehicles. However, these have the problem that the limited range of previous batteries makes the use of electric trucks impractical over long distances.
Electricity from on-board solar cells
This could be remedied by charging the batteries while driving. One approach here are overhead line trucks, which are already being tested on some test tracks in Germany, but would require high infrastructure costs. A simpler and cheaper alternative would therefore be if the trucks could produce the necessary electricity on board – for example using photovoltaics. Scientists led by Christoph Kutter from the Fraunhofer Institute for Solar Energy Systems ISE are working on such solar trucks together with industrial partners and the Fraunhofer Institute for Transport and Infrastructure Systems IVI in the “Charging PV” project.
The aim was to develop particularly light and robust solar modules for retrofitting on the roof of trucks, as well as electronics that integrate the photovoltaic modules into the on-board systems and bring the electricity to the battery of the electric vehicles. The solar panels must be integrated into the truck roof in such a way that they do not require heavy frames and supports and that they remain flat. For this purpose, the researchers developed a high-voltage photovoltaic system in which the modules are connected in series in order to keep the electricity yield as high as possible and the cost of materials low. The solar power is fed into the on-board network via a DC power controller that can be controlled via the vehicle electronics.
Another important point is safety: high-voltage solar modules can generate voltages of up to 400 volts. In the event of an accident, this could pose a significant safety risk. To prevent this from happening, the Fraunhofer researchers have developed a separation device that sits in the junction box of each PV module. In the event of an accident, it disconnects the power connection within milliseconds in a decentralized manner and without additional communication channels. As the scientists explain, there are then only harmless extra-low protective voltages in the entire system.
Street legal received
After all these preparations, the time has come: The first truck with this solar system has successfully passed the technical acceptance and is now approved for driving on Germany’s roads. The 18-ton truck is equipped with a 3.5 kilowatt peak photovoltaic system that feeds solar power into its 800-volt traction battery. The solar power produced directly on the vehicle can cover five to 10 percent of the truck’s energy requirements. “With the successful commissioning of our high-voltage photovoltaic system, we have achieved our goal of demonstrating the feasibility of vehicle-integrated photovoltaics for heavy e-commercial vehicles,” says Kutter. “The components integrated in the truck work as expected.”
The solar truck is now in daily use in the Freiburg area for the company Alexander Bürkle GmbH and is now regularly checked for one year in order to validate the electricity yield forecast and to monitor the components under real conditions. The research team sees this pilot vehicle as an important milestone towards more climate-friendly road freight transport.
Source: Fraunhofer Institute for Solar Energy Systems ISE