Practical measurements confirm potential of solar cars
TNO and other parties have measured the potential of solar cars on European roads.
Published on September 8, 2025
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TNO, the Fraunhofer Institute for Solar Energy Systems ISE, and the three suppliers of solar energy systems for vehicles—Lightyear, IM Efficiency, and Sono Motors—spent nine months measuring the potential of solar cars on European roads. The results confirm that solar panels on vehicles can be a valuable, mobile source of renewable energy for the transport sector. At the same time, the findings point to important challenges, such as shading and user behavior. These and other findings can be found in the report “SolarMoves: Real life irradiance and energy consumption measurements for solar mobility”.
More than 1 million kilometers of measurement data
Since March 2024, 18 vehicles—ranging from trucks and buses to vans and passenger cars—with sensors on their roofs and sides have traveled more than 1 million kilometers on European roads. “The measurements taken in the Netherlands and northern Germany show that side panels receive about 50% less solar radiation than roof panels. This is comparable to previous model assumptions: an average of 2.8 kWh/m² per year for the roof and 1.3 kWh/m² per year for the sides,” says Lenneke Slooff, senior consultant at TNO. The report describes two case studies: a delivery truck in the Benelux (IM Efficiency) and city buses in Slovakia (Sono Motors).
Shade: a crucial factor for solar car performance
The study shows that satellite and meteorological data help to fine-tune the shade factor in models more accurately. This takes into account shade from buildings, trees, and other vehicles. “We recommend further refining shadow models and incorporating route and location data as well as usage-related behavior to obtain a more realistic picture of energy yield and a more effective system design,” says Christian Braun, senior engineer at Fraunhofer ISE.
Model validation and energy consumption
The SolarMoves measurement campaign also confirms the results of the models developed in the first phase of the project, both for solar radiation and for vehicle energy consumption. The Lightyear 0, a Ford E-Transit (via Sono Motors), and an eVolvo truck (via IM Efficiency) were used for model validation. Initial results with the Lightyear 0 show a strong correlation between simulated and measured data, both for solar yield and energy consumption. In Southern Europe, vehicles with integrated solar panels can cover up to 50% of the annual energy consumption of passenger cars, and in Central Europe up to 35%. More seasonal data – especially from spring and summer – is needed to confirm these trends for all vehicle types in the long term.
Expansion of the dataset
To improve geographical and seasonal coverage, SolarMoves will expand the measurement campaign to Southern and Eastern Europe in the summer of 2025. The final report in 2026 will contain updated findings and make recommendations for the optimal use of integrated solar cells per vehicle type and region.
