Researchers at the University of Miyazaki have investigated the real-world performance and fuel-saving potential of vehicle-integrated photovoltaics (VIPV) on heavy-duty vehicles through an extensive field study in Japan, finding that shading is a crucial factor affecting photovoltaic power generation and overall system efficiency.
The project involved 200 commercial trucks with diesel engines fitted with 300–500 W PV modules based on copper, indium, gallium and selenide (CIGS), with data being collected on photovoltaic generation, alternator performance, battery power flow, and vehicle operation. The solar panels are used solely to power auxiliary systems and recharge the main battery, not for directly driving the vehicle.
“We assessed how effectively PV power was utilized by simultaneously monitoring the outputs of both the PV system and the alternator,” corresponding author Kenji Araki told pv magazine. “This enabled us to determine the degree to which solar generation reduced the alternator’s load.”
The scientists explained that shading probability in VIPV is influenced by object geometry and grazing angles, and can be statistically approximated using aperture matrix averaging, which is a computational technique used to evaluate dynamic, non-uniform shading and solar irradiance on curved or complex PV systems by integrating directional light contributions across discretized surface elements within a local coordinate framework. According to the researchers, it enables a consistent and practical calculation of solar irradiance across vehicle surfaces.
The research team monitored power flow between the photovoltaic system and the alternator in truck-based VIPV setups, focusing on energy usage within isolated vehicle systems rather than PV module efficiency. Pyranometers were not used due to installation constraints, and PV output was assumed to correspond to local solar irradiance.
Custom control boxes with charge controllers and data loggers were developed, using current sensors to track PV output, vehicle energy generation, and battery charge–discharge behavior. The system was reinforced with stable wiring, fuses, and underwent vibration and weather resistance testing to ensure reliability in real operating conditions.
The PV system was treated as a full module with integrated charge controller functions, including MPPT, DC-DC conversion, and backflow prevention, rather than just a solar panel. The alternator similarly includes rectification and voltage regulation via DC-DC conversion, and operates independently without synchronization with the PV system, with the higher-voltage source taking priority.
Across 17,901 vehicle-days, the academics recorded total driving distance, operating hours, power consumption, PV generation, and alternator suppression, while noting data synchronization limits in the measurement system. The PV systems were found to contribute measurable energy offsets during operation, alongside significant alternator load reduction under real driving conditions.
Overall, the results showed measurable fuel and energy benefits, but also highlighted that VIPV performance must be evaluated using detailed, condition-dependent models rather than simple averages.
“In addition, evaluation of the measured dataset showed that the solar irradiance received by vehicle-mounted surfaces corresponds to roughly 70% of that on a horizontal plane,” said Araki. “This reduction is attributed to factors such as surrounding urban shading, roadway conditions, and changes in vehicle orientation, and it serves as an important parameter for estimating the annual energy output of VIPV systems.”
Moreover, simultaneous PV and alternator measurements revealed that about 85% of PV output directly offsets alternator load, improving energy utilization in real driving conditions. Fuel consumption reductions of approximately 5.5–7%, meanwhile, were confirmed through multiple validation methods, though benefits vary by vehicle type and driving behavior.
Their findings are available in the study “PV on heavy duty vehicles (HDVs): monitoring 200 trucks with PVs,” published in Energy Conversion and Management: X.
“The findings of this study will establish an essential baseline for the international standardization of VIPV (IEC PT600) and will facilitate the development of subsequent energy rating methodologies. Furthermore, providing a practical tool that enables logistics operators to readily assess the impacts of power-generation and fuel-efficiency reductions using their own operational data will promote the widespread adoption of VIPV,” the researchers concluded.
Last year, another research group at the Miyazaki University unveiled a non-destructive method to investigate solar cell vibrations independently of module components. The study included potential design features for resonance-resistant vehicle integrated PV modules that would increase the natural resonance frequency to above 2,000 Hz.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.
By submitting this form you agree to pv magazine using your data for the purposes of publishing your comment.
Your personal data will only be disclosed or otherwise transmitted to third parties for the purposes of spam filtering or if this is necessary for technical maintenance of the website. Any other transfer to third parties will not take place unless this is justified on the basis of applicable data protection regulations or if pv magazine is legally obliged to do so.
You may revoke this consent at any time with effect for the future, in which case your personal data will be deleted immediately. Otherwise, your data will be deleted if pv magazine has processed your request or the purpose of data storage is fulfilled.
Further information on data privacy can be found in our Data Protection Policy.