Novel Test Method for Curved Vehicle-Integrated Photovoltaic (VIPV) Surfaces

The International Energy Agency's Photovoltaic Power Systems Program (IEA-PVPS) Task Force 17 recently released a report demonstrating a new test setup for curved vehicle-integrated photovoltaic (VIPV) surfaces.

This research effort covers the results of an 8-day study conducted in August 2023 at Le Bourget Dirac, France. The results show that the curvature of VIPV surfaces can induce irradiance inhomogeneities of up to 261 W/m2 and temperature inhomogeneities of up to 13°C, respectively.

According to the researchers, VIPVs with a curvature radius of 3 meters lost 17% of their energy in sunny weather and 6% in rainy weather compared to flat photovoltaic surfaces.

During the experiment, the team measured individual cells every minute. It also analyzed how the curved PV roof affected performance, the uniformity of solar irradiance, and temperature.

The researchers suggested that to optimize energy yield, VIPV product teams could increase the number of maximum power point tracking (MPPT) channels and consider designing the PV surface flatter to naturally optimize energy harvesting.

However, each of the optimization recommendations faces challenges. Bertrand Champion, co-author of the French Commission for Alternative Energies and Atomic Energy (CEA), told PV Magazine, "A roof that is too flat goes against the trend in the automotive industry. Moreover, more MPPT channels increase panel costs and system complexity."

Chambion said the report was released to raise awareness among original equipment manufacturers (OEMs), automakers, stakeholders, and PV industry researchers about the factors affecting VIPV performance and potential solutions.

The outdoor PV monitoring test rig described in the Task Force 17 report was designed specifically for curved solar surfaces on passenger cars. The team used it to monitor solar irradiance and temperature, and to collect data to measure the effects and inhomogeneities of the angle of incidence on the surface of a VIPV module.

In building the test setup, the team chose to design a single solar cell matrix rather than use commercial photodiodes. This is simpler, easier to integrate and more representative of the final application," explains Champion. The resulting measurements can be used to validate the model."

The device utilizes M6-sized, 9-twin-bar PERC solar cells arranged in a 5×5 matrix, equipped with thermocouples, irradiance and temperature sensors. There are also multi-channel data loggers, multiplexers, a VIPV roof model, and a dedicated energy management system (EMS) for monitoring irradiance and temperature data on a minute-by-minute basis.

Measurements are taken on individual cells every minute. The test panel experienced three weather scenarios in an unobstructed location: rainy, sunny, and cloudy. It was oriented toward the south and mounted in a manner representative of the random orientation of the vehicle during the parking phase.

Going forward, the researchers recommend a one-year project to collect representative data, noting that tests should also be conducted in other locations.