Direct solar photovoltaic charging of a high voltage nickel metal hydride traction battery

The electrification of vehicle power trains using batteries and fuel cells is an important technological step forward in the effort to improve the efficiency and reduce the tailpipe emissions of vehicles. The production of electricity and hydrogen in a renewable fashion, such as using solar energy, can provide a clean and sustainable energy source for electric-powered vehicles. In the present work we develop a charging system to prove the concept of direct, efficient, solar-powered charging for battery-electric vehicles using solar photovoltaic-powered charging of the high-voltage nickel-metal hydride (NiMH) battery that is used in the GM 2-mode hybrid system. We utilize a protocol for high-voltage battery charging that was developed in an earlier study that included a DC–DC converter to boost the low-voltage produced by the PV array to the high voltage needed to charge the battery. However, no power conversion was used in the present study. Rather, we use a high-voltage solar array capable of outputting a wide range of voltages, from approximately 250 to 400 V in 50 V increments, at the photovoltaic system maximum power point. By varying the solar system output voltage we measured the solar energy to battery charging efficiency under a variety of conditions to determine the optimal photovoltaic system configuration. The system and methods developed in this work can be used to efficiently charge a range of battery electric vehicles by adapting the PV system output to the battery charging voltage.

► Directly charged high-voltage battery without intervening power electronics.
► Measured the solar to charging efficiency with unique variable-voltage-output PV system.
► Identified PV design with highest charging efficiency over the whole battery charge profile.
► Derived a quantity, the coupling factor, to describe the quality of PV power transfer to the battery load.