A semitrailer that helps propel itself entered commercial road testing in late May, when a power-train kit developed by Nivalis Energy Europe , headquartered in Luxembourg with engineering operations in Germany , was fitted to a trailer supplied by the Amsterdam-based TIP Group . The self-powered trailer was handed over to the German transport operator Sommer for use in its working fleet. The Nivalis Powered Trailer Kit centers on an electric axle codeveloped with the running-gear specialist BPW , based in Wiehl, Germany. The axle, rated at 50 kilowatts-peak, is capable of both propulsion assistance and regenerative braking . It draws on a 60-kilowatt-hour, 400-volt lithium-ion battery pack charged from three sources: the axle itself during braking and deceleration, a full-rooftop array of photovoltaic panels generating up to 3.7 kilowatts-peak, and a 32-ampere, three-phase AC grid connection available during parking stops.…