Long-time Slashdot reader necro81 writes: There are several companies, such as Tesla, trying to make semi trucks fully electric. The capital cost for such a truck, and the MW-scale infrastructure to recharge it, may be a hard sell for some operators. [IEEE Spectrum notes that's a charging infrastructure "that most freight corridors do not yet reliably provide."] But some companies are instead adding batteries and an electric motor to the semi-trailers that trucks haul behind them. "The Nivalis Powered Trailer Kit centers on an electric axle [rated at 50 kilowatts-peak]... 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-amp, three-phase AC grid connection available during parking stops." This approach is more akin to a plug-in hybrid: the truck may still be diesel-powered, but the electric assist from the trailer allows the truck to run more efficiently. Replacing diesel with kWh can save operators money while also reducing emissions. This incremental approach may be more accessible and less capital-intensive than replacing the truck itself. From the article:The driver's only window into the system is a small display readable from the cab's side mirror that shows the system status and battery charge level. Nothing about the trailer's handling or licensing requirements changes. The partners project savings of up to 7,000 liters of diesel per trailer per year, which is enough to keep about 19 tonnes of carbon dioxide out of the air... Trailer Dynamics, an Aachen-based company, has conducted field tests with BMW Logistics, DB Schenker, Duvenbeck, and Volkswagen Konzernlogistik, reporting average fuel savings of around 40% for diesel tractor combinations, substantially higher than the up to 18% reduction implied by the Nivalis projection... Trailer Dynamics prices its system between €145,000 and €195,000 and targets a payback period of no more than five years. Nivalis targets five to six years at current costs.Read more of this story at Slashdot.