Energy futuresHybrid trucks could save fuel and the environment

Published 25 June 2008

Sales of small- to medium-size hybrid passenger cars are growing fast, but hybrid technology for trucks is about a decade behind; U.S. Congress wants to change that

U.S. members of congress are pressing for government to support the development of medium and large trucks with hybrid electric-combustion engines. The call for the Department of Energy (DoE) to help out came after hearings by the House of Repesentatives science and technology committee on the future for hybrid trucks, and U.S. pump prices exceeding a once unthinkable $4 a gallon. Sales of small- to medium-size hybrid passenger cars, like the Toyota Prius, are growing fast, but hybrid technology for trucks is about a decade behind, says Richard Parish of the Hybrid Truck Users Forum, an organization partly supported by the US Army to develop the industry. “We are just now starting to see hybrid trucks coming into production,” he told New Scientist’s Jeff Hecht.

Compared to passenger cars, trucks operate for more hours a day at lower fuel efficiency, meaning hybrid technologies could offer greater cuts in fuel use and emissions per vehicle. Hybrid trucks have developed slowly because the complexity of hybrid vehicles is a bad fit with the way trucks are built, says Parish. Hybrids attain high efficiency by integrating combustion and electric engines, transmission, drive train, and other components into a seamless whole, carefully managed by a computer. Achieving that is difficult for truck vendors who typically add components from various suppliers onto an in-house chassis. Some trucks are well suited to the hybrid approach, though. For example, any that make frequent stops benefit from using an easily switched off electric motor in urban areas, instead of leaving a combustion engine idling. An average light parcel truck can save 40 percent to 60 percent on fuel, for an average annual usage of 20,000 miles, Eric Smith, a power-train engineer at Eaton Corp — a company developing hybrid trucks — told the House committee. At current prices that saves $2,500 a year per truck, leading to recent orders from United Parcel Service and Coca Cola, he said. In Europe, electric vehicles have been used to deliver milk for decades for similar reasons. Electric vehicles are also becoming more common on delivery routes.

Counterintuitively, large long-haul trucks benefit from cutting idling too. The average big rig makes few stops, but idles for 1,800 hours a year to run things like air-conditioning and entertainment systems while the driver rests or sleeps. Smith estimates a hybrid long-haul truck could save 3,270 gallons of fuel a year — 7 percent to 10 percent of usual fuel use. Retail giant WalMart is testing a new hybrid heavy truck, planning to have twenty on the road by the end of 2008, says Bill Kahn of collaborating firm and truck manufacturer Peterbilt. Technological hurdles remain, however. Batteries must become lighter, cheaper and able to power equipment that now runs off idling engines, says Terry Penney, manager of advanced vehicle technology at the National Renewable Energy Laboratory in Golden, Colorado. Equally, equipment from heaters to cherry pickers must be redesigned to run on battery power, he says. In fact, electrical batteries may not be enough for large trucks. Storing energy inside a pressurised hydraulic system to move heavy equipment is one alternative. Another is “plug-in” hybrids that use the electric grid to top-up batteries or run equipment. The science and technology committee is now drafting a bill that would see the DoE support hybrid trucks, adding to a recently announced $30 million program of aid for plug-in hybrid cars.