London, June 25 : The future might see medium and large trucks with hybrid electric-combustion engines running on the roads, provided their production starts in a big way.
According to a report in New Scientist, 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.
"We are just now starting to see hybrid trucks coming into production," said Richard Parish of the Hybrid Truck Users Forum, an organisation partly supported by the US Army to develop the industry.
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," said 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 40-60% on fuel, for an average annual usage of 20,000 miles (32,000km)," said Eric Smith, a power-train engineer at Eaton Corp - a company developing hybrid trucks.
"At current prices, that saves 2500 dollars a year per truck, leading to recent orders from United Parcel Service and Coca Cola," he added.
According to Smith, a hybrid long-haul truck could save 3270 gallons of fuel a year - 7 to 10% of usual fuel use.
However, technological hurdles remain.
"Batteries must become lighter, cheaper and able to power equipment that now runs off idling engines," said Terry Penney, manager of advanced vehicle technology at the National Renewable Energy Laboratory in Golden, Colorado, US.
"Equally, equipment from heaters to cherry pickers must be redesigned to run on battery power," he added.
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 US DOE (Department of Energy) support hybrid trucks, adding to a recently announced 30-million dollar programme of aid for plug-in hybrid cars.