Electric motors in hybrid vehicles save fuel and cut emissions, providing the push that gets a hybrid moving and added get-up-and-go while accelerating or climbing hills. Electric Trucks and Buses have been singled out for optimal adoption of electric power due to their fixed route operation and tight schedules. The pre-planned routes and maintenance allows for charging cycles and repairs to be optimized for peak performance and limited down time.

Although heavy duty electric trucks and buses require an estimated 30% higher initial capital investment, the tradeoffs include lower operating costs, reduced fueling and less maintenance. A Pike Research study found that hybrid powertrains will find a home in 300,000 medium (MD) and heavy (HD) duty trucks and buses by 2015.

AJ Heinen of e-Traction makes the case for electric buses by stating “we do what can be done to improve environmental conditions in inner cities by showing that a retrofit can be done easily. We can even show a business case because we save about € 17500 on energy expenses per year.”

Energy storage and driving range are the main hurdles in rapid adoption of electric trucks and buses. One way to increase the efficiency of electric motors is through increased onboard electricity storage. Another way is eliminating the losses that occur as torque generated by the motor is transferred to the wheels. Conventional drive trains lose approximately 20% of the power generated by the motor to friction.

In wheel motors are currently in operation, generating enough power to run buses for close to an hour without any input from their diesel powered engines. An average bus consumes fuel at roughly 67 liters per 100 kilometers (3.5 miles per gallon) and gives off more than 150 metric tons of carbon dioxide each year.  Buses retrofitted with in wheel motors improve fuel economy to 16 liters per 100 kilometers (14.7 miles per gallon).

Regenerative braking is also used to boost efficiency of electric trucks and buses. In braking, up to 70% of the kinetic energy pushing the bus along is converted to electrical energy. It is estimated that one bus could reduce annual fuel consumption by 55,000 to 75,000 liters (15,000 to 20,000 gallons).

Ultracapacitors have also been used to deliver power to electric drive train trucks and buses. Without the chemical reaction necessary in a traditional battery, ultracapacitors are much better at rapid, regenerative energy storage. 

Clean transportation provider Proterra offers a fast charging option for buses, "the lithium titanate batteries powering their buses can be charged in 10 minutes and therefore can be charged at each bus stop that has a charger setup. The distance between bus stops is normally short making it possible to use very short range batteries which enable them to travel 30-40 miles per charge and keep recharging them frequently."

You might find yourself asking, “Why aren’t these advancements used in hybrid electric passenger autos?” The upfront costs are prohibitive to consumer adoption and recovered more rapidly in commercial application. Many see the future of automotive propulsion lying in zero emission propulsion systems due to the trend of population movement towards megacities. In order to transport the increased rider demand, electric buses are going to need to drive cleaner, last longer and recharge easier. The industry is currently courting a number of potential solutions, which one will gain industry adoption is yet to be determined.

www.proterra.com

www.e-traction.nl

http://green.autoblog.com/2011/02/21/kink-long-hybrid-buses-ziamen-china/

http://spectrum.ieee.org/green-tech/advanced-cars/the-charge-of-the-ultra-capacitors

http://www.isecorp.com/pdfs/passenger_vs_transit_data_sheet.pdf

http://www.isecorp.com/hybrid-systems/

http://www.theoildrum.com/node/5263

http://www.californiahvip.org/article_makingthecase.asp

http://www.ev-info.com/en/ev-busses-news.html