More than 50% efficient, around double that of diesel-powered buses, the proton exchange membrane (PEM) fuel cell is powered by hydrogen that isn’t produced from natural gas. As a result, AC Transit’s hydrogen fuel cell-powered hybrid electric buses emit nothing but water vapor. They produce zero greenhouse gas emissions and no particulates.
“The fuel cell bus operates on hydrogen fuel and produces nothing but water vapor – there are absolutely no tailpipe emissions,” UTC Power’s manager of transportation programs Dana Kaplinksi told CleanTechnica. “Conventional diesel, diesel hybrid, and CNG powered buses all produce CO2, CO, and NOX. Diesel powered buses also produce particulate emissions.”
Durability is one of the key questions that fuel cell developers and manufacturers need to address if the technology is to gain widespread adoption in the transportation sector.
“This is the type of result we and our industry are looking for as we make steady progress toward proving the commercial viability of fuel cell buses for public transit,” Jaimie Levin, AC Transit’s director of alternative fuels policy and hydrogen fuel cell program manager, stated in a press release.
“We’re looking forward to applying the success of UTC Power’s newest fuel cell systems in our new fleet of 12 next-generation buses, as they enter passenger service over the next six months.”
AC Transit has rolled out two UTC Power PureMotion 120 hydrogen fuel cell-powered buses, one in 2006 and another in 2007. UTC Power delivered another 16 to transit agencies from August through December 2010.
All told, UTC’s PureMotion Model 120 PEM fuel cell has accumulated more than 650,000 miles and 62,000 hours of operation in regular transit bus service. “Based on the field data we collect, our laboratory testing, modeling and analysis we believe the majority of the fleet will operate for at least 10,000 hours,” Kaplinksi told CleanTechnica.
A longer fuel cell life span reduces the cost to transit system operators. “The life-cycle cost of the fuel cell engine is important in the transit bus market because a typical bus will operate for 12 years,” Kaplinksi explained. “We recognize the cost to purchase, operate and overhaul the fuel cell is important to the end customer and we are actively developing new designs and improved manufacturing processes for fuel cells.”
The cost of fuel cells also remains relatively high as they are still only manufactured in small quantities. That should change with significant cost reduction realized with “even modest volume production because the fuel cell stack is made up of many repeat parts,” Kaplinksi pointed out.
Another factor is the cost of manufacturing fuel cell-powered hybrid electric vehicles. “It’s not only the cost of the fuel cell but the entire bus that is important,” Kaplinksi explained.
“Compared to a diesel bus, fuel cell buses have a different fuel storage system to carry hydrogen, different cooling systems for the fuel cell and batteries, and an all electric drive system to power the wheels. Bus manufacturers have to build a unique vehicle, that typically cannot be produced using their main production line, which also contributes to their high cost.”
All that said, the cost of fuel cell hybrid electric buses has come down in the last five years as manufacturers have been using some of the same electrical components as diesel hybrid buses, Kaplinksi said, adding that UTC Power continues to reduce fuel cell prices through improved design and manufacturing processes.
And there are advantages to using fuel cell hybrid electric buses in addition to zero emissions. They perform well across varying power demand conditions typical for urban buses and “can be started from a cold state very quickly,” according to Kaplinksi.
Fuel cell hybrid electric buses also have a high power density, “which is important because the fuel cell has to fit in the vehicle and not add a lot of weight, which would reduce vehicle performance.”
Finally, PEM fuel cells with electric drive trains are more than 50% efficient in terms of energy to power conversion, “which results in better fuel economy as compared to a diesel engine on an equivalent energy basis,” Kaplinksi explained.
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