Long Beach study shows gas/hybrid buses get lower mileage than diesel
The National Renewable Energy Laboratory has just completed a two-year study of the hybrid buses being operated by Long Beach Transit in southern California. Unlike most transit systems using hybrid buses, Long Beach has been using a system that combines a gasoline engine with a series hybrid system. The ISE ThunderVolt hybrid uses a Ford 6.8L V10 running at constant speed to turn a generator that provides juice to a pair of electric motors. Only the motors drive the wheels. Instead of batteries, Long Beach also chose to equip their hybrid buses with ultracapacitors. The Long Beach bus routes are comprised of mostly low speed operation with many stops per mile making the rapid energy absorption of ultra-caps desirable. NREL looked at the performance of the buses and found that the gas hybrids got 4.3 percent lower fuel efficiency than the conventional diesel buses in the fleet. When the lower energy content of gasoline is factored in, though, the gas hybrid came out 8.5 percent better. Overall efficiency was about a wash for the hybrids. In the study the hybrid buses got 3.35 mpg. The increased use of regenerative braking from the ultra-cap hybrids has cut brake system maintenance by 90 percent although other service intervals were somewhat higher. The city has 62 hybrid buses out of a fleet of 228 currently and has ordered 25 more.
[Source: National Renewable Energy Laboratory, via GreenCarCongress]
Reader Comments (Page 1 of 1)
CMiller 12:24PM (7/03/2008)
This doesn't surpirse me. You a big V-10 engine that is always producing power. There is your problem. I like the idea, but let's try a smaller diesel engine in these buses. You might have something worthwhile then.
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david burgdorff 12:31PM (7/03/2008)
Why not use a diesel generator instead of gas? Perhaps its the cost of diesel or the diesel emissions?
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Serge 12:32PM (7/03/2008)
Orion VII serial-hybrid bus with diesel generator gets 5 mpg, a 50% mileage efficiency. This bus has been successfully employed by the world's biggest hybrid fleet (NYC).
Long Beach Transit has better options out there.
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meme 1:08PM (7/03/2008)
Thanks for actually pointing out that gas wins when the differences in fuels is taken into account. The headline was quite misleading that way. Most people forget to consider that diesel is a more dense fuel than gasoline, and correspondingly consumes more oil and releases more GHG emissions.
Then there's all of the other pollutants, too.
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Snowdog 1:04PM (7/03/2008)
Considering the price/energy content of diesel it is probably a wash on the carbon/cost front.
But as someone who cycled to work behind diesel buses, the lower emissions are priceless. The black clouds of death pouring out of a diesel bus are just plain evil.
More gas hybrids please.
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Brad 4:20PM (7/03/2008)
In California it's not possible to purchase new diesel busses, so that's why they chose to buy a hybrid gas/electric instead of hybrid/diesel.
I think they would've been better off buying a fleet of CNG busses like the MTA has here in LA. Although I think if New Flyer (bus manufacturer that provides busses to Long Beach Transit) could create a hybrid CNG/electric bus then we'd have a real solution.
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Cary 3:34PM (7/05/2008)
I guess I'll go ahead and tell you you're wrong.
If you can purchase a 2008 Ford F350 powerstoke diesel, why wouldn't you be able to purchase a diesel bus?
Oh, I forgot you can. Now legislation prevents or even discourages it in the state of California.
cm 2:21AM (7/04/2008)
There are better designs for hybrid busses already on the road.
One problem is the ultracapacitors, they have excellent cycle life and are not harmed by total discharge, but the energy density is poor. The voltage varies linearly with charging, which requires sophisticated electronic DC-DC converters that sap a bit of power. Moreover, due to quantum tunneling effects, they slowly loose their charge - they "leak". Hybrids using NiMH or LiIon batteries are more efficient.
The GM/Allison "dual mode" busses transmits part of the power from the IC engine mechanically to the wheels, thus has less conversion losses than a series hybrid design.
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Michael Hoexter 3:32PM (7/04/2008)
We should be building more trolleybus routes...that is the only secure way to deal with the cost of diesel. It involves substantial capital investment but will yield net cost savings if you consider what's going to happen to the price of fuel in the coming years.
If the trolleybuses have a diesel generator or a battery in them, they can also serve partially electrified routes like the Boston MBTA's Silver Line. The Silver Line bus takes about 30 seconds to attach and detach from the overhead wires.
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NeverFollow 6:13PM (7/04/2008)
http://www.autobloggreen.com/2007/05/21/mercedes-benz-introducing-new-series-hybrid-bus/
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The hybrid Citaro bus is expected to cut diesel consumption twenty to thirty percent annually.
The standard 12L diesel has been replaced by a smaller 4.8L unit which is sufficient to keep the batteries charged since it doesn't have the deal with transient loads of acceleration. The smaller engine cuts about 550kg from the weight of the powertrain and the elimination of the transmission also contributes to a net weight penalty of only 1 tonne for the hybrid bus. The engine in the Citaro will only run when the batteries need charging which will also be supplemented by regenerative braking from the motors.
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Roger 9:33AM (7/10/2008)
Or, use fast charging Nanosafe or A123 batteries, and high power charging stations at the ends of the routes:
www.nanobus.org
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