NREL issues final report on Seattle hybrid bus program
The National Renewable Energy Laboratory has been tracking a fleet of hybrid buses operating in Seattle, Washington for the past year and has just issued their final report. The fleet of ten New Flyer buses are equipped with a GM-Allison two-mode hybrid drive-train, similar to the one that will be used late next year on GMT900 SUVs as well as Chrysler and BMW vehicles. The study compared the hybrid buses against standard diesel buses running similar duty cycles. The hybrid buses achieved 27 percent better fuel economy, while the diesels also had 4.5 perent higher maintenance costs. When the fuel and maintenance costs are combined, the hybrids had an operating cost of $1.06 per mile while the diesels were at $1.25 per mile. Emissions testing of a hybrid and diesel bus also showed an advantage for the hybrid.
Related:
- New biodiesel study shows no increase in NOx emissions using B20
- 100,000-mile B20 bus road tests: biodiesel increases operating costs slightly, reduces emissions
Reader Comments (Page 1 of 1)
Phil L. 1:05PM (12/18/2006)
I'm a little surprised at the maintenance cost difference. In general, I'd expect newly developed technology to (initially) cost more to maintain than a well developed design. Does anyone know if the maintenance costs in this one-year study include a pro-rated estimate of battery replacement cost? The article is very short on detail.
Also, do the maintenance costs captured reflect maintenance of a new hybrid bus vs. an older diesel-only bus? Information like this is critical to understand the published results.
Reply
CM 4:11AM (12/19/2006)
2 main reasons for reduced maintenance costs on hybrids:
(1) The IC engine (diesel, in this case) runs less often and shuts off when not needed. Less runtime means less IC engine maintenance.
(2) Regenerative braking with the motor/generators dramatically reduces wear on the regualr brake pads and drums, thus reducing brake maintenance.
The electrical components are all highly reliable and require little or no maintenance. Proper battery management that avoids overcharging and excessive discharging can extend battery life, making battery replacement a non-issue. There are Priuses that have gone over 200,000 miles, and some 9 years old Priuses, that are still running on their original NiMH traction batteries.
Reply
Tim 10:43AM (12/19/2006)
When you turn off your IC engine, the oil drains into the pan. When you restart it, the oil must be re-pumped back into the top of the engine. During this period, the engine is most susceptible to wear due to lack of lubrication. This is particularly acute when the engine is cold and the oil is thick. I see this as a maintenance/longevity problem with mild hybrids where the engine turns off at every stoplight. This will be less of a problem in a series PHEV because the engine will start and then run until the batteries are recharged creating less frequent start-stop cycles. Thoughts anyone?
Reply