Testing Finds Proterra Electric Transit Bus Achieves More Than 20 mpg Diesel Equivalent

05 May 2009
 Proterra battery-electric bus. Click to enlarge.

An all-electric version of the 35-foot Proterra FCBE 35 transit bus, powered by a UQM PowerPhase 150 electric propulsion system and an Altairnano Li-ion battery pack (earlier post), achieved more than 20 miles per gallon diesel equivalent in fuel economy equivalency testing conducted by the Pennsylvania Transportation Institute at Pennsylvania State University.

Testing of the composite body all-electric version of the FCBE 35 transit bus was conducted using a modified Transit Coach Operating Duty Cycle (ADB) that includes simulated central business district, arterial and commuter operations.

Calculated diesel equivalent fuel economy for each phase was: 21.35 mpg on the central business district phase, 17.55 mpg on the arterial phase and 29.23 mpg on the commuter phase. Each test phase simulated transit-type service at seated load weight and included various passenger pickup stops.

Simulated test phases ranged from 7 stops per mile and a top speed of 20 mph during the central business district phase to 1 stop and a top speed of 40 mph during the commuter phase. The FCBE 35 transit bus was tested at a gross vehicle weight of 36,680 based on a seating capacity of 38 passengers, including the driver and 34 standing passengers.

Fuel economy testing was conducted with the air conditioning system turned off. Air conditioned operations are expected to reduce fuel economy results by approximately 30%. The bus was recharged in less than 20 minutes using the Proterra’s TerraVolt fast charge energy storage system at the end of each completed ADB, replenishing the energy consumed and thereby extending the total daily vehicle range.

The UQM electric propulsion system produces peak torque of 650 N·m and peak power of 150 kW (201 hp). The system has a continuous torque rating of 400 N·m and a continuous power rating of 100 kW (134 hp). The system also features optimized four-quadrant performance, dynamic torque, speed and voltage control, regenerative braking and system energy efficiency of more than 90% across substantially all of its performance regimen.

The test validated that Proterra’s 35-foot transit bus achieves up to 400 percent better performance than today’s conventional diesel or competitor’s hybrid transit buses. These fuel economy improvements together with the ability to extend total daily vehicle range through our TerraVolt rapid charge capability offers a tremendous advantage to transit operators who are looking to reduce both emissions and vehicle operating costs.

—Jeff Granato, President of Proterra LLC

Comments

Buses are already the best way of moving people if all you're thinking about is passenger miles per gallon, but only if the bus is kept FULL. However they people who could be riding those buses wont be thinking about MPG, they'll be thinking about ride comfort, time, how far they'll have to walk after they get off, etc.

At 20 mpg, this bus wouldn't have to be full to be effective. Heck, with only 4 riders, it would more fuel efficient than 90% of the vehicles on the road.

Diesel equivalent remember, this is an electric bus.

What I find curious is how great the Altairnano batteries are in so many different ways, but they don't seem to have been taken up properly by EV manufacturers, even those that have made concepts using their batteries (eg lightning).

"..composite body all-electric version.."

If they took off tons of weight here, this probably helped. The stop and go nature of bus routes really uses EV to its advantage.

Cost of bus (WITHOUT incentives)? Years needed to realize savings from all-electric bus vs. regular diesel bus? It's all about the $. A fleet of smaller buses doing limited request services like a taxi from a series of nodes with no set route could work much better than the traditional set route, set time model. With a charging station as part of a rail hub, the bus could take the passengers to their final destination as part of the rail ticket. Door to rail to door would hugely improve the functionality of rail services. A fleet of smaller buses doing limited request services like a taxi from a series of nodes with no set route could work much better than the traditional set route, set time model. With a charging station as part of a rail hub, the bus could take the passengers to their final destination as part of the rail ticket. Door to rail to door would hugely improve the functionality of rail services. I like the small bus more buses idea. If you could get a bus withing 5 minutes going north/south and connect with another going east/west within 5 minutes, more people might ride buses. When it takes you 2 hours to get where a car would get you in 15 minutes...forget it. What does "20 miles per gallon diesel equivalent" even mean? Phrases like this really twist my trousers and make suspect hype and spin. I am hoping that electric bus drivetrains become commercially viable. Low soot, low noise, low carbon - there really seems to be a lot of upside. They just need to get past the cost and range issues. Easier said than done, I know. This bus must be wildly underpowered. 150kW/650n-m for 30-90secs and then 100kW/400n-m continuous (info on UQM website) certainly isn't going to make any operators happy. Granted, it IS a bus an not a race car, but I wonder about pulling into traffic out of a bus stop, will it be a hazard? Also, I realize that it has an electric motor and that the peak torque is available from a stop, but 480ft-lbs (650n-m)is very low torque in the bus world. For example, a 6.7L Cummins ISB diesel engine, the smallest diesel engine you can buy in an American transit bus, produces 620ft-lbs @ 1500RPMs (not far from idle) and transit properties usually only use them for 30' buses. For another example, a Bluetec Mercedes 3.0L engine produces 450ft-lbs @ 1600RPMs (and 255hp @ 3700rpms). So this motor produces the equivalent of a ~3L diesel engine, that's tiny in the bus world. Not to mention that diesel engines use a transmission to get the necessary power they need. I'm sure this bus is a direct-drive platform, so it doesn't get the aid of a torque multiplication in multiple gears. The UQM drive system was really developed for a car chassis, so I wonder about performance of this bus, especially at full loads and on slight grades. So, how does all this add up? It's easy to make a vehicle that gets 4x the fuel economy if you completely ignore performance. I'm sure if you stuffed a Bluetec diesel in a bus it would get ~4x the fuel economy too. I really wish the Altoona Bus Test Reports included performance data with the fuel economy numbers so that they could be factored in. I'm completely in favor of electric vehicles, but it's not wise to introduce vehicles that would give the public a bad taste for them. I'm thinking of the early diesels that hit America, everyone still has the association with plumes of black smoke behind the diesel cars and trucks. Even though that has radically changed in the past decade, many people still have that association, which is evident in the number of diesel cars sold here versus Europe. While I agree with the smaller/more frequent point, the real cost is in the driver, not the fuel. Figure$100k/yr for a driver with benefits times two shifts.

"20 miles per gallon diesel equivalent"

I take this to mean that if a bus gets 5 mpg on diesel, then this bus goes 20 miles on the same energy. Take how many BTUs in a gallon of diesel and calculate how much a diesel engine can get out of it at its rated efficiency.

If a diesel in the bus is 30% efficient and a battery, controller and motor is 60% efficient, that is part of it. Say this bus is 1/2 the weight of a comparable bus, that is another part of it. The fudge factor comes in when calculating the efficiency of the electricity generation in the first place. I do not think that they are factoring that in.

I wonder how many KWhrs an efficient PV array covering the entire roof would bring to the party. Depends if youre talking Chicago or LA of course!

"Transit Coach Operating Duty Cycle (ADB)" First, let's send the A-Team back to acronym school. Second, a good first step, by legend only 11 more to go. On the real positive side is the introduction of duty cycle charging and Altair batteries.

The real test here is what the SOC curve looks like after 5200 hours (annual work load.) What do the batteries cost and how often do they need replacement? MTBF?? And, the arachnid design looks utterly childish.

Sulleny, if you believe altairnano's claims, they say their batteries can last 20,000 fast charge cycles with little degradation (the titanate structure permits this, apparently).

They reckon currently $1,000 per kWh in low volume production, but say eventually it shouldn't be more expensive than the related LiFePO4 chemistry, which is at around$300 per kWh currently from BYD.

Short answer is they should last the life of the bus (and then some).

JMartin is right about the cost of the driver, that's just one of the reasons I prefer rail-based transit. Modern streetcars can carry more people in greater comfort and at lower cost than buses. And if you can get a grade-separate system you don't even need a driver, like Vancouver's Skytrain.

This bus must be wildly underpowered.

Don't forget this is a composite body, and the design was focused on reducing weight, so as F=MA, when M is much smaller, F can be as well to retain the same A.

"I wonder how many KWhrs an efficient PV array covering the entire roof would bring to the party."

At 15% efficient and a 300 square foot roof area, the PVs could create about 4500 watts of power. That might help the bus go an extra 3-4 miles in an hour for about a 20% extended range.

This type of lithium titanate batteries seems to be the best technology available for the future plug in electric cars and other vehicles.

There are already three major battery manufacturers using this technology
- Altairnano
- Enerdel
- Toshiba

Volkswagen has made a deal with Toshiba to develop electric drive for next gnr electric vehicles.

The advantages of lithium titanate batteries are

Rapid charge
Excellent safety
Wide temperature gradient
Long life

All desired properties for car usage

Looks promising :)

Bill:

The average, rather heavy (31,000 lbs), trolley bus use only 150 KW (about 250 KW peak) e-drive motor and has no problem keeping up with traffic. Take-off is normally much better than diesel units. The problem is with overhead cables and limited lateral movements.

This much lighter unit should do very well with 100 KW (150 kw Peak). Seems that the Altair batteries (or equivalent) are well suited for extensive long life use on city buses.

SJC:

With improved futur solar cells (30 % efficiency), something like 6 to 8 Kwh could supply power to AC units and help to recharge batteries for extended range. Quick charges at selected specially equipped regular bus stops could extend e-range to 100% of requirement. The on-board genset could be very small and used during emergencies only or to crawl to the nearest charge station.

E-buses are not only cleaner but make much less annoying noises. Ideal for inner-city uses.

Harvey:

I agree with you on the points about the e-drive motor in the trolley buses. But as you say the drive motor in those are 150kW nominal and 250kW peak. This bus is 100kW nominal and 150kW peak. But, the bigger point is the torque. I wonder what the torque is on the e-drive motor, I'm thinking it is much higher. The batteries can provide all the power in the world, but if the motor is torque limited, you'll still have an underperformer.

"The FCBE 35 transit bus was tested at a gross vehicle weight of 36,680 based on a seating capacity of 38 passengers, including the driver and 34 standing passengers."

Does that mean they had 73 people: one driver, 38 seated and 34 standing? That is one crowded bus.

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