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MicroTurbine Series Hybrid Bus Under Test in New York City

The New York City Transit (NYCT) agency, the largest in the Metropolitan Transportation Authority (MTA) network, is testing a diesel-fueled turbine series hybrid bus from DesignLine International Holdings in New Zealand.

The DesignLine hybrids, a few of which are in service in New Zealand and others of which are under evaluation in cities such as Hong Kong, use a 30kW Capstone MicroTurbine to power an auxiliary power unit (APU) to maintain the approximately 40 kWh battery pack at a medium state of charge. Under normal conditions, according to DesignLine, the buses will return to the depot with -60% SOC remaining within the battery pack.

APU control for the DesignLine system. Click to enlarge.

When the batteries are at a high charge level (>70%), the APU reduces the input to the batteries. At this level, the bus can operate in an electric mode with the APU turned off. At a medium state of charge (40% - 70%), the APU adjusts its output to maintain the average state of charge. Should the SOC drop below 40%, the APU will increase its output to return the battery level back to the required state of charge.

The company predicts that the bus will deliver about 7 mpg in New York. If that is the case, that would be approximately double the fuel economy of New York’s current series hybrid bus fleet, as measured by NREL during a comprehensive evaluation of New York’s Orion series hybrid buses. (Earlier post.)

(A hat-tip to Allen!)


Mr NBK Boston,

On the question of weight (which was the point traffic rules not withstanding), you're comparing the turbine hybrid EV against a normal bus. That's the point: if you only have an electric motor and a pantograph, then you are gaining a significant weight advantange over a diesel and the turbine (hideous thermo effy). That was my point.

WRT to traffic rights of way, there is no way that a bus should be held up in traffic, they should be running on a separate area with priority at lights. That's the way they run in Europe.

Cables are a complete non-argument: lay induction loops in the ground.

The fundamental point of physics remain: central generation and power recycling are more generally more efficient, centralised power does not require heavy local on bus storage which needs to be accelerated and braked (with consequent cycle efficiency losses each time energy is regnerated) nor do they require inefficient turbines. if you want a small engine to do this then why not use a small diesel engine running at high load the whole time which is significantly more efficient than a turbine in any case. Like the 1.9TDI hybrid buses in London.


Alex Kovnat-

Exactly why I asked earlier about how efficent this system would work with CNG. CNG buses tend to be way less efficent than diesels but cleaner, while diesels are dirty but efficient. If the turbine-based series can burn CNG with the efficiency of a normal diesel engine while taking advantage of plug-in power during off-duty hours, it would be a plus for both efficiency and emissions.

Max Reid

Turbines can run on any fuel (Liquid or Gas) and Capstone have been selling Micro-Turbines for quite a long time.

This will take the World's Transport to other fuels.
Very good experiment. New York City has already planned to replace Non-hybrid Taxis with Hybrids by 2012.

Keep it up New-Yorkers.
As we speak, today's Oil prices crossed $86 / barrel.


I don't buy the 7 mpg claim. I see no way a 25% efficient microturbine can deliver twice the MPG of a 40%+ turbodiesel installed in a diesel-hybrid. It just doesn't compute.


I don't buy the 7 mpg claim. I see no way a 25% efficient microturbine can deliver twice the MPG of a 40%+ turbodiesel installed in a diesel-hybrid. It just doesn't compute.

We'll find out, won't we?


Note that the figure Roger provided was for "25% at the electrical terminal output", key word terminal. In other words, the turbine is probably mounted directly to - or within - the generator, effectively taking on the role of the rotor. A diesel engine might be 40% thermally efficient, but there might be transmission losses associated with cranking the generator.

The turbine might also save a significant amount of weight because of its high power density. The diesel engine is probably large and heavy due to its steel construction.


Just to clarify - that 25% is probably calculated once all the efficency losses of the generator and power electronics are taken into account. The 40% probably doesn't take those into account.


GM makes a better system at 1/10 the cost.


According to this article I found:,g,ds&c=z,z,3732

At 70 degrees F, the 30kW (40hp) Capstone microturbine efficiency for converting the fuel's chemical energy to electricity is indeed 25%, where "efficiency is "electrical Btu out" divided by "input fuel Btu". According to one of the NREL PDF links on the last GCC article, the diesel hybrids had 270bhp Cummins diesels. No word on how big the alternator was though - if it couldn't handle 270bhp maybe that's part of the reason for the inefficiency vs the turbine. I'll check BAE systems (the manufacturer of the hybrid system).


The generator is 120kW, or ~161 hp. So is the diesel engine operating at partial load and out of its ideal efficiency range to match the generator's capability?


re:GM, the only source I can find for the GM Allison two-mode hybrid buses (which NYC also demoed) says 4mpg:

I would in no way expect it to beat a be-dieseled series hybrid in cost though, because of the complexity of the computer systems needed for two modes.


Thanks for the links. Truck turbo-diesels can run mid-40s thermal efficiency, I subtracted 10% generator losses for my 40% number. A 120 kW generator sounds about ideal for a 190 kW diesel, in fact I imagine the generator was sized to hit the diesel's sweet spot.

A 190kW diesel would outweigh the microturbine by several hundred pounds, but that shouldn't be a major fuel efficiency driver in something this large. It's not like bus mpg magically doubles when a fat person disembarks.

7 mpg with 25% microturbine efficiency implies the bus only requires a little more than one kWh per mile. That's about twice as much as a full size SUV, yet the bus weighs 5x as much.


If you look at the DesignLine buses, they also apparently have some "aerodynamic" features to them. They may also be less capacious and a bit lighter than the comparison buses - the consumer story on DL's own website says that many new yorkers were unhappy with how narrow, cramped and spartan the prototypes were compared to normal buses.

warren currier

Designline builds their buses from the ground up using some kind of proprietary systems of design and construction.

I read the article to say that their units are 'plug-in hybrids' that actually run as 'all electric' for a good part of the day... and that the turbine kicks in when the battery pack is down to ~40% charge remaining.

I'll bet anyone that if the company is claiming that these buses will get 7mpg in New York City they're not being truthful-- because they know that the real number will be substantially higher than 7mpg!!

Remember, this is a plug-in hybrid that is using electric power from the grid (at night) *and* the when the vehicle is on the street it is recharging itself through a dynamic braking system, ie, regenerative brakes.

So the real question is 'how dirty is the turbine exhaust?' Well it is NOT turned on most of the time, and when it is the pollution is likely minimal.

Maybe Capstone's website will give you the proper numbers.

These buses have been used all over the world for many years now, Japan, Hong Kong, UK, New Zealand, Taiwan Australia... and now they are coming to North America!!

Henry Gibson

Capstone turbines are frequently used in buildings where the heat that physics requires to be expelled is used to heat or cool! the building. This recovered heat makes the electricity almost free except for capital costs. When used to heat swimming pools almost all of the heat in the natural gas can be recovered. Ordinary power plants waste two thirds of the heat.

Capstone turbines as part of combined heating and cooling systems should be required by federal law in every large building that has natural gas heating. Buildings are usually built without consideration of operating costs at lowest bids. Federal efficiency standards should be implemented that require combined heat-power-and-cooling. This not only improves operating costs but also reduces carbon dioxide releases by 40% over purchases of power from the grid and separate boilers. Imbalances of heat and electric production can be reduced by large amounts of heat storage including coils in the soil and rock beneath buildings and the concrete foundations. Vanadium flow batteries, ZEBRA batteries and Sodium Sulphur batteries may eventually be cheap enough to be used for electrical storage in buildings. The artificial high peak power prices in California already make them profitable there.

Honda makes natural gas powered Combined heat and power systems for homes that are sold in the US by climate energy. Rather than buy solar panels, people in Califonia would find it cheaper to install such units if they have natural gas service. When combined with ZEBRA batteries they could allow a complete disconnection from the grid at far lower cost than solar. The electricity could be used to charge full electric TH!NK cars or to run compressors for natural gas HONDA cars.

The capstone heat recovery system is separate from the recuperator built into almost every capstone turbine. Some turbines installed in oil fields do not use recuperators because the gas is too cheap to justify the capital cost of the recuperator and is just burnt in flares anyway otherwise.

Eventually the super high prices of electronic motors and drives for hybrid buses could come down with mass production and the overall costs reduced to below that of standard diesel buses. Hydraulic hybrids, such as developed for the UPS truck may be a cheaper and better solution. Capstone turbines might still be used for their low pollution. But a linear piston diesel hydraulic pump developed by NOAX would be a more efficient choice. All that is needed is mass production of the NOAX pump. A slow speed flywheel, such as used by PARRY PEOPLE MOVERS with a gear pump, can be used for long term high power and regeneration combined with the air pressure tanks of the UPS truck design.

The present infatuation with very expensive electronic drives and motors is detrimental to the implementation of hybrid vehicles, but the efficiencies might eventually make up for the costs. Many european electric locomotives have electronic inverter drives as do some US diesel electric locomotives, and this might indicate the value of electronics for transportation systems.

New York never did try steam powered buses that could be recharged every few miles by the extensive steam system. Modern materials and electronics would allow for robotic arms in the roadway to refill a pressure tank with super hot water in a few seconds. A tiny cheap gasoline engine generator and a cheap electric gear motor with brushes could be clutched to a drive shaft for emergency operation away from steam. This would be the cheapest bus to build and operate.


Kim Fenske

I am trying to convince transit operations in the mountains to adopt hybrid technology to increase fuel efficiency and save fuel expenses. Therefore, I hope that someone has more research information on the DesignLine hybrid bus technology. I recently contacted both DesignLine and New York City MTA, receiving no response. Any particulars on the following:

1] Any source of information on performance of the DesignLine in international applications comparing standard diesels with the hybrids.

2] Any data on the successful application of the Capstone microturbines at 10,000 feet altitude. I know that Lake Tahoe is utilizing a Capstone turbine in a non-transit application at 7,000 feet.

Please offer any resources that may exist supporting the use of turbine technology in hybrid applications.

Bryan Miller

Did the Designline Hybrid achieve the predicted economy?

Two fleets in New Zealand have both hybrid and conventional Designline buses. They may be prepared to share their experiences with other operators.

Redbus were the first to put these hybrids into commercial service, on a city circuit in Christchurch. They also operate similar buses powered by German MAN diesels.

NZBus also operate a city circuit in Auckland, which is a hillier route. They may be able to provide comparisons against Designline's older MAN-powered diesels, and newer Euro4-compliant Scania-powered diesels.

The 7mpg figure may also relate to the fact that they use grid electricity to charge the batteries overnight. Whether they have used the formulas that are used to calculate fuel consumption equivalences for electric vehicels, is not clear. Either way, it would give a substantial reduction in diesel expense, which should more than offset the cost of electricity at off-peak prices.

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