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GE demonstrates dual battery system for electric buses; pairing high-energy density sodium battery with high-power lithium battery optimizes performance and lowers cost

Electric bus with dual battery system. Click to enlarge.

The hybrid systems research team at GE Global Research has successfully demonstrated a dual battery system for an electric transit bus, pairing a high-energy density sodium metal halide battery with a high-power lithium battery. A123Systems—which is a partner in the project, and in which GE holds a significant stake (earlier post)—provided the Li-ion power battery. GE developed a computerized energy management system to manage the vehicle power needs between the two types of battery packs.

The research is being done as part of a $13-million research project GE is engaged in with the Federal Transit Administration (FTA) and Northeast Advanced Vehicle Consortium, funded under the National Fuel Cell Bus Program. Currently, the bus has a top speed of 50 mph (80 km/h) and about a 60-80 mile (97-129 km) range under idealized conditions. The ultimate target is 62 mph (100 km/h) and a real-life 100-mile (161-km) range, while traveling a transit bus route with its multiple stops and starts, according to Lembit Salasoo, principal investigator on the FTA Hybrid Transit Bus project.

The combination of the two systems could reduce the total battery system cost for such a vehicle by up to 20% compared to a single battery system, GE said.

While significant advances in battery technology have been made, further reductions in the size and cost of batteries will be needed to enable the widespread adoption of electric vehicles. GE researchers believe a dual system with high power and energy storage capacity could achieve the optimal electric driving range and acceleration requirements at a more practical size scale and cost for larger vehicles.

GE will conducting another bus demonstration for the project next year, in which it will be using its new sodium battery (earlier post) and a new modern, advanced composites lightweight bus.

We’re entering a decade of unprecedented activity and developments in electrified transportation. With heavier vehicle platforms, both energy storage and power are a premium to deliver optimal vehicle performance, but the exact needs can vary based on a vehicle’s size and drive cycle. The beauty of our dual battery system is that it can be scaled to deliver just the right combination of power and storage.

—Lembit Salasoo, Senior Electrical Engineer and Principal Investigator

Many of the 843,000 buses registered in the US (including most of the 63,000 transit buses and 480,000 school buses) travel less than 100 miles per day. Enabling more of these buses to transition to an all-electric, zero emissions platform would significantly reduce CO2 emissions and petroleum fuel consumption.

Most types of batteries today come with a trade-off between power and energy storage. Lithium-ion batteries can provide a lot of power for acceleration, but are not optimized to store energy for extended driving range. Sodium batteries are on the opposite side of the spectrum. They store large amounts of energy, but are less optimized for power. GE’s dual battery combines the best attributes of both chemistries into a single system. In the hybrid transit bus demonstration, the lithium battery focused on the high power acceleration and braking, while the sodium battery provided an even electric power flow to extend the bus range.

In addition to optimizing performance, the key cost advantage of a dual system is that it provides flexibility to integrate less expensive battery chemistries without having to increase the size of the battery to address a vehicle’s power and energy storage needs. A single chemistry battery system would require a more costly scale up in the size of the battery to achieve the same result.

The development of a dual battery system and partnership with the FTA is a key part of GE’s growing hybrid and electric technology portfolio. GE is actively exploring partnership opportunities across the electric vehicle value chain through its Licensing business to commercialize its dual battery technology.

GE also is developing new technologies and products to support the integration of plug-in hybrid electric vehicles (PHEV) and electric vehicles (EV) into the electric grid.



"Many of the 843,000 buses registered in the US (including most of the 63,000 transit buses and 480,000 school buses) travel less than 100 miles per day."

"Most types of batteries today come with a trade-off between power and energy storage."

Those are two key points that says this has potential.


Combining two existing (not so advanced) battery technologies to power a very heavy bus may not make as much sense as many think. Until much higher performance batteries and/or ultra caps are available, an on-board genset (à la Volt) is the logical way to go.


The bus situation is already being handled by natural gas. I doubt any battery/ electric system is going to be as economical. I could see using a Bloom energy fuel cell to power an electric bus. Still using natural gas though. I keep waiting for the big trucks to get onto natural gas.

Perhaps the recent breakthrough in graphene supercapacitors will make electrical storage more reasonable for all transportation applications.


My city already has a fleet of electric buses, they get their energy from overhead cables. That's the thing about city buses, they travel on fixed routes that can be electrified.

Now if only someone could figure out a way to put rails in the street under those cables our "buses" could carry more people with less energy cost through lower rolling resistance. ;^)


ai vin: What a concept! I wonder why no one ever thought of that before?



Why does that not make sense? Can you explain a bit further.

To me it makes sense if most buses only travel a maximum of ~160 km/day. The higher energy density of hydrocarbon is less of an advantage then.

The other big advantage as opposed to a genset is that it does not create local air pollution in urban areas, where air pollution is already high.

And it reduces noise pollution too.

I see only advantages.


The other aspect of buses energy use is that it is intermittent. A bus travels for 1 to 2 hours at relatively low average speed, around 20 mph, which means total energy needed is relatively low. Then it parks at its destination for 10-20 minutes, changes the driver and then starts another trip on its route. Wouldn't that 10-20 minute wait give the bus to substantially recharge its battery, i.e. the battery would drain from its 100 mile range to 60 miles in a 2 hour circuit, then it would recharge to 80 miles, next circuit would draw it down to 40 miles, you recharge it longer over lunch to get it back to its full range, repeat as needed...
Just because a bus has just a 100 mile range it doesn't necessarily follow that the bus can only do 2 or 3 routes in a regular day, even if you mandate a 40 mile minimum reserve.


Rechargeable lithium-air cells are currently running at around 750 Wh/kg in the laboratory and are set to reach 1 kWh per kg soon. However calcium-air cells would have 60% of the energy density and be much cheaper. These could replace the sodium-metal-halide cells in the above example but be much lighter and provide much longer range.



A pure electric, very heavy, standard city bus does not currently make technology nor economic sense because:

- vehicle is too heavy. A very light weight model would help reduce the e-energy consumption but would currently cost even more.

- current batteries are too heavy and do not have enough e-storage for such heavy vehicles + cooling-heating-lighting in traffic jams.

- very limited endurance-range, specially under heavy cold winter traffic conditions. Similar (but smaller) Quebec City e-buses do not operate during very cold months (December to end of March) for that reason. (N.B- I have used those made in Italy small city e-buses this summer - grossly under powered - no A/C, too slow and noisy e-motors)

- currently too expensive (2x to 2.5x) the cost of equivalent diesel buses and even more than hybrid (more usable) city buses. Adding a $20K genset on a $800K large bus is transparent because you can reduce batteries cost by same amount and more.

A compromise is the use of overhead quick charge spots along the e-bus routes to pick-up a boost on the way and extend e-range with less batteries. That system is used in Switzerland for their city Trams and e-Buses.

With time, as batteries/super-caps technology improves (2x to 4x) and their cost comes down, lighter pure electric (limited range) city buses will make sense. That may be by 2020 or so? The same applies to highway e-cars. The technology has to evolve more.... before it becomes more competitive and usable.


Nice progress in this area - but much more needed. In October the Opbrid overhead bus barr was introduced to recharge buses while parked in certain rest areas

Clearly some company is going to make a good profit on electrifying buses. Will battery storage capacity at 1kW-kg be more economical than NG burning SOFCs...

IMO, noise pollution today is as large a factor as particulates. If you compare electrified city buses to diesel (we have both where I am) they are delightfully quiet and free of belching smoke.


Good questions:

Total life time cost of e-buses versus NG buses or diesel buses or Hybrids? GHG + initial cost + on-going maintenance cost etc would have to be factored in. A price of $50/tonne for CO2 could be used + $/Km for other pollutants including noise.

Depending of factors used, one could make a case for any of the above energy sources.

In the longer term (2020+) when longer lasting, improved performance, lower cost, super caps and batteries are mass produced, e-buses and e-cabs etc may become the only technology to meet public acceptance. With well located overhead bus bars, those vehicles could run 24/7 for years.



for once your are dead wrong in your belief that progresses in electric cars and batteries will come in a predictable, well planned and accelerated way. Nothing will be more uncertain, unpredictable and unscheduled way than introduction of electric cars but new energies in general and we have to live with that.

Look the EPA slashed their prediction for production of cellulosic ethanol by more than 90%, because technology and progresses are struggling big time and this despite wide effort dedicated to that development. Look at the success of wind energy, after 20 year of successful development (wind energy is considered a success)only 1% of electricity is produced this way. On another topic the development of big concentrated solar plant in desert lands is being torn into pieces (to my dismal) as for the electricity produced by silicon cell on the roof of individual house, despite all the hype about it, it is not even visible when you count in %. I don't think the path to developp cheap high energy density reliable battery will be easier in any way. As they are electric car are nice toy but they will only adress a marginal market.



Compare: $3.40/gallon gasoline or $.80-1.10 for electric energy?? And gasoline will get more expensive as demand drops - because oilco's expect escalating revenue.


Treehugger, I disagree on the progress front. Even looking at your example of cellulosic ethanol I think there is a good reason it's not growing. Even current corn ethanol doesn't cut it without major subsidies in every branch of the supply chain. How could anyone with any common sense at all expect cellulosic to add all it's cost on top of that and be economically viable.

You either use sugar cane for ethanol (or something like it which has the right energy mix from end to end) or your kidding yourselves. You can't violate the laws of physics and it takes way too many inputs in corn ethanol, and especially cellulosic ethanol, to ever expect that to make sense. But that is the fault of the people making the silly predictions. It has nothing to do with the progress in other areas such as batteries.

I could make the same argument and say that computer chips double every 18 months so we'll have 1000 mile range in our batteries in 5 years. That would be equally as silly.

Batteries have improved an average of 8% a year for decades and there is no reason to think it would not do at least that. And there was very little research or even incentive to change batteries until recently.

With the historical improvements and NO breakthroughs, the Tesla would go from a range of 220 miles today to 475 miles by 2020.

There is very large money going into R&D now and there are lots of breakthroughs happening on many, many fronts. So the chances are that that it will be quite a bit better than 475 by 2020 anyway.

Panasonic already has shipping samples that Tesla will use which have an energy density of 252Wh/kg compared to the ~120Wh/kg in the Tesla Roadster today. Nissan has already announced they will double the range of the 2015 version of the Leaf to 200 miles for the same cost of batteries. These guys have essentially done everything they said they were going to do to date. So I don't see why you would be so pessimistic about the outlook.



You are right often result don't follow prediction because prediction were silly in the first place. You are absolutely right on this, and precisely in the case of electric car my point is that predicting that electric car will become main stream 10 years from now is just silly to start with. Even doubling the energy density of today batteries won't make the case for EV to become mainstream, 1st of all the price is still way to high so increasing the energy density by a factor 2 is not enough by a fair amount, where we need a breakthough is how to divide the price of the battery by a factor 2 or 3. Li-ion battery industry has already a significant history so if the drop in price was so easy it would happen faster.
I don't think that the Moore law that so far applied for the micro-electronic industry is in any way applicable for the energy industry. What happened this 40 past years in the micro-electronic industry is a very isolated case in the industry. Look at your lap top computer the CPU and Memory have followed the Moore law, but the batteries progresses can't keep up with that because they are not following that law. That doesn't mean there is no progress, there is indeed progress but not as fast as people think. Sure every day you can read discovery of new cathode or anode or electrolyte material that have the potential to improve the batteries performances, but the natural selection process is just so hard that most of these discoveries don't make it through. Breakthrough will happen for sure but they are not predictable, and to make a breakthrough a product requires a decade or two. Asides all the performances that Nissan or Tesla claim are for 25C temperature, at 40C or 0C these batteries will loose half of their power, not mentioning that if you have to Air condition the car you'll need more energy just when the batteries are already struggling.


Your problem is you're taking an overly Americo-centric view of the situation, like when you say "only 1% of electricity is produced" by wind [it's actually closer to 2%]. Other countries are doing much better;

Solar is also bigger in other countries;



"sides all the performances that Nissan or Tesla claim are for 25C temperature, at 40C or 0C these batteries will loose half of their power..."

Ranting is no substitute for doing the homework. You apparently only want to rant.


"where we need a breakthough is how to divide the price of the battery by a factor 2 or 3"

GM's Bob Lutz said in a recent interview that LG-Chem are convinced they will be able to sell their batteries for the Volt at one third the current cost when they ramp up production.


Improved lower cost batteries will be mass produced by 2015 or shortly thereafter. Those 300+ Wh/Kg units will come out of large factories at around $200/Kwh.

By 2020 or shortly thereafter performance could double and price could be down another 50%. That would make affordable highway capable BEVs a possibility.

Post 2020 should see a progressive decline in pure ICE vehicle production in favor of PHEVs and BEVs. The transition will not take place overnight but may be faster than many are ready to admit, specially if Oil/Ethanol Lobbies and the Flower Parties they finance can be overwhelmed or rendered harmless. If not, transition may take many more years in USA. However, it may not be the case in other countries such as China, Japan, Korea, India, etc where does lobbies are not as powerful.



Maybe you know something we don't know to be so confident in your prediction, but I'll take it with a grain of salt


Tree..Secretary Chu predicted yesterday that in about 5 years, BEVs will cost about the same as equivalent ICE, that batteries will have much higher performances (2x to 3x) and their price will be down more than 50%. He should know better than us?


Electric vehicles will make their contribution to reducing OPEC oil imports in the next 10 years, but not much of one.

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