EnerFuel Coupling High-Temperature PEM Fuel Cell With On-board Reformer for Range Extender System for Electric Vehicles
29 May 2010
|EnerFuel is developing a HT PEM cell/on-board reformer system that enables the use of conventional fuels in the fuel cell range extender. Source: EnerFuel. Click to enlarge.|
EnerFuel, a subsidiary of Li-ion manufacturer EnerDel’s parent Ener 1, is developing a range extender system for electric vehicles that consists of a high-temperature (HT) PEM fuel cell combined with an on-board reformer. The use of the reformer in conjunction with the high-temperature 3-5 kW fuel cell would enable the use of conventional hydrocarbon fuels to recharge the batteries in the EV.
In 2008, EnerFuel developed a prototype to demonstrate the advantages of a fuel cell EV range extender. (Earlier post.) The test vehicle, equipped with a 35 kWh lithium ion battery pack, was outfitted with a 3 kW fuel cell range extender fueled by compressed hydrogen (5,000 psi tank, 20 kWhe equivalent). The range extender increased average vehicle range by more than 50% from the battery only base case, EnerFuel said.
The overall weight of that fuel cell system was 160 lbs (73 kg). The weight of a lithium-ion battery pack with similar energy content would have been double that of the fuel cell system.
|HT-PEM cells have much lower susceptibility to CO poisoning than LT-PEM cells. Source: EnerFuel. Click to enlarge.|
The use of an on-board reformer eliminates the need for a hydrogen refueling infrastructure, EnerFuel notes. While the incorporation of a reformer with a fuel cell has been tried in the past, EnerFuel’s effort differs in the use of the higher-temperature operating range (120 °C to 180 °C, vs. low-temperature 60 °C to 80°C PEM fuel cells). Furthermore, the fuel cell system operates at discrete power conditions with minimal transients, and the system is smaller than previously attempted onboard reformation systems.
The HT-PEM fuel cell has much lower susceptibility to CO poisoning than LT-PEM cells; this enables simplified and low-cost integration with reformers. The deep hybridization with batteries also reduces the requirement for immediate fuel cell start-up, which allows EnerFuel to use HT-PEM fuel cells.
EnerFuel has designed HT-PEM fuel cell systems with minimal balance of plant. For example, reactant humidification has been eliminated, an air cooled design eliminates the need for a coolant loop and radiator, and low pressure operation reduces the need for compressor-expander systems.
Balance of plant elimination is critical to the cost and reliability of the fuel cell. While the cost of the fuel cell stack drops almost linearly as its nominal power output drops, the balance of plant of plant costs do not scale down in the same manner. The EnerFuel HT-PEM fuel cell system thus can have a cost advantage over more complex systems in this application, the company says.
To the user, suggests Dr. Daniel Betts at EnerFuel, perhaps the most important difference between a fuel cell and an ICE range extender such as that used in the Chevrolet Volt is that the fuel cell can charge the vehicle battery while parked. Further, fuel cell system efficiency increase at partial loads, whereas ICE efficiency decreases at partial loads. Depending on the state of charge of the vehicle battery or the rate of charging that is required by the user, the efficiency of charging could be many times higher than that of ICE and on occasions higher than the grid efficiency, EnerFuel says.
The EV user would find a reduced dependence on a charging infrastructure. In essence the fuel cell can act as a high efficiency, zero pollution portable-charger for the vehicle.
More complex battery-fuel cell interactions can also occur, Betts says. For example, the heat generated by the fuel cell while running or during its startup phase can be used to warm up lithium ion batteries in cold environments. The fuel cell can also help support battery and vehicle air conditioning loads.
To keep the cost, size and weight of the fuel cell low, EnerFuel is developing lower power fuel cell systems than those traditionally place in vehicles. While the typical fuel cell vehicle uses a fuel cell system that provides 60 kW to 100 kW, EnerFuel is developing 3 kW and 5 kW systems.
As an example, EnerFuel uses a vehicle with a 200 Wh/mi average driving energy consumption (equivalent to a 25 to 33 mile per gallon gasoline ICE vehicle). To travel 100 miles throughout the day, the vehicle would require a 20 kWh battery pack. If a 5 kW fuel cell system were added and allowed to charge the vehicle batteries without limit throughout an 8 hour day, it would be able to add 40 kWh of energy to the vehicle. The daily range of the vehicle would be 200 miles from the fuel cell and 100 miles from the battery.
Because people seldom engage in such a long daily driving cycles, this opens up the possibility of eliminating a portion of the vehicle batteries, EnerFuel suggests. In this way, the overall cost and weight of the vehicle power plant can be reduced.
(A hat-tip to David!)
A PHEV with this very large 35 KWh battery could get enough extended range for occasional longer trips with a very small flex fuel 10 KW rotary type genset. The different in fuel economy and GHG between the above FC and genset would be minimal in real life use.
Posted by: HarveyD | 29 May 2010 at 07:42 AM
The major advantage of this sort of Fuel cell use is that:
'Most consumers would want to charge their EVs at home, however 61% of those surveyed did not have access to a garage with an electric power source.'
This means that many for whom it is currently inconvenient to charge up would be served, including importantly city apartment dwellers who are other than for not having a handy charging point the best demographic for electric vehicles.
Another demographic within reach of this vehicle are those who have a journey of maybe 70 miles to work, this could charge the car during the day for the return journey, and after returning in the evening the car would be good for social use in a couple of hours.
Posted by: Davemart | 29 May 2010 at 08:05 AM
I think Kike slipped, both the original source I linked and the old GCC post Mike linked give the prototype as having a 20kwh battery, not a 35kwh one.
Perhaps it had a 35kw engine?
Posted by: Davemart | 29 May 2010 at 08:12 AM
S/be Mike slipped
Posted by: Davemart | 29 May 2010 at 08:13 AM
I've found the 35kwh reference for the prototype battery in Mike's other link.
Presumably that is the correct number - colour me confused!
Posted by: Davemart | 29 May 2010 at 08:17 AM
This takes un-affordability to a new level..
Posted by: ToppaTom | 29 May 2010 at 08:27 AM
Since we haven't been told the cost, how do you know it is unaffordable?
Posted by: Davemart | 29 May 2010 at 08:33 AM
If I had a vehicle with a 5kW fuel cell. I'd want to be able to plug it into the gas grid at home and have CHP / back up power when it was connected.
Also if it can run on a fuel source (methane) wouldn't it make more sense to store the methane due to its higher energy density.
These fuel cells would be really handy for larger hybrid vehicles as they could run aux electricity loads.
"The overall weight of that fuel cell system was 160 lbs (73 kg)"
The Lotus range extender weighs 56kg and I bet is a damn site cheaper to mass produce!
Posted by: 3PeaceSweet | 29 May 2010 at 09:54 AM
This could be good to commuters that do not have a plug on the other end. If they sell 100,000 Leaf EVs every year, are there going to be 100,000 more charge points every year at work? I doubt it.
Posted by: SJC | 29 May 2010 at 10:34 AM
Looking at the pictures, the 'overall system' on the prototype seems to include a hydrogen storage cylinder, which is pretty heavy.
Low temperature fuel cells run at about a kilogram/kw for the stack.
You have to add the rest of the case and the plumbing plus the reformer, of course, but it seems to me that the petrol burning version will be a great deal lighter than that, and of course you would only need a fuel tank of at most perhaps 4 gallons, as they should be good at 50% efficiency for perhaps 100mpg.
Very roughly over the next few years the approximate doubling in energy density that Nissan plans will save over 100 kgs if the pack size for 20 kwh were held constant, so using this strategy rather than doubling the amount of stored energy should result in a rather lither car even using the 73kg figure, but my guess is that the weight added is only around half of that, and the petrol fuel tank fully loaded should only be around 20kgs or so with the petrol in.
Ener1 are also aware of it's potential to help the home/grid, as the prototype was V2G
Posted by: Davemart | 29 May 2010 at 11:55 AM
How do I know it is unaffordable?
If the article included the cost, and if they said it was low cost.
I would still know it would be unaffordable.
Posted by: ToppaTom | 29 May 2010 at 04:22 PM
Good idea if the FC startup time is fast. Will it use battery energy to maintain HT temp? And can it reform alcohols?
Without a ready alcohol or methane infrastructure how does this make life easier than finding a 110V outlet somewhere?
The only infrastructure needed for EVs at this point is the addition of 220V 100A outlets at home and work. Everything else is solution in search of problem IMO.
Posted by: sulleny | 29 May 2010 at 04:29 PM
M100 is very easy to reform, it was done in the NECAR program decades ago. This is for people without a plug at the other end, which is more likely than having one.
Posted by: SJC | 29 May 2010 at 04:45 PM
It doesn't seem very 'common sense' to blindly make assumptions in the manner you choose.
If you read the links your questions are answered. Initially of course battery energy is used to bring the fuel cell up to temperature, but thereafter the excess heat can be used to provide cabin heat etc so overall the battery has less drain.
You could use a variety of alcohols, but the real point of this is that you could just use petrol and so solve your infrastructure problems.
Posted by: Davemart | 29 May 2010 at 05:59 PM
If the commute is 40 miles, you use 10 kWh getting there and 5 kWh is generated on the way. The fuel cell continues to run another hour while parked and you are fully charged. Going home you do not run the fuel cell, because you will plug in the garage.
At 30% efficiency for the reformer and stack I use 1 1/2 gallons of M100 at $2 per gallon, for $3 of fuel per day, versus 4 gallons of gasoline at $3 per gallon. Even adding the $1.50 for the plug electric I am at $4.50 versus $12. Not bad considering cleaner air and less imported oil.
Posted by: SJC | 29 May 2010 at 06:45 PM
If your commute is 60 miles, then you might use most of your battery on a cold day, and if you have no access to a plug would be in trouble.
This could charge you up and get you home, and once there if you are one of the majority of motorists without a garage would once again do the job.
I would expect more like 50% efficiency from this, as they state that efficiency is high and fuel cells are in this sort of range.
So you would likely be getting around 20kwh out of the ~40kwh in a gallon of petrol, or about 100 mpg.
It wouldn't help much on the holiday vacation long drive, but alters the capabilities of the EV for regular shorter runs.
Posted by: Davemart | 29 May 2010 at 11:51 PM
Bring it on if the price is right.
I was thinking recharging a BEV would be a good use for the excess electricity made by an NG co-generator. Pretty neat if you dont get paid by the power company when the meter spins backwards.
The Honda 1kw unit:
Posted by: Herm Perez | 30 May 2010 at 04:14 AM
We want FCs that burn alcohol or methane/NG. The idea of Green cars is to get off foreign oil and on to a sustainable.
The time delay required to bring a HT cell to operational temp is the problem. People do not want to wait for their car to come up to operating temp before driving it.
Posted by: sulleny | 30 May 2010 at 06:55 PM
You can drive right away because you have lots of batteries. If it takes 10 minutes to bring it all up, no problem. You let the car know if it is a town or commute trip. If commute it starts, if it is town you can come back and charge.
Posted by: SJC | 30 May 2010 at 09:40 PM
Dont forget this is just the start as these things improve they will get alot more durable and powerful and more efficient not to mention cheaper.
It likely wont take many years before this method is the cheapest way to go simply due to emmissions controls alone.
Posted by: wintermane2000 | 31 May 2010 at 08:35 AM
Granted the SOFCs operating at 800C are more of a problem. Here the tradeoff is battery power used to heat a cooled FC. But I agree that this will improve and even disappear as an issue as the vehicle gets smarter. I expect too that this PEM technology will extend to lower temps still.
And there are good ideas for low cost, low power electrolysis coming along - which is the major game changer.
Posted by: sulleny | 31 May 2010 at 09:37 AM
The ideal development would be a reformer which operates on something like pyrolysis oil, which takes far less processing than alcohols. (An SOFC can probably run on pyrolysis oil without modification, though ash would have to be filtered thoroughly.)
Posted by: Engineer-Poet | 01 June 2010 at 05:29 AM
What about the viscousity of pyrolysis oil? I heard it can be a problem. Pyrolysis oil is usually used where you would use bunker fuel; it's thick, bottom-of-the-barrel, stuff.
Posted by: ai_vin | 01 June 2010 at 09:14 AM
Pyrolysis oil is very viscous and heavy and would seem to be unfit for use in an FC reformer without additional treatment. It does make a reasonable replacement for petro oils.
Posted by: sulleny | 01 June 2010 at 09:46 AM
SOFCs could be used, I was a proponent of those in the past. A vacuum box can contain the heat and if you put a turbine on the output you get better efficiency. Also, if the stack is cold, you can just recycle heated air from the fuel around the stack and heat it quickly.
Posted by: SJC | 01 June 2010 at 12:48 PM