My Fuel Cell Tahoe

I was going to do a sports car kinda thing, but I am a SUV kinda guy that needs space to haul my stuff and tow a boat. So if I had the cash, this would be my mean green machine.

Doing the RV of the future I stumbled across a few interesting things. First that in-wheel motors have potential, but if I want my dream Tahoe now, it is better to go with a big honking motor and mechanical gearing. Azure Dynamics makes the big AC90 electric motor that has some serious butt. They also make a mid-range, AC55 Force Drive (TM) which is more of a pick'em up size motor. I will stick to Ballard Power's FC Velocity 9SSL fuel cell, rated at 20 kW. I am going with two, so one can be mounted on each side of the AC55 under the hood. I am a rear wheel drive fan and it is neat to pop the hood to show stuff off and symmetry is pleasing on the eye.

I will use the standard automatic transmission from the 2011 Tahoe to make things simple. I may have to play with the rear end a little, but the RPM range of the AC55 is a pretty good match other than the best performance range is higher than the typical internal combustion engine.

The AC55 provides a pretty flat torque of 280 NM until it hits 2100 RPM then it slope off. Efficiency is pretty flat as well, but there is a hump in the power requirement that means we will have to play with batteries for boosting power during acceleration. I will stick with a pair of 8D lead acids for boost and fiddle with the gearing to reduce their use. The pair of 8D's will provide up to an hour of 6kW boost, so we need to be careful with energy management, but extra battery storage should not be a problem. Going with more expensive Lithium Ion batteries is an option worthy of consideration in the Tahoe's case though.

Hydrogen storage is not as much of a problem with the full size Tahoe frame. Where the normal gas tank would be, a triple set of High Density Polyethylene (HPDE) lined aluminum tanks rated for 3000 PSI will go. We can also stick a pair of longer HDPE lined tanks inside the running boards with a little lift kit to provide clearance. We should be able to get about 20 to 25 kilograms of hydrogen storage with this configuration. The 8D's should fit nicely under the hood below and slightly in board of the fuel cells with the AC55 controller mounted in front of the motor. Split cooling radiators, one for each fuel cell, will be mounted in the normal radiator location. The total weight will be close to the original big V-8 that is being replaced since the AC55 only weighs 106 Kilos. That is pretty simple! We don't even have to fiddle with the suspension other than a lift kit.

280 NM of torque is equal to 206 Ft-Lbs which is less than the maximum torque of the Chevy V-8. With the rear end change, the torque at the wheels will be closer for towing performance. For a towing package, we could even consider a high/low rear end which may be pretty trick. While gearing can over come a lot of issues, it is not much help on top end. 80 MPH for normal load and 70 for average towing is going to be about the limit. I can live with that since I will be getting about 25% better fuel mileage than the standard V-8. That may be more, but with about 54% overall efficiency and much less cost per gallon equivalent, it is not bad.

The cruising RPM of the AC55 needs to be limited to the 1500 to 2000 range to match the 25Kw continuous Kw and Torque of the AC55 drive motor. As I mentioned, this range is a good match for the standard transmission and rear end of the Tahoe. It also means the rather small battery storage should fine for normal use. The beefier AC90 with either larger fuel cells or more battery backup could be a heavy duty option. Since Ballard and Azure Dynamics are not on the same page right now, a better option should be available soon.

Cost wise, the FCV Tahoe will be a little higher than the higher estimated cost of $56,000 for a hybrid. Unlike a RV, a SUV gets plenty of mileage, so the home brewed fuel will be a big factor to consider as well as 10,000 hour PEM maintenance on the fuel cells. Ten thousand hours is about 40,000 miles depending on use of course. If we can get one free PEM service from the dealer along with $2500 for the solar home hydrogen refilling station, that would give us about 3 cents a mile low end fuel cost. Including an estimated $65,000 MSRP, the cost per mile, hoping no significant maintenance costs, would be $0.83 USD based on 80,000 mile life. A little on the high side, but not as bad as five years ago. If the PEM replacement cost is not too high, a used SUV buyer could get a great deal.

PEM maintenance is the biggest factor with fuel cells. While the 10,000 hour limit may be a little flexible, to keep efficiency up, it has to be done. It doesn't look that complicated and the cost of PEM material is way lower than a few years ago. That would be an interesting subject for another post.

In case you are wondering, I selected the Ballard Power FC Velocity 9SSL because it is in production for the materials handling market which reduces the cost per kW considerably. At $1000 per kW they are much more attractive than the larger 75kW bus style at roughly $4000 per kilowatt. Target price for an automotive size fuel cell is $30 a kW (net) which will require some serious production to match. Exactly what that cost per kW (net) translates to for the end user, I am not sure. By 2015 though the $1000 per kW should be closer to $500 which will be more inline with a standard gas power option. Also, the 10,000 life is based on material handling usage. For an automotive application it may be less.

Just playing with off the rack components, the cost and performance of FCV's is getting close. My calculations are pretty rough. With a focused design all sorts are things are possible. Still, I think the twin fuel cells may be something worth looking at because load balancing could really extend the life of the cells. It would also look pretty cool under the hood.