True enough Matt, but there is also a significant difference between a car fueled with Liquid H2 vs. Compressed H2.
The Liquid H2 has significant complexity involving a tank with very high insulation efficiency, to keep the H2 cold, even when sitting out in the Las Vegas sun all day. (No small problem as the heat WANTS to get in and will do so via every pathway), thus making the design of the H2 storage system quite complex. The ideal design would require reasonable cost, use a minimal amount of space, have minimal weight (not including H2). These factors would be in relation to the existing fuel systems. i.e. the ideal solution would not cost, weigh or take up more room then a gasoline system. The H2 system though must also have an extremely high insulation factor. Unfortunately a number of these requirements tend to be contradictory. For example, the ideal insulation is a vacuum, but the cost and weight to build a large vacuum bottle is fairly high and the result, particularly chilled to - is somewhat fragile. Likewise a ceramic insulation is fairly low cost but doesn't have the required strength. A steel pressure tank has the strength but it is much more expensive, heavy and a poor insulator. If you add an insulation layer then the size can become an issue. Like I said, this is a more complex problem then it sounds.
If you solve the storage problem you still have to deal with the similarly complex issue of how to turn liquid H2 to a gas at continuously variable rates, ranging from quite low while creeping along in rush hour traffic to very high when passing on a high speed interstate with a heavily loaded vehicle. The materials problem stems from the fact that the temps at the start of the process are only 20K (- 259 C) degrees, while the operational temperature of the gas needs to be raised 270 C. The easiest way to deal with this is to add an electric heater in the gas delivery system to deal with low gas pressure during high demand, but this is inefficient, the more efficient process would use waste heat from the engine to accomplish this, but alas at start up there is no waste heat, thus the need for dual systems. An electric system that gives way to a waste heat system as well as regulation circuits/controls for each that work in unison. The distribution system has to also deal with a liquid that expands to roughly 800 times its volume as it is raised to operational temperature. Again, a staggering level of complexity not found in a gas system. The valve will also likely be involved in the significantly more complex refueling system. First, the refueling system CAN'T leak, because it would be leaking liquid H2, which would spoil your entire day if it spilled on your hand as you refueled. This not only requires a positive coupling system but in order to meet safety requirement is likely to have to be robotic or remote controlled. Then, because the tank can have relatively high pressure and because it is essentially a closed system, refueling a nearly empty tank would cause excessive internal pressure without a pump/suck dual piping system. You don't exactly pump the H2 fuel in so much as you suck the high pressure H2 gas out causing the liquid H2, under low pressure, to flow into the tank. It will require a positive shut off system and since people are paying for this fuel the system has to be able to quantify how much fuel is sucked out vs. pumped in, with the in and out flows as widely varying densities.

Of course one should not forget that for LH2 to be useful as a general fuel then a whole bunch of filling stations would have to be built. Interestingly it seems less costly to build H2 specific stations then to retrofit existing stations (existing tanks are buried under infrastructure making addition of new tanks/plumbing problematic and costly) a recent "pro H2" study was conducted using the EU15 nations as the subject. A full H2 fleet would require approx 100,000 new filling stations to get reasonably near the existing level of availability. A minimum of 15,000 filling stations would be needed to begin acceptance and provide a minimal level of coverage. Still at this level one would have to carefully plan most longer trips. At 60,000 filling stations, the density of stations is such that about half the people would find them adequately sited. Now the problem is, the cost of a H2 filling station is projected to be 3 times the cost of the existing stations (which have to be phased out, many at a loss) the cost is of a H2 station is ~ 4 million Euros (at today’s rate), thus the SOCIETY cost to get the program at least rolling would be 60 Billion Euros (or roughly 160 Euros for every person in the EU15, OUCH), but don't stop there, to get to the 60,000 level of stations would cost ~ 640 Euros per person. If one assumes roughly 200 million H2 vehicles replace the existing stock this would come to 1,200 E per vehicle. Now that's quite a fuel tax and barely over half way to full rollout. By the way, if they started building these stations in 2010 it would take well past 2030 to get the 60,000 stations built and then even if they worked at a breakneck pace since it would require completing ~ 10 new H2 stations every single work day for the entire 20 year period.

Then there is the venting problem, no matter HOW good the insulation, the system has to allow for venting of what amounts to an explosive gas. Again no small trick since even state of the art liquid H2 tanks vent around 3% of their VOLUME per day (not contents, volume) and this loss is not confined to the vehicle but the "gas station" as well. The venting plays havoc with users wanting to park their car in enclosed garages attached to their houses as a H2/O2 mix can present a real safety issue. Can you say KABOOM? This is a REAL issue for domestic vehicles. Current demonstration models are simply not parked inside while fueled. Sure we could do away with this convenience we've grown used to, but if so it certainly won't speed adoption. Don't underestimate the seriousness of this issue as H2 has an extremely wide flammability range. It will burn at levels as low as 4% all the way to 74% when mixed with air. Then just to frost the cake, H2/O2 require a very small amount of energy to ignite (remember Hindenburg?). If any H2 and O2 mix at almost any ratio it can and will ignite via the tiniest static discharge. This requires all vehicles and fuel handlers to be positively grounded prior to any refueling operation. Likewise the H2/O2 can be ignited by the tiny electrical spark given off by virtually any electrical switch when it makes or breaks contact unless the switch is hermetically sealed. Of course any open flames such as pilot lights or even a very hot object, anything over 1,000 F (like most radiant elements) will do it. Hell, just break a regular light bulb in a H2/O2 mixture and the latent heat of the filament will do the trick. Worse, if it does ignite it will either explode, if a sufficient size mixture is present, turning a garage into a large "cherry bomb" or it will burn with a virtually invisible flame, making the detection and suppression of an H2 fire surprisingly difficult because if a H2 fire is extinguished without stopping the flow of H2 gas, an explosive mixture will rapidly form and quickly create a more serious hazard than the fire itself. Ignition of the mixture is almost guaranteed since the H2 fire (which burns extremely hot) will likely create surfaces that are sufficiently hot enough to insure re-ignition. Because of this fact the accepted fire fighting practice is to try to prevent the fire from spreading while at the same time allowing it to burn until the hydrogen is gone. Bet it won't be a lot of fun watching your snazzy new Fireball 2000 immolate itself due to a refueling accident.

Now all of this is bad enough, but the extreme cold of liquid H2 will also freeze the gases in the air. While O2 will freeze at a temp 70C higher then H2 liquefies at, Nitrogen will not, so absolute care has to be taken to insure no part of the system that is between the temp of liquid N2 and Liquid O2 is open to the ambient air. If so the piping will quickly be coated with frozen O2, or drip liquid O2. In either case a serious risk of creating a local increase in the ambient O2 level will exist, which just increases all the hazards mentioned earlier.

Besides the inherent hazard issue that venting causes it also provides a real disincentive for the multi-car family, where one car is used significantly less then the other. Say one car is only driven on weekends, in that case over 1/2 the H2 fuel would be vented each month. That H2 better be cheap because a LOT of it is destined to be wasted unless the venting problem can be solved (NASA never figured out how to do it). This issue gets even more complicated because if a tank goes to zero pressure it MUST be purged with an inert gas (typically Nitrogen) prior to the refueling step. There is no way to prevent a tank from going to zero pressure so this detection/purging has to be part of the automated refueling process. But wait; is it even safe to refuel a zero pressure system? What if the zero pressure is caused by a puncture or large leak? YIKES, there is a good chance that you would have to have your car inspected and pressure tested before you could refuel it in this condition.


Now we can finally get past the fueling problem to the actual combustion engine.
BMW created the latest tiny fleet of BMW 7 series H2 cars about 5 years ago (this was the 5th model of an H2 car produced by BMW, each one based on the luxury 7 series at the time). They store their H2 fuel in highly insulated, 37-gallon, trunk-mounted tanks. The tanks are quite expensive and have 70 layers of aluminum and fiberglass sheets to provide insulation. Although the car has a 37-gallon tank it has a range of but 220 miles. (The engine is not optimized for H2 however, it also runs on gasoline, sort of a necessity given that there is only 1 filling station in Munich and as mentioned earlier, it is entirely robotic for safety reasons. BMW estimate closer to a 300 mile range is possible given an H2 only engine.) The good news is that the H2 engines appear to show less wear then conventional IC engines (no soot to degrade oil), but still the few number of vehicles, their low total mileage and their pampering makes this a little hard to translate to what real world conditions will yield. Still, while one expects the engines of H2 vehicles to perform and last longer then conventional engines, it is not expected that this longevity will be that significant considering all the other expensive subsystems which will likely force the vehicle's retirement, even if the engine is still working.

It is interesting that almost nothing can be found out about this fleet that wasn't written in 2000/2001. I guess they are still running, but BMW certainly isn't saying much about them, which brings me to the conclusion of this long saga.

I think that liquid H2 fueled autos have a snowball's chance in hell of ever getting past the demonstration phase. The technical issues are substantial, the safety issues are substantial, and the cost of resolving both of these makes the vehicles quite expensive and for that extra expense you get a car which burns a fuel that costs more then even today's expensive gasoline and that assumes some major material break throughs occur that significantly reduce the cost of H2 production. Even with a massive H2 fuel tank the car has limited range and worse it has many fewer refueling locations. Initial operations, for probably the first 5 years would have to be confined either to specific cities or high traffic routes. If the engine is designed to handle both gas and H2, which helps to get around the refueling problems then you get an engine which doesn't really run well on either fuel (from an economy or power perspective), requires two fuel tanks and finally even in the quite densely populated areas of the EU 15 it could easily take 20 years or more to get even 1/2 the H2 refueling stations that are considered necessary built and that would still require a 1,200 Euro "tax" if every EU auto was switched to H2, or a 3,600 EU tax if just 1/3 were. That and the fact that a string of of really spectacular or tragic accidents could easily get the whole thing shelved or regulated out of existance.

If H2 is going to power the autos of the near future it will almost certainly be via fuel cells, and then it would most likely be with CH4 as the fuel stock that the H2 is created from. But that's another discussion.

Arthur