Monday 15 December 2008

Top Gears Electic Car Tests

I was very happy to see Clarkson & Co get stuck into testing some real electric cars in last Sundays episode of Top Gear but like many I suspect I was disappointed that the Tesla failed to withstand their thrashing on the track. To be fair though I was impressed that the Stig managed to get it to post a time that beat the 911 GT3. We're still on the bleeding edge of electric vehicle technology but it seems that good electric cars might now actually be possible even if they aren't quite there yet.

I was rather disappointed with the final segment where James May sang the praises of Hydrogen Fuel Cells without actually taking the time to be the nit picking pedant that I know he can be and in the process failed to identify the major flaws in the arguments being put forward by the Hydrogen Economy evangelists. I'd love it if they were right but frankly I can't see H2 being the answer to our fuel problems. Fuel Cells are wonderful technical marvels but those that use H2 are hamstrung by the fact that H2 is godawful stuff from a mechanical and practical perspective.

So while I appreciated the praise of Fuel Cells in the segment I can tell you now with 100% confidence that we will never see Hydrogen as a common vehicle fuel in our lifetime, it will certainly never be used as a direct replacement for petrol\diesel in an internal combustion engine (H2 combustion is fine but suffers from the same Carnot cycle inefficiencies as all other internal combustion engines so it's a dead end IMO) or (as is the case with the Honda) as a fuel source for direct electric conversion fuel cells.

My initial reaction to the aricle was that I was disappointed that they didn't dig into how much the Honda's fuel-cell\H2 containment system cost\weighed and how long it could store it's full tank of fuel because I suspect both answers would have been very disappointing. Also while the Tesla might take 16 hours to charge, at least you can get electricity in most places - H2 fuel pumps exist in about 4 places on the planet so good luck if you are an early adopter outside of SoCal, Iceland or Germany. That detail was entirely glossed over.

And then (as I tend to, I got carried away ranting to myself) so in case anyone is still reading here are my arguments against Hydrogen as a vehicle fuel.

Hydrogen may be ultra clean, carbon free and able to fill a pressurized fuel tank in three minutes but it has a couple of insurmountable or damn near insurmountable problems:

1) Density and by direct correlation Energy Density. Pound for Pound (or kilo for kilo for the metric inclined) it's more energy dense than (say) petrol by a factor of just over three (so three kg of H2 has as much potential chemical energy as 1 kg or so of petrol) but in terms of volume it requires a _lot_ of space. A kg of Petrol takes up about 1.3 litres of space, a kg of liquid hydrogen takes up about 14.5 litres of space. The problem with liquid H2 is that it needs to be either cryogenically stored or stored under immense pressure. The best pressure\cryogenic H2 fuel storage systems weigh about 10x what a fully loaded tank of petrol weighs that would contain the same amount of convertible energy. That additional weight and volume alone make H2 uneconomical.

2) H2 does not transport or store easily. Look at any rocket on a launch pad - the plumes of vapour that comes off those is a combination of the O2 (at -173C) and H2 (at -250C) boiling off because it is just not practical to keep them well enough insulated or pressured to avoid boil off. Petrol\oil evaporates at room temperature but at about 1 billionth the rate that O2 does and about 100x less again than H2 does. 

3) To make H2 you still have to have power in the first place and creating H2 from cracking water is not an efficient process (25-40% at best) no matter how efficient your initial energy generation is. It's a hard thing to do, hard in the sense that it wastes energy that ends up not being recoverable from the Hydrogen that you produce so it's vitally improtant to tackle this part of the system honestly. Ironically almost all of the commercially produced hydrogen today is produced by steam reformation of hydrocarbons so basically at the moment most hydrogen comes from oil that has the Carbon removed (and vented as CO2\CO into the atmosphere) by combining it with steam produced by (you guessed it) burning oil, coal or gas which gives it about 2-3x the carbon footprint of just burning petrol in the first place. Interestingly some nuclear power plants can actually generate "clean" H2 rather than electricity but then all of us nucleophobes will have to change our minds about nukes to embrace that method of generating fuel for cars (mind you, mine is pretty much changed already, sorry Greenpeace).

4) Compressing H2 into a liquid (or freezing it, it's basically the same process) adds a not insignificant additional power burden to the process because of the difficulties in reaching -250C or 700-1000 atmospheres of pressure _and_ keeping the damn stuff in that state while you store it and move it across continents.

5) An accident involving a H2 fueled vehicle has a non trivial chance of being an instant bomb. It is quite simply not a safe fuel. Sure much has been done to make more robust fuel tanks but right now I would no more get into a car on a public road with a H2 tank in the boot than I would play Russian Roulette with a revolver with 6 full cylinders. Especially on roads full of the sort of people who need to be reminded that objects in their mirrors may be closer than they seem. Safer H2 fuel tanks == stronger tanks == heavier tanks == more expensive tanks and no doubt they are making huge progress there but all of those efforts detract from efforts that should be being made into making the fuel delivery and conversion processes more efficient. And most importantly those safe but big,heavy and bulky fuel tanks make the vehicles they serve significantly more inefficient at the point where it matters most - on the road.

6) James May claimed that in the glorious fuel cell'ed future he foresaw of the car with no moving parts (eh? what about the wheels? suspension? high pressure\cryogenic fuel pumps?!!)  would need no servicing but any vehicle that has a high pressure (700 atmosphere) fuel tank containing the smallest molecules in the universe (and that are explosive when leaked into our atmosphere) is effectively a dormant bomb and as such will need very, very careful proactive maintenance on a very regular basis in order to avoid turning into an actual bomb. 

7) Long distance (more than a couple of km) bulk H2 transportation systems leak about 70-90% of the initial H2 because the molecule is so bloody small and the pressures are so high that it just leaks out of every single joint, valve and connection like water through a leaky tap. Stored H2 in cylinders escapes at about 10x the rate that more normal gases (like CO2\N2\O2 do), the tanks have to weigh more and are so burdened with transportation restrictions due to safety concerns that I cannot see that anyone will ever produce an economical H2 version of our large scake existing petrol distribution mechanism. The physical challenges involved in storing and transporting liquid H2 are not the sort of things that lend themselves to massive changes due to innovation and unless it can be made 10x or more easier (ie cheaper) it will not be efficient enough to be realistic.

That said I do think that the Fuel Cell car idea is the right track but the "clean" power source of the near term future is far more likely to be Fuel Cells powered by methanol ( which is basically just another hydrocarbon). In the fuel cells themselves it runs to about 30-50% the efficiency of pure H2. The fuel handling mechanics are vastly simpler - there's no need for cryogenic\high pressure storage at any stage in the proiduction\distribution chain and the fuel can be stored\transported as simply and for as long as petrol. The challenge is producing methanol cheaply from air - again all you need is power at the front end (to convert 2 CO2 and 4 Water molecules into 2 CH2OH molecules and 3 O2 molecules just add enough power)  and you have an energy storage fluid that is totally "clean" given that you got the components from the atmosphere in the first place. From the numbers that I've seen methanol will always be 2-3x easier to produce from scratch than H2. Note in both cases the "fuel" is really just a transportation mechanism for energy produced elsewhere so where that initial energy comes from is the real green challenge in any case.

Another couple of source fuel options for fuel cells are either Hydrides (in some liquid or fluid powdered form) or Hydrated Clathrates (ie somewhat frozen slushies of some material with lots of H2 dissolved in them) that might beat out petrochemicals but given that liquid petrol (or methanol) contains about 50% more hydrogen atoms (at 116g of H atoms) per litre than pure liquid H2 (at about 70g of H atoms per litre) I honestly cannot see anything better than the evil petrochemicals at storing energy that will be chemically extracted from Hydrogen. And again the clathrates\hydrates need some practical source and distribution mechanism for the raw H2 that they contain and so share many of raw H2's drawbacks. They dont look like winners to me but at least they have some good answers to the worst of H2's problems.

Finally the FCX Clarity that James May waxed lyrical about has a total H2 storage capacity of 5kg of compressed H2 (about 171 litres at 350 atmospheres pressure) in a car weighing 1.7tons.  The fuel cell generates 100kw (134 horsepower) although it does so with a conversion efficiency about 3x a typical car's ability to turn petrol into power so the 5kg of H2 is equivalent to about 45 litres of Petrol. The Fuel Cell alone though is insufficient to power the vehicle in a sustained sense so it too includes a couple of hundred kg of the LiION batteries to store additional juice so that it can actually climb hills and actually accelerate so in that sense it is hampered by the weight of those fat batteries that the lads had so much trouble with in the Tesla. I've tried to find out the total mass of the fuel storage\handling\fuel cell of the FCX but Honda haven't made that easy to find, I suspect it's more than 60% of that total mass though. By comparison the the Tesla can convert energy to deliver about 248 hp (185kw) at the wheels and weighs in total about 1.1 tons. 

Personally I don't see that the difference between the two is as much of a quantum leap as the lads made out - what it needs is a runabout scale DMFC to replace about 25% (say 50-60bhp) of those batteries, a battery improvement of about 25% in efficiency and possibly a bank of improved ultra-capacitors to capture a higher percentage of regenerative braking power to turn it into an actual practical car running on a practical fuel which the FCX will never be while at the same time being a reasonable sports car. And of course a drop of 75% in the price tag will have to happen whether we're talking about the FCX, the Tesla or any of the others in the current array of first generation genuine electric cars.

Even without any major improvements in efficiency a DMFC (Direct Methanol Fuel Cell) would be about 2-3x less energy efficient at the fuel cell point (20-30% vs 40-60% for an efficient pure H2 Fuel Cell) but H2 has the transport and storage losses that are as I've said somewhere from 70-90% whereas methanol has transport\storage losses measured in the fractions of a percent over continent wide delivery distances and months of time so unless someone comes up with a magic way to handle H2, something like Methanol will easily beat out H2 as long term sustainable fuel. And it's just as safe as petrol and can be delivered using the same infrastructure too.

Just my 2cents.  Well 2002 cents I suppose. Now I need to get back to reading about SAN storage and earning a living.