Sunday, January 30, 2011

Cars: Electric vs Hydrogen

Greetings Peaksters

       Assuming that the oil crunch is likely to arrive in the next 2 to 5 years  ( )\
, it becomes pretty important to decide how we are going to get around.  Peak oil is a liquid fuel problem after all,  and that means a transportation problem.   In this country anyway,  98% of transport runs on liquid fuels.   

        So what's plan B?    Will we move to electric  vehicles (EV's)  or perhaps hydrogen  (Fuel cell)?   And which _should_ we move to?    "Clean" EV's run on electricity which in this country is about 45% coal.   Lot's of CO2 there.    On the other hand "clean" hydrogen is made from natural gas, which results in some improvement, but probably not enough to meet our climate change goals.  And it would require a whole new infrastructure!

        Decisions!  Decisions!   

Cheap hydrogen cars coming! Good news? Well… by at 11:47 AM on January 30, 2011.

Autoblog Green has the short story of a surprising claim by one car company,Daimler: Fuel cell vehicles to cost no more than diesel hybrids by 2015.
This is terrific news, right? Hydrogen fuel cell cars emit nothing but water vapor, after all. Can’t get much cleaner than that.
It’s not quite that simple, of course. (Honestly, what is that simple in the general categories of energy and climate?)
There’s always the issue of refueling infrastructure when you’re requiring a new fuel for direct mass consumption. And hydrogen fueling stations are anything but cheap, running into the millions for each one, thanks in part to some of hydrogen’s nastier qualities, like that whole “burns with an invisible flame” thing, plus the fact that it’s very prone to leaking.
But let’s be generous and assume that via the Magic Of The Marketplace and/or brute force government subsidies and mandates we build enough refueling stations and in the locations where needed to avoid the classic chicken-and-egg problem. So consider that non-trivial issue trivialized and dismissed with a hand wave.
Where do we get that steady flow of hydrogen to feed that spiffy new refueling infrastructure, and ultimately, the vehicles?
We can make it from natural gas, which is where the vast majority of our hydrogen production comes from today. Surely we can scale that up to meet the needs of these vehicles. I have no doubt we could do that, although that raises the nasty issue of CO2 emissions. When we crack CH4 to get those four H’s, we wind up with that C joining a pair of oxygen atoms and making CO2. And then we have to either sequester it forever (read: depend on bad science fiction for a solution) or make believe it doesn’t exist and dump it into the atmosphere. Playing with the atomic weights tells us that CH4 + 2H2O = 4H2 + CO2 means we’re turning 16 kg of CH4 and 36 kg of H2O into 8 kg of H plus 44 kg of CO2. Oops. Assuming your roughly Civic-size hydrogen fuel cell vehicle gets 70 miles to a kg of H, that means you’re emitting 5.5 kg of CO2, albeit indirectly, for every 70 miles you drive. That’s about 0.17 lbs of CO2 per mile, compared to roughly 0.5 lbs of CO2 per mile for a plain old gasoline car that gets 40 miles per gallon and will probably still cost less than just the fuel cell in an HFCV in 2015, even if Daimler achieves the stunning price reduction it claims. So you’re not saving 100% of the CO2 emissions, merely 66%, which isn’t nearly good enough, given the reductions needed. Double oops.[1][2]
But wait — you just remembered that we can make hydrogen via electrolysis. You probably did it in a high school or college lab at least once, right? Yes, that works, and it avoids the nasty CO2 emissions during the generation process, but at the cost of a lot of electricity. If you take a few minutes to hop over to the reports page of the European Fuel Cell Forum and download Ulf Bossel’s E21 paper, “Does a Hydrogen Economy Make Sense?”, you’ll see a very detailed analysis that shows an EV can travel three times farther than a hydrogen fuel cell vehicle can using a given amount of electricity. And that’s a very big deal, simply because virtually all electrified countries will be very hard pressed to de-carbonize their electricity production in the coming decades, and throwing away two thirds of the travel potential of every kWh of carbon-free electricity (or increasing the demand for carbon intensive electricity) will only make our challenge that much more difficult.
Let me make this so clear that even those addicted to willfully misinterpreting blog posts won’t be able to miss it: I really wish hydrogen fuel cells made sense for motor vehicles. I desperately want them or other technologies to work as well as car companies claim they will (some day), or even better. As much as I like the idea and the implementation of EV’s, I want us to find more and even better solutions to compete with and surpass them. The problem is that the combination of basic physics and chemistry, plus our existing electricity generation infrastructure, plus the overall timing of our situation, means that the answer to both the question in this post’s title and that in Bossel’s paper is, sadly, “No”.

[1] Yes, I’m mixing metric and American units like a psychotic, drunken chemist. I apologize if I made your brain flinch. I tried to use the units that are both most common for each step and most familiar to my largely US audience.
[2] Please note that cracking CH4 to get that hydrogen is a two-step process that no doubt requires a good bit of energy, which will increase the CO2 emissions even further, unless we make some wildly optimistic assumptions. And don’t even get me started on that consumption of 4.5 kg of water for every kg of H produced.


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