Friday, November 03, 2006

H2 Fuel Cell Vehicle Question

I asked the question on AHF what the impact on local climates would be if all the vehicles on the road were using hydrogen instead of gasoline. we already know that cities produce their own local weather (big hot spot in teh atmopshere...locally). I was curious what might be the consequences of all those cars putting out a nontrivial of water vapor into the local atmosphere. I didn't get any responses. (I also munged the title with a typo too...doh).

So, I went digging around a bit. I found the specs on the GM Sequel: note, I am going to mix and match unit types, so deal. This is the hydrogen fuel cell vehicle set to start being sold in a couple years. The storage capacity of a Sequel is 8 kg of hydrogen according the GM site. This is good for 300 miles of travel. That means, and I am sure that Suzanne will eat me for any miscalculations, we will get about 72 kg of water vapor from a single tank of H2. We seem to refuel once per week for my wife's car, so we'll use that as our benchmark. For the SF Bay area that means that we would be putting about 432,000 tons of water vapor into the air around here. Or Phoenix would get around 95,112 tons. Or El Paso would get around 43,200 tons.

This is per week. And assuming that everyone was driving a Sequel.

So what changes would we see? More rain? Just more misery from the humidity? More, stronger wind currents since wetter air is lighter?

I can't believe that there would be no effects! That's lotsa litres of water!

1 comment:

Suz said...

As far as I can tell you got your stoichiometry correct. However, there is something that you missed regarding your concern about the excess water being produced. I'm not going to flat out tell you what it is, but I'll help you along the path to figuring it out on your own.

The products for *complete* combustion of a hydrocarbon (petrol or gasoline) are _____ and _____.

If you'd like to get even more technical, the products of *incomplete* combustion of a hydrocarbon are _____, ______, _____, and _______. The extra products are why fuels are oxygenated in certain areas of the country for certain times of the year.

Note that these are not the only products, just the ones that we are concerned about with relation to the environment. But, the answers for the first two blanks are why you shouldn't be quite so concerned with the water from hydrogen cars.