was bound to happen in our time, sooner or later.

[North Shore]

Quote:
But it took way way more energy to do it than you can get back out reversing the process


So?

Quote:
Hydrogen is no answer to anything.


Wrong again.

Maybe you should google more often.

CP, come on man, you can do better than that. Unless you happen to live in a place that has an abundance of hydro-electric power, (and most places don't,) then you are relying on coal, natural gas or oil-fired power plants to produce your energy to electrolyse the hydrogen out of water. because of the inefficiency of that process (~20% springs to mind) then you are better off - emissions-wise to simply burn the fuel that you used for the electricity in your vehicle..

[Lommer]

Stinson, settle down. For the record, I agree with you that hydrogen is NOT a solution to automobile emissions (gravimetric fuel density has no benefit there, and the poor volumetric fuel density poses a big problem). For that application, battery-electric vehicles are a viable solution that do not take the efficiency hit associated with electrolyzing water. However, for aviation, batteries are waaaaay too heavy - despite a light electric powered aircraft being demoed at Oshkosh this year they really have no future in aviation. Hydrogen OTOH, has a fantastic energy density and could actually be beneficial. As Driving Rain mentioned there are serious obstacles to be overcome, but that's no reason not to explore it. The other benefits of reduced NOx, SOx, and ozone emissions at altitude are worth something too. As for producing carbon-free hydrogen, you can either produce hydrogen through renewables and eat the electrolyzing efficiency hit, or you can produce it via methane and utilize CCS (carbon capture and sequestration) because the CO2's being generated at a point source. I'm not a fan of CCS for many reasons not the least of which is cost, but if a price of carbon emissions is established (either through tax or a cap+trade system), then the numbers start to work around $50-$100 / kg atmospheric CO2.

Also I'd like to challenge your assertion that fuel cells produce significant heat. While some heat is inevitable from any energy conversion process, fuel cells actually strip electrons from the hydrogen and use a PEM (proton exchange membrane) to generate electricity directly. Indeed - breaking the carnot efficiency limitations of a thermal cycle are a huge advantage of fuel cells.

Stinson, I also resent your accusations regarding the level of my science eduction. I'm not going to challenge yours because you probably have a better understanding of the energy issue that 80% of the population, and the limitations of written internet communications contribute a lot of misunderstanding. Overall, I'm really just exploring options to reduce aviation's environmental footprint. I know that aviation's footprint is comparatively small compared to other industries, but we are a very visible industry and future carbon legislation WILL target us.


P.S. Thanks for a good post driving rain - on the bright side think how easy it would be to dump fuel!

[ottawa,kan]

I wasn't trying to imply that anyone specifically had a lack of science understanding, just that it looked to me that some people did. Obviously Loomer...you know your protons and electrons. And I wasn't trying to say a lot of heat was produced, just that the end result is similar chemically. But anyway, I sure don't want to get into one of these AV Canada tit for tats. The methanol idea is pretty interesting as a hydrogen source, since it would be capturing current "air" Co2 and returning it right back to the atmosphere, but again, burning methanol and skipping the whole fuel cell seems to make more sense. The carbon sequestration thing (for methane)hasn't been proved to work long term...it may turn out to leak back out of these deep injection wells. And as you say, it's expensive. Anyway...total air transport is less than 3%. Farmers put way way more green house gas into the air as urea evaporates than does the whole transport sector. What we need is a logical and international scheme that INCLUDES India and China ( and the USA of course) to solve this mess. Oh and carbon sequestration credits for tree farmers. God I could clean up if I could get a ton for ton carbon payment for the trees I grow. Buy me a Beaver on floats I would.