Fossil fuels vs. renewable energy sources

[Prebe]

For every 100 kJ worth of crude oil you get 14 to 43 kJ back as fuel products.

For every 100 kJ of electricity you put into electrolysis of water you get 62 to 80 kJ back as hydrogen.

[Cail]

That's raw energy, correct?

In other words, you're getting back 14-43kj worth of refined fuel versus 62-80kj of pure hydrogen gas, right?

If that's the case, I'm surprised. That's contrary to what I've been hearing for years.

[Prebe]

Yes, it's raw energy (or Gibs free energy, implying complete combustion, which is obtainable from both the petrochemicals (combustion engine and the hydrogen (fuel cells)).

I think what you have been hearing takes the transport and presurisation into account, which takes large amounts of energy (exergy depends on degree of pressurisation and length of transport). But these will not be factors in decentralised use.

[Cail]

OK, gotcha.

Now when you say "decentralized", are you suggesting that everyone would have the facilities to convert water into hydrogen and then compress it into their furnace or vehicle?

[Prebe]

No. I am talking about hydrogen being used as an energy storage buffer in connection with variable output non-continuous energy sources like wind and solar power. Low pressur hydrogen tanks placed at the windmill fields for instance, combined with fuel cell facilities. The advantage in fuel cells being, that they can run in reverse in energy surplus and perform the water electrolysis (although with an effectivity somewhat less than the article I quote).

I don't think there is a future for hydrogen cars, mainly due to logistic and energetic problems in treatment and transport of the hydrogen. It would be so much easier to use biofuels, as the infrastructure is allready adapted to transporting oil and alcohol.

If hydrogen cars (or using hydrogen for propulsion) is to have a future, we need to bind the hydrogen in other chemical compounds (tying the hydrogen atoms to carbon dervived from biomass), but this will - almost by default - cost potential energy, diminshing the total effectivity of the process. But as the exergy 14% of one step crude oil destilation (the old method) shows, one should never be afraid of loosing some energy in the process. Especially if the energy input is renewable.

[Prebe]

Prebe, CO2 is CO2 is CO2. It doesn't matter where it comes from. All hydrocarbons, when you burn them through combustion, release CO2 into the atmosphere. And when CO2 is in the atmosphere, it will act as a greenhouse gas. It doesn't matter if they come from fossil fuels or from plant oil. At least this is what I've been lead to believe. If I'm mistaken, then I would like some sort of good scientific articles to presuede me that you're right.

(Emphasis mine)

If that's the case, I'm surprised. That's contrary to what I've been hearing for years.

(Emphasis mine)
Do you see why I placed this in the X-forum

[Avatar]

Good posts Prebe. (Sorry, meant to get back here yesterday, but kept losing my connection to the site.)

There's not much I can say in fact, except that I pretty much agree with you.

And I agree with your original premise as well. If tens of thousands (millions?) of anti-war protestors can't prevent the war, how can hundres (thousands?) of eco-protestors stop alternative energy sources? They can't get an emissions reduction legislated...



--A

[Prebe]

Thanks Av. Thought you'd agree. No worries about not joining before. I learned a lot about oil refining in my research. There are, however, VERY few concrete references to efficiency of oil refining in the scientific litterature (at least the part I can get at), probably due to method protection I would imagine. Or perhaps, because it is an area I am unfamilliar with, I was unable to define the optimal search criteria.

[Prebe]

As promissed, exergy (energy conservation) of alcohol production from sugar cane:
www.csa.com/partners/viewrecord.php?req ... cookie=yes
33.8%

[Usivius]

Resounding 'yes'.