Hydrogen Power

[arcticpenguin]

OK, assuming you solve whatever issues you have with nuclear waste, etc.

I then see H2 as being competitive with electrical power. You could use the nuke plant to crack H2, or you could use it to generate electricity.

In either case you have to distribute it somehow. For electric, you pump it onto the existing grid. For hydrogen, you have the choice of whether to crack the H2 right at the nuke plant, then pipe it and ship it around, or distribute electricity to remote H2 plants. In either case you have to build infrastructure to get the H2 to end-use points, but we could assume that by the debate technique of 'fiat'.

It then comes down to which system works best for consumer vehicles.

H2: need to overcome engineering problems with storing large amounts of H2. Need to improve fuel cell performance. Advantage: can refill quickly.

Electric: Disadvantage: Takes a while to recharge. Advantage: this could be done at home or at a 'filling station' (if it becomes fast enough) Would need to improve capacity => driving distance.

Other important issues:
which technology lets you drive furthest on one fill, and
which is more affordable.

There are so many contingencies in there that I'm not sure which would win at any given future date.

This question of H2 damaging the ozone should be looked into; right now there's just one or two preliminary reports.

 

[Chad Noles]

Here are a few sources relating to fuel cells and/or hydrogen....http://www.mrsolar.com/
http://www.homepower.com/
http://www.ballard.com/
http://www.fuelcells.org/
http://www.metallicpower.com/
http://www.protonenergy.com/
http://www.stuartenergy.com/
http://www.electrolyser.com/
http://hydrogenappliances.com

So many answers,so few questions.

 

[toddjh]

Re: HIJACK

So, back to the original, what's wrong with using Nuclear power to crack H2O? Well?

It seems to me that a variety of people are now trying to rain on the idea of H2 without really thinking about it.

Who said there was anything wrong with it? My main concern would be whether it's practical to run a reactor hot enough to crack a sufficient amount of water to cover the public demand -- if everybody's car has a fuel cell, you're talking a lot of H2. If not, you're just using electricity to do it, and it's no different from using a conventional power plant to do it.

Ideally, I'd like to think that we'll have fusion plants in the moderately distant future. If they work well, power might be cheap enough that large-scale hydrogen production is perfectly affordable, in which case we could have an all-hydrogen economy with no emissions across the board.

Jeremy

 

[Chad Noles]

Just a quick thought on the recharging thing.....Do any of you guys barbeque?You know those 20 gal tanks that they just switch out?Why wouldn't "stations" just use a swap out policy to
exchange canisters of H2 for vehicles?Seems more reasonable to me instead of the "filling" concept we are used to for vehicles.

 

[toddjh]

This question of H2 damaging the ozone should be looked into; right now there's just one or two preliminary reports.

I wouldn't have thought that H2 would last long enough in the atmosphere to do any harm. If I recall my chemistry classes, the H2/O2 reaction occurs at well below room temperature, only very slowly compared to the explosive reaction we're used to. Are we talking about dumping millions of tons of H2 into the air or something?

I also thought there was quite a bit of photodissociation of water going on at high altitudes, creating H2 temporarily. I wonder if the amount of leakage we'd produce would even come close to that.

Jeremy

 

[arcticpenguin]

I wouldn't have thought that H2 would last long enough in the atmosphere to do any harm. If I recall my chemistry classes, the H2/O2 reaction occurs at well below room temperature, only very slowly compared to the explosive reaction we're used to. Are we talking about dumping millions of tons of H2 into the air or something?

I also thought there was quite a bit of photodissociation of water going on at high altitudes, creating H2 temporarily. I wonder if the amount of leakage we'd produce would even come close to that.

Jeremy

This was in the news a couple weeks ago. Here's a thread: http://www.randi.org/vbulletin/showthread.php?threadid=21406

 

[jj]

Re: Re: HIJACK

Who said there was anything wrong with it? My main concern would be whether it's practical to run a reactor hot enough to crack a sufficient amount of water to cover the public demand -- if everybody's car has a fuel cell, you're talking a lot of H2. If not, you're just using electricity to do it, and it's no different from using a conventional power plant to do it.

Ideally, I'd like to think that we'll have fusion plants in the moderately distant future. If they work well, power might be cheap enough that large-scale hydrogen production is perfectly affordable, in which case we could have an all-hydrogen economy with no emissions across the board.

Jeremy

Well, I'm still not convinced that we can't ship H2 via the present natural gas system. Yes, it would require a few refits, but would it require new piping? Yes, I know about hydrogen embrittlement. I also know what 1920 gas pipe is like nowdays.

 

[Leif Roar]

Yes, of course, but electrolysis has voltage/current requirements, doesn't it? Or at least I bet it's more efficient at higher current. The output from PV cells is extremely variable. Better to charge a battery and get a more controlled output for the electrolysis.

Actually, I would suspect that it would be more sensible to use capacitators for a "first level" energy storage. But even if you use a small regular battery for this, you will not have to use regular batteries (which have serious weight problems) for the main energy storage.

I'm curious what you have in mind. Can you give me an example of a setup where you think a regenerative fuel cell would be preferable to either a regular fuel cell, an internal combustion engine, or a solar-fed battery system?

Jeremy

Perhaps not the best advertisement, but the recent Helios crash (http://news.bbc.co.uk/2/hi/science/nature/3025242.stm) occured while testing an experimental rechargeable fuel-cell. (At the moment there doesn't seem to be any reason to suspect the fuel-cells caused the crash in any way.)

 

[arcticpenguin]

Well if we're going to postulate improvements in hydrogen storage and fuel cell performance, I think it's reasonable to postulate that competing technologies will also improve over time. In particular, electrical batteries. Current rechargeables are indeed heavy because they are filled with heavy metals. Perhaps improvements in the rechargability of lithium or other lightweight batteries will occur.

I don't think capacitors can compete with batteries for capacity, and certainly not for long-term storage. They store the energy as static electricity, not chemical potential, and there tends to be leakage over time.

I think the current 'hybrid' vehicles use capacitors to store electricity, I'm not sure what the capacitance or voltage ratings are.

 

[RedCoat]

Re: Re: Re: Hydrogen generation

Maybe, but the Japanese manage to do it fine, and seem to be able to sell hybrid vehicles in the US, why can't we? There's other things that kind of make you wonder, like GM recalling its leased electric cars and refusing to let the leasors buy them. I'm not claiming conspiracy, but I do think that Detroit does not take fuel efficiency very seriously.

Cleaner isn't enough, they've got to be more fuel efficient as well. And in that regard we're not making any significant progress (SUV's have offset the gains that were made), and the standards are hardly moving at all...

There are actually a lot of differences between building cars in japan and building them in the US. Without going in to details, suffice it to say that there are vehicles built in Japan that COULD NOT be built in the US, and vice versa. Likewise, for a number of reasons, some vehicles can be profitable for one manufacturer and a complete loss for another. There are a lot of variables (plant location, supplier contracts, union labor, capacity, dealer network, tax codes, etc.) that can influence the business case for certain vehicle. Right now, some of the Japanese companies have *decided* to accept taking a loss on hybrid vehicles. This is (presumably) done as an R&D effort, just like the way GM did the electric car, which was known to be a negative-profit vehicle but was done as a learning venture.

If I had to guess why GM bought back the (lease-only) electric vehicles it is because (by law) manufacturers are required to provide service parts for N number of years after production of a vehicle has stopped. The parts for the electric vehicle were bloody expensive to begin with, and producing parts for a very-low-volume non-profitable vehicle would have been a huge waste of money. Scrapping the vehicles was probably cheaper and easier, and prevents potential future lawsuits, since the high-milage failure modes of an electric vehicle are not known the same way they are for regular vehicle. Imagine if a battery pack leaked on a electric car twenty years and 600,000 miles later - believe it or not, this could be the basis of a lawsuit.

Regarding SUVs - the car companies would LOVE to get milage to be better. Since all the manufacturers are constrained by CAFE requirements, they generally "give away" (sell at a loss) cheap high-mpg vehicles to enable the sale of profitable low-mpg vehicles. Improving fuel economy allows you to sell more high-profit vehicles. The market, however, has an apparantly endless fascination with heavy vehicle with powerful engines. No matter how big and how powerful, there is always a market segment that will pay a premium to get a bigger vehicle with a more powerful engine, and to ignore this market is to essentially give this profitable segment to your competitors.

Finally - may people do not realize that safety standards become more stringent all the time. The gov't keeps upping the speed of crash tests, requiring more content (more air bags, anti-lock brakes, stability control, and now - pending - anti roll over devices) that continuously add more weight and equipment to the vehicles. The market keeps demanding more and more while paying less and less. Since you can't have everything, car companies design around whatever the market is willing to sacrifice. In the US, this happens to be fuel economy. People would rather have a fuel-inefficient vehicle than lose their 14 air bags and quadruple-five-star crash ratings.

If you really want to get companies to build more effiecient cars, the best thing you can do is BUY ONE.

(For the record, I drive a relatively small, efficient 2-door VW golf, and not an SUV.)

Once again, I hope this doesn't sound like a rant, but (from my point of view) people LOVE to beat up the car companies, when all they're doing is building what the market asks for.

 

[jj]

Actually, I would suspect that it would be more sensible to use capacitators for a "first level" energy storage. But even if you use a small regular battery for this, you will not have to use regular batteries (which have serious weight problems) for the main energy storage.

And just how much does the H2 storage weigh per unit of energy?

 

[Leif Roar]

And just how much does the H2 storage weigh per unit of energy?

It's been a long while since last I've opened my chemistry books, and I suspect there's an easier way of calculating this - but here goes, using bond energies (which I don't think is 100% correct, but should be a good approximation).

The reaction we're looking at is 2 * H2 + O2 --> 2 * H2O. We have three different covalent bonds involved: H-H, O-O and O-H - they have the following bond energies:

H-H : 432 kJ / mol
O-O: 146 kJ / mol
O-H: 467 kJ / mol

This bond energy needs to be supplied to break a bond, and is released when a bond is formed. For this reaction we need to break 2 H-H bonds and one O-O bond, and 4 O-H bonds will be formed.

So; dH = 2 * 432 + 146 - 4 * 467 kj/mol = - 758 kJ/mol O2

In other words, this reaction produces 758 kJ per mol O2. (dH is negative since it's a measure of the energy that needs to be added to a reaction.)

Two mol of hydrogen plus one mol of oxygen weights 36g (since we're talking about a rechargeable fuel cell, we have to inclued the weight of the oxygen since we don't get that from the air), so the energy output is 758 kJ / 36 g = 21 kJ / g

21 kJ / g = 21 000 kJ / kg = 21 000 / 3600 kWh/kg = 5.5 kWh / kg

This is of course the absolute maximum energy density you can achieve - as it doesn't take into account energy loss, or the weight of anything else but the reactants. For comparison, the practical (not the theoretical maximum) energy density of a lithium battery would be on the order of 200 - 250 Wh/kg

Edited to fix a error in my calculations, and to add: On second thoughts, I think I might have done something wrong. I'll need to read up on my chemistry a bit. Anyone who knows anything about this, please correct me in the meantime.


Edited yet again to add:

Okay, I've obviously made a serious blunder somehow (perhaps that I've used the bonding energy even though the final product is not a gas). Using the standard enthalpy of formation, I end up with 4.40 kWh / kg - which I believe to be correct.

 

[jj]

Edited to fix a error in my calculations, and to add: On second thoughts, I think I might have done something wrong. I'll need to read up on my chemistry a bit. Anyone who knows anything about this, please correct me in the meantime.

In any case, what is the energy density of the STORAGE, including the hydride, etc...

Not just the H2.

 

[Leif Roar]

In any case, what is the energy density of the STORAGE, including the hydride, etc...

Not just the H2.

From http://www.llnl.gov/str/Mitlit.html:

The team looked at flywheels, supercapacitors, various chemical batteries, and hydrogen- oxygen regenerative fuel cells. The regenerative fuel cell, coupled with lightweight hydrogen storage, had by far the highest energy density--about 450 watt-hours per kilogram--ten times that of lead-acid batteries and more than twice that forecast for any chemical batteries.

 

[daver]

From http://www.llnl.gov/str/Mitlit.html:

The team looked at flywheels, supercapacitors, various chemical batteries, and hydrogen- oxygen regenerative fuel cells. The regenerative fuel cell, coupled with lightweight hydrogen storage, had by far the highest energy density--about 450 watt-hours per kilogram--ten times that of lead-acid batteries and more than twice that forecast for any chemical batteries.

That's a 5,000 psi tank. About 300 atmospheres. You'd want the tank to hold on the order of 10 kg of hydrogen in order to have a cruise range comparable to a gasoline car. If my back-of-the-envelope figures are correct, that's about a 0.25 cu meter tank. The article suggested that it would take 5 min to refuel one of these at the pump, but it's going to require a trained refueller (no self-serve). Someone in a different thread suggested swapping out the tanks (like the LP tanks for barbecues). In which case you'd probably want two or three smaller tanks, so you could empty the tanks before exchanging.

The article didn't mention the weight of the tank (or i missed it if it did). I'd guess relatively light--on the order of 100 lbs, but that's a completely uneducated guess.

 

[TillEulenspiegel]

Or not. The maximum power you can generate by sun-light is 1.8 horsepower per square meter (and in real use you'd average a lot less because of cloud-cover, time of day and year and lattitude) - if you want to generate more power by sunlight, you'll have to somehow increase the energy output of the sun.

A car would need many square meters of surface of photo-electric surface to generate enough power to be equal to even a small gasoline powered engine.

Your correct Leif, but for some reason the methodology has gotten screwed up as people are inferring statements that I never uttered, they seem rather more interested in argument then discussion or enlightenment. The ONLY thing I posted was about the effacacy of the closed loop RFC as VS. the efficiency of I.C motors and in order to make the process of application more accessible, used the car model as an illustration ( with the disclaimer that i was not attempting to BUILD such a car). There was no implication on my part as to use solar cells to do anything other then to recharge the storage batteries( and supply incidental current to the FC.) . I say so in a previous post. I provided direct links to both the DOE and (because someone asked, tho it doesn't appear this person is a chemist) , one to the Journal of the Electrochemical Society and a page of government listed links to the relevant sites.

As far as the phrase "runs on"the attempt was to be general in speech . not deceptive. Kinda like asking what does a waste incinerator/power turbine run on? Waste?, ya but the waste is just burned..it doesn't run any thing. Heat? No that just heats water in pipes. Water?, no because the water is basically static until the heat hits it then it just turns to steam .. Steam? well it does run past a turbofan imparting a force moment in the turbine..so are you wrong to say that the system runs on garbage because it's actually after many steps that steam turns a turbine? Over simplistic , but I'm sure you see my point.

Till:"The base components needed for the system to function is water ( not O2 and H ) and electricity. The water ( pure water yes ) supplies the constituent elements that are separated to O and H, solar cells supply partial E ( to both the cell and the charging system )and the storage batteries provided storage and current on demand.. Occasional charging by house current ( courtesy of the local power barons) is a given but is nominal ..now..with the technology at its infant stage. The main thrust here being one of efficiencies not of brute force"

Now is there anything in that statement that is Wrong?, Misleading?, Outragious? Exclusive of fact and based on opinion? No.

Now compare this idea of a self contained system that requires a minimum of maintenance, that excludes both the specter of huge government infrastructure and interference. whereas all the hydrogen as fuel prospect,entails all the boogiemen of nuclear science, hazardous storage and transport of the product. And the inevitable stranglehold of big business. Which one seems to make more sense as an investment in future power schemes? (both in automobiles and for the home)

So, now I just must remember to avoid small birds that have frozen asses and screech without making sense.


P.S.
Just saw your post Leif, good explaination for understanding , but the info is actually 6 years old now. Significant improvements have been made in the past 2 yrs. Maybe Ill surf and look to some of my old sources and post um'

 

[arcticpenguin]

blah blah blah

Translation: "I made misleading statements and failed to back up my position, but now that someone else has done so, I don't understand why it wasn't clear to everyone else all along, so I will blame them for my failings"

 

[NoZed Avenger]

That's a 5,000 psi tank. About 300 atmospheres.

Is there an impact on safety issues here? I know a problem with some natural gas vehicles is that ithe fuel is held under pressure, and an undetected leak could effectively spread a rapidly burning and highly inflammable mist into the nearby, oxygenated air.

In layman's terms, all the ingredients for a really good incendiary. And the pressure means that it could spray out in a 4-5 block radius before igniting.

Now, cities still use these vehicles (but do not allow untrained drivers to handle any of the refueling), so it may be safer than it sounds. Is this comparable? Is it nothing to worry about?

 

[jj]

Is there an impact on safety issues here? I know a problem with some natural gas vehicles is that ithe fuel is held under pressure, and an undetected leak could effectively spread a rapidly burning and highly inflammable mist into the nearby, oxygenated air.

Well, 5000 PSI in a tank strikes me as explosive if it's 5000 PSI worth of Helium, or Neon, let alone if it burns...

What I noticed in the 'regenerative fuel cell' article was that it requires FUEL, by the way.... It doesn' t just cycle water/H2/water all by its lonesome, it wants fuel, in the form of H2. In that 5000 PSI container.

 

[NoZed Avenger]

Well, 5000 PSI in a tank strikes me as explosive if it's 5000 PSI worth of Helium, or Neon, let alone if it burns...

What I noticed in the 'regenerative fuel cell' article was that it requires FUEL, by the way.... It doesn' t just cycle water/H2/water all by its lonesome, it wants fuel, in the form of H2. In that 5000 PSI container.

It certainly SOUNDS like a safety issue, and the spreading of the hydrogen afterwards is icing on the cake.

/orders asbestos underwear