On Tue, Jul 29, 2008 at 03:37:30PM +1200, Apptech wrote: > > > I don't think that it is possible to compare hydrogen to a > > battery in such a > > direct way. > > You can. They are directly comparable. In both cases and > energy source is used to "charge" a medium or store energy. > In all comparable by energy storage by chemical reaction and > using molecular bond energy. NimH, LiIon, LA, H2, .. . > In the case of H2 you could use eg a fuel cell as the output > device to make the comparison more obvious. You could also > build the charger and fuel cell into one unit (or car) if it > helps. Then it would be electricity in and electricity out, > like the other batteries mentioned. If charging a battery and electrolysis had the same efficiency there is the energy needed to compress and liquefy the H2. This is why I said that the comparison is not so good. > > Hydrocarbon fuels not derived from petroleum may be > > available in the > > future. > > Certainly. And *producing* all such fuels will require > storing energy into them, or using energy which is already > there and which could be utilised in other ways if desired. > eg much organic trash can be converted to hydrocabons > suitable for fuel. But it can also be burnt directly to > release energy, if desired. > > >> Of course. Would you expect net energy out of eg a car > >> battery (lead acid . NimH/LiIon) ? > > > No I wouldn't, but I think the battery would be better in > > this respect than > > hydrogen. > > There is no reason to think this must be so. It MAY be so in > some implementations, but not in all implementations. If metal hydrid systems improve you're right. The compressing, liquefaction, transport, and storage of hydrogen which is what would be done currently is what makes other technologies more promising. Hyrdogen on demand would only cut out the transport and some of the storage inefficiencies. > >> > Hydrogen's properties require you to spend more energy > >> > than you can > >> > earn, > > >> Of course. It's an energy transpirt medium. For Alice to > >> argue this several times over makes it seem that she is > >> trying to con stupid people, or mislead ignorant people. > > > Don't you think she is trying to make the point clear by > > repeatedly stating > > this? > > Yes. I do. And the point is misleading to the point of being > invalid every time that she makes it. Yes, there are some > sources of energy rich materials which can have there > Hydrogen liberated for net energy gain. But they are largely > in the same area as petroleum - finite resource. When you > get to grown bio resources you are storing energy in them. > If this is by eg using sunlight with eg algae the process > may be low effort andf low pain etc - or may not. But it's > still storing energy in the system from another energy > source. Maybe the author should have stated that this problem is common to every energy transport system; I don't think that would have been necessary though. The author's point is that hydrogen is a poor energy transport medium. > >> > because in order to get it you must overcome water's > >> > hydrogen-oxygen > >> > bond, > > >> It's usually called "charging the battery". > >> ALL secondary batteries have this propery. > > > Of course, but to what extent? > > 100%. In all cases. > Some chemistries may have a primary energy component due to > using "partly charged" chemicals (to coin a concept) in > their use, but after the first cycle it's all energy in >= > energy out. Oh, I wan't clear. Sorry. What's the efficiency of charging a battery compared to hydrogen electrolysis? Here are links to some of what I found: http://www.batteryuniversity.com/partone-12.htm http://www.powerstream.com/NiMH.htm www.sandia.gov/pv/docs/PDF/batpapsteve.pdf www.qsinano.com/white_papers/2006_09_15.pdf It seems that charging and electrolysis efficiency is about the same, around 70-80%. Though the first link claims 99.9% for Li-ion, which seems too incredible. > >> > and transport hydrogen to the destination. > > >> And? This is about a portable energy transportation > >> medium. > > > Even after petroleum has been transported somewhere the > > net energy available > > is still positive, with hydrogen this isn't true and may > > not be true for > > whatever fuel we use in the future. :( > > ANY energy storage medium must by definition have a net > energy deficit. All secondary batteries are prime examples. > Petroleum ONLY works becvause we are not factoring in the > energy used to "charge" it originally when the oil etc was > made. Agreed. The energy in oil and coal was deposited millions of years ago, so it's a bit easier to leave that number off the balance sheet! > >> > It doesn't matter if all of these problems are > >> > solved, or how much money is spent. You will use more > >> > energy to create, > >> > store, and transport hydrogen than you will ever get > >> > out > >> > of it." > > >> There she goes again / still !!!! > >> It's a battery. A BATTERY. > > > It's a very poor battery, if you want to call hydrogen > > that. You lose energy > > to generate H2 (70% efficiency from electrolysis), > > Liquefying the gas uses > > ~35% (65% efficiency) of the available energy. > > No reason for electrolysis to be that low. > OTTOMH >90% is doable. I've not seen anyone claim more than 80% for electrolysis efficiency. The US DOE has set an efficiency challenge at 75%, so a lot of work is still needed. > NOBODY is seriously suggesting using liquid Hydrogen for > mobile end use. Great idea though !!! :-). > For mass transport maybe. > BUT even that can be improved if you are keen enough by eg > coolth heat exchanging at the destination. Such an > interesting spinoff is liable Too much for this sort of > discussion ... . > > > So if using a nuclear power > > plant that is 35% efficient > > I don't think that % efficiency is usually applied to > fission stations. Efficient relative to what? Total > potential energy. Or ... ? Good question. I would think it would be the standard n=W/Q_h efficiency. Matthew -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist