RE: Sheer's Fuel Cell Rant

["VanDerWal, Peter MSgt" <vanderwp@fhu.disa.mil>]

> > Marketing hype and misdirection.  They state that 90%
> > efficient electrolysis is possible, they don't say that their
> > system is this efficient.
> 
> A bit strong, I think.  I believe their electrolysis cell operates at
> the efficiencies they claim, but the *system* efficiency is not 90%.

Ok I'll bite.  What makes you think that their cells actually operate at
that efficiency and if they do why don't they actually say that?
They NEVER claim their cells are this efficient, only that 90% is practical.
I'd think if their cells actually were 90% they'd be boasting about it.

> > Theoretical efficiency is near
> > 100%, if you can do it without producing any heat.  If you
> > read that article it mentions their liquid electrolyte helps
> > with heat removal.  If they are generating enough heat that
> > they have to think about how to deal with it; they aren't
> > anywhere near 100%.
> 
> It is not true that they must be far from 100% efficiency to have to
> worry about heat removal.  A 100kW electrolysis cell operating at 90%
> efficiency still has 10kW of waste heat to deal with, and this is not
> inconsequential.  Likewise, the volume in which the heat is generated is
> also a concern: a 90% 1kW cell the size of a kleenex box is dissipating
> 100W, and I can assure you that 100W is sufficient to elevate that box's
> surface temperature well above allowable limits (usually about 60C)

Where did you find a 90% efficient electrolyzer that was only as big as a
Kleenex box?

Electrolyser has a unit that produces 0.5 cubic meters per hour, at 100%
efficiency that would be 1.75 kw.  Not quite twice your figure of 1 kw.
Assuming it's 90% efficient that would be 1.94 kw.
This unit weighs almost 2 tons (3,950 lbs).   Interestingly enough they say
it requires a 220V 30 amp circuit (assuming they only pull 20 amps that's
4.5 kw, or roughly 40% efficient)
http://www.stuartenergy.com/industrialprod/Models.asp

Getting back to your point I seriously doubt that 200 watts of heat is going
to have much effect on 2 tons of equipment.

Let me know where you found that Kleenex box size electrolysis machine that
could run 1kw at 90% efficiency.  I'm interested in buying one if it doesn't
cost the gross national product of a small country.

> unless some attention is given to cooling.  As I recall, Steward is
> making electrolysis cells in the 5kW range, so even at 90% efficiency
> there is 500W of heat generated in the cell itself, and it may well be
> that cell temperature affects the electrolysis process (e.g impacts
> efficiency, or alters the current/voltage requirements, etc.) in such a
> way that it is advantageous to minimise temperature rise even if the
> heat is not otherwise of concern.
>