RE: Sheer's Fuel Cell Rant

["Roger Stockton" <rstockton@delta-q.com>]

> 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.

They are and they do; from Stewart's website:

"Stuart's electrolysis cell and surrounding system technologies have
undergone significant development and improvement over the last decade,
including increased energy efficiency and reduced capital cost. The
Corporation's new DEPT electrolyser, using newly-developed
electro-catalysts, has demonstrated energy efficiency greater than 90%
in multi-kilowatt electrolysis cells, up from its pre-DEPT energy
efficiency of approximately 80% at the same operating conditions of
temperature and current density."

> 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).

If you check Stewart's website you will find pictures of their Personal
Fuel Appliance(TM) protoypes being used to refuel various fuel cell cars
(Frod, Honda, etc.)  The complete unit is between the size of a bar
fridge and a small range.  No specs are offered as to power output or
weight, but I think it is fairly safe to assume these wheeled units are
in the few 100s of lbs.  I believe they are the ~5kW models, and the
electrolysis cell itself is obviously smaller than the entire unit,
hence my suggestion that a 1kW *cell* alone could be about the size of a
kleenex box.

> 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)

Yes, and this is the *overall* efficiency of the unit, not just that of
the electrolysis cell.  A better estimate of the overall system
efficiency for one of their large industrial units is their quoted
figure of 5.9kWh/Nm^3 of H2.  If I correctly understand you to suggest
that 1 m^3 of H2 represents 3.5kWh, then this is an overall system
efficiency of 59.3% *including compressing the H2 to 200-5000psig*.

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

Note that the point was not whether a cell the size of a kleenex box
exists, but just to illustrate that it is both the absolute amount of
heat to be dissipated and the volume/surface area available to dissipate
it that are important.  The electrolysis cell is just one component of
the total piece of equipment and the heat generated in it *may* well be
significant relative to the size and heat dissipation capability of the
*cell*.

Cheers,

Roger.