RE: Sheer's Fuel Cell Rant

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

> 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%.
Neglecting any energy that goes to cooling fans or other loads, you
still have to account for the efficiency of the power source used to
convert line voltage to the DC fed to the cell.  Even at 90% efficiency
for this supply, the system efficiency drops to 81%.

> 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)
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.

Cheers,

Roger.