From: kare@sirius.com (Jordin Kare)
Newsgroups: sci.space.tech
Subject: Re: How cool is water?
Date: Wed, 05 Nov 1997 23:17:54 -0700

In article <EIprH0.6u3%spenford@zoo.toronto.edu>, Henry Spencer
<henry@zoo.toronto.edu> wrote:

> >What I really would like to know is the feasible power efficiency of
> >the entire H2O -> H2,O2 -> H20 loop at low and high rates.  Is this
> >cycle considered to be a "good" battery?
>
> Yes and no.  Under the name "regenerative fuel cell", it's been seriously
> considered for applications like night-time power for a lunar base.  It's
> acceptably efficient; its major wart is that storing H2 and O2, especially
> H2, is a pain.  Cryogenic refrigeration systems are complex and have many
> moving parts, and storage as compressed gas is impossibly heavy.

There's work going on at LLNL on using regen fuel cells with gaseous
storage for a variety of applications.  It's not impossibly heavy
with modern high performance composite tanks.  A key technology
developed by LLNL is "bladder-lined" tanks, in which the carbon fiber
composite layers are wound on a
thin plastic bladder in place of a relatively heavy aluminum liner.
The bladder can be made impermeable to hydrogen.

The technology was initially developed for the Pathfinder solar-powered
aircraft project.  The idea was to store energy to stay aloft at night
in the form of H2 and O2, electrolysed from water during the day.
The neat trick was that the composite "tanks" were the main
wing spars, and thus (nearly) free.

Current interest centers on use for an electric car (which can
either be recharged like a battery car or quickly refilled from
a hydrogen supply), solar-powered aircraft, and selected
space missions in which the vehicle can be launched with a load
of water, electrolyse it (slowly, over the mission life), and use
the stored H2/O2 for both
electricity generation and
short bursts of high thrust propulsion.

The project leader is Dr. Fred Mitlitsky

Jordin Kare