RE: Sheer's Fuel Cell Rant

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

> My batteries are 97% efficient, power in to power out.

Are you sure?  As an example, with PbA, when you discharge at say 20A,
the voltage under load will be between 2.0Vpc and 1.75Vpc.  When you
recharge this same battery at 20A, the cell voltage will be between
2.2Vpc and 2.4Vpc (or more) at 20C.  This >10% difference in charge vs
discharge voltage represents a >10% inefficiency, and your NiZn sag more
than PbA under discharge.

> I'm guessing lead acids are a little worse, LiONs and NiMHes
> are a little better.

I don't know about LiON, but I'm pretty sure PbA is more efficient than
your NiZn, and NiMH is less efficient than PbA.

[snip]

> I take it metal hydride is a catalytic way of storing
> hydrogen without compressing it?

Not catalytic, but yes, uncompressed.  The sponge analogy is a good one;
it takes little energy to get the hydride full of hydrogen, but like a
sponge, it takes energy to wring out.

> Anyway, you can make a good case that 'who cares how
> efficient it is as long as the original source is free and
> guilt-free'.

I think this is really the argument for fuel cells in a nutshell.  As
long as the fuel is plentiful and the exhaust clean, the only concern
with efficiency is to the extent that it impacts how far one can drive
before refueling.  And the emphasis (predictably) is on providing
greater energy storage capacity instead of improved efficiency, not
unlike battery electrics as it happens.

> I'm waiting for GM to buy out Evercel and then make the
> batteries unavailable. Or it'll turn into a SAFT situation
> 'Whatever you need, you can't have, because we don't like the
> brand of your charger. Oh, and there's a six month lead time anyway..'

I don't think this is quite fair.  It is my understanding that SAFT will
sell directly to hobbiests and that the only stipulation is that they
will not warranty the batteries unless you use a charger that satisfies
their charging requirements and your battery box design is approved by
them (to ensure the modules will receive adequate cooling).  Yes, there
is a lead time, but there is also product, and it IS available to
hobbiests.  Let's appreciate what we've got.

Cheers,

Roger.