Xref: utzoo sci.energy:3695 sci.electronics:16663 sci.physics:16179
Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!att!cbnewsh!cbnewse!leland
From: leland@cbnewse.att.com (leland.m.kornhaus)
Newsgroups: sci.energy,sci.electronics,sci.physics
Subject: Re: solar cells
Summary: remember losses
Message-ID: <1991Jan3.171726.16495@cbnewse.att.com>
Date: 3 Jan 91 17:17:26 GMT
References: <939@venice.SEDD.TRW.COM> <1146@blenny.UUCP> <1148@blenny.UUCP>
Distribution: na
Organization: AT&T Bell Laboratories
Lines: 35

In article <1148@blenny.UUCP>, stevek@blenny.UUCP (Stephen Kogge) writes:
> In article <1990Dec31.174455.25630@bronze.ucs.indiana.edu> amirza@silver.ucs.indiana.edu (anmar mirza) writes:
> >In article <1146@blenny.UUCP> stevek@blenny.UUCP (Stephen Kogge) writes:
> >>
> >>	One point on the curve. I have a 30W (18" X 30") array. It charges
> >>a car battery that I keep outside. Here in Maryland it cannot produce enough
> trying various wet cell NiCd and gell cells I decided to put a fresh
> battery in the system. My assumption was that the 34 Amp hour NiCd cells were
> old or damaged, the gell cells I tried next were used and followed
> the same poor charge characteristics. I hesitated using a car battery since
> it had to go outside. A friend of mine runs an electronics surplus store
> (Electronics Plus in College Park Md) and warned me that the acid fumes
> from the batteries he had for his emergency radio transmitter ate holes
> in his plumbing and I really ought to put the lead acid battery outside.
> 	I replaced all the blocking diodes at one point and saw an increase
> in charge current. I have considered using a trick I read about using power
> FETs instead of diodes. (I think it was FETs, I will have to check my notes).
> effeciency of batteries.
> 	It's such an neat concept I continue to work with it.
> 
> Steve Kogge

When you make your power calculations consider this rule of the thumb:

It takes 120% of the power a lead acid cell can hold to charge it 100%
It takes 140% of the power a nicad cell can hold to charge it 100%

These are rough figures but may explain why your results with the
nicads were so poor.  I am assuming 6Ah of charge into a nicad yields
about 4.5 Ah of stored energy. The rest is dissipated as heat.  Also,
a very cold lead acid cell (Probably - I'm guessing) has a higher 
internal resistance which may result in losses.  Im basing this guess
on the fact that at -20 F a car battery can only produce 15-20%
of it's rated Cold Cranking Amps.  This may be due to the "slower" 
chemical reaction within it