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From: stevek@blenny.UUCP (Stephen Kogge)
Newsgroups: sci.energy,sci.electronics,sci.physics
Subject: Re: solar cells
Message-ID: <1148@blenny.UUCP>
Date: 1 Jan 91 17:53:40 GMT
References: <939@venice.SEDD.TRW.COM> <1146@blenny.UUCP> <1990Dec31.174455.25630@bronze.ucs.indiana.edu>
Organization: Underwater Imaging
Lines: 51

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
>>total charge to keep 1 2.4W 12 volt fan running all the time.
>> .....
>>
>That sounds strange, each day your fan will only draw 4.8 Ah, and
>since even in Maryland you get around 3 hours peak sunlight average,
>that would give you around 6 Ah average daily (more in summer, less
>in winter).  Sounds like even a worst case summer scenario (cloudy for
>a week) shouldn't deplete your battery from full charge. Maybe the
>battery is old? Car batteries really aren't good for that application,
>they don't like the cycle rate. Try a marine style deep cycle battery,
>that should give better performance.
>
	The battery I have now is a new car battery. After about 3 years of
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).
	In order to find our what is really happening I need to get
the device driver finished for the ADCs I have connected via SCSI and
MULTIBUS to this Sun 3/50. I could then have a cron driven process
watch the battery voltage and charge/discharge currents. For all I know
the reverse leakage into the array at night through the blocking diodes
is as large as my load.
	One guess is that I am being hit by the less than the 100% charge/use	
effeciency of batteries.
	A second possible problem is that since the array is fixed on the
roof in one position I do not get a full days charge time. But since I
cannot move the house/roof it has become a valid part of this experiment.
The question I am trying to answer is "can anyone get enough power from
solar to make the expense worth it". This implies the most simple setup
and almost no maintenance.
	Like I said this is one point on the curve. With several more
arrays and switches to drop the array off line when there is no charge
and drop the load off line when the voltage drops too far I would probably
see more available power and fewer times when I need to put the battery
charger on the system.
	It's such an neat concept I continue to work with it.

Steve Kogge