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Loss of power from old panels

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Posted by Bernie Dwyer on September 29, 2003, 5:43 am
I have what appears to be be a loss of power from some old panels. A
quick-and-dirty description:

Inherited this system when we bought the place in 1996 - it was at least
5 years old at the time:

12 x 55 watt panels
16 amp regulator
modified square wave inverter
580 amp hour battery bank
meters - amps out (load), battery volts, amps in (panels)

I never saw this system run higher than 20 amps, and that little
regulator could get quite hot - I got worried enough to improve the
cooling for it.

Since upgraded with:

12 x 80 watt panels
40 amp "smart" regulator
1500 watt continuous sine-wave inverter
1100 amp hour battery bank

The old panels and regulator were connected to the new batteries (the
old batteries were disconnected completely) along with the new panels
and regulator - the new regulator would have been pushed to its limit to
cope with the expected full-power input from old and new panels, so the
supplier and I agreed to connect the old panels to the new batteries via
their existing regulator.

The upgrade was 3 years ago and the system has worked almost flawlessly
since then. The new regulator measures and stores 30 days' worth of
data, including daily amp hours in. When the upgrade was installed, an
instantaneous reading of the analog amp meter (old system) and digital
display of amps in (new system) showed that the old panels would
typically show about 75% of the new panel reading, i.e. if the new
panels showed 20 amps (sunny day at midday, etc), then the old panels
would show about 15 amps, and the regulator was quite warm to the touch.
Allowances for error notwithstanding, it's still a useful comparison.

Recently the old panels are only showing about one-third of the "new"
panels. Yesterdays' reading at 11:00am showed 22 amps from the new
panels, but the old panels were only showing 8 amps, and the old
regulator was cool to the touch.

I bypassed the old regulator and connected the old panels directly to
the old battery bank, to test if either the analog meter or the old
regulator were faulty. I periodically charge the old batteries in case I
ever need them, but I haven't done so for a few months and their voltage
was lower than the main bank (24.0 VDC vs 26.7 VDC), but the amp meter
only showed 10 amps going into the old batteries - I left it connected
for an hour, but the amp meter needle stayed on 10 amps.

It seems that one or more old panels have had it. An inspection of the
panels showed that two of them are distinctly yellow - I believe this is
the "potting" degrading with age?

Anyway - I assume I'll have to disconnect the whole string and test each
panel individually. I don't have a portable amp meter, so what voltage
tests can I do that will reveal which panel/s are faulty? They are
12-volt panels connected series/parallel to give 24 VDC. I've got the
data sheets for the new gear, but the paperwork is missing for the old
stuff. Thanks.


Bernie Dwyer
Dump the z to reply to me

Posted by Jerry Krinock on September 30, 2003, 3:24 pm
in article 3F77C672.D17CA33F@caloundra.qld.gov.au, Bernie Dwyer at
berniez@caloundra.qld.gov.au wrote on 03/09/28 22:43:

Connect them, one at a time, with the same sunlight, to some known 12-volt
load, such as automotive lamp bulbs, of reasonable watts to load them
somehwere near their maximum power point, and see record how much voltage
each gives, or how brightly they light the lamps.

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