two arrays [RE-wrenches]

[Allan Sindelar]

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Darryl,
You don't say what the modules are; I'm assuming that you probably have 6
12V modules in series. The 33 cells will probably save you. Most modern
polycrystalline modules have 36 cells, not 34. So you are 1 1/2V lower than
typical per module, or 9V lower on a 72V array at normal temperatures; even
more drop at cold-temperature VOC. Unless there's more to the story, I
wouldn't lose any more sleep.

The MX60 is a great way to make use of any old 30-cell
("self-regulating"-ha!) or 33-cell modules, as long as they're not combined
with higher voltage modules.

I have been following the recent mixed-module thread with interest, as we
are currently working with a long-time client with a "democracy tracker" of
ancient modules. They wanted both to add more PV and move the existing
tracker farther from the house, but had existing buried wire that couldn't
easily be upgraded. We took out the existing SB50 and installed an MX60. We
installed a new 1280-watt array wired 48V (the system is 24V nominal). We
did simple I/V curve testing on the existing modules with a homemade module
load tester, as some had browned and others were good, and picked the best
matches. The new array will use 9 Arco M52L Quadlams (wired in series), in
series with 4 Arco 16-2000s (wired in parallel). On paper it works out to
about 6-6 1/2A at 64V, which matches the MPP of the new array pretty well.
We'll also series two BP75s and two BP80s on the same array, but they also
have pretty similar I/V characteristics. The client accepts the "try it and
see" uncertainty, so it will be interesting to see how it performs. How many
17-module 48V arrays have you seen recently?

Allan at Positive Energy

----- Original Message ----- 
From: "Darryl Thayer" <daryl_solar at yahoo.com>

You have me scared, perhaps I have an unexpected
failure comming.  I did not check with Outback before
making these installations.  Don't do what I did, and
I will not do it either.  These modules are shaded in
the morning in the winter, so they do not have output
when the coldest temperature exist.

The Modules are the polycrystaline, and they are a
discontinued older type, with the 33 cells? as opposed
to the more common today of 34 cells.  Also we have
not had a cold winter for several years.  Our design
temp is -10F I do not believe we got any colder last
year than once a -4F.  I know our record below exceeds
-30 but not once in the last 10 years.

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