-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of John Berdner
Sent: Monday, April 29, 2013 3:12 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] unbalanced string voltages
Kirk:
As noted below the current will be shared by all modules
Hi Larry,
A PV module is not exactly a constant current source. It has a power curve. At
0 volts in any given insolation, it's current will be the highest. As the
voltage rises, the current drops, until the current is 0.
If you put two strings in parallel that have different voltages, they will
David,
Since a PV module is a constant current device, I don't believe this will take
place. For a given amount of light (plus all factors affecting power), the
current potential will be there. What force can act upon the current to reduce
it? Consequently, the lowest Vmp the inverter can
Modules aren't exactly constant current
devices.
They are for much of their voltage range, up to a voltage a bit
below the MPP, and then the current starts tapering down to 0 at
Voc. The entire string can only pass as much current as the
lowest current
So the string with the highest current AND voltage dictates where the inverter
MPP locks. Other strings are pulled up past their MPP which means lower
current from them. Makes sense.
I was only considering constant current under a load equal to the potential. In
that case a module is constant
I question one part of this conclusion,
but have not set up any tests. The only part I question is "the
string with the highest current AND voltage dictates where the
inverter MPP locks". Rather, it seems to me that the voltage at
which the combined current of
] unbalanced string voltages
I question one part of this conclusion, but have not set up any tests. The only
part I question is the string with the highest current AND voltage dictates
where the inverter MPP locks. Rather, it seems to me that the voltage at which
the combined current of all
Hello everyone,
I am at present adding to a -20- panel array of old Sanyo HIT lipped 200
watt panels. They are configured in -4- series strings of -5- panels, with a
string MPP voltage of 279 vdc (55.8 v, 3.6 a each). The customer wants to
add another nominal 2 kw using the (now) Panasonic 235
Kirk
The 43volt 5.5 amp panel will operate at 3.6 amps, so it's voltage will move up
toward open circuit voltage, raising the mppt voltage of that string. I would
bet that the voltage of that entire string will rise to match the higher
voltage string by moving toward open circuit voltage. It
I'd go for using that extra module with the damaged frame. What is the
frame damage going to do to the system?
Is it bad enough that the module could quit working later (bad edge seal)?
The voltage mismatch isn't the end of the world either, but your over
all year round performance will be
Hey Kirk, I'm currently doing a project with Tigo Optimizers. Sounds like they
might work for your project. db
Original Message
Subject: [RE-wrenches] unbalanced string voltages
From: Kirk Herander k...@vtsolar.com
Date: Sun, April 28, 2013 12:02 pm
To: RE-wrenches re-wrenches
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