Panel cell count

Brewman

Solar Addict
Ad long as the voltage is within my SCC's capability does the cell number on panels matter?
 

Tecnodave

Solar Addict
No. normal voltage per cell for monocrystalline and polycrystalline is about .500 volts per cell thus 60 cell panels are about 30 volts at MPP. I have some Sanyo/Panasonic multilayer panels which are monocrystalline with an anamorphic polycrystalline cell on top of the mono cell which are a bit higher at about .600 to .650 per cell for about 55 volts for the 96 cell panel but these are the exception.

The one thing that is often missed is highest voltage at dawn on that surprise freezing morning when the panels are still not loaded and are at V.O.C. which will be 12-15% higher than normal v.o.c . Leave a bit of headroom for that in your voltage calculations.
 

FilterGuy

What, me worry?
The one thing that is often missed is highest voltage at dawn on that surprise freezing morning when the panels are still not loaded and are at V.O.C. which will be 12-15% higher than normal v.o.c . Leave a bit of headroom for that in your voltage calculations.
In cold climates, the 'headroom' needed can be much higher than 15%.

The following shows what the NEC requires if your panels don't have a Voc Temperature coefficient listed.

1631060993153.png

If the panels have a Voc temperature coefficient listed, you are supposed to calculate the value, but I find the above chart is conservative and results in a higher factor than calculating from the Voc temperature coefficient.
 

FilterGuy

What, me worry?
BTW: There have been several threads lately where adjusting the Voc for temperature has come up. This prompted me to write up a resource about how to do it.

 

Tecnodave

Solar Addict
BTW: There have been several threads lately where adjusting the Voc for temperature has come up. This prompted me to write up a resource about how to do it.

Very good thanks, There are several string calculators available online but they are tailored for that manufacturers gear. These can be found at :

Morningstar Solar
MidNite Solar midniteftp.com

BUT......These have been tailored by their respective controllers and as such only list the maximum v.o.c. capabilities of their respective controllers.

The one at Morningstar has the individual solar panels listed including the VOC temperature coefficient, The MidNite one does not list individual solar panels so you need to find the maximum VOC temperature coefficient.

I learned the hard way frying a B-Z 500 controller with First Solar FS-1 CdTe panels which have a very high VOC of 76 volts and a very high VOC temperature coefficient.

Most solar controllers are irretrievably destroyed by VOC exceeding the published limit.

The only ones that i know of having a tolerance of exceeding the maximum VOC is the MidNite Classic and the MidNite Kid units. They have a feature called “Hyper VOC” where the controller shuts down to protect the front end of the MPPT input stage.

Since the controller of the B-17 inverter/controller is based on the Classic units and the Barcelonia is the next generation Classic I would bet that these units also have the “Hyper VOC” feature built in. As these units are still in the ALPHA or BETA testing stage specifications have not been released yet.
 

FilterGuy

What, me worry?
Very good thanks, There are several string calculators available online but they are tailored for that manufacturers gear.
Yup. @upnorthandpersonal has a more generic calculator here

I believe it is important to understand the process even if you are using a string calculator. The more someone understands the process of figuring this stuff out, the less likely they will misunderstand something when using the calculator.
 
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