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Most common Voc for sub-300W panels, +other stats

BerndL

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A lot of people are probably in the situation of buying 400W here and 600W there, or trying to build expandable systems. Does anyone know a list of the most common important PV parameters, especially Voc, Vmp, and Imp?
If you're mixing and matching smaller solar panels, are there particular stats that will make finding well-matching ones easier? Any weird voltages to avoid because that one manufacturer is the only one that uses it?

I get that the most common answer is probably "buy another SCC for the new ones", but that's not the best if you need to overpanel for winter use, have a mobile system with an extra array at home, are moving to a camper with more roof space, switching from 12 to 24V using the same SCC, etc.

I ended up buying 23.7Voc panels that only fit 3 to a string on my Vic 100/30 after temp correction. No regrets, because they were cheap and I probably won't need more for a while, but should I have actively been looking out for e.g. 22.5Voc ones? How would you even go about searching for specific Vocs?

It's sort of odd that there's not too much discussion of optimal panel stats online. Most people seem to buy what they buy and rig the system accommodate the gear, rather than the reverse.
 
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It's sort of odd that there's not too much discussion of optimal panel stats online. Most people seem to buy what they buy and rig the system accommodate the gear, rather than the reverse.

No such thing as "optimal panel stats."

Most panels are either 60 or 72 cells. If you see 120 or 144 cell panels, those are two 60/72 half cut cell panels in parallel in the same panel frame.

60 cells are about 30Vmp/36Voc
72 cells are about 36Vmp/45Voc

Imp = power / Vmp

Isc = about 1.05X Imp

When matching, 2 rules:

All panels in a string will operate at the lowest Imp rated panel.
All parallel strings need to be within about 10% of each other.
 
Thanks. I guess this is a big advantage of buying larger standardized panels. A lot of the smaller 100-200W panels seem to use 36 cells band have very wide Voc ranges: I've seen from 19 to 24.5.

By the way, more of a separate question, but is that parallel string requirement nominal or actual current? If you have east and west facing strings, can you parallel them to one SSC?
 
By the way, more of a separate question, but is that parallel string requirement nominal or actual current? If you have east and west facing strings, can you parallel them to one SSC?
You should be fine parallelling east/west arrays provided they are comprised of the same panels. Voltage isn't as much affected as current in this scenario.
 
Most of the RV (often called 12V panels) panels are around ~22Voc and ~18Vmp. 1 or 2 volts rating differences amongst different brands can be encountered but mixing them will have little penalty (if any) for doing so.
 
Thanks. I guess this is a big advantage of buying larger standardized panels. A lot of the smaller 100-200W panels seem to use 36 cells band have very wide Voc ranges: I've seen from 19 to 24.5.

Yep. Those are "12V" panels. Some manufacturers mess with the cell count - I've seen 39 cells.

By the way, more of a separate question, but is that parallel string requirement nominal or actual current? If you have east and west facing strings, can you parallel them to one SSC?

Just follow the two rules. The parallel string requirement isn't related to nominal or actual current.

Technically, I should add a third rule when quoting the other two...

All panels in a series string must face the same direction.

A string of E panels in parallel with a string of W panels will work fine provided they meet the parallel string Vmp rule.

Since it's physically impossible for those two strings to simultaneously output max Isc/Imp, you have some wiggle room when considering the maximum input current of the SCC. If you really want to nail it down, you can use PVWatts to simulate the E array and the W array separately. Download the hourly data and then combine them in Excel. You'll be able to calculate the maximum current from the data.
 

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