A call to all panel experts and installers - checklist for checking arrays

DIY
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It seems to me that it would be easier to help users with problems if we had a standardised list of array checks we could point users to. For computer issues (my previous occupation a lifetime ago) there are a number of forums where they point users to a standardised bunch of commands they can run which collect all the data that answers almost all the forum expert’s questions. The forum experts won’t touch a user’s issue unless they have attempted to collect that info, and it really cuts down on round-trips asking the same questions.

I was wondering if some of you experts could help check/edit a post that we could a link to, which explained how to do an array check - not a full commissioning, but enough data to point to where the issue might be, or rule out the array being the issue.
If this goes well, i’ll make another one for checking your cabling from SCC to battery, to spot bad connections, a comically common issue.

I’ll start the ball rolling.

[anything in square brackets would be removed - its just my notes]

Tools required:

a multimeter. This doesn’t have to be a fancy digital multimeter (DMM), any cheap multimeter will probably work. In most cases we are looking for relative voltages, so a lack of accuracy can be tolerated. Lack of precision is an issue, but even a cheap DMM will go to at least 2dp.
a current clamp. This can be hard to find compared to a DMM, but its almost essential. There is a work around, but its convoluted and requires at least the SCC and battery to be working, which is possibly not true if the user is asking for help. If you have a small array where the current is under 10A, your DMM may have a 10A current feature.
Tools to open an MC4 - usually thumbnails, or a pair of small flat blade screwdrivers, or the correct MC4 tool for you connectors.

Collect the info we need:

copy and paste the simplified copy of this list at the bottom and fill in the values
Is every panel in this array the same manufacturer, voltage, wattage, and type? If not, describe in #1 what your array is made up from.

  1. Tell us the panel model number : _______________
    [might be important if the panel is strange, such as a type that is not good in high temperatures, but the user is in a hot climate. The user might think a panel is a panel, but this could be the reason they are on the forum. We can probably pull the specs if the user can at least tell us the model #]
  2. Single panel Voc __________v (Voltage open circuit)
  3. Single panel Isc __________A (Current short circuit)
  4. Single panel Wattage __________W
  5. Single panel Vmp __________v (Voltage at maximum power point)
  6. Single panel Imp __________A (Current at maximum power point)
  7. Array configuration: String of ____ panel(s) in series,
  8. with ____ of these strings in parallel.
  9. Total number of panels in this array : ________

Confirm that #7 times #8 equals #9
Confirm that #2 times #7 is less than the SCC’s max voltage
Confirm that #3 times #8 is less than the SCC’s max current

  1. Expected String Voc ________v (at STC) (#2 times #7)
  2. Expected Array Isc ________A (at STC) (#3 times #8)
  3. Array measured Voc: ________v. Measure the string Voc. Do this with the SCC turned off - its important that the SCC is off, otherwise the SCC may be pulling the array voltage down to Vmp - the max power point for that array. If your array only has panels in series, you can just measure at the array isolator. If your array has multiple strings in parallel, you must disconnect the 2-to-1 connectors or combiner box (aka splitters or Y connectors) and test each subarray and report back a Voc for each subarray. For example, on a 4s2p array you would measure the first set of 4 series panels, then measure the next set of 4 series panels. If you can’t reach from one end of the array to the other, you will have to disconnect all but one subarray, and measure at the isolator, where the positive and negative will be close together.
  4. Array measured Isc ________A. Measure the array current while shorting out the array. If you don’t have a current clamp, but your DMM has a 10A current feature, you can use that, but keep the amount of test time to an absolute minimum, and after each test leave the DMM for about 10 minutes to cool down. 10A being dissipated inside your DMM makes a lot of heat!. If you can’t use your DMM, and you know your SCC and battery are good, you can connect your SCC and watch the current. You won’t get the number in #11 (that would be the short circuit current, and your controller will be aiming for Imp (current(I) at (M)ax (P)ower point). You can compare the number your SCC reports, against #6 x #8 - this would be the array’s Imp. There will only be one measurement for array Isc even if the array has multiple subarrays.
  1. Panels :
  2. Panel Voc :
  3. Panel Isc :
  4. Panel Wattage:
  5. Panel Vmp :
  6. Panel Imp
  7. Panel config: Series
  8. Panel config: Parallel
  9. Array # of panels
  10. Expected Voc
  11. Expected Isc
  12. Measured Voc
  13. Measured Isc
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It is timely that you should do this as I was just going to write something to answer the “Why is my MPPT going into float early” or “Why is my 50A MPPT only charging at 10A” or “Why is my panel voltage only 13.4V, the same as the battery” type questions. I would then link into this in the FAQ sticky at the top of the DIY forum.

I will run through your check list and comment separately.

It might be worth having a list of common issues and pointer of what to check.

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I have read through your checklist.

Equipment. For smaller panels which many DIYers have with Isc below 10A many DMMs have a 10A current range as long as people know how to use it and the voltage is low this would be OK. For larger panels or panel strings then agree clamp meter is necessary.

Again, for smaller set ups or single panels, using the current range on a multimeter short the panel leads through the meter.

Everything else looks fine.

This would then stand as a checklist in isolation and can be referred to by a FAQ.

5

Thanks, I’ll make an additional comment about the DMM
Your time on this is much appreciated

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6

Step #13 now says …

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