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Different kW output after changing from 3x2 to 6 string


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Hi All, Mister quiet here (been very quiet on forums lately)

I recently changed out my Axpert (smoke got let out, after all my battery issues it was finally last straw - probably just a diode, but I had had enough) for an Imeon 3.6 (thanks Mike, it works well). But have a question regarding the difference in output of my panels since the change:
* On the Axpert I used my 6 x 280W panels in a 3+3 (or 3x2 if you prefer that terminology), and could get approx anywhere from 1.3kW to 1.8kW (in Summer) from Panels as reported by the Axpert
* After changing to a serial string (all 6 in series, since the Imeon needs a much higher start voltage), I never seem to get more than about 0.8kW.

Items considered:
* Cables - My cables are way oversized for the current and voltage
* Incorrect connection - Definately checked and definately a proper series connection
* MPPT battling due to a shortage of panels??? Not sure, so need some thoughts here

Things I have tried:
* Removed all the Reverse diodes (installed those due to some funny shade situations, but seems irrelevant with a single string)
* Checked that I am getting proper startup voltage (nearly 200-250V when disconnected - Open circuit) from Panels
* Wiring - As mentioned above, I haven't screwed up connecting in serial

Just can't understand why the Imeon reports nearly 1kW lower from the panels than the Axpert. Any thoughts, maybe I am missing something or even just need more panels?

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IMHO, the PV voltage is too low, so the MPPT controller is unable to reach Maximum Power Point on the I/U curve of the PV modules.

Can you check in the manual what is the recommended number of PV modules? I would say that 12 wil be listed as a total minimum.


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Hey KLEVA welcome back

2 hours ago, KLEVA said:

installed those due to some funny shade situations,

If you have funny shade situations it will now affect the entire array whereas previously it was possibly only affecting ½ or the array. I would guess that there are several contributing factors  and not just one cause of the lower production

I am guessing that your VOC for the array is just over 200V (230V somewhere thereabouts) as the PV voltage drops with production so you may end up below the MPPT minimum voltage for the Imeon. @Youda has mentioned this already.

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Thanks for the info/ideas, when budget allows I will try get at least 3 more panels into the string (Always wanted to have 3kW of panels, but oh yes, they cost money<_<). Gonna do the batteries first, still sitting with the remaining unexploded Calciums. Imeon spec sheet doesn't really say number of panels, but they are designed to go up to 400+ on input Voltage... 120 Min, but in parallel I was usually at lowest at 80V when sun barely shining, just assumed that 160V (80+80) would do the trick.

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  • 2 weeks later...

Update: Additional 5 x 270W panels installed yesterday, seems like the Imeon already loves it. It's almost pitch black outside, but already generating 200W at 330V. Today is a bad day for testing as it will be overcast the whole day, but I can already see the performance improvement. Another lesson learned... Imeons's need the voltage, it seems a lot more productive at 300V+ than the 160V before. I didn't really need 3kW of panels when we only draw 400W but such is the lesson. I am so much happier with the Imeon than the Axpert in my setting. Mike - I cant thank you enough for letting me have this kit at such a price, could've never gone this route otherwise.

If I am battling to implement solar PV, I wonder how we can make it affordable to general populace? (my political stance - you don't have to comment, just me ranting)

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