Added second panel in parallel and total power dropped!

Sverige

A Brit in Sweden
I have a pair of identical PV panels from solarv.de and have them mounted both facing due south, but around 10m apart. Specs are below

Technical data: rated power (Pmax): 160 W, max. Voltage (Vmp): 18.1 V, max. Current (Imp): 8.85A -- Open circuit voltage (Voc): 22.32V -- Short circuit current (Isc): 9.56A -- Max. System Voltage: 1000VDC -- Operating Temperature : -45 °C to + 85 °C – Dimensions: 1460 x 664 x 35 mm – Weight: 12 kg.

In testing today I found that with one panel connected, my MPPT charge controller was getting 87W (19.7V and 4.41A) but when the second panel was connected in parallel, total power actually went down (80W, 21.2V, 3.77A). Why would this be?

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curiouscarbon

Solar Enthusiast
Hello,

Please share what size cable between panel and charger (length, AWG/mmsq).

Please also share charger info: rated max amperes, rated max voltage.

Unfortunately I cannot offer a clear explanation for the undesirable hardware behavior you are observing. Thank you
 

curiouscarbon

Solar Enthusiast
I just noticed that, for your second picture with two panels in parallel, the battery voltage has already become close to full. Charge rate declining near completion of charge is normal and to be expected.

Perhaps try using two panels parallel during sunny day and when battery is ~50% state of charge. This might result in different (higher) performance.
 

Sverige

A Brit in Sweden
Ok, from panel 1 (which was initially connected) to the charge controller, there’s around 16m of 9mm square millimetre cable. That’s 16m total run, so 32m circuit length (both conductors).
Adding panel 2 to the circuit adds a further 4m of 2.5mm square cable, which is know is not ideal, but it’s the best I could do at the time I put that panel up.
Charge controller is Renogy Rover 20A Max, 100V Max and I haven’t connected the panels in series because they take shade at different times, so as a series connected pair they would be shaded for hours.
 

Sverige

A Brit in Sweden
I just noticed that, for your second picture with two panels in parallel, the battery voltage has already become close to full. Charge rate declining near completion of charge is normal and to be expected.

Perhaps try using two panels parallel during sunny day and when battery is ~50% state of charge. This might result in different (higher) performance.
Yes, that may be why I saw what seemed like odd behaviour. You’re right, the charge controller has gone into “boost” mode with the second panel connected. I’ll have to try again with flat batteries.
 
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