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Sol-Ark 15K MPPT voltage/current

solarfunnc

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Mar 11, 2024
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North Carolina
I have a Sol-Ark 15K with 2 strings of 8 panels each of this panel in the 395 watt model (Vmp 30.84 V, Imp 12.81 A) run in parallel to MPPT #2.

The Sol-Ark shows a lower voltage (200 - 210 V) than the optimum in the spec sheet (246.72 V for 8 panels), and the current is flat lining at the Sol-Ark max per MPPT (26 A).

Screenshot 2024-08-09 at 3.06.51 PM.png

The MPPT is only hitting 5.8 kW, so in theory there's a little room to grow (up to 6.3 kW according to the panel specs, just shy of the Sol-Ark 6.5 kW limit per MPPT).

Screenshot 2024-08-09 at 2.59.26 PM.png

Is there some way to optimize this further? Or is it already doing the best it can with the PV modules and the environmental conditions at the time (it does get warm here in the afternoon - nearly 90 F presently). The other MPPTs are already in use, otherwise I would split up the strings.
 

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Worth looking at the NMOT ratings. STC ratings are for CELL temps of 25°C. Even when ambient is 25°C, cell temps are going to be much higher, and the Vmp will be lower. In ambient temps higher than 20°C, your cell temps will be over 45°C.

NMOT is 28.6Vmp. That puts you at 228.8V.

If you have an IR thermometer, it would be worth measuring the panel temperature.
 
Good point. Panel temps are 45-50°C. So the voltage is a little low but not so much as I thought.

Interestingly, current and power are coming out higher than they supposedly should be at the NMOT, so I guess I should be happy! Thanks for pointing me in the right direction.
 
Good point. Panel temps are 45-50°C. So the voltage is a little low but not so much as I thought.

Interestingly, current and power are coming out higher than they supposedly should be at the NMOT, so I guess I should be happy! Thanks for pointing me in the right direction.

NMOT also assumes 800W/m^2 instead of 1000W/m^2. If you have closer to 1000W/m^2, the cells will get hotter, have slightly lower voltage, but you'll put out 25% more current, so power will be higher.
 
Got it thanks!

Newbie question. For spec sheets that don't include NMOT, is calculating it as simple as multiplying the temperature coefficients by the difference between the optimum temperature (25 C) and 45 C (i.e., x 20)? Or is there more going on there?
 
Got it thanks!

Newbie question. For spec sheets that don't include NMOT, is calculating it as simple as multiplying the temperature coefficients by the difference between the optimum temperature (25 C) and 45 C (i.e., x 20)? Or is there more going on there?

NOCT rating is the older version of MNOT. Any panels you want to own should have one of these ratings on their datasheet.

The two principal drivers are the 80% less irradiance and the ~20°C higher cell/module temperature.

Vmp loss is about 8-9%
Irradiance loss is 20%.

Factoring those two in, NMOT/NOCT ratings are around 75% of STC.

If you have full irradiance, 20°C ambient, perfect tilt, high noon, then you should get around 90%, and those losses are due exclusively to elevated cell temperature.
 

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