how does MPPT work? Weird Voltages

[CaliSunHarvester]

I have a string of 10 panels, they are LG 355W with Voc = 39.1V and Vmpp = 32.6V

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They are just leaning fairly steep (almost straight up) against a wall. It's sunny with a bit of fog still burning off (slightly overcast). Facing south.

Here's a reading of the recent hours' array power output and the voltage.



Those 10 panels should put out in the 300V neighborhood based on specs, right? And they did (280V until 10:31am). Then suddenly the voltage drops to 128V... and power nearly doubles.

Right now, it's 7A and over 800W power. I'm not nervous about the 7A.. it's 10AWG wire..

I just wonder what caused this to happen?

The sun did not change significantly between 10:31am and 10:36am.

I don't see any shading either.

 

[Mattb4]

Sounds like your SCC found the max power point voltage.

 

[hwy17]

That's weird, are they shaded? More power at 128v just sounds wrong.

My array is like 360 VMP and I'm running it at 330v fixed now after watching the MPPT mode for a while. So I would expect your sweet spot to be around the 280v point.

 

[Mattb4]

Fog.

 

[CaliSunHarvester]

Fog.

it kind of was fog, but the fog was there when the voltage was 280V. Since the fog is gone, it's steady around 124V. Power is up to almost 1kW.

One concern is that 6 panels are leaning in a 80 degree angle and 4 panels are in a 89 degree angle. Eventually, I want to place 20 or 30 panels in this vertical setting (2 or 3 strings @ 10 each). They are for November-February.
.

 

[efficientPV]

Voltage should stay the same regardless of angle. Something is shading the panels, it may only be a line. Many controllers are not very good at finding power point following any shade or overcast. If you have a disconnect switch, remove power for 10 seconds and then reconnect. I have a controller that will locate on a lower voltage bump. I built an automatic control which automatically disconnects panels when voltage drops below 70% of Vmpp.

 

[CaliSunHarvester]

If you have a disconnect switch, remove power for 10 seconds and then reconnect.

actually, I did exactly that. Good news: Voltage is back over 300V. Bad news: Current is down 75%, i.e. power output is down 50%

Compare the % of array 1 (all flat, 81% of nominal power) with array 2 (vertical, 19% of nominal power):

 

[CaliSunHarvester]

Probably unrelated, but output is back to 150V and 7A = 1.1kW

 

[CaliSunHarvester]

I built an automatic control which automatically disconnects

Nifty!!

 

[CaliSunHarvester]

as another test, I removed the 4 vertically mounted panels from the string, so that it's only the 6 that are leaning against the concrete wall.

The output is identical to before. It is as if those 4 vertical panels had contributed *nothing*.

Initially, I had 9 or 10 panels leaning against the concrete. I believe that the power output was higher at that time. My concern is that I spend a lot of time building that rack for vertical mounting and 20 panels produce something like 100W, just because it's a bad angle.

Voc for the 4 disconnected panels is 155V which matches the manufacturer spec.