Fluctuating Power From Panels

[Jafo232]

I just installed a midnite classic 150 at my cabin and it went pretty simple I guess except for some reason the power fluctuates seriously and almost with a rhythm. I thought it was clouds yesterday but today we have full sun, no clouds. Any reason why this might be happening?

I have 8, 100 watt panels, two rows of 4 (series) connected in parallel. All of a sudden voltage drops to the low 20's and then, zoom it bumps back up to normal.

I recorded it:

I never had this issue with my old controller. I am assuming this is a setting somewhere?

 

[efficientPV]

Looks like my make sky blue. Except mine drops down low and has to have the panels removed to reset it. I had to build a circuit to automatically do this. Are you sure you don't have a tint shadow on the panels. This will make it do that. I thought Midnight would handle this better.

 

[Hedges]

400W at 70V, 100W at 20V.

What percentage of the time does it spend away from maximum power point?
Periodic sweep of voltage is one method for MPPT to avoid getting stuck at a local maxima, which can happen with partial shading of series/parallel array (or half-cut panels.)

Looks like they call it "Sweep", with user-adjustable invervals:

https://www.midnitesolar.com/pdfs/classic_manual_Rev_1933.pdf

"Explanations of Solar and Legacy

Solar

This is the default mode for PV systems and has a very fast sweep (typically a half of a second or less) that will re-sweep at user adjustable sweep intervals, unless the Classic finds that it needs to do a sweep on its own because of changing conditions. The timed sweep interval is user adjustable and is in units of minutes. SOLAR mode is typically best for PV systems, especially if there is partial shading at times during the day. SOLAR mode is best suited for shaded or un-shaded PV arrays that are at least one nominal voltage above the battery voltage. For severe partial shading or PV arrays with nominal voltage equal to battery voltage, you may also want to try Legacy P&O (Perturb and Observe) MPPT mode.

Legacy P&O

Legacy P&O (Perturb and Observe) mode is a slow tracking mode similar to the Micro Hydro mode but with the difference that it is slightly faster and optimized for Solar. Legacy mode can be very useful for arrays that experience heavy shading issues as well as PV arrays that have a low voltage. If the array has a VOC (Open Circuit Voltage) of less than 125% of the battery voltage, Solar mode will not work as well so Legacy will be a better choice."

 

[Jafo232]

Thanks for responses guys!

Yeah, no shadows or shade (see images). You all did get me thinking though! I tried the legacy setting but noticed little difference so I set it on this setting:

"Dynamic
This is typically used for PV (solar) input sources and tries to follow, on a slow dynamic basis, the
changing conditions of the input source. This mode has one user adjustment which is a forced sweep
perturb trigger interval for times when the input condition changes do not trigger a dynamic sweep. The
interval is in units of minutes."

That seems to have solved the problem. Any thoughts?

Thanks so much again!

 

[DerpsyDoodler]

Could dusty panels be a cause of this? When was the last time you watered and squeegeed them?

 

[Hedges]

As expected. I knew some have the function but hadn't looked in this manual before.
Infrequent sweep would be good if yours can get shadows when sun is low behind trees.

Is your PV frame tied down to the foundation behind it?
I had a small easel with 2 panels which powered DC fans, and it blew over (didn't get broken but took out the gas meter mechanism so it didn't turn).
I wired to to tent pegs.

 

[Jafo232]

As expected. I knew some have the function but hadn't looked in this manual before.
Infrequent sweep would be good if yours can get shadows when sun is low behind trees.

Is your PV frame tied down to the foundation behind it?
I had a small easel with 2 panels which powered DC fans, and it blew over (didn't get broken but took out the gas meter mechanism so it didn't turn).
I wired to to tent pegs.

No dust on the panels.

Except for the first thing in the morning or at the end of the day, nothing shades the panels.

Yes, that frame is bolted to the foundation of the yurt. It has passed the "black bear test". :D

Putting it on this dynamic setting seems to have done the trick. Any reason NOT to use this setting?

 

[Hedges]

Not that I know of.
Just make that forced sweep infrequent.

I think dynamic makes tiny wiggles to see which direction is uphill to Vmp Imp peak and tracks it. Voltage varies fairly little, and current varies a lot with angle of sun or hazy sky.

Sounds like cloud passing over causing sudden change triggers a sweep.

"Dynamic

This is typically used for PV (solar) input sources and tries to follow, on a slow dynamic basis, the changing conditions of the input source. This mode has one user adjustment which is a forced sweep perturb trigger interval for times when the input condition changes do not trigger a dynamic sweep. The interval is in units of minutes."