SMA OptiTrac in action? Individual MPPT plots.

[MinorDeity]

Below are plots of the power, voltage, and current from three individual MPPTs of my daughter's 10.53kW system on a cloudless day. The system consists 39ea 270W panels in 3 separate 13-panel strings connected to 3 of the 4 MPPTs in her two SB6000TL-US-22 inverters. One string faces ~East (~100 degrees - red), one faces ~South (~190 degrees - fuchsia), and the other faces ~West (~275 degrees - blue). The East and West strings are unobstructed but a chimney shadow sweeps across the South string until about 11:00AM every morning. I believe if the South string weren't shadowed its morning power curve would rise a little faster and certainly be smoother, but I was actually expecting to see something much worse than what the power plot is actually showing. Do you think the downward spikes and stair steps might indicate that OptiTrac is locating new power points about every 30 minutes (it's actually set to 6 minutes) as the shadow moves or is that just the way any tracker works under such conditions? As you can see from the voltage plot, the voltage doesn't actually reach the voltage of the other two strings until the shadowing stops around 11:30. I know I could temporarily disable OptiTrac just to see if there is any difference but I don't actually have convenient access to my daughter's system. What do you think about this performance and how much better do you think the South string might perform without the shadowing (not that that's actually an option!)?

Thanks,
Ray

[sensij]

I doubt optitrac is doing much for you in this situation, relative to what "simple" mppt would do. The steps are in about 10 V increments, which is about how much voltage you would gain as each 20 cell string begins to contribute and is no longer bypassed through a diode.


I think optitrac is supposed to help in more dynamic shade (clouds or leafy trees), when multiple strings are in parallel and the Vmpp on each string becomes mismatched.

To estimate the unshaded south production, you can use PVWatts. Use the hourly output and find a clear day in the data within a few days of the date in question. Adjust the pvwatts parameters until the output for the east and west arrays comes close to matching the actual data, and the see what it spits out using those parameters for south.

[MinorDeity]

To estimate the unshaded south production, you can use PVWatts. Use the hourly output and find a clear day in the data within a few days of the date in question. Adjust the pvwatts parameters until the output for the east and west arrays comes close to matching the actual data, and the see what it spits out using those parameters for south.

Thanks for the suggestion. I did what you suggested for the exact day of my plots and determined that shading is reducing the energy production of the South array by about 13%, which in turn is reducing the energy production of the entire system by about 5%. Due to the location of the chimney I don't see that this will change much over the summer.