Post #3
1)BFL’s question; “Can you look for a peak in Voc or Isc to determine optimum panel orientation?”
I’ve broke this into two conditions. One with the panels not connected to the controller and another with the panels connected to the controller supplying a load to the battery. Basically unloaded and loaded panel conditions.
Condition 1: NO LOAD CONNECTED TO THE PANEL!!!
With no load I measured Voc with the panel vertical and horizontal to see how much Voc varied. With the panel vertical Voc = 20.85V, Horizontal, Voc=20.52, and it peaked at 20.90 at an estimated 60 degrees. Humm….. Might work.
Then with the panel at best orientation by using Voc, I measured Isc to see if I was close to optimum. Isc= 4.94A, and further adjustment showed it was at or very close to optimum position. I couldn’t increase Isc, and much movement caused Isc to drop.
Repeating the alignment, starting by monitoring Isc, got me to essentially the same orientation.
And once connected to the controller, I wasn’t able to get any noticeable improvement in output power. But I only fussed around with it for a few minutes and decided it was “good enough” after all the optimum position is varying all day long.
Conclusion:
Maximizing Isc or Voc seems to get one “good enough” to optimum angle. At least it is “good enough” for me. However, Isc seems to be more sensitive to position than Voc.
Since optimum orientation changes continually during the day, I figured using either of these methods is probably good enough. Once you get max Voc or Max Isc, it’s up to the user to decide how to orient the panel angle to maximize power captured during the entire sunshine period if you choose a fixed angle.
Condition 2: PANELS UNDER LOAD.
This test was done on a different day and different time. 10AM PDT on October 16th, with a few wispy high clouds.
In this case, once the MPPT controller finds it peak power conditions, it will wait some period of time before searching again. I wondered how this might affect trying to find the optimal angle. Also, one the panels are connected to the MPPT controller, it is not easy for me and probably others, to monitor panel or MPPT voltage while adjusting the panel. So that leaves monitoring current.
So, with my panels connected in series via a short run I hooked my clamp on DC current probe onto one output lead and watched current as moved the panels from horizontal through vertical. I did see about 0.75A change in current, and when the current peaked it did so over a fairly narrow angle. I then repeated with the second panel. However, with panels in series what happens is the current is set by the panel with the highest output current, and the second panel will increase/decrease output voltage as it is moved. Good news/bad news. Good news is that the second panel would be expected to be in the same orientation as the first. Common sense. So with that as a starting point, I tried adjusting the second panel, then the first. Careful adjustments gave me about another 0.1A in peak current. But my final orientation was darn close to the optimal position with one panel.
Then I went in and looked at the trimetric. 9.1A. given the wispy clouds and early morning, not bad. I then waited a few minutes to see if the controller was able to get any more power once it did another search. A little later another 0.1A, but don’t know if that was the controller or a little more sun.
Conclusion:
I think it is easier to find optimal angle with unloaded panels, but it certainly is doable with loaded panels. So if in the AM you adjust for optimum, and later in the day want to adjust, using the clamp on meter to optimize current does seem to work and is a lot easier than asking DW to monitor the trimetric as you tilt the panels.!!
But WAIT there appears to be a better method:
One proposed by Jim Denver and expanded by CA Traveler.
Put some form of cylinder on the panel. When the sun is perpendicular to the panel (the optimum position), there should be no shadow. Jim Denver suggested a TP tube, CA Traveler a dart with a suction cup. I’ve got a spare Garmin suction cup mounting system I’m tempted to put a plastic tube on and use that. I tried a TP tube. Very quick, very accurate.
So after all those current/voltage measurements, SIMPLE is better, thanks Jim and CA Traveler!!
