Array size & voltage VS shadowing

dogman
dogman Registered Users Posts: 9 ✭✭
in Advanced Solar Electric Technical Forum #1
Hello:

I have a radio tower that puts small shadows on a few of my panels.
i also get small shadows from some other antenna mast.
After seeing a utube video online of someone putting a hand in front of a panel and the effect it had I started looking at my own setup and noticed the number of small shadows on diffrent panels and also the shadows being created by the panels in front of the next panel.

The question is does it help to reduce the number of panels in the string.
I understand that a shadow on one panel can disrupt the rest of the string so I was thinking that reducing the string size would make the shadows that I can't fix have less effect on the other panels.

This week I did a test, but as usual the sun has been hiding since I made the change so I have not been able to see the effect. What I have seen is that with the smaller array size now I don't get my voltage up as soon in the mornning.

I am running a 48 volt battery bank, with 3 panels to a string. I get arround 100 volts from the array early in the mornning and the TS-MPPT-60 controler comes out of night mode and it starts producing power. Now with 2 panels it takes longer in the morning until the panels start producing over 48 volts and it comes out of night mode. With 2 panels I only get about 60-70 volts from the array.

I have 18 220 wat panels, I had them in 6 strings of 3 panels each.
They are connected to a TS-MPPT-60 controler and I have only see about half the
power from them that I think I should see, however they have only been installed during the winter so far so It may just be the angle.

Is my thinking correct on all this ?
Am I better off with lower voltage and less charge time VS loss from shadowing ?

Off grid with 6 Simpliphi 3.4KWH 48 volt batteries, 2 Morningstar TriStar MPPT controllers with TS-RM-2  monitor, 1 with 9 Silfab 310 watt panels and 1 with 18 Grape solar 220 watt panels, Magnum MS4448PAE inverter with BMK battery monitor, Tri-Metric battery monitor and Utility company style KWH used meter.

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Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: Array size & voltage VS shadowing

    dogman,
    any shading will degrade your pv performance. now exactly how bad it is depends on exactly how much of the pvs are shaded and where along with how many are in a string and how many bypass diodes there are per pv. i am assuming the voltages you are listing are open circuit voltages, but charge voltages are lower. now without knowing what specific pvs you have i can say that many of them lack the voltage to charge a 24v battery bank and for 2 in series just means that it is most likely still lacking so 3 in series and maybe 4 depending if the voltage may slip too high or not for each string.
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  • dogman
    dogman Registered Users Posts: 9 ✭✭
    #3
    Re: Array size & voltage VS shadowing

    The panels are Grape Solar CS-P-220-DJ rated at 220 watts 29.4 Vmpp and 35.87 Voc. The voltage I refered to was what was being reported as max from the charge controler. Even though the book said not too, I just could not keep from opening the connection box on the back of one and If memory serves me, I think it had 4 bypass diods.

    Before I changed to 48 volts and was at 12 volts I had 2 strings of 2 panels each and I got around 900 watts from them. By the time I upgrated to 48 volts and added more panels it was comming into winter and the sun angle has changed a lot. Now I only get about 2000 watts max on some days. That is only about half what I calculate that I should get (18 * 220 = 3960).

    I am assume that with the lower sun angle that I am just not able to get as much. I even increased the angle on the panel and that has helped to get me where I am.

    I would realy like to understand where I am loosing half my power.
    Even using the CEC value of 194 I should at least see 3492 watts.

    Off grid with 6 Simpliphi 3.4KWH 48 volt batteries, 2 Morningstar TriStar MPPT controllers with TS-RM-2  monitor, 1 with 9 Silfab 310 watt panels and 1 with 18 Grape solar 220 watt panels, Magnum MS4448PAE inverter with BMK battery monitor, Tri-Metric battery monitor and Utility company style KWH used meter.

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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: Array size & voltage VS shadowing

    when the sun is out during the day you should observe more closely any minor shading and on what pvs in what strings. the bypass diodes may help in bypassing some sections that are shaded, but if there are too many it will severely cut your production, unfortunately. it really need not shade most of a pv to do this either. tower legs and masting could cut across many pvs. i hate to say this, but if this is the case then something will need to be moved be it either the tower and whatever you have on it or move the pvs.
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