How to Determine Actual Output from Solar Panel Banks

gridman
gridman Registered Users Posts: 18 ✭
in Grid Tie and Grid Interactive Systems #1
I've been using my new solar panels for 4 days now. Was in Grid Support Mode for 3 days but today I turned off the grid and am running off solar. I'm just getting a feel for how the system behaves.

The past few days have been mostly cloudy, with today being partly cloudy with more sun, so more energy production. I understand that the XW6048 is going to draw different amounts from each of the 2 SCCs. I can scroll through the display on the SCCs and see the Input and Output values.

But, with the way the Xantrex system is set up, there doesn't appear to be any way to see the actual output from both banks of panels on the SCP or SCCs, is there? If I go outside to the Midnite Solar Combiner box and measure the voltage output of each bank (with a handheld meter), it's within .1V or .2V of each other. As a solar newbie, it would be interesting to know the available power at any time, not just the power being harvested.

I'm asking because I don't think I have something configured correctly in the system. For example, just a moment ago I looked at the SCP and the loads were 950w, yet the solar harvest was 650w (reading from front panel of SCCs) in late afternoon sun (non-obscured by clouds). For 32 panels, 650w seems a bit low even for this time of day (it may be my newness to solar and this is acceptable).

I'm not just referring to this one event. I have noticed the same thing several times over the past few days.

Just curious for thoughts?
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  • gridman
    gridman Registered Users Posts: 18 ✭
    #2
    Re: How to Determine Actual Output from Solar Panel Banks

    I've been doing some more reading and the 650w havested for 950w load values in the previous post may be normal and I'm just new at this.

    It's supposed to be sunny for the next few days. I'll pay close attention during the peak sun portion of the day, under ideal conditions and see what I find. I'll report back.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: How to Determine Actual Output from Solar Panel Banks

    Perhaps I can help clarify how these things work.

    The charge controller will put out Watts according to how much power is available from the panels (which would be the maximum they could supply) and how much power is demanded by the system (charging of batteries which varies by their SOC and supplying loads).

    If the panels are able to put out 650 Watts at any given time and the loads at that time are 950 Watts the 300 Watt deficit is made up by the batteries.

    In practical operation what matters is not the Watts at any given time but the total Watt hours supplied by the panels in a day and the Watt hours consumed by the loads (including charging batteries).

    In your first post you indicate that what you are looking for is the panels' potential output at any time. There is no simple way of determining this. MidNite's "waste not" function comes closest to maximizing panel potential. To be able to read this potential at any time you would need one panel dedicated to this purpose: with a fixed resistance on it the insolation of a known panel capacity can be read as V*A at any time.

    There; clear as mud, right?
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #4
    Re: How to Determine Actual Output from Solar Panel Banks

    Your batteris may be full. Discharge them overnight to 50% SOC, then, while the batteries are in bulk, you'll be able to see the full production.
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  • gridman
    gridman Registered Users Posts: 18 ✭
    #5
    Re: How to Determine Actual Output from Solar Panel Banks

    Thank you both for the answers. It was very helpful. I'm learning as I go.

    Rod
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  • etcm
    etcm Registered Users Posts: 11 ✭
    #6
    Re: How to Determine Actual Output from Solar Panel Banks

    FWIW, my 6.1 kW total rated output (2 arrays x 3.05 kW) have been producing ~ 1.7-2.5 kW (total) per hour during the the cloudy/rainy daytime periods for about the last month (Central Indiana). Almost every day I have a peak production from each array in the 3.1 to 3.5 kW range. One day in May, I had a 7.1 kW peak production. I had calculated a maximum current using the 1.2 temp correction and plus 1.25 solar factor at about 63 amps and I have already achieved this once on one of the arrays (at a much higher temp than the -20C temp correction factor). Of my two (same model) MPPT charge controllers, one consistently produces a higher current at a lower voltage and usually a 1-3% higher kWH value for the day.
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