edge of cloud events

Ralph Day
Ralph Day Solar Expert Posts: 1,022 ✭✭✭✭
in General Solar Power Topics #1
Nov 1, temp about 10C, sun peeking between clouds all day, MX60 Highwatts reading 3228 watts. The array size is 2100 watts, that's 161% of rated.

Now, one will have to wonder what an edge of cloud event will be like 6 weeks on the other side of the winter solstice (Dec 21) when the temps could be -10C?

Anyone else want to post edge of cloud peaks? This could get interesting.

ralph
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Comments

  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #2
    Re: edge of cloud events

    Ralph,

    161% is certainly the highest EOC output I've heard of. This is a good example of why the U.S. NEC requires multipliers for Voc and for Isc. The highest I've seen out of my 725 W array (that's several miles south of you ;)) is ~840 W (~28 V x 30 A; 116%). It might have gone higher but I had my MX60 output current limit set at 30 A at the time.

    Regards,
    Jim / crewzer
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: edge of cloud events

    I've seen similar things and have read the complex explanations posted by some.
    Any such events I've witnessed are easily explained by simple common sense.
    If you have a bright but cloudy sky, your PVs of course produce. Now ADD to that, the light of the full sun as it shines through a clear hole in those bright clouds and guess what - - you get the original output + the output you would get from the sun in a clear but otherwise dark sky. Extra light = extra power, no matter if it's from the bright clouds, bright snow or water surfaces. My system has prospered from all three and it's awesome. I love it, and like you suggest, it's going to be all the better using the MX-60 when those really cold winter days arrive. Gotta love it.
    Wayne
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  • GreenerPower
    GreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    #4
    Re: edge of cloud events

    Watch out the voltage produced by the array (especially when the battery floats). If it potentially gets close to the MX limit, you might need one of those PV "bypass" device from Apollo (expensive though).

    GP
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #5
    Re: edge of cloud events

    The intensity of the Sun effects the current not the voltage ... so edge of cloud will have no effect on the VOC of the panels.

    Temperature is what effects the voltage
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  • Roderick
    Roderick Solar Expert Posts: 253 ✭✭
    #6
    Re: edge of cloud events

    The edge of cloud on a cold fall day pegs our inverter at rated output, so I can't really tell how high it's going. It never gets super cold here. There's frost in the morning in mid-winter, but 29 F would be a rarity.

    I don't actually like edge-of-cloud days, because they're STILL cloudy days, and total production is down. Big flat-topped spikes don't make up for the low baseline output.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: edge of cloud events

    "I don't actually like edge-of-cloud days, because they're STILL cloudy days, and total production is down. Big flat-topped spikes don't make up for the low baseline output."

    you are quite right about that.
    as to the wattage output you are getting you may suspect that 1> the pvs may be normally higher in output than the wattage rating given to them as many pvs have a +/- rating and that usually starts out higher and slides lower over time, but that +/- is what is refered to when the pvs are fairly new from their advertised wattage rating. 2> it probably was an event like edge of cloud, but it's also possible for reflection/ refraction from seperate points focussing onto the pvs at the same time. (rare) 3> the wattage indication from the mx may be reading higher than it should be as i've heard of this being somewhat typical of them. that you may be able to verify with seperate readings from a different meter. 4> all of the above.
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,022 ✭✭✭✭
    #8
    Re: edge of cloud events

    Hi all

    Neil, i'd like to check the actual current with a clamp meter, but the events are so transient...there and gone...that you'd have to spend days just to catch the right conditions. I realize the event only spikes the output for a very short duration, but it's fun to see all the same.

    The conditions that produce edge of cloud events in my experience are brilliant sun, when it's not hiding. Very few events of note if it's warm or hazy and clouds skid in front of the sun...the temperature of the panels just doesn't get low enough in the "dark".

    I should say that the panels are all at about 50 degrees inclination..a few degrees off of optimum. The folks with 2 axis tracking must see these more often than i do.

    ralph
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