sell watts going up and down

t00ls
t00ls Solar Expert Posts: 250 ✭✭✭
in Grid Tie and Grid Interactive Systems #1
I have a a xw 4548,xw mppt 60-150,12 105Ah 12 volt batteries(3 parallel,4 series),
6 sun190's 26.7Vmp 7.12Imp 2 strings of 3 for 80.1 Vmp 14.24 Imp

In full sun today in southern Kentucky,the input was 1084 watts 14.2 amps,output was 53.5volts @18amps when selling at 54.5 volts

What I am seeing is the sell wattage go up to 980 then go down to 700 - 600.
also the batt amps in the inverter display will not go to the full -18 amps only -14 amps

Is this normal or should I try to get this looked at....the inverter is less than 6 months old the charge controller I bought last year
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #2
    Re: sell watts going up and down

    Lower you sell voltage to 52V
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  • t00ls
    t00ls Solar Expert Posts: 250 ✭✭✭
    #3
    Re: sell watts going up and down

    Thanks SG.I will do that this morning,it's going to be another bright sunny day.

    I just got this on grid march 18th.I'm the guinea pig for this area....no one else around here is doing this,cant imagine why.Anyways I've run into a few problems with the local utility,we sometimes butt heads,this last butt seems to be a snag in how they pay me or I pay them(first bill).It seems they think I'm supposed to be charged their going rate for what I produced ,then pay me the .15 cents afterwards...TVA says not so...ri county hasnt got back with me yet

    I will see what happens today
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  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
    #4
    Re: sell watts going up and down

    t00ls, I had the same issue with our XW and as usual Solar Guppy nailed it. The bottom line is if the batteries are full the XW will bounce the voltage, if the batteries are a not quite full they stabilize the bouncing quite a bit. I have found the lower you set it the better the bouncing gets, but setting it to low will start to draw power from the batteries. I have mine set at 52.5 right now with about a 200w bounce :)

    Here is the other thread with more useful info.

    http://forum.solar-electric.com/showthread.php?t=4399
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #5
    Re: sell watts going up and down

    Another way to find the magic sell voltage is to first, make sure the batteries are fully charged. Then, find out the resting voltage of the batteries. You know... The voltage they will be at when you let them sit for a day or so with NO load. That voltage might be around, say for example, 51.0 Volts.

    Now, adjust the sell voltage for something higher than that resting voltage. Anything over 51.1 volts or so, but of course, a little higher than that. Like your 52.5 Volts. This will ensure that your batteries have a very slight float charge and will not discharge them, but very little energy will be used to keep the batteries at this higher than rest voltage and the PV will try to bring the voltage up, but of course will be sold off to the grid.

    Hope that makes some sense.

    boB
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  • t00ls
    t00ls Solar Expert Posts: 250 ✭✭✭
    #6
    Re: sell watts going up and down

    bob what you just said made perfect sense and I had already thought that it might be the case...as some 12 volt batteries at rest want to be at 12.3 and others at 12.8...hypothetically and since the inverter and charge controller always want to keep it at a certain level...(not sure how its measured) that the batteries just refuse to stay there ...so while its selling ...it also keeps trying to get the batteries to a level they dont want

    got it
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