Advice on maximizing

elesaverelesaver Solar Expert Posts: 185 ✭✭
As some things become clearer, others become more fuzzy. The fuzzy part has to do in determining which is more critical to maximizing output from PV. I know that watts/volts = amps. So, by doing the math, higher watts and lower volts will result in more amps. So, is it more wise to have PV wiring so that the voltage output is lower so that more amps will result? Battery chargers running on 120 VAC are based on amps. I have a 6 amp charger that takes forever!

My PV array is 1800 watts (300W @ 8.18 amps X 6 ea). They are wired as 3 strings of 2 into a combiner. Each string, then, is 72V @ 8 amps. The combiner (acts as a parallel connection?) bringing the amps to 24 but keeping the voltage at 72. If this is correct, I question why I do not see higher watts at some point during a sunny day resulting then in higher amps. Today...very sunny and 63 degrees...on a visit to the controller, I did see 70.3V and 16.3 amps which is the highest I have recorded. This seems to be a far cry from what I think should be happening. But, then again, perhaps my expectations are too high.

There is not a load on the system at this time as I am still working on the "details." If there were, I am concerned that there would not be enough amperage generated to keep the batteries full during the day so that there would be enough power stored for use overnight. Any help to understand more fully is always appreciated. Thank you.
1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

Comments

  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Advice on maximizing

    All things are dependent. What is your battery bank voltage? Is your charge controller mppt or pmw? Was your battery full and cutting back on the amps it could accept? Lot of things affect pv production, You need to offer more info to get an answer. The three questions above, if answered, may give a start to helping us help you understand what is going on.
    gww
  • PhotowhitPhotowhit Solar Expert Posts: 5,023 ✭✭✭✭
    Re: Advice on maximizing

    Watts = energy (more properly watt hours)

    So there isn't a simple answer for this, since watts in and out will be marginally the same.

    What you want is a the most efficient conversion of the incoming watts to usable watts to charge your battery. For MPPT type charge controllers this is around 2x the nominal battery voltage. If the voltage is higher more energy will be wasted as heat.

    The addendum to this if you have a long run from your panels to your charge controller, a higher voltage running the longer distance might loss less energy (as heat) in the wiring (or require much larger gauge wires for the same energy loss)
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • elesaverelesaver Solar Expert Posts: 185 ✭✭
    Re: Advice on maximizing

    More info on the question referenced above: charge controller: Midnite Solar 200; 60' from panels to controller with #10 wire; 24V battery bank with 8 batteries in series/parallel to equal 480 aH.

    Overnight, the temps were low 40's. The controller shows the batteries are 100%...although the charge stage is at absorb. I used a HydroVolt this morning to measure the SG before much sun was on the panels. The regular digital voltmeter showed all batteries at a high reading...all were over 7V at the time. The SG, however, showed an entirely different story. I didn't test all cells but randomly tested and those were below 1.20 SG. Meanwhile, the aH showing on the Whizbang Jr showed a large loss of aH overnight with no load...down 53 aH.

    I've read that cold affects the batteries so that may contribute to some of the changes in readings of the batteries this morning. BUT, I still would like to know the most efficient way to configure the panel wiring if it's possible to know that.
    1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

    2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Advice on maximizing

    Something is not consistent there. If the classic is saying 100% but that you drew 50Ah overnite that doesnt add up. Dont pay much attention to the "net Ah" figure, that tends to drift. There are a number of causes of hitting 100% reported SOC preior to end absorb:

    1. if your wbjr settings (Bat AH, temp comp) arent bang on, you might hit 100% prior to float.
    2. a watchdog type controller reboot during the last charge cycle will revert SOC to the last known midnight value, which will make the SOC inaccurate until float is reached.
    3. new system where float hasnt reached since WBjr installed.
    4. End amps setting not set right. Check EA is ticked to use WBJR, and that EA trigger value tallys with your target SG.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Advice on maximizing
    elesaver wrote: »
    As some things become clearer, others become more fuzzy. The fuzzy part has to do in determining which is more critical to maximizing output from PV. I know that watts/volts = amps. So, by doing the math, higher watts and lower volts will result in more amps. So, is it more wise to have PV wiring so that the voltage output is lower so that more amps will result? Battery chargers running on 120 VAC are based on amps. I have a 6 amp charger that takes forever!

    This is far off the mark.
    PV is a current source. The current is not a function of Voltage differential. If you were to wire two panels in series you get the same Imp but at 2X the Vmp. If you wire them in parallel you get 2X the Imp. As far as panels are concerned the Voltage can do whatever it wants; they will try to produce the current first and foremost.

    Enter the MPPT controller. It doesn't care what the panel/array specs are. It needs only that the Voltage on its input be above battery level and that the PV produces some current. If more Voltage than is needed is available it will turn this into additional current. It will pick its own best I*V point for the prevailing conditions, hence the term Maximum Power Point Tracking.

    If the array Vmp is too far above battery Voltage the controller will have to do too much work to down-convert the higher Voltage into current and efficiency suffers. This is sometimes balanced against power lost to wiring runs.

    Have a look at this thread: http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller
  • elesaverelesaver Solar Expert Posts: 185 ✭✭
    Re: Advice on maximizing

    I haven't read the thread that Cariboocoot suggested yet but I will do so. I wanted to add this info. I didn't check any values at the controller until around 5 pm so it had been a few hours. The maximum absorb time is set to 5 hours. I thought this was to say that the batteries would be absorbing at least 5 hours or until it would be triggered to go to float. The batteries were still absorbing but the Whizbang JR said that there were 493 aH. The aH were programmed in as 480 so why in the world would the batteries continue to be charged, exceeding what was programmed? I had to go into the TWEAKS menu and "induce" a float.

    End amps is set at 0.1 as was suggested. I do not know how to set EA to be consistent with SG.

    This is a real puzzle for me. Any help is always appreciated.
    1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

    2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

  • Alaska ManAlaska Man Solar Expert Posts: 252 ✭✭
    Re: Advice on maximizing

    You might want to call Midnight Solar. They have great customer service and technical help. Ask me how I know.......... ;-)
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Advice on maximizing
    elesaver wrote: »
    ... The maximum absorb time is set to 5 hours. I thought this was to say that the batteries would be absorbing at least 5 hours or until it would be triggered to go to float.

    IF you have end amps turned on, and configured correctly, then yes, the absorb time is the max absord time, and tthe actual time it takes is based on the end amps setting being reached, or the absord time which ever comes first.
    The batteries were still absorbing but the Whizbang JR said that there were 493 aH. The aH were programmed in as 480 so why in the world would the batteries continue to be charged, exceeding what was programmed? I had to go into the TWEAKS menu and "induce" a float.

    The figure to read is the SOC %. See reasons above as why it can be at 100% during absorb.
    End amps is set at 0.1 as was suggested. I do not know how to set EA to be consistent with SG.

    This is a real puzzle for me. Any help is always appreciated.

    0.1A? That sounds too low, way too low. For a FLA bank start with 2% of C20. For an AGM bank start at 0.5% of C20.

    But you dont want to just use some random figure, the best and recomeneded way to calibrate this as a one off exercise is to turn EA off, and set max absorb to 12 hrs, then either:

    a) through asborb periodically check SG, when it hits target value, check the WBJr amps. Adda midgin for the noise floor, and set that as your end amps.
    b) through absorb watch the WBJr amps figure, plot it out on a graph every half hour, when it begins to flatten out right at the bottom, thats your end amps figure. Add a midgen to be sure it triggers, then as above add a midgen for the noise floor.

    Reset your max absorb time to something that will act as a backstop to EA, ie longer than it will take on 99/100 days, but low enough to prevent excessive boiling.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • elesaverelesaver Solar Expert Posts: 185 ✭✭
    Re: Advice on maximizing

    OK, Zoneblue, sounds like a plan. I will work at this for a few days and update if/when I get this figured out.

    Another question, though, as I re-read the suggestion. In "a," you mention to check SG periodically through the absorb stage and when it hits target, check the WBJr amps. The reading I see on WBJr is the amp hours, not amps. What am I missing here? On the MSGP, the battery voltage is not consistent at each screen during my looking around at other functions. It can say 26.4V for the batteries on one screen and 29.8 on another.

    If I don't made headway, I'll call Midnite Solar. Thanks again, all.
    1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

    2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Advice on maximizing

    The classic also reports the WBJr amps, in the local app its called "system amps" not sure what its called on the MNGP.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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