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  • Open circuit voltage

    Hi,
    I bought some 1.75W/0.5V cells from ebay. Aim is to make small (proto) off-grid system for next summer. Total power would be around 100-150 W. I am also designing mppt charge controller for this, but as it happens I dont have any earlier experience with PV systems.

    For this reason I need to know some basics from PV. How much voltage fluctuates as weather changes. What should be the oc voltage be in 12V system? I understood that PV acts like current source where amperage stays the same while voltage travels. Is this so?
    I
    Last edited by jynkky; 12-15-2009, 01:44 PM.

  • #2
    The standart for 3x6 cells is 36 cells/panel which generates you about 60W.

    I'm using a sandwich glass made panel, you can see them in my thread "my tiny proyect in Ecuador" in the DIY section.

    Depending where you are located they have between 18 to 21V without load.

    The watts/daily depend on the intensity of sun and your isolation factor for your zone.

    [QUOTE=jynkky;5929]Hi,
    I bought some 1.75W/0.5V cells from ebay. Aim is to make small (proto) off-grid system for next summer. Total power would be around 100-150 W. I am also designing mppt charge controller for this, but as it happens I dont have any earlier experience with PV systems.

    For this reason I need to know some basics from PV. How much voltage fluctuates as weather changes. What should be the oc voltage be in 12V system? I understood that PV acts like current source where amperage stays the same while voltage travels. Is this so?
    I

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    • #3
      Originally posted by jynkky View Post
      Hi,.... What should be the oc voltage be in 12V system?


      I understood that PV acts like current source where amperage stays the same while voltage travels.
      a 12V battery needs about 15V to get fully charged. The charge controller consumes 2 volts, of internal diode drops. Allow another volt for losses on a hot day.
      So your panel Volt Max Power should be around 18 or 19V Open ckt voltage around 21V


      PV is crrent sounce, at a constant voltage. So when there is enough light in the AM to start the panel, you are at 20V, 5mA Brighter light = 19V, 3A Noon sun = 18.7v 5A As panels get hot, their voltage begins to sag. Amps vary according to intensity.
      spreadsheet based voltage drop calculator:
      http://www.solar-guppy.com/download/...calculator.zip
      http://www.solarpaneltalk.com/showth...oss-calculator

      http://www.mike-burgess.org/PVinfo_2.html

      solar: http://tinyurl.com/LMR-Solar
      gen: http://tinyurl.com/LMR-Lister ,
      battery lugs http://tinyurl.com/LMR-BigLug
      Setting up batteries http://tinyurl.com/LMR-NiFe

      gear :
      Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||

      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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