Low wattage output

bob20021
bob20021 Registered Users Posts: 1
I'm sure this had been addressed somewhere here before but I wasn't able to find the answer. I was using a 2 harbor freight kits. But as you guess it was to slow. So I purchased two used 36v 320 panels and a mppt controller. My problem that I can't figure out is even though I have 2 320 watt panels. 640 watts. My mppt controller is showing 40 volts but only 40 watts with both panels in parallel. Best I have gotten out to the batteries in mid day is 15 volts at 5 amps. Can't seem to get full watts out of panels. Well know not full but at least reasonable.

Comments

  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Likely has to do with what type of batteries you are charging or if the solar panels are in direct sunlight.

    Solar panels are likely to produce very little if not in direct sun light.

    A lead acid battery is likely to absorb no more than 13-15% of it's capacity when reaching it's max voltage through the charge controller. after that the controller will limit the voltage and the battery will accept less current (amperage) as it completes it's charging.

    Could you describe you system, charge controller and battery a bit more?

    During charging, there are basically 3 stages of charging, Bulk, Absorb, and Float.

    BULK;
    First thing when charging starts you will be in bulk, the voltage rises from what ever the system voltage was to a set point, around 14.5 volts. At that point the Charge controller stops the voltage from rising. Higher voltage can damage sealed batteries.

    ABSORB;
    Once the battery hits the preset point the charge controller keeps it at that point. Your batteries are roughly 80% full. Flooded batteries will start accepting less current at 80-85% full AGM/Sealed may go a little longer before accepting less current.

    On many controllers you can set this point, Some will have different presets for Flooded, and sealed batteries, or flooded, AGM, and sealed batteries. 

    The charge controller has a couple ways to know when to switch to float, Most inexpensive Charge controller are just timed for 1.5-2 hours. Some will also see less current flowing through the charge controller and shut it down when minimal current is flowing through the controller. On more expensive charge controller. You can set battery capacity to give the Controller a better idea of when to stop. you can also set a longer Absorb time. Or set 'end amps' a amount of amps flowing through the charge controller to stop Absorb and switch to the final stage.

    FLOAT;
    Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

    While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • MichaelK
    MichaelK Registered Users Posts: 234 ✭✭✭
    You measure the output of your panels by putting a load on them.  As the batteries approach full charge, the controller throttles back amperage.  That might be what you are seeing.  Place a load on the system as large, or somewhat larger than your total solar capacity.  For 640W, maybe a toaster.  Around noon, when the sun is at an optimal angle, plug in and turn on the toaster, and see what happens to the amperage.  If it suddenly shots up to 40-50A, then you know it was battery charge.  If it stays at ~5A, then something is wrong.

    What's the make/model of your MPPT controller?  If it was off Ebay, it might be a fake; a PMW controller with a MPPT label slapped on it.
    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)