Question about charging batteries

TerkoTerko Registered Users Posts: 4
Hello! I am new here. I will be happy if you help me with one problem I have.
I made for myself solar panel with 36 solar cells, monocrystaline. They must give me 100 W of power (12V). I've connected them to solar controller and the controller is connected to 3 12v batteries. Every battery is 7 amps /20H for total 21 amps. I use one volt and amp meter connected between solar panel and the controller and at the morning the power is: 12.5V at 1 amp. This is at 9 am. I expect at 1PM to have much more amps, but they are 2-2.5 amps with 14 V.
What can be the reason to not make 6-7 amps from the solar panel? Maybe the controller is reducing the amperage? Or maybe I have to connect the amp meter to the battery?
When the battery is fully charged the meter show me values like 19 V and 0.5 amps.
Thank you in advance!


  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Welcome to the forum,

    You are experiencing the difference between STC and NOCT. The specs for your panel are at STC (standard temperature and conditions). When your panels heat up in the sun, that is the Normal Operating conditions and temperature. Lower voltage and less power when they heat up.

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • TerkoTerko Registered Users Posts: 4
    Thank you very much! I spent two days to find the answer searching in Google and now you helped soo quickly. Thank you!

    So I will investigate from now how much energy the panel will produce in not so bright day. The panel is DIY and 2 of the cells are broken (they have all the connectors and works).
  • BB.BB. Super Moderators, Administrators Posts: 32,235 admin
    Depending on how the cell(s) broke--They typically would be expected to go "high resistance"--That can significantly reduce the through current.

    Also, a big problem with DIY panels is the risk of fire--Many folks build their panels out of wood and/or plastic. That when mixed with the "high resistance" in a cell (or wiring) greatly increases the risk of fire. Here is the tale of a gray market factory panel used on a permitted installation:

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TerkoTerko Registered Users Posts: 4
    Hello again!
    The solar panel that I made is made from 36 cells with these characteristics:
    Average Power (Watts): 2.6 Wp
    Average Current (Amps): 5.2Imaxa
    Average Voltage (Volts): 0.5 Vmax
    Efficiency upto 16.64 %

    All they are soldered in series. 9+9+9+9, Today I started live broadcast to watch the readings. They start at 8 AM till 1.30 - You can see them here:
    It's enough to slide the time hour by hour to see the difference. In short, at 9 am I produced near 1 amp and by 12 PM they was 2.50 amps (14 volts). Then when the sun was directly over the panel the readings started to drop. Overheating? It's strange that in the peak hours the power produced is lower than in the morning. I can't explain that :( Today was very hot and bright sun day. Please, help!
    I wonder if there is mistake in my panel, maybe there is not good connection in some elements? Any glue will be helpful.
  • TerkoTerko Registered Users Posts: 4
    BB. wrote: »
    Depending on how the cell(s) broke--They typically would be expected to go "high resistance"--That can significantly reduce the through current
    Thanks for the reply! They broke.. how to say, the leading wire was fine. I didn't removed and replaced them, because this was difficult to achieve without risk to break other cells.
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