Solar Panel Question - Basic

rktortrrktortr Registered Users Posts: 2
Hi All,

Searched, but clearly not using the right terms. I have a very basic question about solar panel output.

Do solar panels typically output:
1. constant voltage, variable current based on amount of available solar energy, or
2. constant current, variable voltage based on amount of available solar energy, or
3. both current and voltage vary based on amount of available solar energy.

Surprisingly difficult to track down. Thanks for indulging me.

Comments

  • PhotowhitPhotowhit Solar Expert Posts: 5,653 ✭✭✭✭✭
    Pretty much #1, volt will fluctuate a bit due to temperature higher temps slightly lower voltage lower temps slightly higher temps.

    You can look for a temperature coefficient in the spec sheet for a solar panel to give you some idea.
    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.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    And, as current draw is reduced, the voltage will rise to Voc. Voltage open circuit (when no current is flowing).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rktortrrktortr Registered Users Posts: 2
    Perfect. Thanks so much for the responses.
    Interesting on the Voc. I had always assumed that it was literally for an "open circuit", i.e. no closed wiring (like when a panel is not connected to anything), not just no current/draw. Thanks for the clarification.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Open circuit and no current draw is pretty much the same thing on different words.

    Note that charge controllers while not drawing current (battery full), are still connected to the solar panel. So if Voc is too high (panels in series, very cold weather, etc.,) it is possible to damage the charge controller input circuitry.

    Matching panels to charge controller to battery bank is actually not a trivial exercise to design correctly.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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