The Nature of Solar Panels

KnowledgeSpongeKnowledgeSponge Solar Expert Posts: 173 ✭✭✭
I'm a Solar Noobie.

I just got my first serious Solar Panel yesterday.

A 100W Q-Cell panel (supposedly made in Germany).
MonoCrystalline.

Anyway, I was doing some tests on it (always feel I should immediately test things like this for performance
rather than set them aside for a month or two and find out later they don't work properly)

Anyway, I found that the panel would meet or exceed it's advertised Amperage and Voltage DEPENDING on certain things.

For example, if I moved my hand over the panel ANYWHERE and caused a small shadow, the Amps (current) dropped significantly.

Also if the panel is not exactly perpendicular to the sun, it would drop.

So, this panel is rated at 5.68 Amps, 17.75 Volts

In full sunlight, perpendicular to the sunlight, I got 5.71 amps (nice) and 17.88 volts.
But, If I moved my hand over the panel and created ANY shadow, it fell immediately to 3.68 amps

So, does this sound good to go? Any obvious problems?

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: The Nature of Solar Panels

    Perfectly normal.

    Exposed to just about any amount of light a PV will achieve Voc, but not necessarily be capable of current. For that they need intense, direct light. Since they are a current source they will try to produce Imp and will allow Voltage to sag depending on illumination and load.

    Ratings: 5.68 Imp (current at maximum power) * 17.75 Vmp (Voltage at maximum power) = 100.82 Watts.
    These are Standard Test Condition ratings, and standard test conditions don't exist in the real world.

    Don't expect to see that all the time, or possibly ever. The reason being that panels are also affected by temperature, and they do not operate at ambient. The average output of a panel is usually 80% of its rating (77% if you include controller loss).

    Shadows will definitely have a negative affect.

    Nothing wrong with the results you got. :D
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: The Nature of Solar Panels

    for the current we can assume this was a short circuit test of it and should be a higher figure than the imp rating given most good sunny conditions.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: The Nature of Solar Panels

    In full sunlight, perpendicular to the sunlight, I got 5.71 amps (nice) and 17.88 volts.
    But, If I moved my hand over the panel and created ANY shadow, it fell immediately to 3.68 amps

    So, does this sound good to go? Any obvious problems?

    This is typical, and it's why a shading analysis is critical to the design of any PV system; partial shading of a module can cut its output back to nearly zero, and if it's in a series string, the whole string's production is brought down.
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