%w panel output voltage drops

[John1234]

I have a 5w solar panel which shows about 20V open circuit voltage. If I connect it to a load- no current.
The voltage drops to almost zero as soon as I introduce a 2.9 ohm load. I can not detect any current at any load.
Can anyone tell me whether the panel is faulty?

[Mike90250]

So far, it looks right. 20Voc indicates a 18v panel 5W / 18V = 270milli amps in full noon sun. Much less under less favorable conditions, The moment there is less than full sun, power output drops significantly. Indoors under bright light (jewelry store light) I'd expect no more than half (138mA)
So you need a meter with about a 200mA scale. That's 0.2A

[John1234]

Thank you for the reply. Is there a chance that panel is faulty? If I connect this panel to a 12V battery it should be able to top up the battery. Is there any way I can tell that the panel is charging the battery?

[Mike90250]

> If I connect this panel to a 12V battery it should be able to top up the battery. Is there any way I can tell that the panel is charging the battery?

ONLY if the battery is already 98% full. 5W will maintain, but not charge.

Do you have a volt meter? Hook the panel up, and early in the morning, check the battery voltage, Check it again about 2 in the afternoon, it should be higher from being charged, 12.52 in the AM, 12.79 in the afternoon, something small like that,, Don't expect to see 14V unless it's a really new battery in really good shape.

[inetdog]

I have a 5w solar panel which shows about 20V open circuit voltage. If I connect it to a load- no current.
The voltage drops to almost zero as soon as I introduce a 2.9 ohm load. I can not detect any current at any load.
Can anyone tell me whether the panel is faulty?

As Mike stated, it will depend on how you are measuring the current and how sensitive your meter is.
A 2.9 ohm resistor is much too heavy a load for that 5W panel.
If the panel is good, then in full noonday sun you will see the greatest power output with about a 5 ohm load.

There is a good chance that there is a cracked or defective cell in the panel that is limiting the current output. If this is the case, there is no practical way to repair it.

Even if it is good, a 5 watt panel is not going to be enough to charge any useful sized battery (more than about 4 Amp Hour at 12V). It may be enough to keep an already charged battery at full charge by offsetting the self-discharge losses.