Testing solar panels

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I have 4 x 48 watt panels on my boat that were made in 12/89. I put
them on the boat in early 1990 when they were new. I am wondering
about their current output and if I should replace them. The panels
are marked 2.88 A optimum current and 16.7 V optimum voltage. Those
numbers produce 48.0 watts. Seems like I'd need a 5.8 ohm 50 watt
resistor? New panels give quoted Isc - short circuit current. How can
I test my panels with a multimeter to see if I should replace them?
Thanks

 

[Blue Cat]

I have 4 x 48 watt panels on my boat that were made in 12/89. I put
them on the boat in early 1990 when they were new. I am wondering
about their current output and if I should replace them. The panels
are marked 2.88 A optimum current and 16.7 V optimum voltage. Those
numbers produce 48.0 watts. Seems like I'd need a 5.8 ohm 50 watt
resistor? New panels give quoted Isc - short circuit current. How can
I test my panels with a multimeter to see if I should replace them?
Thanks
-----------------

Best way is to test the panels under load. I use a set of power resistors,
or a rheostat. As you approach the panel's maximum power, you will need a
resistor rated 50 watts.

 

[Eeyore]

I have 4 x 48 watt panels on my boat that were made in 12/89. I put
them on the boat in early 1990 when they were new. I am wondering
about their current output and if I should replace them. The panels
are marked 2.88 A optimum current and 16.7 V optimum voltage. Those
numbers produce 48.0 watts. Seems like I'd need a 5.8 ohm 50 watt
resistor? New panels give quoted Isc - short circuit current. How can
I test my panels with a multimeter to see if I should replace them?

I can't fault your calculations but the nearest 'standard value' resistor
is 5.6 ohms. It shouldn't make much difference in practice. The resistor
will need to be rated at 50 *in free air* or it will need heatsinking.

You'll also need a 'calibrated day' to check their output. This may prove
more problematic. ;~)

New panels should also give optimum values. Suggest you shop elsewhere or
google the data.

Graham

 

[Martin Riddle]

Easiest would be to check Open circuit voltage and short circuit
current.
If its close to the original panel rating then your good to go.

Cheers

 

[Kees]

DC clamp on ammeter, voltmeter, and a calculator?

Problem is that the Isc is very dependent on the solar irradiation. The 48
Watts are defined under STC (standard test conditions), o.a. 1000 W/m2
irradiation, defined spectrum and at 25°C.
In my opinion it is not straightforeward to test the quality of the panels.
I don't know for which you are using them. But if they deliver enough power
most of the time, it iis still OK. When you run "always" out of power,
either minimise your power consumption or replace he modules (or add
additional panels to them).

cheers
Kees