Testing a solar collector

[Lumatic]

I am removing a solar system from one Airstream and want to install it in/on another. First the 170 watt solar collector. How can I test to make sure it is putting out juice before I install it on the other Airstream?

[rmkrum]

There are a couple quick tests that come to mind IF you have the specifications of the panel. Check the max voltage ands current specs for that model panel. Keep in mind that they deteriorate as they age, and you will not see full specification outputs even in a brand new panel...

As always, if you do not know how to use a multimeter safely, and work around electricity, hire an expert...

One is "open circuit voltage" where you use a multimeter to measure the output voltage of the panel when it is in full sunshine. That will tell you it can put out voltage.

The other is a "short circuit current" test, where you hook the leads to a DC ammeter that is rated to carry at least the rated current of the array, and see what it does in full sunlight.

For a nominal 170 watt panel for RV use, I'd guess its rated at about 15-18 volts open circuit, and that implies 9 to 11 amps absolute maximum, assuming it puts out full rated current (it will not...the specs are under lab conditions only). So I would expect a decent 10 to 20 amp multimeter could handle this check.

I'd expect about 50-60% of max current under bright sun. Don't do this test for longer than enough time to read the meter. Cheap multimeters tend to melt their innards if you push a lot of current through them. (at least the Harbor Freight ones may do so...)

Best bet would be to a;so ask "Lewster". He's the expert on the forums, and can tell you better. I'm an electrical engineering sort, and this is somewhat guessing on my part...pm him!

[Lumatic]

Originally Posted by rmkrum

T Keep in mind that they deteriorate as they age,

What is the average life expectancy of a solar panel?

[Mattirs]

Originally Posted by Lumatic

I am removing a solar system from one Airstream. .... How can I test to make sure it is putting out juice before I install it on the other Airstream?

There is great short sheet that shows how to measure a solar system's performance using a multimeter. I can not find a way to attach a pdf file. Does someone know how to?

[waninae39]

click on advance when posted
then you can add attachments

[Mattirs]

See attached

[waninae39]

@mattris

no attachment seen

you have to choose the file
then
upload
wait for the file to be listed, then close the dialog box and then
submit

[rmkrum]

Originally Posted by Lumatic

What is the average life expectancy of a solar panel?

It totally depends on the construction of the panel and the mounting system.

1) Monocrystalline cells last longest-20-30 years

2) Polycrystalline cells can last 20-25 years

3) Amorphous cells can last 5-10 years if you get lucky (cheap Harbor Freight crap)

Metal framed, tempered glass covered cells are best protected against environment and sun damage, then based on technology used, see above.

Flexible cells are having issues with sun damage--jury not in on whether they are worth the money.

Lewster could chime in here and give better information...Lew?

[Mattirs]

Here is a nice shortsheet on how to test the various aspects of a solar set up.

Matti

checked and it worked
O frabjous day! Callooh! Callay!

[Lumatic]

Thanks for the replies so far.

[Paprika]

Thanks for uploading that, Matti! It's a useful summary. A couple of caveats. First, the expected results shown there assume you have a 100 watt, 18 volt panel. For larger panels, the results will of course be different.

Second, their diagrams showing how to measure operating current and how to test the "regulator" (solar controller) are incorrect, as they show the positive wire continuing straight through. To test current, you have to disconnect the positive wire and bridge the gap with the multimeter leads. Indeed, their printed instructions tell you to do this--but their diagrams don't. So do as they say, not as they show. :-) The attached picture shows what their illustrations should have looked like.



One final caveat: they say "Ensure that the multimeter is set at 10A." With most multimeters it's not enough to change a dial setting; you must also move the positive test lead to a different socket on the multimeter--one that's marked as being for amperage measurements. If you don't do this, there's a good chance you'll burn out your meter, or at the very least, blow an internal fuse. So when planning to make a current measurement, be very certain that you have the meter lead plugged into the "A" socket on the meter.

[rmkrum]

As long as ALL the current in the negative side of the circuit is going through the meter, it does not matter where you put the meter in the circuit. It's going to be the same current readout. (That's why we call it a closed circuit...)

In some ways, putting the meter in the negative side is safer, because an accidental positive side short from meter leads to the Airstream body will be much less spectacular! Don't ask how I know this...

For another example, battery monitor system current shunts are pretty much always placed in the negative lead, but absolutely must be wired so all the battery current goes through the shunt. That way the monitor knows how much current and in what direction it is going to effectively measure and display an accurate battery State of Charge (SOC).

[Paprika]

"As long as ALL the current in the negative side of the circuit is going through the meter, it does not matter where you put the meter in the circuit."

Right. My point was that the diagrams showed current measurement without actually inserting the meter into the circuit--without breaking the normal positive (or negative) connection. That won't work.

"putting the meter in the negative side is safer, because an accidental positive side short from meter leads to the Airstream body will be much less spectacular"

Agreed!

[rmkrum]

Originally Posted by Paprika

------------------snip-----------------------------
"putting the meter in the negative side is safer, because an accidental positive side short from meter leads to the Airstream body will be much less spectacular"

Agreed!

OOPS! This should read "...an accidental negative side short..."

Not that I have dyslexia, or anything like that....

[Paprika]

Well, if you do then so do I, because I didn't even catch that--I knew what you meant. ;-)

[Mattirs]

Originally Posted by Paprika

Thanks for uploading that, Matti! It's a useful summary. A couple of caveats. First, the expected results shown there assume you have a 100 watt, 18 volt panel. For larger panels, the results will of course be different.

Second, their diagrams showing how to measure operating current and how to test the "regulator" (solar controller) are incorrect, as they show the positive wire continuing straight through. To test current, you have to disconnect the positive wire and bridge the gap with the multimeter leads. Indeed, their printed instructions tell you to do this--but their diagrams don't. So do as they say, not as they show. :-) The attached picture shows what their illustrations should have looked like.

It funny I had looked at that diagram half a dozen times already, checked the amps per the written instructions and never noticed the error. Lol

What I do is pull the blade fuse between the controller and the batteries and test there. No wires are exposed, no chance of a short unless I am careless with the probes.

Thanks for catching that, and I am sure future folks will thank you also.