Picked up some solar panels. Have a few questions

[hidesertwheelin]

My boss bought a pallet of these from an auction. I bought 2 of them off of him. Is there a good beginners guide to solar? I have googled the model # (Siemens SP150-CPL) and have not been able to find any info on them. I my goal is to make a frame out of aluminum channel & the plastic fittings and mount it to my trailer. I can't even figure out how to test them.

 

[hidesertwheelin]

I hope they are OK. Without aluminum frames, unusual connector, and cell layout makes me suspicious they are fairly old then wonder why removed from service, stripped of valuable aluminium & sold at auction...

As far as ”guide to solar” All one needs is a beginners understanding of DC electricity. That is easily found all over Web-Land.
Testing these modules requires a voltmeter & ammeter. With module laying in good sun, measure its output voltage and current. Those values should be fairly close to values printed.

They were not stripped of aluminum frames, they never had them. They had some thick styrofoam backing that was connected to some kind of fiber board. I will try and get some pictures of the ones in the yard. They were definitely roof panels.

 

[dwh]

Older panels sometimes get replaced when the (usually 20 year) warranty wears out. Often by then the panels are putting out somewhat less than their rating. Most warranties say something like "guaranteed to produce at least 80% of rated power for the life of the warranty".

So if they work (they probably do), they might put out a bit less than they did when new.

Another reason they get replaced is because newer panels produce more watts per square foot, so if the warranty is expired anyway, and the cost has been amortized, what the hell, buy some new ones and get more power on the same size roof.


Those are "24 volt nominal" panels. The open circuit voltage (in sun, no load) is 43v, but the "rated voltage" (that's the same as Vmp - voltage max power (under load)) is 34v. 34v is high enough to fully charge a 24v battery bank, but not high enough to fully charge a 36v battery bank. Hence, "24v nominal".

To charge a "12v nominal" battery or bank, you will need an MPPT charge controller to step the voltage down from 34v (if panels in parallel) or 68v (if panels in series) to the 10v-15v range needed to charge a "12v nominal" battery.

 

[hidesertwheelin]

Right now I am only planning to mount 1 panel on my trailer. Would this controller work? The 75/15 model. Link

 

[dwh]

You can test them by first checking the Voc (voltage open circuit). Put them in full sun (NO shadows on them AT ALL) and use a meter to check the no load voltage.

You can then do a half-assed check of the amperage by connecting them one at a time to a 12v battery. Because they will be operating at battery voltage instead of their optimum Vmp (rated voltage) they won't be producing their full rated amperage. But at least you can see if they produce some amperage.

 

[john61ct]

Actually the higher voltage is ideal, stick to parallel for partial shade handling.

If you want ideal partial shade handling, one mppt SC per panel.

Victron 75/15 "smart solar" includes the dongle functionality, "blue solar" little cheaper without it, one dongle can be shared among all the SCs.

If you want both panels on one SC, go to the next size up.

 

[dwh]

Right now I am only planning to mount 1 panel on my trailer. Would this controller work? The 75/15 model. Link

That would work for one or both in either series or parallel.

 

[dwh]

That would work for one or both in either series or parallel.

Oops sorry, hit post too soon. That would work for both paralleled, but in series, the 86v Voc would be too much for the 75/15.

 

[john61ct]

Putting both on one 75/15 is overpanelling by 80W, yes save some money on the SC, but throwing IMO too much away in peak conditions.

 

[Rando]

You would probably want go up to the 100/20 (and the 'smarts' are definitely worth it). The current rating is the maximum charge current, so with 300W of panels at 13V you could easily exceed the controller rating, even if these were down to 80% of their original rating.

The other thing is that solar panels are much cheaper and better that they used to be, so while it is nice to get something for cheap, consider is it really worth the effort to adapt these to use on your trailer as opposed to starting with something more appropriate? Based on the amount of dead space between the cells, I am going to guess these are pretty low efficiency.

 

[dwh]

Hell, I'd use 'em if they were cheap enough. Is your boss in SoCal and want to unload a couple more?

 

[hidesertwheelin]

Was just testing one out in the sun and the wind caught it and dropped the panel on it's corner. The entire glass top is shattered, but still held together. I think I may just ditch the other one and buy something a little more hardy. Luckly i'm only out $100 for both.

 

[dwh]

D'oh!

 

[llamalander]

With a good MPPT controller, you can use panels built for residential installation. You might check with local solar installers for a good deal on a single panel or a few that are left over or orphaned. Most installers buy large lots of panels and ultimately have to pay to store the ones they don't manage to use. When they are local, they have already covered the shipping, and are often happy to see the extras out the door. I've found panels for about $.50/ watt that are middle to high quality, not more than a few years old.

 

[Coachgeo]

Was just testing one out in the sun and the wind caught it and dropped the panel on it's corner. The entire glass top is shattered, but still held together. I think I may just ditch the other one and buy something a little more hardy. Luckly i'm only out $100 for both.

obviously you will loose some clarity..... thus amps...... but there is a way to fix it with Polyurithane. even fully shattered as you describe. Great for a project.


there is higher dollar (50 bucks?) Poly stuff that is said to work better.... and made specifically for this type repair. Don't recall name