skipped a solar panel!

[fungus]

So I was going to the local skip yard to get a cast iron elbow for connecting our woodburner up and there was these solar panels in a skip- was 4 of them but the other three had big gashes/holes in them, but they let us have this one for free! The glass is all cracked on it but the cells underneath seem to be fine, it does only put out about 48V OC on a cloudy day-not sure what's really within normal variation for a panel this size?
I vaguely remember a post here where someone cracked the glass on their solar panels and just stuck a big sheet of sticky-back plastic on top- does anybody have any experience or have any recommendations for what'd be best to use?
I do want to try to rewire it for 12v but not quite sure how to do it, see the picture below for the connections with the diodes, not sure if it's possible without digging into the panel to get at the connections on the other side..

[dnix71]

The tag on the panel says the Voc is 59. You got 48 on a cloudy day, so it probably works okay. That was an expensive panel new, someone probably got the insurance money and let it go. Keep the panel on an angle so it doesn't pool water. I have rolls of EVA but I don't know if it would help to try and reseal the top with a sheet of it.

[DanG]

Go back and get the other three for their junction boxes and frames?

[fungus]

Probably should've done, they're nice boxes .. but it was a couple weeks ago so they're probably in china by now
Measuring between the diodes it's a constant voltage on each section but it looks like they're all connected in series and that's just the bypass diodes, only way I could really see to rewire it for 12v would be to try and trace the connections back inside the panel and dig them out, not really sure...

[dinges]

Nice score! The price was good too.

Unfortunately, it was thrown away for a good reason: it's broken, as is pretty obvious in the picture. So it needs to be disposed of properly, as it contains all kinds of hazardous materials. Normally, disposing of hazardous equipment costs a lot of money, but I'll cut you a deal.... it won't need to cost you more than shipping it to The Netherlands. There's a special disposal facility here just for that kind of stuff....

On a more serious note: try to keep it in a warm, dry environment for a while so it can dry thoroughly. Then, maybe build an external glazed frame for it? Or use it indoors. I wouldn't try to rewire it for 12V but use it as is - they're current sources, so charging a 12V (or 24V) battery shouldn't be a problem, as long as you stop charging when the battery is full using a charge controller. Or, if you want full power, you might consider a DC-DC voltage converter.

The Scottish dumpsters are obviously better hunting grounds than the ones we have over here.....

[fungus]

^I figured that's why they let us have it ..
But I guess I could charge two batteries at once with it.. will see ..
Although I'm thinking it might not even need much protection since the cells have EVA on both sides of them, I was thinking more of just protecting the glass so bits don't pop out (got a couple shards in my finger ouch) .. shall see.
Really need to get a better position for the panels, just now they're west facing, surrounded by trees, and not to mention the fact I'm on the west coast of scotland (several months there's been rain every single day!)..

[DamonHD]

Hi fungus,

A good MPPT controller with a decent input voltage range would suck all the available power out of that panel without any rewiring, and some are happy to output at 12V or 24V (ie whatever battery you have).  I've seen some inexpensive-looking (but plausible) controllers that can even step up from a lower input voltage.

I understand that there may be zero budget, but anyhow...

Rgds

Damon

[oztules]

It looks like the strips are going to be 24 cells wide.... so only 12wv per strip jump in the j box.... not enough to charge a 12v battery.

It would normally be a simple job to isolate the wiring in the panel itself, and cut and terminate the panel for other voltages, but you only have 96 cells..... so really 2x24v panels are possible..... ie 10A@24wv.... also the panel is now delicate, and doing mining operations will not help.

In reality, Damon has the best idea for my money. Check the SC current to see if it is worth the investment. It's one thing having volts, but at what current.

If the cells are cracked, and the silver paint is broken (fine white lines across the cell is silk screen painted on), the volts will still be the same, but we no longer have access to all the silicon on the cell surface.

As it is all in series, the cell with the least surface area still electrically attached to the central bus lines will be the weak link. It will still have .55voc ( thats an electric field thing across the depletion layer of the PN junction), but it's current capturing area may be compromised... surface area = amps.

If you still get 3-5A, then the exercise of buying a mppt unit may be worthwhile.....



................oztules

[ghurd]

Lots of conflicting opinions, and I will add a one more.

Connect it to a 12V battery.
Measure the V between each set of tabs.
Work backwards through the math.

To me, it looks like a PV for grid tie. Should be able to reconfigure the box for 24V.  Or 12V with less amps. Maybe 12V, but marginal Vmp.

There are 4 series strings of cells?  Get the 1st test done, then get the dang diodes out of there for better testing.
That kind of box has 'push points' to relase the diode leads.
Do not break the box.

I saw one worse than that work for a few years, and for all I know it is still working.

There are spray cans of 'clear paint' made to pass light waves that may seal/solididify the glass a bit.
G-

[hydrosun]

Last time I checked a panel with broken glass was still working after 15 years.  I assume it will eventually fail from a corroded lead.
On another project I discovered some panels were mislabeled as 12 volt when they were actually wired as 24 volt. i tried to internally rewire but gave up unless I wanted to dig out under the sealer. Luckily we were able to reconfigure the series/parralel arangment  to make it work. on a mppt controller.
The easiest thing is to hook it directly to a 12 volt battery and accept the loss of half the potential power. the panel was free so you aren't wasting your money. to add a mppt controller would be costly for one panel. A dc to dc converter might work at a low enough cost.
Chris