Specific testing method for 50cent/watt laminate panels?

meridiansolar
meridiansolar Solar Expert Posts: 34 ✭
in General Solar Power Topics #1
I'm sure other's have gotten these 50 cent/ watt panels from sunelec.com because they were so cheap. I have a multimeter which wires do I exactly test to make sure the panel is good? There are 4 sticking out the back of each panel. I'm assuming the voltage is the same and the 4 wires are put together in parallel to increase the total juice out of the panel.
any guidance on these reject panels is appreciated.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Specific testing method for 50cent/watt laminate panels?

    I don't know how the panels are wired, but it sounds like you can place them in series or parallel--and you need to add the bypass diodes (and blocking diodes if you think you need them).

    We do not know where the panels came from or why the junction boxes were stripped.

    There are three tests you can perform:
    1. Open Circuit Voltage (Voc with a volt meter--under any good sun)
    2. Short Circuit Current (Isc with a current meter--under full sun near noon on a clear day)
    3. Current into a load (roughly Imp--maximum power into a load, again measuring current--again, under full sun near noon).
    If you do #1 and #2, you will probably weed out 80-90% of any bad panels.

    If you do #3, you should have a 100% good panel.

    #1 does not induce current flow, so you do not know the quality of the cells or the current paths.

    #2 does flow maximum current through all connections, but you could have cells that do not develop full current... Probably more of an issue if you have an assembled panel with bypass diodes.

    #3 is the optimum test--but actually a bit difficult to setup. Vmp/Imp needs the correct loads to ensure that you can adjust the current to obtain Imp and Vmp. An OK substitute is to connect a "12 volt panel" to a 12 volt battery and measure the current (should be near Imp).

    Of course, current is, more or less, proportional to the amount of sun hitting the panel. Depending on time of day, how clear the air is, etc... You may get a measured current that is less than Imp/Isc rating. If you have other known good panels, you can estimate the amount of sunlight during your testing (i.e, a Isc=5 amps reading 2.5 amps during testing would indicate sun is ~50% of the 1,000 Watts/sqmeter standard the panels are tested under).

    As always, solar panels that you add junction boxes too would not keep their UL/NRTL Listing and should not be used for Grid Tied Inverter type applications (connected to your utility/home wiring).

    Use your "repaired" panels with caution on your home projects. Solar panel fires are possible for many reasons. Repaired panels with non-factory parts are always at the risk of the buyer.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • meridiansolar
    meridiansolar Solar Expert Posts: 34 ✭
    #3
    Re: Specific testing method for 50cent/watt laminate panels?

    I got the 185W mono panels
    Model Sun-P-185
    Power (W) 185 Watts
    Open Circuit Voltage (V) 30.20 Voc
    Short Circuit Current (A) 8.54 Isc
    Maximum Power Voltage (V) 24.00 Vmp
    Maximum Power Current (A) 7.71 Imp

    What kind of load could I use? a 24v sealed lead acid battery? I have a couple of 12V tractor batteries lying around, can I just hook those up in series to act as a load?

    Also I got some chinese junction boxes off ebay. How do I test/know if the right diodes are installed?

    thanks for your help. I'll try to post my results back here.
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #4
    Re: Specific testing method for 50cent/watt laminate panels?

    If the panel's Vmp is 24V, there is not enough voltage left over to properly charge 24 V of battery.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: Specific testing method for 50cent/watt laminate panels?

    As BMET says, for your panels, the "optimum" load voltage would be in the 20-24 volt range...

    As you approach and/or exceed ~20-24 VDC, the current flow will fall (as you approach Voc). This is assuming the two strings in the panels are connected in series with bypass diodes. If you check each 1/2 panel individually, the Vmp/Voc will be 1/2 the rated voltage--and will be ~Imp/Isc.

    You can charge a 12 volt battery (~12 to ~15 VDC) with your Vmp~24 volt panels. For a short time (minutes, 10's of minutes), you should not hurt the batteries--assuming the batteries are > 20-80 AH or so rated (to absorb the current without overheating). Larger batteries can be connected longer without fear of damage from overheating/overcharging.

    Using a 12 volt load (or a 12 volt + 6 volt battery bank in series) is better than nothing.

    We have no idea why the panels had their connection boxes removed, so we do not really know what panel problems we may be looking for (if any).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Specific testing method for 50cent/watt laminate panels?

    You might want to read through this thread which I believe is about the same panels:
    http://forum.solar-electric.com/showthread.php?t=12706

    bmet is right: 24 Vmp won't charge a 24 Volt battery and it's too high for 12 Volt systems without an MPPT controller; much of the panel's power will be lost.

    As for testing them, use a controlled light source (doesn't have to be full sun) and your multimeter to check which tabs put out what Voltage and the polarity of them. That should tell you how they are meant to be connected together. To check for power output you will need full sun and a meter capable of 10 Amps DC to read the short circuit current and see if it is close to spec. Beyond that there are other potential problems but if you get that far you probably have a viable experimenter's panel. Not sure I'd want to trust it on a critical install, though.
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  • meridiansolar
    meridiansolar Solar Expert Posts: 34 ✭
    #7
    Re: Specific testing method for 50cent/watt laminate panels?

    got some panels in late today
    There are 4 wires on the back. I'll call them A, B, C, D
    A+B=8v
    A+C=16v
    A+D=24V

    Anyone have a wiring diagram of how the diode would go in?

    I'm guessing it goes inbetween wires B&C?

    when the sun is out tomorrow I will test amps.
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  • Shane Jackson
    Shane Jackson Solar Expert Posts: 49 ✭
    #8
    Re: Specific testing method for 50cent/watt laminate panels?

    Here is a close up of a junction box installed. You can see the diodes. They would be between a+b,b+c,c+d.

    solar-back-close.jpg

    As for testing I connect 2 meters to the panel. One to measure voltage and the other connected inline with a 24v battery bank to measure amperage.

    Wish I had my XW-MPPT60... would make testing easier..... STILL waiting on sunelec to ship it.........

    Shane
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  • meridiansolar
    meridiansolar Solar Expert Posts: 34 ✭
    #9
    Re: Specific testing method for 50cent/watt laminate panels?

    thanks
    so postive is on left side?
    how do you know the diodes that you used are the right size?
    how are bus wires held down? Looks like some kind of clamping pressure?
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  • Shane Jackson
    Shane Jackson Solar Expert Posts: 49 ✭
    #10
    Re: Specific testing method for 50cent/watt laminate panels?

    The diodes were installed in the junction boxes already (purchased from ebay). They are good for up to 280watt panels if I remember correctly.

    Anyways the diodes in the box are Schottky and are part # 10SQ050

    Here is a spec sheet:

    http://pdf1.alldatasheet.com/datasheet-pdf/view/222844/HY/10SQ050.html

    And yes the bus wires are held via a clamp.

    Shane
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  • meridiansolar
    meridiansolar Solar Expert Posts: 34 ✭
    #11
    Re: Specific testing method for 50cent/watt laminate panels?

    where did you get the bus wire?
    I see it on solarcellwire.com
    but $51.90 for 150 feet wonder if there is a place that sells it for less?
    Had to buy a $58 multimeter today and will probably blow another $60 on a solder gun tomorrow (any recommendations, seems like home depot sells crap ones as I've gone through several over the years) hopefully this all works.

    the panels them selves look great on the front. they were listed as seconds/cosmetics but they are in perfect condition on front.
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  • Shane Jackson
    Shane Jackson Solar Expert Posts: 49 ✭
    #12
    Re: Specific testing method for 50cent/watt laminate panels?

    I bought mine on ebay:

    http://www.ebay.com/itm/150597003615

    I offered $18 (+4.50 S/H) and he took it. That's 60' which should be more than enough for the 30 panels I am doing.

    As for soldering iron..... I use a Weller WES51 soldering station, but I build electronics and had it already.

    http://www.tequipment.net/WellerWLC100.html

    That would probably be good enough for what you will be doing. Or just buy a cheap $10 one from radio shack.

    Hope that helps.

    Shane
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