Using bare panels

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  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Using bare panels

    These sound like my home made panels. I built 30 watt half panels. No frames. Good glass that make them plenty stiff without framing. Nothing but encapsulant or eva. No juntion boxes. Just tabbing wire with a diode connected to the pos. tabb. I wired them in series to the number that would give the voltage I needed. 18 volts, 27 volts or 90 volts. I used 12 awg wire with solder from the tabbs pos to neg to pos till I got whatever voltage I wanted. I made half panels so I could match voltage with bought panels and they were easyer to move but more connections to make. I have had them out in the wether for over a year and saw no degrading of the exsposed tabbs except for two that where touching the wood they were mounted on. The two touching wood corroded almost immedeatly. The rest seem to be ok. If I do more I will probly spray with varnish. If I go with higher voltage then twenty seven volts I would probly use shrink wrap on the connections. I find this to be fine on my ground mounted system. I don't know about a school.
    Simple if the price is good enough.
    gww

    PS I hooked 180 watts worth of panels though a cheep 12 volt $12 or $19 dollar solar controller and put it at a creek where we camp and hang out. Two car batteries and a 750 watt ac inverter. Gives enough light to find the out house and run a radio. Have a rv parked there and have watched movies on a projection screen and dvd at 16 watts. Going for maby a year and half.
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Using bare panels
    Well urk! 6.45 Volts isn't much at all. You could wire the two halves in series and get 13.90 Volts, which also isn't much at all.

    Can I hook these up in series? It seems to me that if I measure voltage from one of the positive tabs to either of the negative tabs and vice-versa then they are not really two separate halves, unless that's how solar panels work. It seems to me there are two tabs from the same source. Does that make sense?
    With no load on them they should be putting out Voc which ought to be around 17 Volts for a "12 Volt" panel (8.5 Volts per half - this fits with the 8.6 stamping). The series wiring will require connections across from one (+) to the other (-). You could also wire the individual panel halves in parallel, then put two or more panels in series. Neither is ideal given the Voltage and physical layout of the panels.

    The printout of the panel test that I posted earlier shows that these are not nominal 12vDC panels but are actually pretty close to what I measured. My planned use is to run all six of these in series with an MPPT charge controller to charge a 12vDC battery bank.
    Next thing to do if you can is test each half of one panel for short circuit current. You need bright sun directly on the panel and an Ammeter capable of reading the expected current connected from (+) to (-) on one half. These are supposed to be 50 to 60 Watts? That should be under 4 Amps current.

    Measuring DC amps is no problem. Do I have a time limit before I cook something when measuring the short circuit current? My DC ammeter is a Fluke clamp on for my multimeter so that is not a concern. I just don't want to see flames from the panel!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Using bare panels
    Can I hook these up in series? It seems to me that if I measure voltage from one of the positive tabs to either of the negative tabs and vice-versa then they are not really two separate halves, unless that's how solar panels work. It seems to me there are two tabs from the same source. Does that make sense?

    If either positive to either negative results in the same Voltage then they are as one. If one positive measures against one negative and the other positive to the other negative then they are two halves meant to be wired in series to produce higher Voltage.


    The printout of the panel test that I posted earlier shows that these are not nominal 12vDC panels but are actually pretty close to what I measured. My planned use is to run all six of these in series with an MPPT charge controller to charge a 12vDC battery bank.

    Yup. Saves a ton of trouble over trying to configure them for an "actual 12 Volt panel (17.5 Vmp)". However, you have no bypass diodes so shading will kill the whole string. You need to figure out the individual panel wiring first if that is a concern.


    Measuring DC amps is no problem. Do I have a time limit before I cook something when measuring the short circuit current? My DC ammeter is a Fluke clamp on for my multimeter so that is not a concern. I just don't want to see flames from the panel!

    Nope. Isc can be produced by a panel indefinitely, unless it is defective. Using a Fluke DC clamp-on Ammeter? Couldn't be better! :D
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Using bare panels
    If either positive to either negative results in the same Voltage then they are as one.

    This is how they seem to work. Should I just tie both positive and both negatives together then?
    ...you have no bypass diodes so shading will kill the whole string. You need to figure out the individual panel wiring first if that is a concern.

    Are the diodes simply for shading? These will be on the roof of a building that has no surrounding trees to shade it. If the junction boxes are not usable can I use the diodes from those? I'm still not clear on what the problem is with the junction boxes and panels. If I can run the leads to one end of the panel is there any reason why the junction box would not work? What does the wiring look like to use diodes? Since these will all be wired in one series string doesn't current need to flow through all panels?
    Nope. Isc can be produced by a panel indefinitely, unless it is defective. Using a Fluke DC clamp-on Ammeter? Couldn't be better! :D

    I'd get on this when we get back. Out in the "big city" of Freetown right now for our monthly supply trip.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Using bare panels
    This is how they seem to work. Should I just tie both positive and both negatives together then?

    If both are the same then it would make no difference and I don't know why they'd construct it that way.
    Are the diodes simply for shading? These will be on the roof of a building that has no surrounding trees to shade it. If the junction boxes are not usable can I use the diodes from those? I'm still not clear on what the problem is with the junction boxes and panels. If I can run the leads to one end of the panel is there any reason why the junction box would not work? What does the wiring look like to use diodes? Since these will all be wired in one series string doesn't current need to flow through all panels?

    Bypass diodes are for shading. Otherwise with segments connected in series if one gets shaded its output drops and it becomes a resistance in the series rather than a contributor. The bypass diode allows the output from the other segments to travel around the resistance rather than through it. It doesn't stop power loss, just reduces it.

    Those junction boxes are designed to be attached to a panel that has three segments all terminating in the same location. It is a matter of them being physically incompatible, since the negative and positive of these panels are at opposite ends of the panel. That's not saying they couldn't be attached, but it looks to me as though there would be no point in doing so: simply connecting leads to the (+) and (-) is all you've got. Since there are no bypass diodes (apparently) and the two 'halves' seem to be the same you may want a bypass diode around the whole, assuming you can get one that will handle the full current of a panel (which is yet to be determined).
    I'd get on this when we get back. Out in the "big city" of Freetown right now for our monthly supply trip.

    That's definitely the next step. You should have some idea of panel Voltage, current, and layout after that. Although that's still no guarantee it will work well. :roll:
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Using bare panels

    Shorted the panel out to terminals "kitty corner" to each other. 7.7 amps short circuit in full sun. Essentially 0 vDC on the other two legs. I'll simply connect both positive terminals together and both negative terminals together and go with that.

    How would one use diodes in this instance?
  • BB.BB. Super Moderators, Administrators Posts: 32,013 admin
    Re: Using bare panels

    This Tech FAQ has some information on diodes (blocking and bypass):

    http://www.windsun.com/General/tech_tips.htm

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Using bare panels

    OK, I now see how the diodes for shading are hooked up. Getting back to the junction boxes I have and remembering that I am 6 hours from Freetown and even there the selection of parts is severely limited I need to do the best with what I have on hand sometimes.

    It is clear that the box will not fit over all the leads but for the purposes of the bypass diodes would it be possible to mount the junction box over one set of leads and run the other set to the junction box? Could I, or is it advisable or not to run the positive and negative leads into this junction box, both positive side by side and both negative side by side thereby having a lead in each "slot". Is there any harm in having the extra diodes? If the extra diodes are of no use or will rob power could they not be bypassed? Is this a reasonable way to get the bypass diodes in the system knowing that getting them some other way is months away?

    The way I see it, the final system configuration will be all six panels in a series chain for approximately 40vDC at 7.7 amps short circuit. This will go to a Blue Sky SB3024iL MPPT controller c/w IPNPRO remote display for programming purposes, and charge a pair of 6v flooded Interstate deep cycle batteries also in series for a 12vDC battery bank. From the battery bank the power will go through the "load" terminal in the controller to allow lights for a given amount of time after dusk or until the batteries reach a preset level of discharge, whichever comes first. The lights will be about 10-12 12vDC LED lights, the total amp draw of which should be well below the 20 amp maximum for the load terminals. There will also be a couple of 12vDC motion sensor lights that will operate directly off the battery bank so they can operate all night as needed.

    The purpose of the system is simply to provide lighting for a given amount of time after dusk.

    There is a remote chance of a small MSW inverter as well which would be controlled from a relay connected through the load terminals so it too is only operable for a set amount of time and cannot deplete the batteries excessively. The inverter would be used to charge mobile phones which otherwise would be charged off a communal generator (the type that ate two of my adaptors yesterday:grr). The purpose of the relay is to avoid overloading the "load" terminals with the higher amps needed for the inverter.

    Please critique this as necessary. I want to know why or why not this is a reasonable plan.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Using bare panels

    You are going to have to run wires from those panel tabs to someplace to connect them to the next panel and so forth. One of those junction boxes has three diodes in it, but we don't know the specs on the diode (particularly current rating). If they are under-rated for 7+ Amps and you do get shading of a panel, the diode will fry. If they aren't (or no shading occurs) they are fine in terms of electrical connection; just a bit messy mechanically. One junction box handling three panels, another handling the other three. The two joining via the connector cables and the other cable ends feeding the lines to the controller. This is something you should wire up and try before taking it over, just to be sure it functions. How long it functions for could be a separate issue.

    Yes you can use the LOAD terminals to operate a relay to control battery connection to a small inverter. Finding a relay capable of handling the inverter will depend on how much power it draws. a big inverter has the potential to draw a lot of current on 12 VDC. Multiply the relay contacts' rating by 10 Volts for maximum inverter capacity (i.e. 5 Amp contacts = 50 Watts, et cetera). Don't ask me where to get a suitable relay; that's not in my venue.
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Using bare panels

    OK, maybe I wasn't as clear as I thought I was. I have six bare panels and six junction boxes. As I see it, each junction box has four potential connection points. Each panel has four tabs. If I mount a junction box on each panel, run the positive tabs to the locations in the junction box nearest the positive lead and the negative tabs to the locations in the junction boxes nearest the negative lead, and then plug junction boxes in to a series configuration will that work? I'm not anticipating any shading at the site. If there is shading it would be from clouds passing over rather than a more direct shade like a tree shadow.

    Once all is wired can I still put it all in short circuit and see the amps? Will the added wattage do any damage to things?

    The inverter would likely be a 600 watt MSW inverter. At 10vDC that's 60 amps. I have a 70 amp 12v automotive relay here so that should not be an issue.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Using bare panels

    No reason why you can't use one box per panel if that's what you've got. As far as needing to run wire from each tab on the panel, I'm not sure that's necessary as they seem to be electrically the same on each (+) and each (-) tab. If it's convenient for you to mount a box to a panel at one end then run wires from the opposite tabs, go ahead. Parallel wires should be attached to the same point in the box.

    The odd bit is the three diodes in between the (+) and (-) leads of the boxes. Since a panel is (apparently) one segment, there only needs to be one diode (or diode pair if they are doubled to handle more current). Adding in two more in series would drop Voltage even more across the set if shading occurs. You may jumper from one diode to the output (shorting across the other two).

    If you wire them all up, test each one individually to make sure all are identical, then connect the six in series and test the whole array. The short circuit current should be the same for six in series as one individual panel +/- tolerance. Only the Voltage should climb. Reading the Voc is easy, but you may want to concoct some test load to see how much Vmp you get.

    How much power does that relay draw? Just remember it will be eating in to the battery capacity all the while it is engaged. So long as that is understood, it should be fine.
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