solar panel output

conntaxmanconntaxman Solar Expert Posts: 125 ✭✭✭✭✭
Testing a solar panel made of 36 -3x6 cells.If i have 4 -65 watt panels and want to test them for voltage/amps.If i test each one with my volt meter, {in the sun same brightness for all test]To test for volts, red led to + black led to - Thats easy. now for amps. My meter will go to 10 amps.Move red wire on meter to amps, then do the same as above? right.It was just a bright day little sun, got 18 volts I didn't check the amps at the time.But I should of had about 3amps ?
So now if i wired all 4 parallel, the Voltage will stay the same,but the amps would be 12 ??
Now if I put them in series [4] i would get 72 volts and about 3 amps ?
Reason is that I hooked up a 500 watt grid inverter and I had the 4 panels in parallel, and the kilowatt meter was saying only about 22 watts. Don't sound right to me.It was like LATE in the afternoon, not a BRIGHT sun.
To night i just hooked up a amp meter before it goes into the 500watt grid inverter.
tks
John
I forgot to mention. I had one panel that only was putting out 13 volts. oh thats right when i checked the voltage at the end it was 15 volts coming from the 4.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: solar panel output

    Legal disclaimer: these are homemade panels, yes? It is not legal to use non-UL listed components for a grid-tie system. It isn't likely the 500 Watt GT inverter is listed and legal either.

    Now then, four 65 Watt panels adds up to 260 Watts - under ideal conditions. On average it would be more like 200 Watts. Also with a GT inverter there has to be enough Voltage to activate it. Not knowing the specs on the inverter we don't know if you've got enough panel to activate the inverter. 22 Watts on a K-A-W @ 120 Volts = 0.18 Amps which is not very much from 260 Watts of panel.

    Otherwise, four panels connected in parallel will result in increase in current with consistent Voltage (one panel being 17.5 Volts @ 3.7 Amps ideally) for 17.5 Volts @ 14.8 Amps. Four panels connected in series would be 70 Volts @ 3.7 Amps. Both work out to about 260 Watts (17.5 * 14.8 = 259 Watts, 70 * 3.7 = 259 Watts).

    I don't wish to sound mean, but this is why you do not use homemade panels and off-brand GT inverters. You really need to know about the basics of electricity before you start experimenting with it.
  • conntaxmanconntaxman Solar Expert Posts: 125 ✭✭✭✭✭
    Re: solar panel output

    caril. but isnt a solar cell a solar cell no matter were it is being tested or used. exp. a bought panel say 65 watts, that should put out about the same as a diy. Im saying if they Both used 36 -3x6 cells. Is that right or wrong? I think so.
    Lets just talk about the panel if you don't mind. not ul approved and all that other stuff.I know all about it.
    thank you.
    John
  • conntaxmanconntaxman Solar Expert Posts: 125 ✭✭✭✭✭
    Re: solar panel output

    Caril. i found out what it was, i had one panel that was only putting out 13volts, I changed it out and now both the volts and amps are coming up.It's now only 9:50 am and the sun isn't hitting my rack of panels stright on. I cant belive how much all this little stuff means,oh and their was a little shade on some of the panels.
    Its already up to 90 watts on the killawatt meter. I know their is a loss with this grid tie inverter.
    tks
    John
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: solar panel output

    The problem with home made panels is the lack of availability of "A" grade cells most that are available are either damaged or rejects {cant meet specs)
    Obtaining genuine "A "grade cells is not easy. AND usually end up costing MORE than a bought panel.

    As an experiment at work myself and another person built a solar panel using the best components and used a vacuum machine and a sealer better that can be commercially bought. It took to 2 of us a whole day to construct it. In the end it tested to be slightly better than a similar sized bought quality panel. All up cost above that of a bought one..

    So why would you bother???

    Playing around with home made panels and grid tied inverters IS NOT FOR THE INEXPERIENCED. ,DONT DO IT its dangerous to yourself and others.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: solar panel output

    conntaxman;

    You have indeed answered your own questions, including the one you asked of me. One of your homemade panels was only putting out 13 Volts. That is the whole problem with homemade panels: 1 way to do it right, a million ways to do it wrong. Starting with, as john p mentioned, the fact that the cells you buy to build them with are inevitably ones rejected by commercial manufacturers for not being up to spec.

    Even if you get it to work, the lack of UL certification and permitted install means that if anything should go wrong the liability will be entirely yours. It will not matter whether or not your panels & system were actually the cause; you will be blamed. Considering the extent of the potential destruction, we consistently advise people not to use homemade panels for GT systems. Building your own to learn about panels and how they work is fine (but more expensive than commercial panels) but relying on them for power output, even off-grid, is not sensible.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: solar panel output

    Okay, we will call this a science fair project. Not legal for real implementation.

    A good quality cell in full sun (1000 watts/sq. m.) will put out about 35 mA per square centimeter of area. 3"x 6" half cell is 116 cm sq. so the current from the cell should be close to 4 amps.

    Unloaded, open circuit each cell should be about 0.62 vdc at full sun, depending on how long you let them heat up in the sun. Times 36 cells is 22.3 vdc for Voc. Vmp is about 0.5 vdc per cell or 36 cells x 0.5v is 18 vdc.

    Illuminated cells are current sources so you can short circuit the 36 series cell panel and should get close to 4 amps in a full sun. Being it is winter time you may not be able to get a full sun illumination because the sun is not high in the sky at noon time (depends on your latitude). So maybe 80% or 3.2 amps.

    You should not be putting 36 cells in series without breaking them up into two 18 cell groups with two bypass diodes. All cells have some defects. The ones we are concerned about is shunt defects and particularly severe point concentrated defects with low shunt resistance. This is the most common problem with aftermarket (eBay) sold cells. They are rejects from manufacturers of commercial panels. They make full output current but are potential fire hazards if there is shading on a panel. When a cell gets shaded it can be reverse biased by the other non shaded cells. This creates a high voltage that is applied across the shunt defect that can get really hot. Hot enough to melt solder and delaminate the cell's top metalization. The bypassing diodes every so many cells keep the maximum reverse bias down on any shaded cell.

    A way to check a cell for shunt resistance performance is to apply 10 volts of reverse bias and measure leakage current with an ampmeter with the cell face down so it does not have illumination on it. Should not use any cell that has leakage greater then 1 amp @ 10vdc of reverse bias. This does not check for hot spots caused by a single severe defect. The only way to do that is with an IR temp sensor gun, or IR imager if you have one, or at minimum running your fingers across back of cell feeling for hot spots.
  • conntaxmanconntaxman Solar Expert Posts: 125 ✭✭✭✭✭
    Re: solar panel output

    well now im about going Nuts. The other day i disconnected the 500watt grid tie inv. and put it in a box to send it back to Cail.[USA] Be cause Tops i was getting only 120 watts showing on the watt meter. Since then it was bothering me about the low wattage. seeing that my LCD amp meter dosent work, what i did was use my muli meter,put it on the 10 amps and it read 11.1 and the volt meter said 40volts. I mul. 40x11.1 and it came out 444 and that is suppose to be watts. STOP...STOP..
    ........................... Found out the problem the JUNK EEEE ..LCD volt meters from china are NO....NO good. while typing this ,i went and tested the voltage with my mul. meter and it read 19.9 volts not 40. peace of junk meters.
    so now i feel better seeing that the panels are putting out about 220.89 watts. Like i said it was 4 panels each of 36 3x6 cells.should be about 260 watts.
    I guess that that "sun 500g" was not good on eff." or the kill a watt meter was wrong.
    ha ha ha ...a learning experience.
    John
    Just though I would tell you what i found out, so you can get a laugh.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: solar panel output

    Let's just say that sometimes the extra money for the name-brand equipment actually does by better quality. :roll: This goes for panels, inverters, and even multimeters.
  • conntaxmanconntaxman Solar Expert Posts: 125 ✭✭✭✭✭
    Re: solar panel output

    ha ha ha LOL..LOL... I must be going nuts, or just getting tooooo old. ha ha ha. I REchecked that LCD volt meter and come to find out it had it tied into my < OTHER > set of panels .lol and their wired in series. I feel like a FOOOOOOL.
    ha ha ha ha ha ha ha
    John
    Im just in a hurry i guess.
  • BB.BB. Super Moderators, Administrators Posts: 29,728 admin
    Re: solar panel output

    Get a DC Current Clamp meter so you can confirm current readings once in a while without having to take connections apart/tracing wiring... (Horse, dead, being beaten ;))

    -Bill :D
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.