Solar Cell Voltage loss

hotdawg23

I was able to get the wiring all straightened out on my prototype. I have a panel that is 13 solar cells in a column and 3 columns wide. All 3x6 cells that are rated at .5V , 3.98 Amps and 1.98 watts.
Before putting the bus wire on i tested the voltage of each column and the maximum i got for each column was 6.75 volts which i guess i am happy with.
Problem started after i put the bus wires on and then tested the panel as one and was able to get about 12.5 volts. It appears that one column is not there??
Would appreciate some insight on this if anyone has a similar or exact problem.

waynefromnscanada

Re: Solar Cell Voltage loss

Without seeing it and not being there, can only guess - - - perhaps two strings by error were wired in parallel, then that pair wired in series with the third? Or perhaps one string somehow electrically bypassed? Are there bypass diodes on the strings?, if so, perhaps one wired in reverse, or perhaps shorted? While they are still wired as you have them, check each string for it's voltage, a short would result in no voltage on that string.

mike95490

Re: Solar Cell Voltage loss

Unless you are an expert solderer, I'd look closely at the tab wires on the cells, cracks in the cells.....

Urbandialect

Re: Solar Cell Voltage loss

This happened to me, you have to change your technique...trying to find where you went wrong is going to be hard, take a picture and post it and maybe someone will beable to see the probably...

What i do is tab the front of all the solar cells, make a small cup of clear epoxy and paint it on the front of the solar cell going in the same direction as the tabbing wire so not to lift any, then I place them directly onto the glass face down, wait a day for it to harden, Now i can tab the back of the solar cell without worrying about the cells moving around breaking the solder bonds on the front tabbing.

hotdawg23

Re: Solar Cell Voltage loss

waynefromnscanada wrote: »

Without seeing it and not being there, can only guess - - - perhaps two strings by error were wired in parallel, then that pair wired in series with the third? Or perhaps one string somehow electrically bypassed? Are there bypass diodes on the strings?, if so, perhaps one wired in reverse, or perhaps shorted? While they are still wired as you have them, check each string for it's voltage, a short would result in no voltage on that string.

no bypass diodes yet as i was just testing voltage before i went any farther and good thing i did.
All cells are soldered together the same, neg to pos and conected by bus wire the same way neg to pos on all 3 columns.
i will check the voltage while they are still together and go from there tomorrow in the sun.
Thanks for the help

hotdawg23

Re: Solar Cell Voltage loss

mike90045 wrote: »

Unless you are an expert solderer, I'd look closely at the tab wires on the cells, cracks in the cells.....

Mike
I do have a couple of cells with cracks but that column tested out the same voltage as the other two.
Can cracked cells have an effect ? Cause i read somewhere that broken cells are OK and will produce same voltage as whole ones??

hotdawg23

Re: Solar Cell Voltage loss

Urbandialect wrote: »

This happened to me, you have to change your technique...trying to find where you went wrong is going to be hard, take a picture and post it and maybe someone will beable to see the probably...

What i do is tab the front of all the solar cells, make a small cup of clear epoxy and paint it on the front of the solar cell going in the same direction as the tabbing wire so not to lift any, then I place them directly onto the glass face down, wait a day for it to harden, Now i can tab the back of the solar cell without worrying about the cells moving around breaking the solder bonds on the front tabbing.

This rings a bell! I do have some cells that the tabbing came loose on the front of the cell but only about a half inch and maybe 3or 4 cells at the most. How much of an effect will that have on the string?

bsolar

Re: Solar Cell Voltage loss

sorry to jump in unannounced .. if you have a tab popping up chances are it was a 'cold' solder job .. its a balance act between enough tin on the solder gun and enough heat without going so hot it starts busting things .. gluing the tab down wont make a good contact if the joint is cold, i didnt read this all, but if you didnt use a flux pen definitely you need one of those to ..

Urbandialect

Re: Solar Cell Voltage loss

hotdawg23 wrote: »

This rings a bell! I do have some cells that the tabbing came loose on the front of the cell but only about a half inch and maybe 3or 4 cells at the most. How much of an effect will that have on the string?

I think so, same thing happened on my first panel i ever built, I DID NOT use a flux pen, i used the store flux when I built it, Flux pen works much better, anyway 2 rows of 18 cells, because the way the glass was made, some of the front solders lifted up as I was working on it, and I had gotten to a point where if I tried to fix were they lifted up I might mess up the other cells that I've already linked together, as you know, the more you move the cells the more likely you'll break one, after finishing I tested the voltage... it was 11 to 12.5 volts, I was like WTF? That's why i changed my technique on how i build them, Tabb the front of all cells then glue them face down onto the glass, securing the front tabbing and making it easier to tabb the back and add bus..

NOTE: Trying to wire 2 low volt panels together that have "36 cells or more a piece" to boost the voltage to charge a 12 volt battery bank WILL NOT WORK with a PWM charge controller, I doubt it will work with a MTTP charger too, but I can't confirm that, but i can confirm it won't work with a PWM charge controller.

The reason why is because of the unseen voltage or the voltage that you're unable to measure which is VMP. VMP max is 30 on a 12 volt battery bank.. even doe when u measure the voltage with a volt meter shows 12 volts, the VMP on that panel you built is still 18 volts because each cell is .5 volt regardless of what that volt meter says, once you go over 30 the charge controller looking for a 24 volt battery to charge, which it won't beable to do because the voltage is to low....

You have to start over, If you can. I ended up destorying my panel(cells) and salvaging the glass to make a new panel out of. You can always hook a diode to the hot wire and hook it up to a single 6 volt battery and trickle charge it. But trying to wire it in series to another failed panel won't work i don't think, u can look at the specs of a MTTP charge controller and see what the max VMP it can take for a 12 volts system.

mike95490

Re: Solar Cell Voltage loss

The wonders of DIY

hotdawg23

Re: Solar Cell Voltage loss

bsolar wrote: »

sorry to jump in unannounced .. if you have a tab popping up chances are it was a 'cold' solder job .. its a balance act between enough tin on the solder gun and enough heat without going so hot it starts busting things .. gluing the tab down wont make a good contact if the joint is cold, i didnt read this all, but if you didnt use a flux pen definitely you need one of those to ..

I did use a flux pen on the ones i did but problem is the ones that came from the factory. In looking closely i can see that the undertab is white and if i scrape it with a sharp knife i see the solder under the white. I then use my flux pen and solder it down.
Question here is... what is the white coating?

hotdawg23

Re: Solar Cell Voltage loss

mike90045 wrote: »

The wonders of DIY

You are right, but practice makes perfect. (sometimes) Anyway, that is why i am building the prototype first. I keep a log of all my mistakes so i won't make them again. I will start my main system which consists if 14 panels that will produce just over 2 KW.