Low current from Solar Panels

[RobNCD2]

The Open circuit voltage is between 17-21 volts and the Short circuit current is around     3.5 amps. The problem lies when I hook the panels to a load. The current drops to about 40 percent of short circuit current. I have tried different batteries and heavier wire from the panels. Anyone have any idea what would cause that difference?

Thanks for any help.

[kurt]

that sounds about normal to me short circuit amps would be 3.5 amps at 0 volts. you raise the volts to 12v and the amps are gonna be lower. what is the panel rated at watts wise and what are you getting if you are getting 80% of rated watts at noon you are doing really good.

[RobNCD2]

No actually under load at 12 volts I can barely see an amp.  They are 60 watt panels.  I am just wondering why since the short circuit amp is around 3.5 amps (which should be absolutely the max the panel should output) that I cannot get any current out of it under a battery load.  Very strange indeed...

[jimjjnn]

Are the batteries at full charge and are the panels connected to a controller?

[RobNCD2]

I have tried a discharged battery and also a fairly well charged bank, with about the same results.  I would expect the current to be higher when the battery is discharged more.  I have also tried two different controllers with the same results.  The last thing I tried was heavier gage cable (4/0).  Still cannot come close to the shorted current.  I was expecting about 80 percent of short circuit current.

[kurt]

what time of day are you checking?? and this panel is positioned facing south at the proper angle for your latitude?? they are not inside behind double pane windows like the last guys were are they??

[AbyssUnderground]

My fault with the panels behind double glazing :-) I learned from that (tho I do still have one behind it!)

If they're not outside, then move them outside. Try testing the current with a 12v 50w automotive bulb and see what the current is then. The battery may not be pulling all the current from the panel.

[ghurd]

Chronar's are getting pretty old now.  Is it used, or New Old Stock?

Assuming it is thin film, they wear out, and were not very well sealed against moisture.

Try it with a lower battery, like 12.2V.  You should get 80% Isc if everything is right.

Maybe try it with a 6V battery, or 5 AA NiCDs, without a controller.

Could try the head light test, and check the amps into the head light, and the voltage.

Glass backed?  Hold it up to a bright light.  

Can you see any areas of the film just "missing"?  

Especially look at the edges, where nearly a whole single stripe is damaged.  

If so, there is a good chance it is worn out or damaged.  Not repairable.

May be worth peeling the tape over the terminals back to check for a corroded connection.

G-

[Nando]

If the panels are 17-21 volts, then check the current with a 12 volts battery, they may seem to have a very low MPP voltage/power.

The right way is to use a resistive load, decreasing its value down to short circuit and with a high value resistance that should be not greater than drawing 20 % power.

This way you attain the voltage/current curve and define the MPP value.

They may be very old and not producing enough voltage.

Nando

[RobNCD2]

I get the best readings around solar noon (12:15 here right now).  The panels are all pointing south and at the right angle (latitude +- season).  Voltage goes from 17-20 open down to battery voltage when applied.  It also, doesn't seem to matter using a controller or not.  These are old Chronar 3x4' 60 watt panels.  

I was thinking maybe they just couldn't sustain the voltage under heavy load??  I am at a loss of what to do except be happy with a lot of used space with very little power out, and start budgeting for new panels.  I guess I write these off as getting taken from the previous owner, as he said they would produce about 2 amps each.

[finnsawyer]

Try an eight or ten ohm resister instead of the battery, and see what load current and voltage you get.  This should eliminate any problems with the batteries, which while being rare can occur.

[RobNCD2]

I think that is the problem  Under load the panels cannot sustain the voltage.  When hooked to a 6 volt battery they do perform better.  

Question:

Would it help to wire the panels in series to get an open circuit of about 20 volts and apply this to the C40 and then my 12 volt bank (1740Ahr).  Would this increase my charging current or would the result still be about the same?

Thanks again for the help

[RobNCD2]

I have to correct that.  Wiring them in series would bring the open circuit voltage to about 40 volts.

[AbyssUnderground]

The current would be the same. You need to parallel them to increase the current.

[drosne01]

Just curious--how does having solar panels behind a double pane of glass affect output?