Solar Panel Configuration

[Operastone]

Hello guys,
I have following system(see attahments) installed at my home. It comprises of 6 panels; each of 200 watts,a dual inverter(utilizing both solar and Utility power to charge battery)+charge controller, and two batteries 150Ah each. I live in Pakistan where we get of 9-10 hours average sunshine and very little cloudy days.I have these panels connected in parallel and the panel current for 5-6 hours is 38-42 Amps and voltage 28.5-29v and during 2h in morning and evening 1 hour Amps drop down to 30-35 depending upon sun.These measurements have been taken directly from solar panels without connecting to Charge controller/inverter or Battery.
Now the problem is when i connect panels to charge controller and batteries the batteries seem to take only 6-8Amps even when they are 25% and no matter how much load i apply the current from charge controller remains the same.In contrast when i switch the inverter to utility charging mode and disabling solar charging mode the batteries start taking 22-25Amps of charging current and they charge pretty quickly.But When i switch inverter to Solar charging mode the Charging current Declines and batteries take only 6-8Amps and when i increase load to 200-250 watt the batteries start excess power instead of Charge controller increasing Amps from panels.
I have tried 2 different types of charge controllers but the problem persists.Please Reply if anybody knows Why charge controller is wasting 20-30 amperes and giving 6-8amps only to Batteries Thanks in Advance.

P.S: i think the person in this thread http://www.solarpaneltalk.com/showth...rge-controller is suffering from same problem but i have checked all my connections but still no luck.

[inetdog]

Either you Charge Controller (CC) is defective OR your panel voltage is just too low to match your 24V battery system. Or you have really outrageous resistive losses in your wiring. Or some combination of the above.
Since you cannot force the CC to load down the panels completely, I will assume that the 28V figure is the Voc of the panels and the 40A figure is Isc.
A suitable panel for charging a 24V battery system will have a Vmp of close to 36V and a Voc of about 40V.

If you look at the current versus voltage curve for your panels, you should see that at the 24-28V needed to charge your batteries the current is far less than the Isc value or even the Imp value.
If you are stuck with those panels, you may have to put them in a series circuit and use an MPPT type charge controller. Probably two parallel strings of three panels each in series.

[Operastone]

Either you Charge Controller (CC) is defective OR your panel voltage is just too low to match your 24V battery system. Or you have really outrageous resistive losses in your wiring. Or some combination of the above.
Since you cannot force the CC to load down the panels completely, I will assume that the 28V figure is the Voc of the panels and the 40A figure is Isc.
A suitable panel for charging a 24V battery system will have a Vmp of close to 36V and a Voc of about 40V.

If you look at the current versus voltage curve for your panels, you should see that at the 24-28V needed to charge your batteries the current is far less than the Isc value or even the Imp value.
If you are stuck with those panels, you may have to put them in a series circuit and use an MPPT type charge controller. Probably two parallel strings of three panels each in series.

Can u tell me the exact method to measure Voc and Isc. If u look at attachment i posted the info on back of panels say Voc is 34.5v. I think i have been measuring Vmp

[Operastone]

Plz demonstrate more on Series and parallel config you mentioned and please explain by wiring panels in series will i have to switch to 48v system? i am completely new to solar panels.

[inetdog]

Can u tell me the exact method to measure Voc and Isc. If u look at attachment i posted the info on back of panels say Voc is 34.5v. I think i have been measuring Vmp

You measure Voc by looking at the terminal voltage with nothing connected to the panels but the meter.
You measure Vmp by putting enough load on the panels to draw exactly the listed Imp current.

If the controller is taking all the power it can from the panels, the current would be close to Imp and the voltage will be less than Vmp (approximately equal to the battery voltage) for a PWM controller.

At this point, I would say that there is a major error in your wiring or the CC is defective. If you have put the panels in series rather than in parallel, it would match the voltage and current that you are seeing, but the string Voc will be high enough to damage your CC.

How are you measuring the 40A from the panel array?

[Operastone]

You measure Voc by looking at the terminal voltage with nothing connected to the panels but the meter.
You measure Vmp by putting enough load on the panels to draw exactly the listed Imp current.

If the controller is taking all the power it can from the panels, the current would be close to Imp and the voltage will be less than Vmp (approximately equal to the battery voltage) for a PWM controller.

At this point, I would say that there is a major error in your wiring or the CC is defective. If you have put the panels in series rather than in parallel, it would match the voltage and current that you are seeing, but the string Voc will be high enough to damage your CC.

How are you measuring the 40A from the panel array?

I have measured current by connecting +ve and -ve wires from panels and placing clamp meter on one of the wires.Today at 1 PM i measured that current and it turned out to be 41Amps Isc.I did one more thing i disconnected the charge controller and connected batteries directly and measured the current again It turned out to be only 8Amps. So that means my Imp is only 8 Amps and Isc is 41Amps.

[inetdog]

I have measured current by connecting +ve and -ve wires from panels and placing clamp meter on one of the wires.Today at 1 PM i measured that current and it turned out to be 41Amps Isc.I did one more thing i disconnected the charge controller and connected batteries directly and measured the current again It turned out to be only 8Amps. So that means my Imp is only 8 Amps and Isc is 41Amps.

That can happen if you have one or more bad cells in a panel. The bypass diode of the section containing the bad cell will be activated and you will get a voltage which is reduced by 1/2 or 1/3 compared to Vmp. The result would be a voltage too low to properly charge the battery, so the effective current will end up being the current which can be passed by the weak or defective cell.
If this is your problem, then either a small part of each panel is being partially shaded (improper mounting, for example) or you have been sold a bunch of defective panels.

You will need to measure the panels one at a time, connected to the batteries, and compare the Isc for that panel to the observed I under load.
Rule of thumb: Vmp should be about 80% of Voc and Isc should be about 120% of Imp.
The defective or shaded panel will have the same Voc but a greatly reduced Vmp and Imp.

The bottom line is that for some defects or installation problems, just measuring Voc and Isc is NOT sufficient to tell a bad panel from a good one.