Solar Panel efficiency loss of 50%

solaris3000 · June 2011

Having some trouble with a panel that is rated at 125 watts but only outputs 63 watts during Full sun conditions.

Output of Rogue,
snapshot taken at 14:30 PST with FULL Sun Conditions/

IN: 17.0 3.7a 63w
Out 12.8 4.9 MPPT
487wh 38ah 23c

My panel is 125 watt panel. I don't understand why I would be getting 50% loss of rated output.. Is this due to misconfiguration of Rouge on my part or defective solar Panel.....
Panel is 15feet from Rogue and battery bank.....

Thanks in advance
Brian
SanDiego

Cariboocoot · June 2011

Re: Solar Panel efficiency loss of 50%

The output of a charge controller is not the best judge of the panel's power; if the battery won't take any more charge current the panel won't produce it. But at 12.8 Volts you certainly would expect to see full charge current as the controller tries to bring the battery up over 14 Volts.

There are many things that can affect a panel's power output. Chief among these would be angle; if it's not getting full insolation it will not produce full power. Another big factor is temperature, which you can't do anything about. You can check the angle with a shadow cast against the panel at midday: a stick parallel to the panel's surface should make a shadow as long as the stick. Not longer, not shorter.

You can also check the panel's output by disconnecting it from the Rogue and testing the Isc with a properly set multimeter. Again this should be done around midday with the correct panel angle and the panel oriented at least close to due South.

BB. · June 2011

Re: Solar Panel efficiency loss of 50%

What brand/model of solar panel? What Vmp/Imp ratings?

The Vmp voltage looks fine (assuming Vmp~17.5 volts).

Solar panel current is, more or less, proportional to the brightness of the sun.

I would not expect full output at 2:30 pm if this is fixed south facing array, but 50% loss seems a bit much.

I don't know the Rogue details--but "MPPT" would seem to indicate that the controller is maximizing solar panel output. And the 12.8 volt battery voltage would indicate that the controller really does need to recharge the battery bank (if the battery was near full--~14.5 volts or so--then the controller could be cutting back on output current).

Tomorrow (or next time you can), around noon, try placing a DMM set to 10 Amp full scale current and measure the short circuit current of the solar panel. Isc should be within 10-20% of the panel's Isc rating. If it is 50% of that rating on a clear/bright day--then there is probably something wrong with the panel or the wiring (don't think wiring is bad--Vmp/Vpanel looks OK).

Also measure its Voc value... That should be pretty close to the rated Voc (especially if the panel is kept cool).

Clean the panel glass (soap and water if needed) and look for brown/black scorch marks on the solar cells. I had some bad panels and they showed a light brown/coffee colored staining (and a few panels has "air bubbles" from the beginning of decontamination) above the junction box.

However, even "bad panels" may have no visible defects.

If you had a second "good panel"--You could measure its Isc vs Isc-rated and compare against your "unknown" panel Isc/Is-rated output.

-Bill

solaris3000 · June 2011

Re: Solar Panel efficiency loss of 50%

I do remember seeing some localized discoloration on the panels. I will take a closer look tomorrow when I start testing with the meter after cleaning the glass.. If it is defective I hope the company will send me a replacement.

UL-Solar Model STP125P-F4S
Power at STC ( Pm): 125 Watt
Maximum Power Voltage ( Vpm ): 18.1 Volts
Maximum Power current ( Ipm ): 7.14 Amp
Open circuit voltage ( Voc ): 22.4 Volts
Short circuit current ( Isc ): 7.72 Amp

BB. · June 2011

Re: Solar Panel efficiency loss of 50%

The glass may have to be very clean to see the discolorations... My panels would get a brown stain from the local trees that looked very much like a problem (mostly at the lower corners where water would collect and evaporate).

-Bill

solaris3000 · June 2011

Re: Solar Panel efficiency loss of 50%

Hi, I just wanted to upload a few images of what I'm seeing on the Solar panel.
They resemble sunspots due to the irregularity but only seem to be affecting a few of the individual cells.
I will start testing around noon pst and see what the numbers look like. In addition to a DMM I have a Watts-Up meter I use for my RC stuff. I will connect that and see what it reads.

thanks

regards
Brian

BB. · June 2011

Re: Solar Panel efficiency loss of 50%

I do not know--In the first picture, is there spotting on one of the cells?

-Bill

bmet · June 2011

Re: Solar Panel efficiency loss of 50%

The 2nd two images are of a Moire patten, nothing to worry about. The first image has both the shadow of the Op, and geometric shading which may also be Moire, just less apparent. A shadow stick at high sun is your easiest alignment tool, for your best readings.

solaris3000 wrote: »

Hi, I just wanted to upload a few images of what I'm seeing on the Solar panel.
They resemble sunspots due to the irregularity but only seem to be affecting a few of the individual cells.
I will start testing around noon pst and see what the numbers look like. In addition to a DMM I have a Watts-Up meter I use for my RC stuff. I will connect that and see what it reads.

thanks

regards
Brian

solaris3000 · June 2011

Re: Solar Panel efficiency loss of 50%

Thanks for the technique for setting alignment.

Is it normal to see a voltage drop when checking direct from the panel or from the DC load center/charge controller. Should I be concerned about this voltage discrepancy of 6 volts.

Noon time-frame

Voltage at PV cable ends.. 20.3 thru 20.5 vdc

Voltage bus bar inside DC load center.. 14.1 thru 14.5 vdc

Am I getting impedance due to my wiring. I am using AWG 4 and AWG 6

bmet · June 2011

Re: Solar Panel efficiency loss of 50%

Those look like input to CC, and output from CC. Yes those are typical. The CC is regulating charge rate based on battery select.

solaris3000 wrote: »

Thanks for the technique for setting alignment.

Is it normal to see a voltage drop when checking direct from the panel or from the DC load center/charge controller. Should I be concerned about this voltage discrepancy of 6 volts.

Noon time-frame

Voltage at PV cable ends.. 20.3 thru 20.5 vdc

Voltage bus bar inside DC load center.. 14.1 thru 14.5 vdc

Am I getting impedance due to my wiring. I am using AWG 4 and AWG 6

BB. · June 2011

Re: Solar Panel efficiency loss of 50%

Depends... You have a Rogue mppt controller which will try for Vmp of 17.5 volts or a bit less when on mppt mode. As the controller cuts back on current as the batteries approach full charge.

20 volts or a bit more would be an unloaded panel.

Your 14.5 volt battery voltage is near full, or full. All appears to be fine at low load current.

-Bill

Solar Panel efficiency loss of 50%

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