Solar module inefficiency

[kudu]

I sent the following email to Matrix Solar.  They manufacture or market Photowatt modules.  I have not received a reply to date but would be interested in feed back from the discussion board.

Thanks,

Kudu

In 2003 I purchased two PW750 80 watt solar modules.  The accompanying installation manual rated the modules at 17.3 operating volts and 4.6 amps.  To date, the maximum amperage achieved is less than 4 amps for both modules combined.  I am using a Solar Boost 2000E power point tracking charge controller.  Amperage is checked on a clear day between 11:00 and 1:00 CST(such as today, October 26,2005, Fort Worth, Texas, maximum outside temperature about 65F, cloudless sky).  During that time the modules were pointed directly at the sun.  The modules are mounted atop a pole approximately 15' from the charge controller and batteries(six T105 6 volt Trojans).  10 gauge multi-strand copper wire carries the current from the modules to the charge controller.

Even factoring in as much as 30% module inefficiency, the two modules should still be able to produce in excess of 6 amps.

Is my math faulty?  Have I overlooked something?

I have room on the solar mount assembly for an additional module and the wire has already been run.  I wish to purchase another 80 watt module to match the other two; however, I am concerned with the inefficiency of the two panels I have.

I would very much appreciate a detailed response addressing my concerns and clarifying this inconsistency.

[Dreadstar]

are you wiring these in series for higher voltage or parallel for the higher amperage?

  Also post the peak wattage noted aswell as the total AH into what vdc battery bank for a day of good sun.

[Volvo farmer]

There are a lot of variables in a complete solar system. You've got wiring, a charge controller, batteries (possibly too full to accept a charge?) and your amp measuring device that could all contribute to the numbers you are seeing.

Want to test the panels? Go out to the rack with a multimeter in your hand. Disconnect all the wiring. Check the DC voltage in full sun, the panels should have a Voc rating. See how it compares. Now set your meter to 10ADC and measure the amps across the terminals, this is the short-circut amp rating or the Isc, see how it compares. If those numbers are within 10% of the panel's rating, there is nothing wrong with the panels. BTW that 17.3V number is probably the voltage at peak power. your Voc should be higher, in the neighborhood of 20-22V.

Okay, I just looked it up for you. Voc should be 21.6V and your Isc should be 4.7A

If your numbers are in that range, you might want to send Matrix a little letter of apology.

[kudu]

Modules are wired parallel to retain the 17.3 volt rating and to increase the amperage.  Six Trojan T105 6 volt batteries wired for 12 volts, 660AH

Batteries had 11.97 volts when I began to monitor the charge rate.  Maximum amps, per the current meter of the mppt charge controller, was 3.8 amps.  That would translate to 65.7 watts for the two panels which should be able to produce at least 112 watts if you factor in 30% inefficiency.  I do not have a separate watt meter.

Thanks for your comments,

Kudu

[kudu]

I suspect the modules may produce close to specs when tested as you outlined but in real world conditions, when I fail to achieve even close to rated amps, I am concerned, actually frustrated.

The installation brochure gives the following specs for a PW750 80 watt module.

Typical power(W)                       80.0

Operating voltage(V)                   17.3

Current at rated operating voltage(A)  4.6

Short circuit current(A)               5.0

Open circuit voltage(V)                21.9

Minimum power(W)                       75.1

That means the two modules I have should be able to produce 9.2 amps.  Factor in even 35% for inefficiency and various other anomalies, and you are still left with 5.9 amps.  So I am consistently two amps or more shy of rated output.

Thanks for your comments,

Kudu

[TomW]

kudu;

It sure seems to me like you are condemning the panels based on an uncalibrated reading from your controller.

Personally, I would not simply trust what it says. It very well could be that your controller is actually at fault! Do as another poster suggested and check the panels directly if they test good then you KNOW that the panels are not at fault. This is standard troubleshooting methodology and will give you the facts concerning what is going on.

Just my advice after 40 years of either tinkering with electronics or working in the field.

Any other approach will yield substandard results.

Cheers.

TomW

[Dreadstar]

Try disconnecting one panel and check your charge controller then disconnect the one that was working and check the other one.

Using a meter (DVM) will let you know if each panel is functioning open circuit. if you have a combiner box check each connection with the dvm to make sure that power is at each point. you may have one panel not wired.

I was getting 50-63 watts out of my old soleq sq-080 80 watt panels dont remember the watts but peak was 126 for the pair at this time of year. had alot of overcast while using them.

[Flux]

Yes I agree that the panels are likely not to be the problem.

Test them as Volvo Farmer suggests. If that test is ok, measure the current from one panel directly into the battery with your meter. Leave the charge controller out of the circuit. If you get 3 A or more then the trouble is not the panels.

Flux

[sandovalch]

Kudu, what is the wire gauge from the panels to the controller and the lenght of the cable?

Christian

[ghurd]

The problem is likely somethink else.

Connect a low battery and try again.

Then check all the connections, retighten the screws,

check for corrosion in the PV box, remove and reinstall the fuses,

Check for corrosion at (inside) the cables at the battery.

Our PW750 80W's regularly make over 4.85A each.

Our PW750 75W's regularly make over 4.55A each.

That is into low batteries.

For a 12V system, cut the diodes out of the PV box,

if they are installed.

Are they US or France made panels?

G-