Hi Guruji,

What is the rated open current and open voltage? How long are the cables and what gauge? If the panel has been outside for a while make sure the connections are clean no rust or oxidization (yellowing/white powder coloring on the clips).

I have one 15 watt panel that I accidentally shorted out for the whole day, doh!. The panel puts out voltage still but very little amps now, the panel is essentially damaged. Did anything happen to short your cells out(moisture, wiring)?

Sometimes all it takes is one bad cell to bring down the whole series. If you have access to the cells check each one individually and see if a bad one is located in there.

If it's a commercial panel look for cracks in the glass or peeling in the plastic film around the edges, this will allow moisture in and do damage. Look for dark discoloration or pits in between the lines of solar cells to see if there is water damage. If you notice any water inside take it in the house away from the sun and see if you can dry it out, may have to leave it in a dry, dark room for awhile keep checking the output every other day. Then try to repair the any cracks with a silicone window sealer if it starts to stabilize. It's better to catch this early.

Some of the bigger panels have blocking diodes, check that to see if it's bad. They are sometime buried in a silicone, where the wires come out, if you take an Exacto knife you can carefully cut the material out to get to the diode.

Hi Guruji,

The cell you checked was in full sunlight? giving off .55v@150ma ? May have to check each cell individually if all 35 are giving around the same reading then the cells are rated wrong.

If you have some that are near what is rated then some bad ones are bringing down the chain. Have to remove the bad ones and replace them.

Hi;

Technical newbies almost always get this wrong. The power of a solar cell array
needs to be measured at its MPP maximum power point. That means you must
load the array down with various resistors measure the volts and amps at the
same time then multiply volts and amps to get the power at that resistance
then find which resistor gives you the maximum power. Both the array's temperature
and illumination level will affect the MPP. Unlike some electronic devices the MPP
of solar cells is very far from the short circuit current times open circuit voltage.
So it forces someone making measurements to do things technical correctly. 
You might as well go the whole nine yards and figure out how to use a current
shunt resistance 100A or 1000A. That way you don't have to run large power currents
through your small DVM and small gauge wire leads. If you use milliamp range of
your DVM then 1000A = 1A reading or 1amp = 1MA reading on the DVM. Another
half way technical technique down. 

By the way your battery charge controller should have something called MPP
automatic adaptation. This causes it to continually seek out an array's MPP.


:S:MarkSCoffman

Hi;

Technical newbies almost always get this wrong. The power of a solar cell array
needs to be measured at its MPP maximum power point. That means you must
load the array down with various resistors measure the volts and amps at the
same time then multiply volts and amps to get the power at that resistance
then find which resistor gives you the maximum power. Both the array's temperature
and illumination level will affect the MPP. Unlike some electronic devices the MPP
of solar cells is very far from the short circuit current times open circuit voltage.
So it forces someone making measurements to do things technical correctly. 
You might as well go the whole nine yards and figure out how to use a current
shunt resistance 100A or 1000A. That way you don't have to run large power currents
through your small DVM and small gauge wire leads. If you use milliamp range of
your DVM then 1000A = 1A reading or 1amp = 1MA reading on the DVM. Another
half way technical technique down. 

By the way your battery charge controller should have something called MPP
automatic adaptation. This causes it to continually seek out an array's MPP.


:S:MarkSCoffman

The maximum power voltage is always close to 80% of open circuit voltage.  If you read an open circuit voltage that is close to the module ratings adjusted for temperature, and you get a short circuit current that is also close to the module rating adjusted for the operating temperature then the module is good.  There is no need to find the specific maximum power point when testing a single substring module.  Modules with multiple substrings require additional testing to determine that each substring is good.

A failed cell limits the current through the entire substring.  In typical modules there are three substrings each bypassed with a diode.  Pulling current will drop the module voltage and power until the diode kicks in, at which point the power rises with additional draw up to the true MPP point of the remaining substrings.  At short circuit as long as one substring is good one will get close to the temperature adjusted short circuit of the module.  Modules with multiple substrings should be loaded down to about 80% of the open circuit voltage.  If there is a bad cell in one or more substrings, then the current at 80% VOC will be limited by the damaged cell or cells.