What went wrong on my Solar panel?

[mscoffman]

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

[MarkE]

What could be that went wrong with my 40w solar panel? It's only giving me 0.18amps with 15.55v. Is it maybe connections?
Any suggestions?
Thanks

Test your module in full sunlight by disconnecting the load and measuring the open circuit voltage.  Then short the module and measure the current.  Compare those numbers to the module ratings.   If the output current is low then you could have a cracked cell.  Within a single substring of which a 40W module may only have one, the current is limited by the weakest cell.  The short circuit test will show up a failed cell.  Make sure you don't have severe fouling on any cell, like debris, bird poop, etc.

Your problem may also be with your inverter.

[MarkE]

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.