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If you ever have a customer call who has a solar panel that is not listed on our sizing tool (GT or XW), and they want help sizing their modules, you might run into an issue where their Temperature Compensation Coefficient is stated as a % rather then deg C/mV.
As an example,
Lets say that: Module CS5P-200M Canadian Solar (view PDF)
Our Voc at 25deg C is: 57.4 Vdc and Isc at 25deg C is: 4.78 A
Somewhere down the specs, we might hear or see this.
Temperature Coefficient at Voc = -.35%/Deg C
Temperature Coefficient at Isc = .060%/Deg C
Then they say, their record low temperature is: 22 deg Fahrenheit.
Now, we must convert this to degrees Celsius. http://www.wbuf.noaa.gov/tempfc.htm
So, from the link, 22 Deg F = -5.55 Deg C
Now we know that the swing in temperature for record low is (25degC room temp) + (5.55degC, record low) = 30.55Deg C
From the above temp coefficient, we know that Voc temp comp is -35%/Deg C
30.55Deg C x .35(Voc temp comp) = 10.693% (rounded up)
10.693% divided by 100 = .10693 ( This is our coefficient )
The Voc of the Module was: 57.4Vdc x .10693(temp comp) = 6.137782 @ 5.55deg C (22 deg F)
6.137782(temp. comp) +57.4(Voc) = 63.537782 Voc
Finally, let's say we use the XW MPPT controller.
Max Voc = 150Vdc
150 / 63.537782 = 2.361 (rounded) modules in series.
We can only fit 2, so 2 modules x 63.537782 = 127.08Voc (rounded) @ record low temp.
Same procedure to figure out how many modules can be run in parallel. Use the Isc Amperage and temperature Coefficient.