pvlib

PVlib: Temperature coefficients

I'm modeling a module not found in the databases, so the data I got on the module is from the datasheet.

What is the recommended way of doing this?

The temperature coefficients in the datasheet is given with delta tempearature percentage gain.

in pvlib it's delta temperature * temperature coeficient.

If I understand this correctly I would use an exponential function to calculate the short circuit current given a temperature like so:

Isc * (1 + a_isc^(temperature - referance temperature))

while the way pvlib does it is linear? %/C vs. A/C

Anyway, how to give the best number to pvlib?

Edit: link to datasheet https://www.jasolar.com.cn/uploadfile/2020/1128/20201128025603510.pdf

Edit2: Example conversion

From datasheet: Isc = 11.58A a_Isc = 0.044%/C (STC values)

conversion: a_Isc / 100 * 11.58 = 0,0051 A/C

Solution

  • Isc * (1 + a_isc^(temperature - referance temperature))

    Maybe exponential-style temperature coefficients like that exist, but I've never seen one in PV. This particular equation doesn't make much sense anyway -- when temperature == reference temperature, it should return Isc right? But this equation would return 2*Isc.

    Anyway, to give these coefficients to pvlib, checking the units is the main thing. Temperature coefficients can be "raw" and have units A/°C, V/°C, or W/°C, or they can be normalized by their STC values and have units %/°C or 1/°C. The values in that datasheet are normalized (values in %/°C, convert to 1/°C by dividing by 100). Coefficients in 1/°C can be converted to non-normalized units by multiplying by the corresponding STC value.

    It's a shame that pvlib is not consistent in what units it wants; some pvlib functions want the coefficients to be normalized and some don't. You have to check the documentation of the function you're using to see what units it wants. For example the documentation for pvlib.pvsystem.calcparams_cec says:

    alpha_sc (float) – The short-circuit current temperature coefficient
of the module in units of A/C.

    And pvlib.pvsystem.pvwatts_dc (docs):

    gamma_pdc (numeric) – The temperature coefficient of power.
Typically -0.002 to -0.005 per degree C. [1/C]