CEC Module Database Attribute Confusion

When looking through the CEC Performance Model with Module Database, is there an available description of the column headers from "alpha_sc" through to "gamma_r" in the red box in the attached image? What do each of these parameters represent?

Similarly, where are the Nominal Efficiency and Temperature Coefficients being pulled from? When I open up the CEC Modules.csv file I dont see either parameter in there. Are they being calculated from other parameters? If so, which ones using which formulas? Thanks!

Hello,

The 'alpha_sc' parameter is the temperature coefficient of short circuit current in A/°C. For the module in your screenshot, the value in the library is 0.00297882, and is shown in the blue cell on the Module page rounded to 0.003.

Similarly, 'beta_oc' is the temperature coefficient of open circuit voltage in V/°C, and 'gamma_r' is the temperature coefficient of power in %/°C. The nominal operating cell temperature (shown in blue under "Temperature Correction") in °C is 'T_NOCT'.

The 'beta_oc', 'alpha_sc', and 'gamma_r' parameters can be expressed either in V/°C, A/°C or W/°C, respectively, or %/°C. For example, to convert the 'gamma_r' value -0.457 %/°C to W/°C, multiply 'gamma_r' by 'Pmp': -0.457 %/°C * 300.120 W / 100 % = -1.373 W. For 'beta_oc', multiply by 'Voc', and for 'alpha_isc', multiply by 'Isc'.

The remaining parameters, 'a_ref', 'I_L_ref', 'I_o_ref', 'R_s', 'R_sh_ref', and 'Adjust' are coefficents of equations in the modified 6-parameter single diode module model, which in SAM is called the "CEC Performance Model". These coefficients are not provided in the module list from the California Energy Commission . We calculate those coefficients for SAM's module library using the tools provided here in the SAM GitHub repository . Calculating the coefficients from the database parameters requires a mathematical solver -- these are not calculated using simple equations.

The nominal efficiency is the module's conversion efficiency at standard test conditions. It is calculated as follows:

eff = ( Vmp * Imp ) / ( 1000 W/m2 * A )

where

eff = module nominal efficiency
Vmp = voltage at maximum power at standard test conditions (STC) in VDC
Imp = current at maximum power at STC in A
1000 W/m2 = irradiance at STC
A = module area in m2 (from the library and shown at the bottom of the Module page)

Best regards,
Paul.

Paul, thanks for the detailed explanation.