CALCPARAMS_CEC

Overview

The CALCPARAMS_CEC function calculates five parameter values for the single diode equation at a given effective irradiance and cell temperature using the California Energy Commission (CEC) model. These parameters are essential for modeling the current-voltage (I-V) characteristics of photovoltaic (PV) modules.

This implementation wraps the pvlib.pvsystem.calcparams_cec function from the pvlib-python library, a widely-used open-source tool for solar energy modeling.

The CEC model is based on the work by Dobos (2012) and differs from the earlier De Soto et al. (2006) model by introducing an Adjust parameter that modifies the temperature coefficient for short-circuit current. This adjustment improves the accuracy of module performance predictions under varying environmental conditions.

The function returns five parameters required by the single diode model:

Photocurrent (I_L): The light-generated current in amperes
Saturation current (I_o): The diode reverse saturation current in amperes
Series resistance (R_s): Resistance in ohms
Shunt resistance (R_{sh}): Resistance in ohms
nNsVth: The product of diode ideality factor (n), number of cells in series (N_s), and cell thermal voltage (V_{th})

Key reference parameters such as EgRef (energy bandgap, default 1.121 eV for crystalline silicon) and dEgdT (temperature dependence of bandgap) are consistent with values used in the SAM (System Advisor Model) CEC module database maintained by NREL.

For further details, see the original paper: A. Dobos, “An Improved Coefficient Calculator for the California Energy Commission 6 Parameter Photovoltaic Module Model”, Journal of Solar Energy Engineering, vol 134, 2012.

This example function is provided as-is without any representation of accuracy.

Excel Usage

=CALCPARAMS_CEC(effective_irradiance, temp_cell, alpha_sc, a_ref, I_L_ref, I_o_ref, R_sh_ref, R_s, Adjust, EgRef, dEgdT, irrad_ref, temp_ref)

effective_irradiance (int, required): The effective_irradiance value
temp_cell (int, required): The temp_cell value
alpha_sc (float, required): The alpha_sc value
a_ref (float, required): The a_ref value
I_L_ref (float, required): The I_L_ref value
I_o_ref (float, required): The I_o_ref value
R_sh_ref (int, required): The R_sh_ref value
R_s (float, required): The R_s value
Adjust (int, required): The Adjust value
EgRef (float, optional, default: 1.121): The EgRef value
dEgdT (float, optional, default: -0.0002677): The dEgdT value
irrad_ref (int, optional, default: 1000): The irrad_ref value
temp_ref (int, optional, default: 25): The temp_ref value

Returns (list[list]): [photocurrent, saturation current, series resistance, shunt resistance, nNsVth]. If input is invalid, returns a string error message.

Examples

Example 1: Demo case 1

Inputs:

effective_irradiance	temp_cell	alpha_sc	a_ref	I_L_ref	I_o_ref	R_sh_ref	R_s	Adjust	EgRef	dEgdT	irrad_ref	temp_ref
1000	25	0.004	1.5	6	1e-10	200	0.5	0	1.121	-0.0002677	1000	25

Excel formula:

=CALCPARAMS_CEC(1000, 25, 0.004, 1.5, 6, 1e-10, 200, 0.5, 0, 1.121, -0.0002677, 1000, 25)

Expected output:

Result
6	1e-10	0.5	200	1.5

Example 2: Demo case 2

Inputs:

effective_irradiance	temp_cell	alpha_sc	a_ref	I_L_ref	I_o_ref	R_sh_ref	R_s	Adjust	EgRef	dEgdT	irrad_ref	temp_ref
800	35	0.004	1.5	6	1e-10	200	0.5	0	1.2	-0.0003	1000	25

Excel formula:

=CALCPARAMS_CEC(800, 35, 0.004, 1.5, 6, 1e-10, 200, 0.5, 0, 1.2, -0.0003, 1000, 25)

Expected output:

Result
4.832	5.756e-10	0.5	250	1.55

Example 3: Demo case 3

Inputs:

effective_irradiance	temp_cell	alpha_sc	a_ref	I_L_ref	I_o_ref	R_sh_ref	R_s	Adjust	EgRef	dEgdT	irrad_ref	temp_ref
1000	25	0.004	1.5	6	1e-10	200	0.5	0	1.121	-0.0002677	900	20

Excel formula:

=CALCPARAMS_CEC(1000, 25, 0.004, 1.5, 6, 1e-10, 200, 0.5, 0, 1.121, -0.0002677, 900, 20)

Expected output:

Result
6.689	2.347e-10	0.5	180	1.526

Example 4: Demo case 4

Inputs:

effective_irradiance	temp_cell	alpha_sc	a_ref	I_L_ref	I_o_ref	R_sh_ref	R_s	Adjust	EgRef	dEgdT	irrad_ref	temp_ref
950	30	0.004	1.6	6.2	2e-10	210	0.55	0.01	1.15	-0.00028	950	30

Excel formula:

=CALCPARAMS_CEC(950, 30, 0.004, 1.6, 6.2, 2e-10, 210, 0.55, 0.01, 1.15, -0.00028, 950, 30)

Expected output:

Result
6.2	2e-10	0.55	210	1.6

Python Code

import micropip
await micropip.install(["pvlib"])
from pvlib.pvsystem import calcparams_cec as pvlib_calcparams_cec
import numpy as np

def calcparams_cec(effective_irradiance, temp_cell, alpha_sc, a_ref, I_L_ref, I_o_ref, R_sh_ref, R_s, Adjust, EgRef=1.121, dEgdT=-0.0002677, irrad_ref=1000, temp_ref=25):
    """
    Calculate five CEC model parameters for the single diode equation at given irradiance and cell temperature.

    See: https://pvlib-python.readthedocs.io/en/stable/reference/generated/pvlib.pvsystem.calcparams_cec.html

    This example function is provided as-is without any representation of accuracy.

    Args:
        effective_irradiance (int): The effective_irradiance value
        temp_cell (int): The temp_cell value
        alpha_sc (float): The alpha_sc value
        a_ref (float): The a_ref value
        I_L_ref (float): The I_L_ref value
        I_o_ref (float): The I_o_ref value
        R_sh_ref (int): The R_sh_ref value
        R_s (float): The R_s value
        Adjust (int): The Adjust value
        EgRef (float, optional): The EgRef value Default is 1.121.
        dEgdT (float, optional): The dEgdT value Default is -0.0002677.
        irrad_ref (int, optional): The irrad_ref value Default is 1000.
        temp_ref (int, optional): The temp_ref value Default is 25.

    Returns:
        list[list]: [photocurrent, saturation current, series resistance, shunt resistance, nNsVth]. If input is invalid, returns a string error message.
    """
    # Define helper function inside main function as per guidelines
    def is_scalar(x):
        if isinstance(x, (list, tuple, np.ndarray)):
            return False
        return True

    args = [effective_irradiance, temp_cell, alpha_sc, a_ref, I_L_ref, I_o_ref, R_sh_ref, R_s, Adjust, EgRef, dEgdT, irrad_ref, temp_ref]
    if not all(is_scalar(arg) for arg in args):
        return "Error: All arguments to calcparams_cec must be scalar values."

    try:
        vals = pvlib_calcparams_cec(
            float(effective_irradiance), float(temp_cell), float(alpha_sc), float(a_ref), float(I_L_ref), float(I_o_ref), float(R_sh_ref), float(R_s), float(Adjust), float(EgRef), float(dEgdT), float(irrad_ref), float(temp_ref)
        )
        # Return values without rounding as per Excel Python Function Guidelines
        row = [float(vals[0]), float(vals[1]), float(vals[2]), float(vals[3]), float(vals[4])]
        return [row]
    except Exception as ex:
        return f"Error: {ex}"

Overview

Excel Usage

Examples

Python Code

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