I_FROM_V

Overview

The I_FROM_V function calculates the device current at a given device voltage for a photovoltaic (PV) cell or module using the single diode model (SDM). This function is useful for modeling the current-voltage (IV) characteristics of solar cells and modules, which is essential for PV system design and analysis. The calculation is based on the single diode equation, as described in Jain and Kapoor (2004):

where $I$ is the output current, $V$ is the voltage, $I_{ph}$ is the photocurrent, $I_0$ is the diode saturation current, $R_s$ is the series resistance, $R_{sh}$ is the shunt resistance, and $n N_s V_{th}$ is the product of the diode ideality factor, number of cells in series, and cell thermal voltage. For more details, see the pvlib i_from_v documentation .

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

Usage

To use the function in Excel:

=I_FROM_V(voltage, photocurrent, saturation_current, resistance_series, resistance_shunt, nNsVth, [method])

• voltage (float, required): The voltage in Volts under desired IV curve conditions.
• photocurrent (float, required): Light-generated current (photocurrent) in amperes under desired IV curve conditions. Often abbreviated I_L.
• saturation_current (float, required): Diode saturation current in amperes under desired IV curve conditions. Often abbreviated I_0.
• resistance_series (float, required): Series resistance in ohms under desired IV curve conditions. Often abbreviated Rs.
• resistance_shunt (float, required): Shunt resistance in ohms under desired IV curve conditions. Often abbreviated Rsh.
• nNsVth (float, required): Product of diode ideality factor, number of cells in series, and cell thermal voltage (V).
• method (str, optional, default=“lambertw”): Solution method. One of "lambertw", "newton", or "brentq".

The function returns a single value (float): the device current in amperes at the specified voltage, or an error message (string) if the input is invalid.

Examples

Example 1: Typical Silicon Cell at MPP

In Excel:

=I_FROM_V(0.5, 8.0, 1e-10, 0.01, 1000, 1.5)

Expected output:

Example 2: Open Circuit Condition

In Excel:

=I_FROM_V(0.6, 8.0, 1e-10, 0.01, 1000, 1.5)

Expected output:

Example 3: High Series Resistance

In Excel:

=I_FROM_V(0.5, 8.0, 1e-10, 1.0, 1000, 1.5)

Expected output:

Example 4: Using Newton Method

In Excel:

=I_FROM_V(0.5, 8.0, 1e-10, 0.01, 1000, 1.5, "newton")

Expected output:

This means, for example, that at 0.5 V, the current is approximately 7.99 A for a typical silicon cell under standard conditions.

Python Code

import micropip
await micropip.install('pvlib')
from pvlib.pvsystem import i_from_v as pvlib_i_from_v
 
def i_from_v(voltage, photocurrent, saturation_current, resistance_series, resistance_shunt, nNsVth, method="lambertw"):
    """
    Calculate the device current at a given device voltage for a PV cell/module using the single diode model.
 
    Args:
        voltage: Voltage in Volts (float).
        photocurrent: Light-generated current in Amperes (float).
        saturation_current: Diode saturation current in Amperes (float).
        resistance_series: Series resistance in Ohms (float).
        resistance_shunt: Shunt resistance in Ohms (float).
        nNsVth: Product of diode ideality factor, number of cells in series, and cell thermal voltage (float).
        method: Solution method (str), one of 'lambertw', 'newton', or 'brentq'. Default is 'lambertw'.
 
    Returns:
        Device current in Amperes (float), or an error message (str) if input is invalid.
 
    This example function is provided as-is without any representation of accuracy.
    """
    try:
        V = float(voltage)
        IL = float(photocurrent)
        I0 = float(saturation_current)
        Rs = float(resistance_series)
        Rsh = float(resistance_shunt)
        nNsVth_ = float(nNsVth)
        if method not in ["lambertw", "newton", "brentq"]:
            return "Invalid input: method must be 'lambertw', 'newton', or 'brentq'."
    except Exception:
        return "Invalid input: all arguments must be numbers, except method."
    try:
        result = pvlib_i_from_v(V, IL, I0, Rs, Rsh, nNsVth_, method=method)
    except Exception as e:
        return f"pvlib.i_from_v error: {e}"
    return round(float(result), 2)

Live Notebook

Edit this function in a live notebook .

Live Demo