Irradiance and Isc and Voc of a solar cell

In summary, as irradiance increases, the open circuit voltage and short circuit current of a solar cell do not increase linearly. Temperature affects the open circuit voltage, causing it to decrease, and the short circuit current increases with radiance. To achieve maximum power, the voltage and current must be balanced, which is achieved at the maximum power point (MPP). The temperature of the solar cell also affects its performance, with the PN junction voltage decreasing slightly as temperature increases. It is important to note that a solar cell is never operated at open-circuit voltage or short-circuit current, but rather close to the MPP. This is because at open-circuit voltage there is no current, and at short-circuit current there is no voltage
  • #1
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When irradiance increases what happens to open circuit voltage and short circuit current of a solar cell? Do they both increase linearly? Because temperature affects open circuit voltage, so I'd assume open circuit voltage doesn't increase linearly then...
 
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  • #2
Voltage does not increase linearly with radiance. Current does increase with radiance.
But you want power so you must find the point where the product of voltage and current is close to the maximum.
That cannot be with short circuit current because then there is no voltage.
That cannot be with an open circuit voltage because then there is no current.
https://en.wikipedia.org/wiki/Maximum_power_point_tracking#I-V_curve
Voltage drop across the resistance of the cell increases with temperature and dominates voltage reduction due to rising temperature.
PN junction voltage falls slightly with temperature increase.
 
  • #3
Ok, so open circuit voltage doesn't increase with irradiance, so then it must decrease due to temperature effects.

I was confused between light intensity and irradiance. As light intensity increases open circuit voltage and short circuit current increase, but light intensity and irradiance are two different things.
 
  • #4
says said:
Ok, so open circuit voltage doesn't increase with irradiance, so then it must decrease due to temperature effects.
Correct. All other things being equal, the open circuit voltage will have the negative temperature coefficient of the cell material, probably silicon.
says said:
I was confused between light intensity and irradiance.
Avoid the confusion by referring to incident power. Only photons with wavelength, energy sufficient to overcome the semiconductor band gap are being considered.
Twice the power, is twice the photons, is twice the electrons, is twice the current.
 
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  • #5
As irradiance increases, we can assume temperature will increase (more irradiance=later in the day=temperature increasing), this means that Voc decreases due to temperature effects, and short circuit current increases due to more irradiance.
 
  • #6
A cell is never operated at open-circuit voltage or short-circuit current. It is operated close to the MPP.
As output current increases the voltage falls since the cell internal resistance drops more voltage.
There is also the smaller drop due to the temperature of PN junction.

The rising panel temperature is is due to heat from;
1. Internal I2R resistive losses.
2. Incident long wavelength radiation with insufficient energy to overcome the bandgap.
3. Thermal environment later in the day as angle to Sun changes and as air warms.
 
  • #7
"
A cell is never operated at open-circuit voltage or short-circuit current.
Solar cell is operated close to the MPP.
That cannot be with short circuit current because then there is no voltage.
That cannot be with an open circuit voltage because then there is no current."

thank yall for this simple summary
 

1. What is irradiance and how does it affect solar cell performance?

Irradiance refers to the amount of electromagnetic radiation that is incident on a surface. In the context of solar cells, it is the amount of sunlight that falls on the cell's surface. The higher the irradiance, the more energy the solar cell can convert into electricity.

2. What is Isc and how is it measured?

Isc, or short circuit current, is the maximum current that a solar cell can produce when there is no external resistance in the circuit. It is typically measured by connecting an ammeter in series with the solar cell and recording the current when the cell is short circuited.

3. What is Voc and why is it important for solar cell operation?

Voc, or open circuit voltage, is the maximum voltage that a solar cell can produce when there is no external load in the circuit. It is a measure of the cell's ability to generate electricity without any resistance. Voc is important because it indicates the maximum potential power that can be generated by the solar cell.

4. How do irradiance, Isc, and Voc relate to each other in solar cell performance?

In general, as irradiance increases, Isc and Voc also increase. This is because more sunlight means more energy for the solar cell to convert into electricity. However, there is a limit to how much Isc and Voc can increase with irradiance, and this limit varies depending on the type and design of the solar cell.

5. Can Isc and Voc change over time for a solar cell?

Yes, Isc and Voc can change over time for a solar cell due to various factors such as temperature, shading, and aging. Higher temperatures can decrease both Isc and Voc, while shading can decrease Isc but have a smaller effect on Voc. As solar cells age, their Isc and Voc may decrease due to material degradation, but this depends on the specific materials and manufacturing processes used.

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