Shunt Resistor, Grain Boundaries & Solar Cell Circuit

In summary: On the other hand, it is said that the higher the shunt resistor, the better the current output. So how is it possible that the shunt resistor can both reduce the current output and increase it?
  • #1
cemtu
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Homework Statement
Why does the value of shunt resistor need to be very high for solar cell's efficiency?
Relevant Equations
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In the circuit equivalent of a solar cell, shunt resistor is described as "The irregular polycrystalline lattice grain boundaries that resist to the flow of electrical current in the silicon material."
If this explanation is correct, shouldn't it be "lower shunt resistance increases the current flowing".
However, the shunt resistor is connected in parallel to diodes. That means "higher the shunt resistor better the current output".
How and why so? I thought not having many grain boundaries is what makes the monocrystalline cells more efficient than polycrystalline solar cells?!
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  • #2
The better term is "Shunt Resistance" (as shown in the screenshot that you posted), not shunt resistor. You don't add a shunt resistor to a PV panel for some application reason.

Shunt resistance for any power source is bad. It shunts current from the power source through a resistance, which wastes some of the source power in heat generated in that shunt resistance.

So in PV cell design, you want to minimize any shunt paths for the generated photocurrent. Does that make sense?
 
  • #4
berkeman said:
The better term is "Shunt Resistance" (as shown in the screenshot that you posted), not shunt resistor. You don't add a shunt resistor to a PV panel for some application reason.

Shunt resistance for any power source is bad. It shunts current from the power source through a resistance, which wastes some of the source power in heat generated in that shunt resistance.

So in PV cell design, you want to minimize any shunt paths for the generated photocurrent. Does that make sense?
Screenshot 2021-06-13 071745.png

Screenshot 2021-06-13 072013.png
 
  • #5
berkeman said:
The better term is "Shunt Resistance" (as shown in the screenshot that you posted), not shunt resistor. You don't add a shunt resistor to a PV panel for some application reason.

Shunt resistance for any power source is bad. It shunts current from the power source through a resistance, which wastes some of the source power in heat generated in that shunt resistance.

So in PV cell design, you want to minimize any shunt paths for the generated photocurrent. Does that make sense?
As I understand it, the shunt resistance means that higher the polycrystalline lattice irregularity and many grain boundaries. This means higher current resistance and thus less current output, so efficiency of solar cell decreases. However, in the circuit model of a solar cell, a shunt resistor is connected in parallel to the diode and they say that it must have infinite resistance for the highest current output because it is in parallel. However infinite grain boundary irregularity means that there is infinite resistance to the whole current in the solar cell so no current flowing is produced.

There is a conflict here...
 

1. What is a shunt resistor and how does it work?

A shunt resistor is a type of resistor that is connected in parallel with a circuit or component. It is used to measure or divert a portion of the current flowing through the circuit. Shunt resistors have very low resistance values and are designed to handle high currents. They work by creating a voltage drop across the resistor, which can then be measured to determine the current flowing through the circuit.

2. What are grain boundaries and how do they affect the performance of a solar cell?

Grain boundaries are interfaces between different crystalline grains in a material. In solar cells, they can occur between the different layers of semiconductor material. These boundaries can cause defects in the material, which can decrease the efficiency of the solar cell. They can also act as barriers for charge carriers, reducing the overall current output of the cell.

3. How does a solar cell circuit work?

A solar cell circuit is made up of several components, including the solar cell itself, a shunt resistor, and a load. When sunlight hits the solar cell, it creates an electric field that separates the positive and negative charge carriers. This creates a voltage difference, which can be measured across the shunt resistor. The load, such as a light bulb or battery, is then connected to the circuit, allowing the flow of current and the conversion of solar energy into electrical energy.

4. Can grain boundaries be eliminated in solar cells?

While grain boundaries cannot be completely eliminated, there are techniques that can minimize their impact on solar cell performance. These include using high-quality materials, optimizing the fabrication process, and using anti-reflection coatings to reduce the amount of light reflected at the boundaries.

5. How can shunt resistors be used to improve the accuracy of solar cell measurements?

Shunt resistors are commonly used in solar cell measurements to accurately measure the current flowing through the circuit. By creating a known voltage drop, the shunt resistor allows for precise current measurements. Additionally, shunt resistors can be used to divert excess current away from the solar cell, preventing damage to the cell and ensuring accurate measurements.

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