# Why does the value of shunt resistor need to be very high for solar cell's greater efficiency?

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 diode. That means "higher the shunt resistor greater 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?!

https://www.scirp.org/html/7-6401007/fe85a7b6-645d-4341-8f35-dde69e519017.jpg

Warning this is a crosspost, though no one answered my question anyway I share the links: https://physics.stackexchange.com/questions/645123/why-does-the-value-of-shunt-resistor-need-to-be-very-high-for-solar-cells-great

https://engineering.stackexchange.com/questions/44659/problem-with-relationship-between-shunt-resistance-and-grain-boundaries-in-a-sol

• As the community rules suggests, I put a hyper-link to the original post in the stack exchange Physics site, though there are no answers given to me there, that's why I had to cross-post it. Jun 13, 2021 at 4:51
• You shouldn't cross-post--ask for it to be moved, instead. Jun 13, 2021 at 4:59
• How and why so? I thought not having many grain boundaries is what makes the monocrystalline cells more efficient than polycrystalline solar cells? How grain boundaries affect both series resistance and shunt leakage losses is a physics and materials science thing, not really electrical engineering. Jun 13, 2021 at 5:16
• I don’t know the intricacies of crystal lattice photon absorption efficacy but I do know the Rs is inverse to the cell area and the Rp affects Voc but more importantly, maximum power transfer point occurs when the load matches the panel’s negative incremental impedance. This also happens to be equal to the ratio of open circuit voltage and short-circuit current Zmpt=Voc/Isc which is typically 82% of Voc and declines towards 72% at 10% of max solarity. Jun 13, 2021 at 5:50
• series resistance should be 0 ideally and shunt should be infinite. this is also what your material says. imperfections deteriorate both properties. shunt resistance is in parallel to the load basically through the solar cell itself. both resistances scale inversely to the area which is usually big. therefore shunt is much more important usually and avoiding it is important. Jun 13, 2021 at 6:20

If this explanation is correct, shouldn't it be "lower shunt resistance increases the current flowing".

No.

However the shunt resistor is connected in parallel to diode. That means "higher the shunt resistor greater the current output".

How and why so?

The cell generates a current proportional to light. Current that goes through the shunt resistance bypasses the output. The higher the shunt resistance the lower the 'shunt' current is, so more of the generated current gets to the output.

I thought not having many grain boundaries is what makes the monocrystalline cells more efficient than polycrystalline solar cells?

Yes. Monocrystalline cells are more efficient because they don't have defects that allows current to 'leak' internally through the cell instead of going to the output.

This is all perfectly obvious, so I'm not sure what your problem is.

• It is said that higher shunt resistance = high defects on solar cell crystal = lower total current output = lower solar cell efficiency ; so, It must be in series not in parallel to the diode. Since, Parallel means, higher the shunt resistance = more total current output. However defects lowers the total current output of a solar cell! Gotta be in series! Please explain I am confused. What I say makes total sense... @Bruce Abbott Jun 13, 2021 at 9:22
• "It is said that higher shunt resistance = high defects on solar cell crystal" - not in anything you have shown us. Your ringed bullet point says "low shunt resistance due to material defect". Another says "high conductivity paths". Conductivity is the inverse of resistance. The final one just says "parallel resistance", implying the presence of a resistance lower than infinite or an open circuit. You do know that R = V/I means higher resistance = lower current, right? Jun 13, 2021 at 9:38
• "not in anything you have shown us" please look at last picture in the OP. @Bruce Abbott Jun 13, 2021 at 9:40
• pveducation.org/pvcdrom/solar-cell-operation/shunt-resistance Here it says "shunt resistance=material defects", I think, "increase in material defects = reduce in total current resistance, that's why monocrystal is more efficient than polycrystal." Jun 13, 2021 at 9:44
• "Parallel means, higher the shunt resistance = more total current output. However defects lowers the total current output of a solar cell!" - the diode, the shunt resistance and the series resistance are all inside the cell. Only current that gets to the output (where RL is connected) can be measured and used. The rest is absorbed inside the cell. The output does not include the internal current that goes through the diode and shunt resistance. Jun 13, 2021 at 9:44