The fill factor is never equal to one in solar cells and this feature decreases the solar cell's power efficiency. In the equivalent circuit of all kinds of solar cells, even if the shunt resistance is considered infinite and the series resistance is considered zero, the fill factor can never be one because of the exponential waveform of the diodes' I-V curve. The area of the rectangle with surface area of (Impp)*(Vmpp) is always smaller than that of (Is.c)*(Vo.c). The difference between these two areas is both because of losses of resistances and the difference between the exponential I_V curve of the diode and the rectangle with (Is.c)(Vo.c) surface. I know that the portion of this difference due to the nonzero and finite values of series and shunt resistance is converted into thermal energy. But I cannot understand that what type of energy the portion of optical energy lost due to the difference between exponential and rectangular curves, is converted to?
Thank's.
Dear Kianoosh Karimi
Please see these attachments sites
Best regards
https://www.researchgate.net/post/Why_is_the_Fill_Factor_of_Solar_Cells_low
http://www.supercomputingchallenge.org/14-15/finalreports/88.pdf
https://www.pveducation.org/pvcdrom/solar-cell-operation/fill-factor
Dear Kianoosh Karimi
Please see these attachments sites
Best regards
https://www.researchgate.net/post/Why_is_the_Fill_Factor_of_Solar_Cells_low
http://www.supercomputingchallenge.org/14-15/finalreports/88.pdf
https://www.pveducation.org/pvcdrom/solar-cell-operation/fill-factor
Omar Hazem MOHAMMED
Dear doctor Omar Hazem Mohammed,
Thank you for your answer, according to your attachments I construed that the mentioned energy loss is the result of a certain portion of recombination rate and reverse saturation current of the cell which varies in different operating points. Also the recombination rate which is corresponding to the black body effect does not appear in FF and appears in Is.c, the total recombination rate is a function of operating point which is minimal in the maximum power point. The ideality factor, n, is also an indicator of recombination which exists in the diode part of the equivalent circuit and is related to the energy loss due to exponential waveform of the diode's I-V curve.
Are these interpretations correct?
Perhaps this is a logical explanation but it is still not completely convincing
Mohamed Azab
Thank you Doctor Mohammad Azeb,
The incident photons which pass without exciting the atoms are affecting the total efficiency through quantum efficiency and spectral losses. The fill factor demonstrates the maximum power extracted from the solar cell when the impedance matching is done. I think it should be the result of electrical interactions which happen for the excited carriers.
Omar Hazem MOHAMMED
Thank you Dr. Hazem Mohammed,
A more complete explanation may be that this energy loss is divided to two parts: 1- recombination 2- reverse current.
The energy loss due to recombination is lost through electromagnetic radiation and the energy loss due to reverse current is a pure electrical energy loss without any resistance or creating heat. An special kind of physical energy loss that if we want to model it with circuit theory, we should assume that there is a parallel branch in the equivalent circuit that some energy is spent to produce reverse current through that branch and some another energy is lost because of the direction of this current which opposes the main generated current and decreases the total current. In other words, drift and diffusion currents are considered in two parallel branches in the equivalent circuit with opposite current directions.
Is it correct?
Fill factor is mainly responsible for the resistive losses in a solar cell and also thermal voltage where the thermal losses are more...In practical applications the fill factor of a solar cell is usually 0.8. It also effects the efficiency of the solar cell..
Prasanth kumar Enaganti
Thank you for you answer,
According to the band gap of the materials used in solar cells, some photons with energies higher than band gap excite electrons to high energy levels and they loose some energy to reach to the edge of the conduction band. This energy is converted to heat due to phonon radiation. On the other hand, in most solar cells, the photon radiation which happens because of recombination is also in IR region and could be assumed as thermal radiation. Could you please tell me that the thermal voltage that you mentioned is responsible for which of these two kinds of energy losses?
Thank's in advance.
thank you for your response.. The following attached link will be helpful for you for the better understanding of thermal voltage and also the losses.
https://www.pveducation.org/pvcdrom/solar-cell-operation/open-circuit-voltage
https://www.pveducation.org/pvcdrom/design-of-silicon-cells/voltage-losses-due-to-recombination
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