Solar Cell Fill Factor Explained

Commonly shortened as FF, the fill factor of solar technology simply represents the measure of the closeness in a solar cell and how it acts as an ideal source. In short, the solar cell fill factor measures the efficiency of a solar PV module.

In this article, you’ll learn the solar cell fill factor, the mathematical expression, the range of the solar cell, the effect of the solar cell fill factor on the efficiency of a solar panel, and many more.

Solar Cell Fill Factor Formula

Solar cell fill factor is mathematically expressed as the maximum power ratio denoted by Pmax to the product of the VOC & ISC. This can be further expressed as:


Fill Factor (FF) = Pmax
Voc * Isc

The solar cell fill factor is simply the ratio of the highest achievable power.
In this equation, we have two key players, which include:

Open circuit voltage (Voc): The open-circuit voltage explains the highest amount of voltage that can be generated by a solar panel under standard testing conditions. Where there is an absence of loads connected to the output circuit, the current produced is zero.

Short circuit current (Isc): On the other hand, the short circuit current represents the higher current that a solar panel can generate under standard testing conditions.

In this scenario, the panel wires are connected directly, which indicates that the short circuit produces no voltage.

Impliedly,
Pmax denotes the maximum power, and it occurs when the voltage and the current combine, generating the most significant power. This maximum power can either occur at the open circuit (VOC) point or the end of the short circuit (ISC).

Ideally, the voltage is zero at Isc while the current in the cell is also zero at Voc.
Therefore, the maximum power Pmax doesn’t occur at the maximum current. Instead, it occurs at a voltage that is less than the VOC.


Thus,
Pmax=VMPP X IMPP

This implies that the VMPP and IMPP represent the voltage and current respectively at the maximum power point on the current versus voltage curve.

What’s the Range of Solar Cell Fill Factor?

The range of solar cell fill factors is from 50% to 82%. For instance, the silicon PV cell usually has a fill factor of 80%.

Which Fill Factor is the Best for Solar Cell?

The best fill factor for a solar cell is one that has about 80%. This is because the higher the fill factor determines the level of efficiency of the solar cell.

How does Solar Cell Fill Factor affect Solar Panel?

The solar cell fill factor affects the solar panel in that it influences the efficiency of the solar panel by impacting the values of the cell series. It also impacts energy efficiency in the solar panel by affecting the shunt resistances and diodes losses.

When you increase the shunt resistance in a solar cell, the series resistance automatically decreases, thus resulting in a higher fill factor. Meanwhile, a higher fill factor in a solar cell indicates a greater efficiency of the solar cell, ultimately increasing the output power to match its theoretical maximum.

Differences Between the Fill Factor and the Efficiency of a Solar Panel

Here is a table explaining the differences between the fill factor and the efficiency of a solar panel;

Fill FactorEfficiency of a Solar Panel
1The fill factor of a cell represents the ratio of the theoretical power to the maximum power.The efficiency of a solar panel is simply the ratio of the highest power that a solar panel can generate with respect to standard testing conditions compared to the input power.
2The efficiency of a solar panel is denoted by (n) and the formula is Pmax/PinThe efficiency of a solar panel is denoted by (η), and the formula is Pmax/Pin.
3Achieving a maximum theoretical power depends largely on several factors. These include silicon-based PV modules. If there are any deviations from the expected value in the fill factor, it indicates a faulty module.The efficiency of a solar panel can be maximized through a high fill factor (FF), Isc, and Voc.

What are the Factors Affecting the Efficiency of a Solar Panel?

  • The factors that affect the efficiency of a solar panel include;
  • The fill factor
  • The light intensity
  • Solar spectra and temperature and
  • Accumulation of dust

Let’s take a brief look at how each of these factors affects the efficiency of a solar panel.


Fill Factor: In a solar panel, it is observed that the specific cell with a lower magnitude of fill factor results in a reduced efficiency than the one with a higher magnitude of fill factor.

Solar Spectra and Temperature

The primary function of a solar panel is to generate electricity through sunlight rays. However, the efficiency of a solar panel to produce electricity decreases as the irradiance increases.

For instance, if the temperature of a solar panel reduces down the limit of an optimum. In this case, the solar panel becomes overheated. Consequently, the Voc and Isc drop, thus decreasing the overall efficiency of the panel.

The Light Intensity

The efficiency of a solar panel is also affected by the variation of the illumination intensity. The fill factor:

  • Increases the irradiation of less than 500 watts/m2, thus, bringing about low irradiation.
  • Decreases the irradiation greater than 500 watts/m2. This brings about high irradiation.

Similarly,

  • The efficiency increases for irradiation less than 400 watts/m2, resulting in a low irradiation.
  • The neither increases nor decreases for the irradiation more than 400 watts/m2, leading to high irradiation.

Dust Accumulation

When a solar PV panel is filled with a vast amount of dust and other particles, the solar panel’s quality and fill factor deteriorates. For instance, there are cases where a single dust storm decreases the output of the module by 20% and 50% increases for over six months.

When does Fill Factor Decrease?

The fill factor of a solar cell decreases as a result of high series resistance. A typical example is a noticeable decrease in the depletion region due to the reduction of the doping density of the p-type axis of the device. This further increases the bulk resistance as well as the contact resistance of the p-type side. Ultimately, the skyrockets the series resistance of the solar cell, hence, resulting in the decrease of the fill factor.

When does Fill Factor Increase?

The fill factor of a solar cell increases as the squareness increases. Remember, the fill factor is the measure of the squareness of the IV curve.

How to Increase the Efficiency of a Solar Cell

To increase the efficiency of a solar cell, here are some tips:

  • Keep Your Solar Panels Clean and free from dust accumulation
  • Install the PV Panels Correctly
  • Desist from installing solar panels in shaded areas
  • Use a solar concentrator

Now, we have addressed some of the essential things you need to know about the fill factor and the efficiency of a solar panel. We also covered areas such as:

  • The formula for calculating the fill factor of a solar cell
  • How the fill factor affects the solar panels
  • The difference between the fill factor and the efficiency of a solar panel
  • The factors that affect the efficiency of a solar panel and
  • How to increase the efficiency of a solar panel

Ying Xu

Graduated from the University of Kansas with an Aerospace Engineering degree & served 4 years as an US Air Force officer. Experienced with basic survival skills, weapon system security,  technical disaster recovery, and system troubleshooting

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