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Articles Informational Topics Solar Panel

Calculate Solar Panel Efficiency- Explained!!!

Before counting the purchase of solar panels, have you ever checked the efficiency of the solar panel or how much efficient the panel is for power conversion?

If not, then you are lacking because efficiency is the prime factor defining the working of the solar panel.

Calculate Solar Panel Efficiency

But, before that, are you familiar with “how to calculate solar panel efficiency”?

Again no, Well, it’s fine because, with the handy, informative guide, we made it facile for the users to calculate the solar panel efficiency effortlessly by following the stepwise process with relevant information and easy-to-understand facts.

Calculate Solar Panel Efficiency – Quick Solution:

Solar panel efficiency is calculated using;

Efficiency = Pmax / Solar Irradiance x 100


Efficiency = Solar Panel Power In Kilowatts / Total Panel Area x 100

Solar efficiency is the ratio of maximum power output to solar input, and by putting the values of both terms, you will get overall solar efficiency.

Efficiency is measured in percentage, so after getting a ratio, multiply the resultant by 100 to get the % efficiency.

For finding Pmax and solar input, you need to go through a detailed stepwise procedure to calculate the efficiency of the solar panel.

What Is Solar Panel Efficiency:


Efficiency is the ratio of max work output to work input multiplied by 100.

Based on the working, the solar panel has its efficiency for the generation of electric power, so to know what it is solar panel efficiency, let’s get to the main part.

Solar Panel Efficiency:

Solar panel efficiency is defined as the ratio of overall power output in watts to the incident rays falling on the panel in watts/m2


It’s the percentage resulting from calculating the ratio of conversion of solar energy into electric current.


Efficiency isn’t related to solar panel power but its area, and how is that so?

For instance, if two panels are provided with the same power, but one panel reaches max output over a small area.

In contrast, another provides an output over an area larger than the first; in that case, panel 1 is more efficient than panel 02 as “the smaller the area used for generating maximum output, the more efficient the panel.”

Is Solar Panel 100% Efficient?

Solar panel efficiency is considered 100% when all the incident rays falling on the panel are converted into electric power outages, but that’s a theoretical figure.

Till now, it is not achieved because of many factors.

Shockley – Quiesser Limit:

According to the Shockley-Quiesser limit, the theoretical standard for high efficiency up till now is 30% and above under lab conditions.

Still, upon daily use, the value gets almost 20 or above, e.g., 22% for efficient solar panels, especially those made of high-quality, efficient material.

Standard Test Conditions:

It is necessary to have a standard for calculating and comparing solar panel efficacy, so scientists have tested and provided standard conditions for solar efficiency called STCs, which are as under;

Solar Irradiance- 1000W/m2 (1000 watts/m for 1 m area)
Nominal Cell Temperature- 25 degrees Centigrade
Air Mass-1.5

Formula Used For Calculating Efficiency:

Formula 1:

Efficiency = Pmax / Solar Irradiance x 100

Pmax = Maximum Solar Power Output
Solar Irradiance = Incident Solar Energy Per m2
100= For percentage

Formula 2:

Efficiency = Solar Panel Power In Kilowatts / Total Panel Area x 100

Power = From Solar panel specification sheet (current-voltage)
Area = Total Panel Area (length width)

Explanation :

You will need Pmax, maximum power output, and solar input to calculate solar panel efficiency. For solar input, let us take the standard solar irradiance of 1000 w/m2.

To calculate the max power output, you need to check the solar panel specification sheet, where you will find various ratings.

Calculate Power:

First, find the power, which is a combination of current and voltage so,

Power= Voltage x Current

Power = Vmp x Imp
Put the values from the specification sheet of your solar panel.
Power = 37.29x 8.72
Power = 325 watts

You can also find the power output from the specification sheet, but if the value isn’t mentioned, you can calculate it using maximum power current and voltage.

Calculate Total Area:

Before finding Pmax, calculate the total panel area by multiplying the length and width of the solar panel. Check the specifications for the values and find the area.

Area= Length x Width

Area = 1960 x 992
Area = 1944mm

Convert mm into m so,

Total Area = 1.944 m2

Calculate Maximum Power Output Pmax:

Now that you have calculated power and area, let’s calculate the max power output.

Max power output, Pmax = Power/Total Area

Pmax = 325 / 1.944
Pmax = 167 w/m2

Calculating Solar Panel Efficiency:

Using the efficiency formula adds the value of Pmax and solar irradiance to get the efficiency of the solar panel.

Formula 1:

Efficiency = Pmax / Solar Irradiance x 100

Efficiency = 167/1000 x 100
Efficiency = 0.167x 100

Efficiency = 16.7%

So the efficiency is 16.7% at the ideal temperature and solar input.

Formula 2:

You can also find efficiency by;

Efficiency = Solar Panel Power in Kilowatts / Total Panel Area x 100

Power = 325 watts, so divide it by 1000 to get Kilowatts. 325/1000 = 0.325 KW. Putting values,
Efficiency = 0.325 / 1.944 x 100
Efficiency = 0.167x 100

Efficiency = 16.7%

The resultant efficiency is 16.7% at the ideal 25-degree C temperature and, 1000w/m2 solar input.

Actual Efficiency Vs. Ideal Efficiency:

The one we calculated is ideal efficiency, but what if the operating temperature is 30 instead of 25 degrees? Then how would you estimate the efficiency?

The formula would remain the same, but once you find the ideal value, further extra steps are required to find the efficiency in the desired temperature range.

Follow the steps for calculating actual efficiency.

  • Find the difference of temperature, i.e., ideal 25 and real 30, so 30-25 = 05 degrees.
  • Find the Pmax coefficient, which is -0.4 for solar temperature rise.
  • Multiply both values, 05 x -0.4% = 02%
  • Then take the resultant and subtract it from the efficiency you previously calculated for 25 degrees, so
  • Subtracting 02% from 16.7%, you will get 14.7%.
  • So, the panel’s absolute efficiency is 16.7, and the actual efficiency is 14.7% for temperature rise.

Factors Affecting Solar Panel Efficiency :

Understandably, getting an ideal efficiency requires strict regulation and STCs.

Still, in real life, solar panels have to abide by various conditions that can affect their overall efficiency.

To know which factors are the prime reason for affecting efficiency, the following section best explains it.

Temperature :

In the previous section, you may observe that a temperature change directly affects solar panel efficiency.

A temperature of 25 degrees or a Nominal Cell Temperature is considered ideal.

Still, if the temperature is not in the range with the nominal temperature, then the panel is said to have a loss in efficiency per coefficient Pmax.

Solar Input :

The solar panel works by solar energy incident on the solar plate, so if there is an increase or decrease in the solar energy, it can directly affect the efficiency.

If the sun’s intensity is less, it will directly affect the panel’s efficiency; to have maximum efficiency, the panel needs high-intensity solar rays for more energy conversion to generate electric current.

Those areas where the sunlight remains all day are primarily favorable for solar panels compared to the areas where solar energy or sunlight falls adequately.

Climate Changes :

In some divisions of the world, there are abrupt climate changes, and different environmental factors may also affect the Solar Panel efficiency; in areas where there is snowfall or rain all the time, you cannot opt for a solar panel because, again, the solar energy is the major drawback for using the solar panel at such sites.

Inter Solar Cell Gaps:

The solar cell cannot provide high efficiency because of the presence of solar cell gaps where energy conversion doesn’t occur in case of light falls, so from incident rays, those are prone to conversion that directly falls in the solar cells.

The Angle Of The Solar Panel:

A panel is installed in the right direction and angle to achieve maximum efficiency.

An angle of 45 degrees and a horizontal plane for the solar panel so considered best for capturing most of the incident light rays for efficient conversion, high output rate, and increasing overall efficiency.

Other factors may include;

  • Durable and efficient inverter technology
  • Low maintenance
  • Quality and durability of the panel
  • Solar panel age
  • The degradation rate of solar panel

Conclusion :

Support renewable energy sources like solar panels as a future power generation unit to prevent your future generations from getting deprived of power. We are trying to provide the best authentic multiple formulas for a smooth and effortless way to calculate solar panel efficiency. Keep the solar panel specification sheet values for calculating the efficiency without inconvenience. Remember that efficiency is also affected by certain factors that need to be considered while calculating the actual efficiency.

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About the author

Anthony Miller

Hello Guys! I am Anthony Miller, a high dynamo, communicative author, and editor of the Renewable Cop, always providing amazing, engaging, informative, unique, highly researched, and verified content based on all sorts of generators. Read more.