Calculate Solar Panel Efficiency with Simplest Method

To calculate the solar panel efficiency, you need to divide the Wattage per unit area (Pmax/total area in sq.m.) of the solar module by the STC Irradiance value (1000W/sq.m.). This is the simplest way to get any solar PV module’s efficiency.

Solar Panel Efficiency Formula:

Efficiency (%) = (Pmax ÷ Area) ÷ (1000) x 100%

where, Pmax = solar panel peak power (in Watts)
Area = length x width of the solar panel (in sq.m.)
1000 = Standard Test Condition (STC) irradiance (in Watts/sq.m.)

By this simple method, you will know how efficient a solar module is, aside from looking it up on its specification sheet or at its back panel. Additionally, you will now be able to confirm the module efficiency details when you see a solar panel using this calculation.

What is solar panel efficiency?

Solar panel efficiency can be simply described as the ratio of the module’s power absorption to the input irradiance on standard test conditions. The power absorption of the module is the maximum solar module Wattage divided by its surface area. On the other hand, the input irradiance is the radiant power supplied per unit area which is equal to 1000 Watts per square meter at Standard Test Conditions (STC).

Therefore, solar module efficiency tells us how effective a solar panel is in transforming solar energy into useful electricity through the Photovoltaic effect.

The challenge on the part of solar panel manufacturers mainly boils down to improving sol ar module efficiency. They aim to build a module that effectively converts solar energy to useful electricity using less surface area.

Solar Panel Efficiency Calculation

Most of the time, solar manufacturers will readily show the details about the PV module’s efficiency on its specifications sheet or at the back of the panel itself. However, if you want to know how the solar panel efficiency is calculated, you can follow the simple steps below:

Step 1. Know the module’s maximum power capacity

You can easily know this by looking at the module datasheet, or by looking at the back of the solar panel itself. It will have its details shown at the back sticker usually. They normally label it as Pmax or maximum power of the module. They normally put it on the model name itself so this is not a hard thing to do.

Step 2. Get the module’s physical dimension

This step is as straightforward as it seems. Just take a tape measure, get the length and width of the solar panel and you’re done. Or, you can also look for its dimension from the module’s specification sheet.

Step 3. Get the power per unit area of the solar module

Once you have the measurements of the module’s length and width, you can now get its power per unit area. Just divide the solar panel’s maximum power capacity to its entire area. This will be in terms of Watts per square meter.

Step 4. Know the solar irradiance value at STC

Irradiance is defined as the radiant power (in Watts) received by unit area of the surface (in square meter). In solar panel tests, this means the amount of radiant energy that is beamed to the surface of the module.

Moreover, STC stands for Standard Test Conditions. This is the set of criteria that the solar industry follows for the conditions under which a solar panel will be tested. The conditions are as follows:

• Solar Cell Temperature at 25°C. This refers to the temperature of the solar cell itself, not the temperature of the surrounding.
• Solar Irradiance at 1000 Watts per square meter. This refers to the amount of light energy received by a unit surface at a given time.
• Air Mass at 1.5

Step 5. Solar panel efficiency calculation

After carefully following the simple steps above, you will have all you need to know how efficient a certain solar panel is. This is done by dividing the power per unit area of the solar module (in Watts/sq.m.) by the solar irradiance at STC which is 1000 Watts/sq.m.

The ratio that you get after the calculation will be the efficiency of the solar PV module that you are looking for.

Solar Panel Efficiency Breakthroughs

What affects solar panel efficiency?

The limitation in solar cell efficiency directly affects how efficient a solar panel converts solar energy into electricity.

“In physics, the Shockley–Queisser limit (also known as the detailed balance limit, Shockley Queisser Efficiency Limit or SQ Limit, or in physical terms the radiative efficiency limit) refers to the maximum theoretical efficiency of a solar cell using a single p-n junction to collect power from the cell where the only loss mechanism is radiative recombination in the solar cell. It was first calculated by William Shockley and Hans-Joachim Queisser at Shockley Semiconductor in 1961, giving a maximum efficiency of 30% at 1.1 eV.” – Wikipedia.

This boils down to the materials used, the reflective efficiency, and how well the solar panel handles heat.

The efficiency of solar cells

Solar cell efficiency refers to the ratio of the power output of a solar cell to its power input while considering its surface area. It is the portion of energy in the form of sunlight that can be converted via photovoltaics into electricity by the solar cell.

It is true that solar cell efficiency directly affects the solar panel efficiency. However, we need to be understandd that they don’t equate to each other.

You may ask, why? Isn’t a solar panel made up of individual solar cells? Yes, you are correct. However, when calculating the efficiency of a solar PV module, you take into consideration the whole surface area of the panel. This is because of the gaps between solar cells inside the solar panel. Additionally, you will also need to consider the surface area of the aluminum frames since it is also part of the PV module.

What is solar cell IV Curve?

When we look at the power output of a PV module on its datasheet, we will also see its IV Curve. The IV Curve is also known as the Current (I) Voltage (V) characteristic of an electrical device like a solar cell.

Typically, this is represented as a graph that shows all the possible power points of the power output at any given sets of conditions. The set of conditions includes the solar cell temperature, air mass, and irradiance, or light intensity.

Solar cell manufacturers conduct tests to see how their products perform in various temperature and irradiance level exposure. The results will then be reflected in a graphical format and the maximum value they get in terms of Watts will be the maximum power capacity of the certain solar cell.

Endpoints

Looking back at the past several decades, we can see how the efficiency of solar PV modules has increased significantly. And, this will eventually continue to go up to its peak. It is great to see how the solar industry is thriving towards better solar module efficiency. Considering the benefits we can get from it, we know this is going to the right direction.

Eventually, we will have solar power plants that produce clean energy even in a little amount of space available. More importantly, the cost has also come down tremendously. This makes utility-scale solar among the cheapest electrical power source you can build.

References

• https://aip.scitation.org/doi/full/10.1063/1.4973117
• https://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/
• Current–voltage characteristic
• H. J. van der Bijl (1919). “Theory and Operating Characteristics of the Themionic Amplifier“