Solar Panel Efficiency is the ability of the panel to convert sunlight into electricity. For example, if two panels of same physical size but different efficiency ratings are placed under the same amount of sunlight for the same duration of time, then the panel with a higher efficiency rating would produce more power compared to the one with less efficiency rating. As we know, panels are made up of several Photovoltaic cells that convert the sunlight falling on them into electricity. The amount of electricity produced by them, in turn, depends upon the cell’s composition, electrical configuration, surrounding components, and more.
The efficiency of cells inside the panels is always higher than the overall solar panel efficiency. It is because when they are placed inside the panels, they get prone to losses due to the physical layout of the frame, connections between cells, and optical losses from being enclosed inside a glass.
Solar panels or modules are tested in laboratories under Standard Test Conditions. STC are industry-standard conditions used to measure the amount of power produced by different modules under the same conditions.
Standard Test Conditions are as follows:
1. The temperature of the cell should be 25ºC.
2. Solar irradiance level should be 1000W per square meter. (This is the amount of light energy falling on a given surface at a given time.)
3. Air mass 1.5 spectra.
But the real-world conditions are quite different from STC, and they vary almost every day. To give you more clarity, let’s take an example for reference. A 250W rated solar panel with 15.1% efficiency means if 1000W of light energy is falling on panel (per meter 2) having a cell temperature of 25ºC, then it would produce 250W of power by converting 15.1% of light energy falling on it into Direct Current.
Solar Panel Efficiency matters, but it is not the only factor to consider. As the panel efficiency is directly proportional to electricity generation per m2, this means a more efficient solar panel will take slightly lesser space than a less efficient panel. If you consider roof space, the more efficient solar panels should be your first choice. Currently, majority of the panels have efficiency between 15% to 20%. Only very high-efficiency panels go up to 22% or 23%.