How to calculate solar panel efficiency?

Let us take the SAIL SOLAR 550W solar panel as an example and calculate the module efficiency.

PV module power (Pmax in watts) ÷ PV module surface area in square meters

= 550W / (2.279m * 1.134m) / 1000 =21.3%

What is solar cell efficiency?

Solar cell efficiency refers to the energy efficiency with which a solar cell converts it into electricity through photovoltaic technology. Also take the SAIL SOLAR 550W as an example.

SAIL SOLAR 550W is made of 182mm solar cell ( dimension: 182*91mm). 144cells.

550W/144=3.82W per cell

3.82W/(0.182m*0.091m)/1000= 23.1%

Why is there a difference between solar panel efficiency and solar cell efficiency?

Compared to the example of the SAIL SOLAR 550W mentioned above, solar cell efficiency is 23.1%, while solar panel efficiency is 21.3%. The reason for this difference is that cell efficiency calculations refer to individual cell, while solar panel efficiency refers to the entire solar panel module. Some energy is lost due to the spacing between solar cells.

Similarly, the bus bar on the solar panel is also covered on the surface of the cell. The thinner the bus bars, the less efficiency is lost to the solar panel. Moreover, the shadow of the bus bar on the cell will also affect the efficiency. For example, the thickness of the bus bar of a 5-bar solar cell is 0.4mm, while that of a 9-bar solar cell is 0.1mm. This also leads to a difference between solar panel efficiency and solar cell efficiency.

In fact, other raw materials used to produce solar panel, such as glass, EVA, junction boxes, etc., will also have a certain impact on efficiency.

Then, there's the "fill factor," often abbreviated as FF, which is a measure of how close a solar cell is to being an ideal light source. This is a key parameter for evaluating performance. It can be simply understood that this parameter is used to determine the maximum power from the solar cell.