One of the most frequently asked questions by people researching a solar power system for their home or business is the difference between panel and cell efficiency, both which work to determine the energy production and cost saving benefits of a system.
In the solar industry, efficiency refers to the percentage of sunlight energy hitting a cell or panel that is converted into electricity. SunPower’s world-record efficiency Maxeon cells, for example, achieve efficiencies of 22.4%, which means they convert 22.4% of the sunlight that hits them into electricity. Solar technology on the market today is available in a range of efficiencies, from about 10% in the lowest efficiency thin film solar panels to SunPower’s high efficiency products, which are two to four times more efficient than thin film and up to 50% more efficient than standard efficiency solar technology.
The efficiency of a panel is always lower than the efficiency of the solar cells used in that panel. This is primarily because glass is used to cover and protect the cells in the panel, and glass reflects light, preventing some of the sunlight from reaching the cells.
The example below shows the mathematical formulas for determining how 22.2% efficient cells produce a 20.9% efficient panel:
- If, by shining 1,000 Watts of light directly onto a number of cells, you generate 222 Watts of electricity, then you can measure the efficiency of the cells to be 22.2%.The formula is 222/1,000 = 22.2%.
- Now, what if those 22.2% efficient cells were used in the manufacture of a solar panel, with glass placed over the top of them? If you then exposed that panel to 1,000 Watts of light, approximately 60 Watts of the light will be reflected by the glass, and only 940 Watts of light energy will hit the cells. Since the cells receive less light, they will produce less electricity. This is the formula for calculating how many Watts the panel will produce: 940 Watts x 22.4% = 209 Watts. Applying the formula in the previous example (209/1,000 = 20.9%), you can determine that the panel is 20.9% efficient.
Panel construction, shading, temperature, mounting and positioning are all factors that affect the amount of power generated by an installed solar power system, but high solar cell efficiency helps ensure that the number of kilowatt hours generated by a system is maximized, maximizing the cost savings realized by the system owner.
Here is an informative interview with SunPower’s founder and president emeritus Dr. Richard Swanson in which he explains SunPower Maxeon solar cell technology.
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