Understanding solar panels
By Dr Tan Swee-ching, Assistant Professor, School of Energy and Environment, City University of Hong
Before I go into the details of how solar panels work, here’s a brief introduction to the properties of light and the material that is used to make a solar cell – a device that turns sunlight into electricity.
Light can behave like a particle called a photon. A photon carries energy. Different colours of light have different energies.
Red, which has a longer wavelength, will have less energy, while blue, which has a shorter wavelength, will have more energy.
The material used to make a solar panel is known as a semiconductor. Different semiconductors have different band gaps.
The band gap is the minimum energy required for an electron to jump from the atom it is bound to.
For semiconductors to conduct electricity, the electrons must gain enough energy to jump free, and flow as an electrical current.
In other words, these band gaps determine what range of light a solar cell can capture.
A semiconductor can only absorb the specific amount of energy determined by its band gap. If the material’s band gap matches the energy of blue light, it will only absorb blue light and will not respond to lower energies of light.
On the other hand, the higher energy photons from ultraviolet light carry a much higher energy level than is required to make free electrons conduct electricity.
This excess energy is lost as heat and will not contribute to the freeing of more electrons.
Hence one obvious method to increase the efficiency of solar cells is to increase the absorption range of the solar spectrum from the semiconductor materials.
As mentioned earlier, different semiconductors have different band gaps and, therefore, absorb different parts of the solar spectrum.
With that in mind, we can see that stacking different types of semiconductors with different band gap properties is one way to increase the efficiency of solar cell.
What is the material used to make a solar panel?
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