Physics Case Study Solar Electric Panels

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Physics Case Study – Solar Electric Panels

The case study is the physics of solar electric panels and how they work. I am going to discuss the process in which these panels operate and their implications to society and their benefits and risks.

The physics of solar panel cells

How light interacts with the solar cells

When light hits a solar panel, the solar panel material can reflect, transmit or absorb the light. When light does the latter of the three options, energy is transferred from the photons that make up light into the atoms of the material. If the energy of the photon, determined by the frequency, is higher than a specific level, it will cause an electron-hole pair. The process is known as the photoelectric effect.  The specific energy level that is required signifies the ‘band gap’ between the valence and the conduction band. These bands are ranges of energy levels in which electrons rest at when under no excitation. When a photon has a higher energy level than the band gap hits an electron, it will excite it to the conduction band. In this band, electrons have enough energy to dissociate from its original atom and form free electron gas. Each material will have different bands and band gaps, and some don’t even have a band gap. The process of creating an electron-hole pair is most notable in semiconductors as a band gap exists, but is also relatively small. The electron-hole pair occurs when only a few electrons are in the conduction band in a material. When an electron leaves an atom, it breaks a covalent bond, leaving behind a positively charged ‘hole’ in a metallic lattice. An electron bordering this hole will move to fill it up, but also leaves a hole. This causes the apparent movement of a positive charge through a metal lattice, along with the movement of an electron.  

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Figure 1. Diagram to show photoelectric effect

How charges create electricity

Semiconductors that form solar panels can be doped with acceptor or donor impurities which creates more positive holes or more free electrons and are called p-type and n-type semiconductors respectively. Within a solar panel, p-type and n-type semiconductors are placed next to each other. Initially, the electrons in the n-type semiconductor and positive holes in the p-type semiconductor diffuse and create charged regions known as the ‘space charge region’.  When they reach this point, it leaves behind a negatively charged area at ...

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