PHOTOVOLTAIC MODULES — THE PRINCIPLE OF PHOTOVOLTAIC CELL OPERATION
Nowadays, it is a common situation for household illumination systems or even electric cars to be supplied with solar energy provided by photovoltaic cells.
H
owever, it does not mean that everybody, including PV system users, knows the principle of operation of such systems and recognises the processes transforming solar energy into electric power. In this article, most of these issues are precisely explained.
What is photovoltaics? Photovoltaics is the technology of converting solar radiation into electric power through the use of photovoltaic panels and DC-to-AC converters to supply energy to consumers connected to a power network or to store energy in batteries. This is the simplest and most narrow definition, so it is worth adopting a slightly broader perspective and going back to the beginnings of this technology. By definition, “photovoltaics” is a science interested in converting solar energy into electric power that has evolved into an important field of technical engineering that is now present in the majority of highly developed countries. In parallel,
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numerous technologies related to obtaining energy from renewable energy sources have been developed. However, obtaining energy from the sun’s radiation is the most important and remains the leading method of providing ‘free-of-charge’ and infinite energy. Moreover, note that solar energy could completely replace fossil fuel-based energy sources, which would significantly reduce air pollution levels. However, there is one major drawback to it, namely the demand for a large surface area resulting from a PV panel size.
Photovoltaic panels — principle of operation The process of converting solar energy into electric power taking place in the internal cell layers starts under the reflective layer, where two silicon plates are located, ie, the upper one acts as a negative conductor made of silicon with a phosphorus admixture. The lower plate acts as a positive conductor and is made of silicon with a boron admixture.
When a photon strikes a silicon atom, it knocks the electron out of its place and forces it to move. Since there are a lot of photons and such knocks, the electrons attempt to pair up with the vacant places left by the previously knocked out neighbouring electrons, and, as a result, they begin to circulate between the plates and in this way generate electric charge movement. However, the electric field present at the contact point of the positive and negative layers separates the electron-vacant space pairs, which results in arranging the electron movement and generating voltage. This process is easy to connect with a local power grid; however, the system must be provided with a frequency converter to transform DC into AC. As mentioned above, silicon is used as a basic material of PV cells, as the photon energy is equivalent to the energy required to move one electron in a silicon atom. Despite the fact that pure silicon is not a perfect conductor, the best solution is obtained when it is mixed with
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