In the previous article, we have described basic electrical terminology and some essential components required for solar installation in a commercial and residential area.
Solar radiation is available in plenty for since long but was not usable until photovoltaic technology came into the existence.
Isn’t this amazing? the way these powerful solar radiations are captured and converted into electrical energy to cater to our electric demands.
The entire solar energy generation concept revolves around the photovoltaic effect.
What is the photovoltaic effect?
Photovoltaic effect or PV effect is the simple technology that converts solar light incident on the semiconductor material into electrical energy.
Does the solar radiation incident on any surface is converted into electrical energy?
Well, we wish if this was true but only semiconductor material that holds the photovoltaic property is capable of converting the incident photon energy into electric energy.
Semiconductor material such as silicon, gallium arsenide, copper indium diselenide, cadmium telluride etc. is used in the manufacturing of solar cells due to its photovoltaic property.
A small history of the photovoltaic effect and solar cells
The photovoltaic effect was first introduced by Edmond Becquerel in the year 1839.
During an experiment related to wet cells, he noticed that the silver plates exposed to sunlight lead to an increase in the voltage level. In the year 1941, the first monocrystalline silicon solar cell was developed.
Since the 1950s, solar cells were used to power satellites in space. The oil crisis in the 1970s caused attention to fall on solar technologies, and photovoltaics gained popularity as a potential source of electric energy for the residential and commercial sector. Since 2010, the price of solar cells has dropped rapidly (~80%), the volume of solar cells produced has increased rapidly, and the efficiency of commercially available cells has increased.
Working principle of the photovoltaic effect
- When solar rays are incident on two unlike material in close contact, voltage and an electric current is generated.
- When light energy of certain intensity falls on the semiconductor material photon energy is absorbed that leads to the generation of electron-hole pair.
- When incident photon energy is higher than the minimum potential energy required for the excitation of electrons, electrons become free and flow.
- When electrons are set free and placed in a closed-loop, an electric current is generated.
How does the solar cell/photovoltaic cell generate electricity?
The solar cell forms the base of the solar panel, it generates electricity with the help of a photovoltaic effect. The solar cell is made up of semiconducting material such as silicon or germanium.
Silicon is the most common material used in the manufacturing of solar cells; it consists of four valence electrons in the shell. These silicon atoms create a covalent bond with their nearest silicon atom thus forming a tetrahedral lattice structure.
When solar radiations are incident on silicon cell following process takes place:
- Solar radiation consists of photons, these photons have zero mass and travel with the speed of light with a certain wavelength.
- These incident photons have different wavelengths and energy.
- When solar rays strike on the silicon material, the portion of the solar rays is reflected, while some are transmitted or absorbed.
- If the incident solar energy is greater than the minimum energy required by the electrons to excite, the electrons get excited and jump from valence to conduction band. A hole is created in the covalent bond each time an electron is moved.
- This hole-electron pair can freely move in the silicon material, but to produce the electricity we need an additional element.
- The silicon layer at the top is doped with a phosphorus atom that consists of one additional electron and this layer act as a negative n-terminal.
- Whereas the bottom layer doped with boron atoms is considered a positive p-type layer with one electron less
- An electric field is created at the junction between these two layers.
- Electrons get excited and swept towards the n-type layer by an electric field and the holes drift towards the p-type layer
- These electrons and holes are directed to the applied electrical field and flow towards the external circuit in the form of direct current.
- The generated electric current is supplied to the DC load through wires or is converted into the AC supply through the inverter and is further supplied to the load/grid through the wires.