In order to limit global warming humanity will need to replace fossil energy with renewable energy sources during the next decades. Those are basically endless natural energy sources that don’t pollute the atmosphere with additional carbon dioxide. Technically providing 10.000 times the amount of energy used by the entire humanity, sun is the largest energy source on our planet. Thus photovoltaic can be considered one of the key technologies when it comes to renewable energies. Today it already covers more than 13% of the energy demand in the European Union. However solar energy first needs to be converted to electric energy in order to make it usable for heating, household appliances or industrial processes.
That’s exactly what solar cells were invented for. Every solar cell is composed of the semi-metal Silicon that is arranged in two layers. The upper layer additionally contains phosphorus atoms which is why there is a surplus of electrons. On the other hand the lower layer contains Boron atoms that are each lacking one electron. As a result of this different distribution of negative particles, the electrons from the upper layer now move to the Boron atoms and occupy the vacant spaces. Consequently a new layer is being formed that is neutral and therefore separates the two initial layers. Furthermore there is an electric field because of the different distribution of electrons. The processes that have been described so far explain the state of the solar cell without sun light but now the additional energy is necessary in order to generate a current. Firstly the light arrives at the anti reflection coating that is the outermost layer of a solar cell and serves to minimise the loss of energy. Then the photons ,that are light particles consisting solely of energy, reach the neutral layer in the centre. There they activate some of the electrons that previously travelled to the Boron atoms which makes them move to the upper layer that is in lack of electrons. Now it is important to note that the upper and the lower layers are connected by conductors creating a circuit. The vacant electrons flow through the circuit to the lower layer where they occupy free spaces of the Boron atoms. This process creates a direct current that finally needs to be converted to an alternating current using a power supply device. Now the current can be fed into the grid or also be directly used to power electric devices.
If more sun light is arriving at the solar cell, more electrons are being activated which results in a larger current. Therefore solar parks appear to be way more effective in regions with great sunshine duration and intensity. Typically solar cells posses an efficiency of 19% which is still pretty low compared to coal-fired power plants that have an efficiency of 45%.
There are also other ways of using the energy provided by sun besides the classical solar cell. Those systems are called concentrated solar power (CSP). They use huge arrays of mirrors that bundle the reflected light in one central point. Most CSP systems use the heat provided by the bundled light to power a turbine. Since concentrated solar power is still more expensive than photovoltaic it is not very popular today. However their potential to save the energy is believed to be better which might make them became more important in the future.
sources:
https://ec.europa.eu/eurostat/statistics-explained/index.php/Renewable_energy_statistics#:~:text=Wind%20and%20hydro%20power%20accounted,renewable%20sources%20(9%20%25)
https://de.wikipedia.org/wiki/Photovoltaik#Technische_Grundlagen
https://de.wikipedia.org/wiki/Sonnenw%C3%A4rmekraftwerk#Verbreitung_der_CSP-Kraftwerke