The Physics of Solar Panels

Solar panels are made up of a series of interconnected solar cells to form a circuit. These solar cells are also known as photovoltaic (PV). This word comes from the words ’Photo’ (which comes from the Greek word for ‘light’) and ‘volt’ (the unit of electro-motive force). The word volt comes from the Italian Alessandro Volta who invented the battery.

Solar cells are made from silicon. Silicon is what’s known as a semi-conductor. This means that they don’t normally conduct electricity but under certain conditions we can make them do so. The first ever solar cell was developed in 1954 by scientists Daryl Chaplin, Calvin Fuller and Gerald Pearson. It was the first solar cell capable of converting enough of the sun's energy into power to run common electrical equipment.

How does a solar cell convert the sun’s energy into power you may ask? Well, sunlight is composed of miniscule particles called photons. These tiny particles radiate from the sun. When they hit the silicon atoms of the solar cell, they transfer their energy to loose electrons, knocking them clean off the atoms. One way to think about it is a game of pool. The photon is the white ball and it passes all its energy on to the coloured balls it hits.

However, freeing the electrons is only half the work of a solar cell. It then needs to bring all these stray electrons together into an electric current. This involves creating an electrical imbalance within the cell, which acts a bit like a slope, down which the electrons will flow in the same direction. Creating this imbalance is made possible by the internal organisation of silicon. Silicon atoms are arranged together in a tightly bound structure. By squeezing small quantities of other elements into this structure, two different types of silicon are created. The n-type (negative type), which has too many electrons, and the p-type (positive type), which is missing electrons, leaving ‘holes’ in their place. When these two materials are placed side by side inside a solar cell, the n-type silicon’s spare electrons jump over to fill the gaps in the p-type silicon. This means that the n-type silicon becomes positively charged, and the p-type silicon is negatively charged, creating an electric field across the cell. Because silicon is a semi-conductor, it can act like an insulator, maintaining this imbalance. As the photons smash the electrons off the silicon atoms, this field drives them along in an orderly manner. This provides the electric current to power equipment from calculators to satellites and everything in between. The more light that shines, the more the electrons will jump and the more current will flow.