Solar panels are clever little things. By utilising sunlight, a few simple atomic principles, and something called the Photovoltaic Effect, this technology could be the world’s main source of renewable energy in just a few years’ time.
This Ted-Ed video made by Richard Komp is a nice introduction to solar panels:
The science behind solar panels
Without going into too much detail, the sun is like a giant fusion reactor emitting vast amounts of light energy into space. This light energy (specifically the ‘photons’ – a quantity of light) is absorbed into the solar panel, causing the electrons of a semiconductor to become excited. The electrons break free from their atoms and pass along conductive metal ‘fingers’ and ‘busbars’ of the solar panel as an electric charge. This is known as the Photovoltaic Effect, which is where the term solar PV comes from.
The electric charge then passes through an inverter to convert it from direct current (DC) into usable alternating current (AC), before powering your electrical devices and finally returning to the solar panel.
What is a semiconductor?
Just like our own bodies, solar panels are made up of cells. A semiconductor is an element that creates an electric current when it’s exposed to light, and it’s the main component in a solar cell. As the name suggests, semiconductors have the conductivity between an insulator and a conductor.
Silicon is the most commonly-used semiconductor in commercial solar cells. It’s also one of the most abundant elements on earth, but it must be subjected to the doping process before it’s ready for use. Doping is when other elements are added to the silicon crystal, resulting in a deliberately unstable number of electrons. There are two types of semiconductor required:
- An N-type semiconductor is negatively charged due to its concentration of electrons. Phosphorus is commonly added for making N-type semiconductors.
- A P-type semiconductor is positively charged as it doesn’t have enough electrons. P-type semiconductors are usually formed by adding elements such as boron.
Unlike other stable elements, the electrons in doped semiconductors are in constant motion, moving away from negatively charged areas into positively charged areas or ‘holes’ where there’s a shortage of electrons.
The two types of oppositely-charged semiconductors are then layered one on top of the other, and this is termed the P-N junction. It’s the nature of this junction – the opposite charges stacked together – that causes the usual random electron-and-hole movement to flow in a single organized direction, creating a current.
So what does this mean?
A solar cell can only generate about ½ a volt on its own, so you’ll need a large number of them all working simultaneously to get a usable amount of electricity. In more practical terms, it takes 12 cells to charge a mobile phone, and several solar panels (also called a solar array) to meet the electricity demands of a whole house.
As you might expect, it’s difficult to predict how much electricity your solar panels will generate. From sunlight levels and installation to the model of solar panel you choose, there are many factors that have an impact on the performance of solar panels. Click here to read more about calculating a solar panel’s electrical output.