The Complete Guide on How Solar Panels Work
Updated: Oct 19, 2020
Solar energy has become more and more popular these days as a cleaner and cheaper energy source than conventional fossil fuel sources like coal and natural gas. And even though this technology has been around since the 1950s, many are still not familiar with the process of how solar panels really work or how they produce energy. But before we dive into the details, let us first clarify some misconceptions and define our terms.
Misconception #1: Solar panels produce electricity from heat.
This misconception is very easy to have since from our everyday experience, heat and sunlight always go hand in hand. However, we must first understand that the energy that we get from the sun is in the form of light only. This light is only converted into heat when it hits and is absorbed by objects like our atmosphere, the ground, and our roofs. And as the name suggests, solar energy is the energy from the sun, which is light.
Solar panels, therefore, convert sunlight into electricity instead of heat. In fact, similar to electronic devices, they even work better and produce more energy when the ambient temperature is lower, with similar levels of irradiance or sunlight. And since solar panels are not 100% efficient in converting sunlight into electricity, they even produce heat as waste in this process.
Misconception #2: The correct name for solar panels is actually solar modules or solar panels. However, for most purposes, they have been used interchangeably, so we will still use the term solar panel/s throughout the rest of the article.
Solar cells are the smallest power-generating unit of a solar panel. You may have noticed that some solar panels are made up of small blue or black squares inside. These are solar cells, which produce only a very small voltage of less than 1V. This is why the most common solar panels in the market today have 60 or 72 solar cells inside of them, which are all connected in series to raise the voltage to a usable level.
When these solar cells are connected in series, they are placed in a panel, hence, the name solar panel. A solar panel, on the other hand, is a complete, ready to use module that consists of the solar panel, the aluminum frame, the glass, the electric junction box, and the wires.
With these misconceptions out of the way, we can start digging into the details of the science of how solar panels produce energy.
What Solar Panels are Made Up Of
The solar cells are made up of a class of materials called semiconductors. Semiconductors are a class of materials that have an electrical characteristic that is in the middle of that of conductors and insulators. You may be already familiar with conductors and insulators because you encounter them and use objects that are made up of them in your everyday lives. Conductors are basically metals that easily conducts heat and electricity, while insulators are the exact opposite as they do not conduct both heat and electricity very well.
The most common type of semiconductor that is used for solar cells is Silicon, mainly because it is the second most abundant element in the Earth’s crust after Oxygen. 90% of the soil, rock, and dust in the Earth’s crust is made up of silicate materials (rock-forming minerals that are made up of Silicon and Oxygen). Semiconductors have also been used to create transistors, which makes up all of the modern electronic devices that we use today.
Energy Bands in an Atom
To understand why semiconductors have their unique electrical characteristics, we must dive into the physics of it. Remember that an atom is composed of the nucleus, which is composed of protons and neutrons and the electrons which are located in shells that are centered in the nucleus. Depending on the total number of electrons in the atom, it can have multiple larger and larger shells. What’s important here is that the farther an electron is to the nucleus, the higher its energy state.
The outermost shell in an atom is called the valence shell. It is also the farthest shell from the nucleus, which means that the electrons in it(called valence electrons) also have the highest energy levels. The different levels of energy that the electrons can have while in this shell are spread out in an energy band which is called the valence band.
For a material to conduct electricity, a valence electron must receive some amount of energy for its energy level to be higher than the valence band. When this happens, that electron can now freely move away from the atom and flow as electricity. Its current energy level is now in the conduction band and it is said to have “jumped” from the valence band to the conduction band.
For conductors, the conduction band and the valence band overlap with each other, which means that all of their outer electrons already have enough energy to freely move around the whole material. These electrons are called free electrons and this is the reason why this type of material can easily conduct electricity.
For both semiconductors and insulators, there is a certain gap(called the band gap) to their valence and conduction bands which represents the amount of energy that must be added to the valence electron for it to be free. The band gap is very large for insulators and this makes it also very hard for an electron to gain enough energy and jump to the conduction band.
Valence electrons usually get additional energy from heat. For semiconductors, this is sufficient to have a few valence electrons to jump into the conduction band but for insulators, the band gap is so large that it makes this virtually impossible through heat alone. For semiconductors in absolute zero, the valence electrons get no more additional heat from energy, and they also act like insulators.
The great thing about semiconductors is that you can significantly alter and control its characteristics through a process that is called doping. This is done by introducing certain atoms as impurities into a pure semiconductor. When this happens, the semiconductor’s electrical, optical, and even structural properties can be altered. A doped semiconductor is referred to as an extrinsic semiconductor, while a pure semiconductor is called an intrinsic semiconductor.
There are two types of extrinsic semiconductors, n-type and p-type semiconductors. The resulting type from doping depends on the impurity that is added. Phosphorus (P) or Arsenic (As) is used to create n-type semiconductors while Boron is used to create p-type semiconductors.
The valence band of Phosphorus and Arsenic is very close to the semiconductor’s conduction band which makes it very easy for their valence electrons to jump to the conduction band. When this happens, the conductivity of the whole material is increased. On the other hand, the valence band of Boron is very close to the semiconductor’s valence band. This then makes it very easy for the semiconductor’s valence electrons to jump here. An empty space is left behind on the semiconductor’s valence band, which is called a hole and the conductivity of the whole material is also increased.
An amazing thing happens when you put together an n-type and a p-type semiconductor. First, remember that an n-type semiconductor has gotten extra electrons in its conduction band from doping while a p-type semiconductor got empty spaces or holes in its valence band. When these two materials meet, the extra electrons on their point of contact release some energy and move to the holes, creating a portion that is devoid of free electrons where the two materials me