ust a few decades back, people could hardly imagine generating electricity right at home by harnessing sunlight. Solar technologies are increasingly integrated into our lives, and rooftops of homes and business premises covered with solar panels don't really surprise anyone.
Yet many don’t even imagine how fascinating the technology behind solar panels is. Understanding solar systems is well within everybody's grasp (well, at least their basic working principles), and this guide is designed specifically for those not particularly versed in physics or chemistry. Hopefully, it will help you build up a picture of how solar systems work to turn sunlight into usable energy.
Silicon – the backbone of the solar industry
Why does silicon work best for solar?
Silicon is the most common material for solar panel production. It has been in use since the very beginning of solar panel manufacturing and currently leads the market with a share of as much as 95%.
Solar panels can be manufactured only from semiconductors – materials with intermediate electrical conductivity. While conductors allow electric charge to pass through them freely (these are, for example, most metals) and insulators prevent the charge from flowing (for example, glass or plastic), semiconductors can conduct electricity but only under specific conditions. Some examples of semiconducting materials are silicon, germanium, and gallium arsenide.
At this point, you may wonder why silicon is better for solar panels than any other semiconductor. There are many factors at play there, but in a nutshell, silicon has a unique set of properties most suitable for solar manufacturing, such as wide availability, conversion efficiency, cost-effectiveness, and long lifespan.
How is silicon for solar production obtained?
Silicon is the second-most abundant element on Earth after oxygen, making up almost 30% of the planet's crust. It can’t be found uncombined in nature and occurs bonded with other elements (usually oxygen) in the form of silica minerals such as quartz, rock crystal, amethyst, and agate. Silicon for solar panels is typically extracted from quartz sand.
From sand to solar panels: how are PV panels made?
First, silicon must be purified to be suitable for solar panels. The manufacturers remove oxygen through a reaction with carbon in an arc furnace at a temperature of about 1410° C. The next step in solar production is forming silicon ingots: either a cylindrical bar created from a single large silicon crystal (monocrystalline ingots) or brick-shaped blocks formed from multiple crystals (polycrystalline ingots). During making the ingots, solar manufacturers add doping materials to make our future solar cells electrically conductive.
Once the ingots are ready, they are cut into thin discs (wafers) by a wire saw. These wafers will form the basis of the solar cells. The next step is texturing - a process when the surface is roughened to increase solar efficiency by reducing the reflection loss. The manufacturers also apply antireflective coatings to enhance solar cell performance further.
After that, conductive metal contacts and busbars are printed across a solar cell. Conductive contacts are thin grid-like lines that collect the electricity from the solar cells and bring it to busbars - thicker lines that carry the current out of the cell.
Now it is time to assemble a solar panel. Solar cells are sandwiched between a back sheet and tempered glass to protect the silicon from external impacts. All three layers are then enclosed into an aluminum frame that holds them together.
Photovoltaic effect. The science behind solar
Working principle of solar power
Now let’s move on to the most exciting part and see how solar systems harness sunlight. Everything is built around the photovoltaic effect - a physical and chemical phenomenon that creates voltage or current in a solar cell when exposed to sunlight.
Discovered in 1839, the photovoltaic effect came into focus only decades later when the first solar cells and solar panels were made from selenium. However, these panels could convert only 1% of sunlight into electricity and were too expensive to manufacture. In 1905, Albert Einstein worked on the nature of light and described how it reacts with electrons inside a material. This set the stage for the creation of the first practical silicon solar cell in the middle of the 20th century by Bell Laboratories.
How do solar cells convert solar radiation into electricity?
Silicon atoms have four valence electrons, meaning each atom is bonded with four other silicon atoms forming a symmetrically arranged lattice structure, but we need an imbalance to make solar cells capable of generating current. Therefore, each cell consists of two silicon layers doped with elements that have different valencies: one layer is doped with boron giving silicon a positive charge, and the other is doped with phosphorus giving a negative charge. When placed in contact, these two layers create an electric field.
When sunlight strikes a solar panel, photons (the smallest particles of light) knock the electrons within solar cells free of their atoms, and an electric field forces them to move in a single direction in a circuit. This movement of electrons creates an electric current.
Solar system isn't just solar panels
Solar panels have done their job, but a few more steps are left before we can power our homes with solar energy. The panels generate direct current (DC), where the charge flows in one direction, while our homes need alternating current (AC), where the charge periodically reverses. To do this, a solar system includes an inverter that converts DC from the panels to AC, making it suitable for home consumption and the electric grid.
Sometimes solar panels generate more power than a household needs. That’s why many homeowners add a battery bank to their solar systems to ensure that none of the unused energy is wasted. It stores the excess electricity, which can be used later on overcast days, at night, or during power outages.
On top of this, every solar system includes a host of other equipment, such as cabling, combiner box, utility meter, racking, etc. All these components ensure that the entire system works without any hiccups.
Solar technology keeps advancing
Today we have covered only the basics of how solar panel systems work. Photovoltaics keeps getting more sophisticated, and the efficiency of solar cells keeps increasing at a rapid pace. For example, IBC solar cell technology, or Interdigitated Back Contact, puts electrical contacts on the cell’s rear, substantially increasing light absorption. Another technology often referred to as the next generation of solar cells is TOPCon (tunnel oxide passivated contact) which adds an extra tunneling oxide passivation layer to the cell allowing it to collect more light from its rear side.
All this gives reason to believe that solar will play a pivotal role in the transition from fossil fuels making renewable energy both efficient and affordable for everyone.