Solar PV systems are one of the most widely considered and installed examples of renewable technology in the world. But, for some, how they actually work might be something of a mystery — almost magical.
But, it really doesn't need to be. Exactly how they work and what makes up a PV system is actually pretty interesting.
So, if you have ever wondered what a solar PV system is actually is, or indeed how it works, then we've made a very short guide to help you get to grips with the basics.
How do solar PV panels actually work?
Put simply, solar PV panels convert sunlight into electricity through a process known as the photovoltaic (PV) effect. Closely related to the photoelectric effect, the PV effect was first demonstrated as early as the late-1830s by Edmond Becquerel.
Becquerel noticed that when plates of platinum or gold were immersed in acid, neutral, or alkaline solutions and exposed to solar radiation, a small electrical current could be generated. A little later, in the 1880s, Charles Fritts managed to develop the first true solar cell made from selenium covered with a thin layer of gold.
While this panel did work, it had a very low efficiency.
Modern solar panels work when photons from sunlight knock electrons free from atoms, generating a flow of electricity. The panels are actually made up of smaller units called photovoltaic cells. These solar cells are a sandwich of semiconductors made from silicon that is "doped" with other materials.
Boron or indium are usually added to one layer, giving it a positive charge. Essentially, adding a boron atom to a group of silicon atoms creates a “hole” — a space that would be occupied by an electron in pure silicon. This is called p-type doping or a p-type semiconductor (p is for positive). The other layer is usually doped with phosphorous or arsenic, which adds extra electrons, or a negative charge, to that layer (this is called n-type doping, or an n-type semiconductor, for negative).
Sandwiching the two layers creates an electric field at the junction — called the p-n junction. When exposed to light, an electrical field is generated within this junction as electrons absorb energy from photons and are break free from their "parent" atom.
This process leaves behind a "hole" in the valence bonds of the material the atom escaped from. Because of the preexisting electrical field in the p-n junction, these electrons and "holes" move in opposite directions — the electron to the n-side and the "hole" to the p-side.
This motion of the electron creates an electric current in the cell. Metal conductive plates on the sides of the cell collect the electrons and transfer them to wires, allowing the electrons to flow like any other source of electricity.
Interestingly, most photocells tend to be more efficient the smaller they are, so each PV panel is usually made up of many small cells. If you look closely at a solar panel, you will be able to see all the smaller subunit photocells that make up the main panel.
Typically made from doped silicon (though germanium, lead sulfide, and other semiconductors can be used), PV cells are the powerhouses of any modern PV panel.
More on that in the next section.
What materials are PV panels made from?
PV panels, like any piece of technology, are a jumble of different materials that make up different parts, from the photocell to the frame and everything in between. However, what most people mean when asking a question like this is what is the magical ingredient that gives the PV panel its seemingly magical ability to create electricity from sunlight.
That wonder material happens to also be one of the most abundant substances on plant Earth — silicon. In fact, it makes up about 30% of the Earth's crust, give or take.
Silicon is the second-most abundant material on the planet, behind oxygen, but is rarely found in its free state in nature. Typically it will be found combined with other elements to form one of the plethora of silica minerals that make up the Earth's crust.
It also happens to have some interesting physical and electrochemical properties that make it pretty handy for building electronics.
One of these is the fact that it is a semiconductor. A semiconductor, as the name suggests, is any material that has a conductivity between that of an insulator (like a ceramic) and that of a conductor (like a metal).
Being a metalloid (neither metal nor non-metal), silicon shares some properties of both — hence its role as a semiconductor.
This means that while it can conduct electricity, albeit less well than metals, its ability to do so increases as its temperature rises (unlike metals).
For this reason, silicon is used to make many important electrical components, including transistors, which amplify or switch electrical currents and are the backbone of all types of electronics, from radios to iPhones.
With regards to solar cells, pure silicon is a poor conductor of electricity. To overcome this, most solar cells blend silicon with other elements, like gallium or arsenic, to either produce electron-deficient layers or electron-rich layers respectively. This is important, as we've seen, to produce electron-hole pairs to generate electrical fields.
While very abundant, there are some limitations to using silicon as the base material for solar cells. The main one being that the panels are inherently fragile and rigid. This can complicate transportation and installation, among other things.
Typically, silicon-based solar cells come in a few distinct forms in most solar panels that are commercially available. These include:
- Monocrystalline solar cells — Made from almost pure silicon, these are the most efficient form of solar panel but tend to be the most expensive. These panels are usually pretty dark in color and tend to have the longest lifespans (often 25 years plus).
- Polycrystalline solar cells — Also known as polysilicon or multi-silicon cells, were the first commercially available type. They are more affordable than monocrystalline panels but are less efficient and generally take up more space. These panels also have a relatively low heat tolerance compared to monocrystalline panels.
- Amorphous solar cells — Composed of non-structured silicon crystals, these panels are easier to install and transport but have a much-reduced efficiency compared to the other two forms. These are the kind of panels used in relatively cheap solar-powered electronics like pocket calculators and other thin-film applications. They are relatively cheap to produce but are by far the least efficient. Their limitations can be overcome by stacking several of them on top of one another and they also tend to be less fragile and rigid than other forms of solar cells.
Which type is chosen is usually a trade-off between manufacture and installation cost and an acceptable cap in electrical generation efficiency.
Organic solar cells might be the future of solar PV
Silicon-based solar cells make up the vast majority of existing PV panels, but are not the only kind of solar PV panels in existence. One rising star is something called an organic solar cell/panel.
Organic solar cells, or OSC for short, are an exciting development in the world of renewable technologies. Typically made from special conductive organic polymers or small organic molecules, this technology can produce more lightweight and flexible solar panels.
OSCs, while relatively new, also have higher efficiencies per area when compared to more traditional PV panels. Existing OSCs tend to be very strong absorbers of light, and are touted by many experts in the field as the future of solar technology.
Because of the way they are built, organic solar cells/panels have other inherent advantages over their non-organic counterparts. Foremost among these is their lightweight nature, flexibility, large area coverage, and low cost of manufacture.
Some organic solar cells are manufactured using a process called roll-to-roll production. This process is considerably cheaper than conventional non-organic solar cell production and enables organic solar cells to be manufactured with a large area.
An organic solar cell, sometimes called a plastic solar cell, is a type of polymer solar cell that uses organic electronics. This is a branch of electronics that deals with conductive organic polymers or small organic molecules, for light absorption and charge transport to produce electricity from sunlight via the photovoltaic effect.
This enables organic photovoltaic cells to convert solar energy into electrical energy more efficiently than other types of solar cells, including the silicon cells found in most common solar panels.
However, current OSC systems tend to have shorter expected lifespans when compared to more traditional silicon-based panels. This is because of their generally lower stability and lower strength.
Another issue with OSCs is their relative material extinction coefficients (a measure of light lost due to scattering and absorption per unit volume). Materials with higher absorption coefficients more readily absorb photons, which excite electrons into the conduction band. The extinction coefficient of OSCs is not, as yet, as good as that of silicon-based solar panels.
However, it is important to note that OSCs are still very much in development, and breakthroughs in new materials, processing methods, and device architectures will likely fix this shortcoming.
OSCs can also be used for some interesting applications that would not be possible with non-organic solar panels. For example, they can be made transparent and specialized for specific wavelengths of light.
This could have applications in structures like greenhouses, where OSC panels can form the main glazing of the structure. Such a setup could allow wavelengths of light commonly used by plants to permeate through the OSC panels, while using other wavelengths to generate electricity.
They can also be easily integrated into portable electronic devices, meaning consumers would be able to power/charge their electronics on the move — even in low light levels.
What are the main components of a PV solar panel?
And so, on to the main event.
While solar PV installations may vary in shape and design, a typical solar PV system will generally have the following key components.
1. The photocells are literally the face of a PV unit
Solar or photocells are the main workhorses of any solar PV system. These are the bits that are most noticeable mounted on rooftops of buildings, or, in some circumstances, on walls or even on the ground.
The job of the photocells is to convert sunlight into electricity. They do this by using the process we outlined above — i.e. the photovoltaic effect.
Most solar PV cells are made of a mixture of silicon, aluminum (for the frame), and a polymer backing. Solar PV cells can vary widely in size, color, and shape, but all follow the same basic design.
The size of a solar panel is usually dictated by the maximum wattage range that the panel is designed to generate. Typically, for domestic applications, that can range anywhere between 200 and 400 watts per panel, though most are generally around 260 watts.
Other than the main components of the solar cell, solar cells tend to be sandwiched between encapsulant layers - metal backing plates and front tempered glass layers. All of these layers are then held together in, typically, an aluminum frame.
2. The mounting racks are obviously very important components too
Having the panels is great, but generally, you'll need something to mount them on and a way to orientate the panels. This is where the mounting racks are vitally important.
Roof mounting systems are the most common, as roof installations are generally considered more aesthetic and efficient than ground installation. They also make use of "wasted" space on existing structures, such as houses, without the need to use valuable land or green space.
However, roof-mounted systems are typically harder to maintain given their elevated and often inaccessible location. Other mounting methods like pole-mounting and, of course, ground-mounting are also fairly common.
The latter is the simplest form of mounting system to install, and is ultimately the easiest for long-term maintenance and repair. However, they do have the downside of taking up ground space that could be used for something else, like another building, parkland, farmland, etc.
Whichever mounting location is chosen, most racking systems tend to be either fixed or tracking. The former, as the name suggests, "fixes" the panels at a given height and angle and they are, as such, unable to move in orientation to the Sun.
Solar panels tend to work best when sunlight hits the panel directly. This is all well and good for a fixed light source, but when relying on the Sun (which is constantly in motion relative to the panel) this can be near-impossible to maintain through the day and year with a fixed system.
For this reason, fixed systems will often be fitted at a set angle that is something of a compromise for all-around use. This is typically about 37 degrees.
Tracking mounting systems, on the other hand, are able to track the motion of the Sun throughout the day and year by constantly moving their facing direction. They can also adjust their angle to maintain the optimum angle of incidence throughout the year.
3. The inverter is the workhorse of any solar panel system
Solar panels are great, but the electricity they produce tends to be direct power (DC). While DC can be used for some applications, most solar panels are installed for the purpose of providing useable electricity for a home or commercial premises.
This means another piece of technology is required to convert DC into alternating current (AC). That is the job of the inverter.
The inverter is a hard-working piece of kit that is in near-constant operation through the lifespan of a typical solar panel. For this reason, if a solar panel system fails for some reason, the prime culprit is usually the inverter.
For this reason, most inverters tend to have a shorter warranty than the main panel itself — something to bear in mind if you are considering installing a solar system.
Two different types of inverters tend to be used in a solar panel system. These are called string inverters and microinverters.
The former are larger devices and are typically installed on a wall, roof space, or shaded area of the site. As the name suggests, these inverters convert "a string" of electricity generated by a PV array, rather than per panel.
Microinverters, on the other hand, are installed on each panel (typically to the rear). This allows the DC to be converted on a panel-by-panel basis before being fed into a building or the grid.
While both types have their pros and cons, one of the main advantages of microinverters is the fact that when some panels are shaded in a string inverter system, the efficiency of all panels is directly impacted. This is not the case with microinverters, where only the shaded panels are affected.
4. The utility meter measures how much juice the panels make
Whether or not your solar PV system has battery storage, or not, it will integrate some kind of a utility meter to measure the electrical consumption per property. Meters installed on properties with solar PV arrays will also record the amount of electricity generated by the panels and, in some cases, allow you to export any excess power back to the grid.
Depending on where you live in the world and the arrangement you have with your electricity supplier, you will usually be paid for any excess energy you export — which is nice.
5. Batteries are an increasingly important part of a solar panel system
One of the main criticisms of renewable technology like solar PV cells, is their unreliability during unfavorable environmental conditions. In the case of solar, the lack of sunlight (i.e. during the night) tends to means they effectively become very expensive roof tiles and little more for a good chunk of the time.
To combat this, solar PV arrays are increasingly being combined with some form of a battery storage system. This setup means that electricity can be stored and tapped later, without resorting to using grid-supplied electricity when the sun goes down.
In the case of Tesla's Powerwall, such systems also offer backup protection for places that suffer from frequent power outages, too.
More usually referred to as energy-storage systems, solar PV batteries effectively store excess electricity from PV panels for use later. Big names on the scene include the likes of Samsung and Tesla, and many energy companies will also offer combined solar PV and battery packages.
Batteries tend to come in one of a few forms, but by far the most common are rechargeable lithium-ion. This is because of their relatively small size and excellent capacity to store electricity.
However, there are some considerations to take into account before actually installing them. For example, if most of the energy produced by the PV array is actually consumed during the day, or is used to heat water, then a battery may not be cost-effective.
6. The charge controller is also a very important component of any solar PV system
For PV systems that also integrate a battery storage system, charge controllers are another critical part of the system. Primarily tasked with protecting the battery packs from becoming overcharged, they constantly regulate the charging capacity of a battery and adjust supply to them accordingly.
When the battery is full, the charge controller will automatically shut off the power supply from the PV panels to prevent the batteries from becoming permanently damaged.
Charge controllers tend to come in one of two forms: Pulse Width Modulation (PWM) and Maximum Power Point Tracking (MPPT). The former is more suitable for smaller domestic-scale PV arrays and tends to vary between 4 and 60 amps.
The latter is more suitable for larger installations with higher voltages — often up to 160 volts DC.
And that, solar-PV initiates, is your lot for today.
Now that you have a basic understanding of what a solar PV system is, and what the main components of one are, you may want to research potentially installing one in your own home?