How Solar Panels Work (And Why They’re Taking Over the World)
Solar energy is crucial to many futures. On the micro level, there’s a booming solar industry in America and across the globe. Since Congress passed a tax credit in 2006, the Solar Energy Industry Association (SEIA) says that the industry has been averaging an annual growth rate of 50 percent in the last decade. In most fields, that would be macro news. But solar energy has a mission beyond making money—it’s supposed to save the planet.
There’s no plan to prevent man-made global warming from permanently warping the Earth’s climate without solar panels and the energy they can convert. “The role of renewable energy solutions in mitigating climate change is proven,” says the United Nations Development Program. Some in the industry think that solar will grow 6,500 percent as an industry by 2050 in order to mitigate that need.
But for all their importance, solar panels still feel mysterious. Stiff and slightly menacing black rectangles, they have neither the look or the feel of a savior. Majestic waterfalls and dams look heroic, but solar panels do not. So…how do they work anyway?
A Brief History
Work in solar energy started in 1839, when a young French physicist named Edmond Becquerel discovered what is now known as the photovoltaic effect. Becquerel was working in the family business—his father, Antoine Becquerel, was a well-known French scientist who was increasingly interested in electricity. Edmond was interested in how light functioned, and when he was just 19 their two interests met—he discovered that electricity could be produced through sunlight.
The years went on and the technology made small but steady steps. During the 1940s, scientists like Maria Telkes experimented with using sodium sulphates to store energy from the sun to create the Dover Sun House. When investigating semiconductors, the engineer Russell Shoemaker Ochs examined a cracked silicon sample and noticed that it was conducting electricity despite the crack.
But the biggest leap came on April 25, 1954, when chemist Calvin Fuller, physicist Gerald Pearson, and engineer Daryl Chapin revealed that they had built the first practical silicon solar cell.
Like Ochs, the trio worked for Bell Labs and had taken on the challenge of creating that balance before. Chapin had been trying to create power sources for remote telephones in deserts, were regular batteries would dry up. Pearson and Fuller were working on controlling the properties of semiconductors, which would later be used to power computers. Aware of each others work, the three decided to collaborate.
These earliest solar cells were “basically hand-assembled devices,” says Robert Margolis, senior energy analyst at the National Renewable Energy Laboratory (NREL).
How Do Solar Panels Work?
To understand how silicon solar panels make electricity requires shrinking down to the atomic level. Silicon has an atomic number of 14, which means that it has 14 protons in its center and 14 electrons circling that center. Using the classic imagery of atomic circles, there are three circles moving around the center. The innermost circle is full with two electrons, and the middle circle is full with eight. However, the outermost circle, which holds four electrons, is half-full. That means it will always look to fill itself up with help from nearby atoms. When they connect, they form what is called a crystalline structure.
With all those electrons reaching out and connecting to each other, there isn’t much room for an electric current to move. That’s why the silicon found in solar panels is impure, mixed in with another element, like phosphorous. The outermost circle of phosphorous has five electrons. That fifth electron becomes what is known as a “free carrier,” able to carry an electrical current without much prodding. Scientists boost the number of free carriers by adding impurities in a process called doping. The result is what’s known as N-type silicon.
N-type silicon is what’s on the surface of a solar panel. Below that resides its mirror opposite—P-type silicon. Whereas N-type silicon has one extra electron, P-type uses impurities from elements like gallium or boron, that have one less electron. That creates another imbalance, and when sunlight hits the P-type, the electrons starts to move to fill the voids in each other. A balancing act that repeats itself over and over again, generating electricity.
What Makes Up a Solar Panel?
Solar cells are made out of silicon wafers. These are made out of the element silicon, a hard and brittle crystalline solid that is the second most abundant element in the Earth’s crust after oxygen. If you’re at the beach and see shiny black specks in the sand, that’s silicon. As Ochs discovered, it naturally converts sunlight into electricity.
Like other crystals, silicon can be grown. Scientists, like the ones at Bell Labs, grow silicon in a tube as a single, uniform crystal, unrolling the tube, and cutting the resulting sheet up into what are known as wafers.
“Visualize a round stick,” says Vikram Aggarwal, the founder and CEO of EnergySage, a comparison-shopping marketplace for solar panels. That stick is cut like a “pepperoni, a roll of salami cut thin for sandwiches—they shave them very thinly,” he says. That’s where it has historically been very difficult—either too thick, a waste, or too thin, making them not precise and prone to cracking.”
They try to make these wafers as skinny as possible, to get as much value out of their crystal as possible. This type of solar cell is made out of mono-crystalline silicon.
While the first solar cells resemble today’s cells in terms of look, there are a number of differences. Back at Bell Labs, the initial hopes was that solar cells would be good for the coming space race, Margolis says, so there was a premium on keeping weight down. The photovoltaic cells, as they came to be known, were put into a lightweight encapsulate.
And it worked. Just four years after the first working solar cell was developed, on March 17 1958, the Naval Research Laboratory built and launched Vanguard 1, the world’s first solar-powered satellite.
Solar Panels Today
Nowadays, photovoltaic cells are mass-produced and cut by lasers with greater accuracy than any scientist at Bell Labs could have imagined. While they’re used in space, they’ve found far more purpose and value on Earth. So instead of putting an emphasis on weight, solar manufacturers now put an emphasis on strength and durability. Goodbye lightweight encapsulate, hello glass that can withstand the weather.
One of the main focuses on any solar manufacturer is efficiency—how much of the sunlight that falls on every square meter of the solar panel can be converted into electricity. It’s “a basic math problem” that lies at the center of all solar production, says Aggarwal. Here, efficiency means how much of the sunlight can be properly converted through P and N-type silicon.
“Lets say you have 100 square feet available on your roof,” he says in a hypothetical. “In this limited space, if panels are 10 percent efficient, its less than 20 percent. Efficiency means how many electrons they can produce per square inch of silicon wafers. The more efficient they are, the more economics they can deliver.”
Around a decade ago, Margolis says, solar efficiency was hovering around 13 percent. In 2019, solar efficiency has risen to 20 percent. There’s a clear upward trend, but one that says Margolis has a limit with silicon.
Due to the nature of silicon as an element, solar panels have an upper limit of 29 percent. So…where do we go from here?
The Future of Solar
Some scientists are working on using new materials. There’s a mineral known as perovskite that Aggarwal describes as “very exciting.” First discovered in the Ural Mountains in western Russia, perovskite has raised eyebrows in testing—from 10 percent efficiency in 2012 to 20 percent in 2014. It can be made artificially with common industrial metals, making it easier to find, and it uses a simpler process than the balancing dance of P and N type silicon to conduct electricity.
But both Aggarwal and Margolis caution that it the technology is still in its earliest phases. “Efficiency in the lab has gone up rapidly, but there’s a difference between the lab and the real world,” Margolis says. While perovskite has shown great progress in clean environments, it has shown rapid declines when introduced to elements like water, which it could encounter in daily use.
Rather than new materials, Margolis and his team are working on a concept he calls “solar plus.” As solar energy use increases, there’s a potential to improve how “solar interacts with other buildings as a whole,” he says.
So imagine it’s a brutally hot summer in the city. You go to an office for work, and then back home at night. It’s hot and humid, so you turn on the air conditioner—and so does every other person in the city. The electrical grid becomes strained.
But Margolis imagines it could be possibly to store and utilize solar energy to lessen the strain. “Two hours before you come home, when the sun is still running, the AC could pre-run and get your house cool beforehand.” The same applies during a cold winter, risking frozen pipes. “You can super heat your water during the heat day, and still use that hot water to clean your dishes or take a shower the next morning…we’re just at the beginning of thinking of how to integrate solar into our system.”
Despite struggles facing solar domination like competition from natural gas and a political climate favors fossil fuels, Margolis is optimistic.
“We’re at this point where the utilities and the engineers are understanding that solar is getting big enough that we have to deal with it. They’re fun challenges.”
What are solar panels made of?
That depends on what type of solar panel you’re looking at. There are two main types of solar panels, or modules, used in rooftop and ground-mounted installations: crystalline silicon and thin-film.
Crystalline Silicon Solar Panels
Crystalline silicon (c-Si) solar panels are the most common. They’re the ones that look like blue or black rectangular grids of smaller squares. Those smaller squares are silicon solar cells, and they link together in a series to form a circuit. The more interconnected cells in a series, the more electricity produced by the system.
Crystalline panels are more commonly grouped in 60-cell and 72-cell panels. Smaller panels are also used in the off-grid market. These series of cells are connected together usually by busbars. Busbar ribbons (typically made of aluminum or copper with silver) wire solar cells together to create higher voltages. The more busbars across a solar cell, the more electrons generated that can pass through, and power and efficiency of the solar panel increases.
There are two core types of crystalline silicon designs: polycrystalline and monocrystalline. Monocrystalline silicon solar is made by growing a single crystal. Because these crystals are usually an oval shape, monocrystalline panels are cut into the distinctive patterns that give them their recognizable appearance: the sliced silicon cells expose the missing corners in the grid-like structure. The crystal framework in a monocrystalline is even, producing a steady blue color and no grain marks, giving it the best purity and highest efficiency levels.
Polycrystalline solar is made by pouring molten silicon into a cast. However, because of this construction method, the crystal structure will form imperfectly, creating boundaries where the crystal formation breaks. This gives the polycrystalline silicon its distinctive, grainy appearance, as the gemstone type pattern highlights the boundaries in the crystal. These impurities in the crystal makes polycrystalline modules less efficient and also cheaper than monocrystalline.
Thin-Film Solar Panels
Thin-film panels are more traditionally used in large utility-scale installations. A thin semiconductor is deposited on glass, plastic or metal foil substrates. Thin-film, by its name, can be very thin and sometimes flexible. Its light weight and flexibility has led to its use on curved roofs, automobiles and other unique installations.
There are three common thin-film divisions: amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS). Thin-film solar cells are often created through a co-evaporation process of chemicals on a glass sheet. They have lower conversion efficiencies than silicon, but reduce the amount of material required in creating the cell.
In general, all solar panels consist of solar cells with a glass layer on front and a protective backsheet on the rear. Usually made from a type of polymer, backsheets adhere to the backside of modules to provide electrical insulation. White backsheets are most common, although more black backsheets are being used on high-efficiency modules looking for a certain aesthetic.
Aluminum frames usually finish a module. They add strength to the panel and protect the edge of the glass. The frame helps racking and mounting systems attach to the panel to secure it to the roof or ground.
But all of this is changing. With new bifacial designs (when solar cells are exposed on both the front and back sides of the panel), backsheets are no longer needed. Some panels are also going frameless, choosing to either sandwich solar cells between two pieces of glass or using sturdier backsheets that don’t warrant a frame
HOW ARE SOLAR PANELS MADE ANYWAY?
Despite the tremendous source of energy shining in the sky, deniers keep debating and downplaying the merits of solar power and other renewable energies, asking the same questions over and over again: How effective is solar energy? Isn’t it more expensive? What happens when the sun goes down or it’s cloudy?
We’ve busted those myths before, but a question we always get is a sheepish, OK, but what are solar panels made of and are we hurting the climate by creating them?
No need to be sheepish. It’s a bit complicated!
FIRST, THERE’S THE PANEL ITSELF.
The large black solar panels you see on homes and businesses are made of a bunch of solar cells (or photovoltaic cells) made of silicon semiconductors that absorb sunlight and create an electric current. These individual cells are connected together to make one solar panel.
If you want to get even more technical, you can look at the structure of these individual solar cells. They’re made of two types of semiconductors: a positive (p-type) and a negative (n-type) silicon layers.
While the n-type silicon layer has extra electrons which can move around relatively freely, the p-type layer has electron vacancies referred to as holes. When you bring the layers together, electrons begin to move from the n-type to the p-type which forms a special junction and produces electric potential in the material. When sunlight hits this junction, the photon can knock an electron free and leaves behind a hole. As more electrons fill the newly created holes, the free electrons begin to collect at the pole. The collected electrons then flow through a conductor and an electric current is produced.
In the 1940s, a researcher at Bell Labs named Russell Ohl discovered the functionality of the P-N junction and that that silicon – an element found in sand and the second most abundant element in the Earth’s crust after oxygen – exhibited properties that were conducive to the formation of this junction.
Scientists continued to work and build on Ohl’s discovery, and in 1954, Bell Labs unveiled the first modern solar cell.
The demonstration inspired a 1954 New York Times article to predict that solar cells would eventually lead “to the realization of one of mankind’s most cherished dreams — the harnessing of the almost limitless energy of the sun.”
Nowadays, photovoltaic (PV) cells are mostly mass-produced and cut by lasers – a far cry from their humble origins.
Next, there’s the inverter. The solar cells collect the sun’s energy and turn it into direct current (DC) electricity. Most homes and businesses, however, use alternating current (AC). Inverters change the DC electricity from solar panels into usable AC electricity.
Finally, there’s the mounting system to keep the whole thing on a roof or secured safely to the ground. Generally, in the northern hemisphere, solar panels should face south and be installed at a 30- or 45-degree angle, depending on the distance from the equator. Fixed mounts keep the panels in place, but track mounts that “follow” the sun throughout the day are also available, although usually more expensive.
OK, SO HOW GREEN IS ALL OF THIS?
Yes, it’s true that manufacturing solar panels creates carbon dioxide, like the manufacturing of most things. There’s also some legitimate concern about solar panel disposal.
But as solar panel manufacturing becomes more efficient, its carbon footprint has been shrinking significantly. A 2016 study reports that the overall emissions produced decreased by 17 to 24 percent every time install capacity has doubled in the last 40 years.
And the overall greenhouse gas emissions involved in solar energy is still (unsurprisingly) much lower than coal or natural gas. Solar panels themselves can last for decades without much upkeep – and because their parts don’t wear out easily, PV panels are well-known to continue producing clean electricity well beyond their often-lengthy warranties, though sometimes at slightly less efficiency as the years fade from one to the next.
At the end of the life for a panel, some manufacturers offer global recycling programs for their customers.
A June 2012 National Renewable Energy Laboratory (NREL) study investigating the photovoltaic degradation rates of about 2,000 solar installations over a period of 40 years found the median solar system lost just 0.5 percent of its power output per year. So, by the end of a typical 25-year warranty, the solar panels on your roof could still be operating at about 87 percent of their original capacity.
Plus, with the rising popularity of solar, recycling programs and companies are expected to grow and become more robust in the future.