Photovoltaic Solar Panels
A solar panel system is a system that usually contains photovoltaic solar panels as well as the equipment that is needed to collect the solar panel to the electrical grid. This way, excess energy from the panels can be sent to the electrical grid during the daytime and energy can be taken from the electrical grid when it is required at night.
What is a solar panel and how does it work?
The most common type of solar panel is photovoltaic, the familiar blue panels that are sometimes seen on rooftops. These panels contain two layers, one doped with a compound containing extra electrons, the other doped with a compound that is missing electrons. The incoming sunlight causes electrons in the panel to bounce around, inevitably jumping from the layer with extra electrons toward the layer with missing electrons. This flow of electrons is then harnessed as electricity.
What is a solar panel used for?
Solar panels are used to absorb sunlight and provide electricity or heating to a house or some other structure. The most common type is the photovoltaic solar panel, which captures sunlight and generated low-voltage electricity that can then be either used or sent to the electrical grid.
Solar Energy and the Sun
The primary energy source for all of the life on Earth is the sun. Almost all of the energy humans consume comes from the sun, from the plants that we farm to the animals that we eat to the fossil fuels that we burn. Of course, there are a few exceptions, such as geothermal power, nuclear power, and tidal power. However, it’s hard to deny the sun as the primary giver of life for all thing on Earth.
The sun is about 864,000 miles (1.4 million kilometers) wide, more than one hundred times the diameter of Earth. It is primarily made up of hydrogen and helium. In fact, the fusion of hydrogen atoms into helium is the process that produces the massive amounts of energy that the sun emits. A tiny fraction of that energy splashes down on planet Earth. Yet, it is enough to give life to all of the plants and animals, heat the land, drive the wind, and warm the oceans.
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The Sun
The sun is a hot ball of gas that generates enough energy in just one hour to easily meet the energy needs of planet Earth for an entire year. The challenge is how to harness all of that energy. So, the problem that man faces is not a lack of energy; it’s a lack of ways to capture the existing energy from the sun, and efficiently convert it into usable energy that can heat our homes and provide electricity. So, I guess you could argue that we don’t have an energy problem here on Earth, we have a conversion problem. In this lesson, we will take a look at some of the technology man has developed to capture what the sun has to offer.
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What is a Solar Panel?
Technically, a solar panel is defined as any panel designed to absorb the sun’s energy and generate heat or electricity. In modern day, the most common type of solar panel is the photovoltaic (PV) solar panel. These are the familiar blue solar panels that are often seen on rooftops or at the roadside. Each of these panels is a group of much smaller solar cells, each of which is only a few inches wide. The full panel contains a linked group of anywhere from 32-96 of these cells. With each cell providing roughly half of one volt of electricity, panels can produce anywhere from 15-50 volts depending on the intensity of the sunlight.
An image of a typical photovoltaic solar cell.
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Photovoltaic Solar Panels Explained
The term photovoltaic connects the world of light (photo-) and electricity (-volt). The word refers to the production of electric current by substances that have been exposed to light. Thus, a photovoltaic solar panel is a panel that generates electric current when exposed to sunlight.
This can be accomplished in a few different ways. There are monocrystalline silicon, polycrystalline silicon, and thin film solar panels, all of which have different costs as well as a different list of pros and cons. However, they all contain individual cells that, once linked together, can created usable amounts of electricity.
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Solar-Thermal Energy vs. Solar-Photovoltaic Energy
Solar-photovoltaic energy refers to electricity that is generated directly by solar panels. However, in most industrial-scale solar power plants, the electricity is generated in a different method altogether. This technology is referred to as solar-thermal energy.
Solar-thermal power plants are typically constructed in sunny locations, close to the equator, with little Cloud cover. A typical design will feature a large tower that houses a sunlight-receiver containing a fluid (water or molten salt). The tower is surrounded by ground-level mirrors which reflect incoming sunlight up toward the tower. When the fluid reaches a sufficiently high temperature, it is pumped to ground level where it is used to generate steam and drive a conventional steam turbine. This turbine creates electricity that is then sent to the electrical grid.
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Lesson Summary
The sun’s energy has long been used by humans for warmth, but it has only been recently that we have discovered how to convert this energy into electricity. Modern solar panels can do this work directly, taking advantage of the photoelectric effect and funneling the light-driven motion of electrons into wires. The sun is also used in solar power plants, which either contain massive arrays of solar panels or takes advantage of the sunlight as a heat source to generate electricity indirectly. The solar-thermal plants collect sunlight and use it to heat a fluid, sometimes using towers and other times using a parabolic trough. Then these warm, large quantities of water create steam which drives a turbine and creates electricity. In some plants, the heat is stored at an industrial level in thermal energy storage plants so that electricity can be generated at nighttime.
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Photovoltaic Solar Cells
Solar energy is energy obtained from the sun, so if you think about the sun’s rays, you will notice that they are spread out. In order to use the energy from the sun, we need ways to collect and absorb solar energy. For this, we use solar collectors. You may not realize it, but you are probably using solar collectors every day. For example, there is a good chance that calculator lying on your desk is run by solar energy.
Small devices, like calculators, require only a few watts of power, and they can generate this power without the need of batteries, using just a few photovoltaic solar cells. These small cells are often referred to as simply ‘photovoltaic cells’ or ‘solar cells,’ and they are devices that directly convert light from the sun into electricity. So, as long as there is light, these little cells seem to power your calculator forever. You can recall the term ‘photovoltaic’ by remembering that the word ‘photo’ refers to light, and the word ‘volt’ is a unit of electric potential. Therefore, a photovoltaic cell converts light to electricity.
Solar Panels
If photovoltaic cells are connected together, you have a solar panel. You have likely seen solar panels on rooftops of homes or businesses, but they can also exist as large arrays on open fields and can even be found powering satellites out in space. Photovoltaic cells use thin layers of a semi-conducting material called silicon. Silicon is an element, and you can find it on the periodic table along with all of the other elements. It is also what makes up sand.
When light particles hit the photovoltaic cells in a solar panel, electrons in the silicon atom dislodge and bounce around, which starts a chain reaction. These electrons dislodge and move, one after another in a continuous flow, providing an electric current that can be used to power homes and workplaces.
We learned that photovoltaic cells directly convert the sun’s light into electricity. So what happens when the sun is not shining? Unfortunately, when there’s no light, solar panels cannot generate electricity. Therefore, some type of battery or back-up energy system is needed to use this energy at night or during cloudy days.
Solar Thermal Energy
We also use solar thermal energy to collect solar energy. Solar thermal technology creates electricity indirectly, as opposed to photovoltaic technology that directly creates electricity from light. Solar thermal energy collects the sun’s light, which heats a fluid, such as water; the resulting steam is used to run a generator that makes electricity.
You can recall this term by remembering that the word ‘thermal’ refers to heat. Essentially, solar thermal energy works as a giant water heater, and this form of solar technology is primarily found in very warm places where the sun is reliable.
Solar thermal plants are capable of creating massive amounts of energy. These power plants often use parabolic troughs, which are the solar thermal collectors used to collect the sun’s radiation. These parabolic troughs are shaped somewhat like a half-pipe that you see skateboarders use and are lined with mirrors. These mirrors FOCUS sunlight onto a focal point where the fluid can be heated until it becomes steam. This steam then spins a turbine for electricity generation.
Like photovoltaic solar cells, solar thermal electricity generation can only occur when the sun is shining. Therefore, a type of thermal energy storage is required that allows heat energy to be collected and stored for later use. With solar thermal energy systems, high-pressure liquid storage tanks can be used to allow plants to store hours of potential electricity.
Lesson Summary
Let’s review. Solar energy, which is energy obtained from the sun, is plentiful. However, in order for this resource to be used, it must be captured and converted to heat or electricity. Photovoltaic solar cells are devices that directly convert light from the sun into electricity. If photovoltaic cells are connected together, you have a solar panel. When light particles hit the silicon atoms within the solar panel, the electrons get dislodged, and flow in a continuous pattern to provide an electric current.
Solar thermal energy works like a giant water heater to create electricity indirectly. Solar thermal energy collects the sun’s light, which heats a fluid, such as water; the resulting steam is used to run a generator that creates electricity. Solar thermal electric generation may use parabolic troughs, which are solar thermal collectors used to collect the sun’s radiation. One major drawback to solar energy is the fact that the sun does not shine consistently. Therefore, a type of thermal energy storage is required that allows heat energy to be collected and stored for later use.
Learning Outcome
When you have finished this lesson, you should understand the use of solar energy by photovoltaic solar cells which create direct electricity and when these cells are linked you have solar panels which can run a house or business. Solar thermal energy is a storage system which uses solar energy to heat a liquid to create steam and run a generator.
The Sun
The sun is a hot ball of gas that generates enough energy in just one hour to easily meet the energy needs of planet Earth for an entire year. The challenge is how to harness all of that energy. So, the problem that man faces is not a lack of energy; it’s a lack of ways to capture the existing energy from the sun, and efficiently convert it into usable energy that can heat our homes and provide electricity. So, I guess you could argue that we don’t have an energy problem here on Earth, we have a conversion problem. In this lesson, we will take a look at some of the technology man has developed to capture what the sun has to offer.
Photovoltaic Solar Cells
Solar energy is energy obtained from the sun, so if you think about the sun’s rays, you will notice that they are spread out. In order to use the energy from the sun, we need ways to collect and absorb solar energy. For this, we use solar collectors. You may not realize it, but you are probably using solar collectors every day. For example, there is a good chance that calculator lying on your desk is run by solar energy.
Small devices, like calculators, require only a few watts of power, and they can generate this power without the need of batteries, using just a few photovoltaic solar cells. These small cells are often referred to as simply ‘photovoltaic cells’ or ‘solar cells,’ and they are devices that directly convert light from the sun into electricity. So, as long as there is light, these little cells seem to power your calculator forever. You can recall the term ‘photovoltaic‘ by remembering that the word ‘photo’ refers to light, and the word ‘volt’ is a unit of electric potential. Therefore, a photovoltaic cell converts light to electricity.
Solar Panels
If photovoltaic cells are connected together, you have a solar panel. You have likely seen solar panels on rooftops of homes or businesses, but they can also exist as large arrays on open fields and can even be found powering satellites out in space. Photovoltaic cells use thin layers of a semi-conducting material called silicon. Silicon is an element, and you can find it on the periodic table along with all of the other elements. It is also what makes up sand.
When light particles hit the photovoltaic cells in a solar panel, electrons in the silicon atom dislodge and bounce around, which starts a chain reaction. These electrons dislodge and move, one after another in a continuous flow, providing an electric current that can be used to power homes and workplaces.
We learned that photovoltaic cells directly convert the sun’s light into electricity. So what happens when the sun is not shining? Unfortunately, when there’s no light, solar panels cannot generate electricity. Therefore, some type of battery or back-up energy system is needed to use this energy at night or during cloudy days.
Solar Thermal Energy
We also use solar thermal energy to collect solar energy. Solar thermal technology creates electricity indirectly, as opposed to photovoltaic technology that directly creates electricity from light. Solar thermal energy collects the sun’s light, which heats a fluid, such as water; the resulting steam is used to run a generator that makes electricity.
You can recall this term by remembering that the word ‘thermal’ refers to heat. Essentially, solar thermal energy works as a giant water heater, and this form of solar technology is primarily found in very warm places where the sun is reliable.
Solar thermal plants are capable of creating massive amounts of energy. These power plants often use parabolic troughs, which are the solar thermal collectors used to collect the sun’s radiation. These parabolic troughs are shaped somewhat like a half-pipe that you see skateboarders use and are lined with mirrors. These mirrors FOCUS sunlight onto a focal point where the fluid can be heated until it becomes steam. This steam then spins a turbine for electricity generation.
Like photovoltaic solar cells, solar thermal electricity generation can only occur when the sun is shining. Therefore, a type of thermal energy storage is required that allows heat energy to be collected and stored for later use. With solar thermal energy systems, high-pressure liquid storage tanks can be used to allow plants to store hours of potential electricity.
Lesson Summary
Let’s review. Solar energy, which is energy obtained from the sun, is plentiful. However, in order for this resource to be used, it must be captured and converted to heat or electricity. Photovoltaic solar cells are devices that directly convert light from the sun into electricity. If photovoltaic cells are connected together, you have a solar panel. When light particles hit the silicon atoms within the solar panel, the electrons get dislodged, and flow in a continuous pattern to provide an electric current.
Solar thermal energy works like a giant water heater to create electricity indirectly. Solar thermal energy collects the sun’s light, which heats a fluid, such as water; the resulting steam is used to run a generator that creates electricity. Solar thermal electric generation may use parabolic troughs, which are solar thermal collectors used to collect the sun’s radiation. One major drawback to solar energy is the fact that the sun does not shine consistently. Therefore, a type of thermal energy storage is required that allows heat energy to be collected and stored for later use.
Learning Outcome
When you have finished this lesson, you should understand the use of solar energy by photovoltaic solar cells which create direct electricity and when these cells are linked you have solar panels which can run a house or business. Solar thermal energy is a storage system which uses solar energy to heat a liquid to create steam and run a generator.
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Solar cells
by Chris Woodford. Last updated: January 22, 2022.
W hy do we waste time drilling for oil and shoveling coal when there’s a gigantic power station in the sky up above us, sending out clean, non-stop energy for free? The Sun, a seething ball of nuclear power, has enough fuel onboard to drive our Solar System for another five billion years—and solar panels can turn this energy into an endless, convenient supply of electricity.
Solar power might seem strange or futuristic, but it’s already quite commonplace. You might have a solar-powered quartz watch on your wrist or a solar-powered calculator. Many people have solar-powered lights in their garden. Spaceships and satellites usually have solar panels on them too. The American space agency NASA has even developed a solar-powered plane! As global warming continues to threaten our environment, there seems little doubt that solar power will become an even more important form of renewable energy in future. But how exactly does it work?
Photo: NASA’s solar-powered Pathfinder airplane. The upper wing surface is covered with lightweight solar panels that power the plane’s propellers. Picture courtesy of NASA Armstrong Flight Research Center.
Contents
- How much energy can we get from the Sun?
- What are solar cells?
- How are solar cells made?
- How do solar cells work?
- How efficient are solar cells?
- Types of photovoltaic solar cells
- How much power can we make with solar cells?
- Power to the people
- Why hasn’t solar power caught on yet?
- A brief history of solar cells
- Find out more
How much energy can we get from the Sun?
Solar power is amazing. On average, every square meter of Earth’s surface receives 163 watts of solar energy (a figure we’ll explain in more detail in a moment). [1] In other words, you could stand a really powerful (150 watt) table lamp on every square meter of Earth’s surface and light up the whole planet with the Sun’s energy! Or, to put it another way, if we covered just one percent of the Sahara desert with solar panels, we could generate enough electricity to power the whole world. [2] That’s the good thing about solar power: there’s an awful lot of it—much more than we could ever use.
Photo: The amount of energy we can capture from sunlight is at a minimum at sunrise and sunset and a maximum at midday, when the Sun is directly overhead.
But there’s a downside too. The energy the Sun sends out arrives on Earth as a mixture of light and heat. Both of these are incredibly important—the light makes plants grow, providing us with food, while the heat keeps us warm enough to survive—but we can’t use either the Sun’s light or heat directly to run a television or a car. We have to find some way of converting solar energy into other forms of energy we can use more easily, such as electricity. And that’s exactly what solar cells do.
What are solar cells?
A solar cell is an electronic device that catches sunlight and turns it directly into electricity. It’s about the size of an adult’s palm, octagonal in shape, and colored bluish black. Solar cells are often bundled together to make larger units called solar modules. themselves coupled into even bigger units known as solar panels (the black- or blue-tinted slabs you see on people’s homes—typically with several hundred individual solar cells per roof) or chopped into chips (to provide power for small gadgets like calculators and digital watches).
Photo: The roof of this house is covered with 16 solar panels, each made up of a grid of 10×6 = 60 small solar cells. On a good day, it probably generates about 4 kilowatts of electricity.
Just like the cells in a battery, the cells in a solar panel are designed to generate electricity; but where a battery’s cells make electricity from chemicals, a solar panel’s cells generate power by capturing sunlight instead. They are sometimes called photovoltaic (PV) cells because they use sunlight (photo comes from the Greek word for light) to make electricity (the word voltaic is a reference to Italian electricity pioneer Alessandro Volta, 1745–1827).
We can think of light as being made of tiny particles called photons, so a beam of sunlight is like a bright yellow fire hose shooting trillions upon trillions of photons our way. Stick a solar cell in its path and it catches these energetic photons and converts them into a flow of electrons—an electric current. Each cell generates a few volts of electricity, so a solar panel’s job is to combine the energy produced by many cells to make a useful amount of electric current and voltage. Virtually all of today’s solar cells are made from slices of silicon (one of the most common chemical elements on Earth, found in sand), although as we’ll see shortly, a variety of other materials can be used as well (or instead). When sunlight shines on a solar cell, the energy it carries blasts electrons out of the silicon. These can be forced to flow around an electric circuit and power anything that runs on electricity. That’s a pretty simplified explanation! Now let’s take a closer look.
How are solar cells made?
Silicon is the stuff from which the transistors (tiny switches) in microchips are made—and solar cells work in a similar way. Silicon is a type of material called a semiconductor. Some materials, notably metals, allow electricity to flow through them very easily; they are called conductors. Other materials, such as plastics and wood, don’t really let electricity flow through them at all; they are called insulators. Semiconductors like silicon are neither conductors nor insulators: they don’t normally conduct electricity, but under certain circumstances we can make them do so.
When we place a layer of n-type silicon on a layer of p-type silicon, a barrier is created at the junction of the two materials (the all-important border where the two kinds of silicon meet up). No electrons can cross the barrier so, even if we connect this silicon sandwich to a flashlight, no current will flow: the bulb will not light up. But if we shine light onto the sandwich, something remarkable happens. We can think of the light as a stream of energetic light particles called photons. As photons enter our sandwich, they give up their energy to the atoms in the silicon. The incoming energy knocks electrons out of the lower, p-type layer so they jump across the barrier to the n-type layer above and flow out around the circuit. The more light that shines, the more electrons jump up and the more current flows.
This is what we mean by photovoltaic—light making voltage—and it’s one kind of what scientists call the photoelectric effect.
How do solar cells work?
Artwork: How a simple, single-junction solar cell works.
A solar cell is a sandwich of n-type silicon (blue) and p-type silicon (red). It generates electricity by using sunlight to make electrons hop across the junction between the different flavors of silicon:
- When sunlight shines on the cell, photons (light particles) bombard the upper surface.
- The photons (yellow blobs) carry their energy down through the cell.
- The photons give up their energy to electrons (green blobs) in the lower, p-type layer.
- The electrons use this energy to jump across the barrier into the upper, n-type layer and escape out into the circuit.
- Flowing around the circuit, the electrons make the lamp light up.
Now for more detail.
That’s a basic introduction to solar cells—and if that’s all you wanted, you can stop here. The rest of this article goes into more detail about different types of solar cells, how people are putting solar power to practical use, and why solar energy is taking such a long time to catch on.
How efficient are solar cells?
A basic rule of physics called the law of conservation of energy says that we can’t magically create energy or make it vanish into thin air; all we can do is convert it from one form to another. That means a solar cell can’t produce any more electrical energy than it receives each second as light. In practice, as we’ll see shortly, most cells convert about 10–20 percent of the energy they receive into electricity. A typical, single-junction silicon solar cell has a theoretical maximum efficiency of about 30 percent, known as the Shockley-Queisser limit. That’s essentially because sunlight contains a broad mixture of photons of different wavelengths and energies and any single-junction solar cell will be optimized to catch photons only within a certain frequency Band, wasting the rest. Some of the photons striking a solar cell don’t have enough energy to knock out electrons, so they’re effectively wasted, while some have too much energy, and the excess is also wasted. The very best, cutting-edge laboratory cells can manage just under 50 percent efficiency in absolutely perfect conditions using multiple junctions to catch photons of different energies.
Chart: Efficiencies of solar cells compared: The very first solar cell scraped in at a mere 6 percent efficiency; the most efficient one that’s been produced to date managed 47.1 percent in laboratory conditions. Most cells are first-generation types that can manage about 15 percent in theory and probably 8 percent in practice.
Real-world domestic solar panels might achieve an efficiency of about 15 percent, give a percentage point here or there, and that’s unlikely to get much better. First-generation, single-junction solar cells aren’t going to approach the 30 percent efficiency of the Shockley-Queisser limit, never mind the lab record of 47.1 percent. All kinds of pesky real-world factors will eat into the nominal efficiency, including the construction of the panels, how they are positioned and angled, whether they’re ever in shadow, how clean you keep them, how hot they get (increasing temperatures tend to lower their efficiency), and whether they’re ventilated (allowing air to circulate underneath) to keep them cool.
Types of photovoltaic solar cells
Most of the solar cells you’ll see on people’s roofs today are essentially just silicon sandwiches, specially treated (doped) to make them better electrical conductors. Scientists refer to these classic solar cells as first-generation, largely to differentiate them from two different, more modern technologies known as second- and third-generation. So what’s the difference?
First-generation
Photo: A colorful collection of first-generation solar cells. Picture courtesy of NASA Glenn Research Center (NASA-GRC).
Over 90 percent of the world’s solar cells are made from wafers of crystalline silicon (abbreviated c-Si), sliced from large ingots, which are grown in super-clean laboratories in a process that can take up to a month to complete. [3] The ingots either take the form of single crystals (monocrystalline or mono-Si) or contain multiple crystals (polycrystalline, multi-Si or poly c-Si).
First-generation solar cells work like we’ve shown in the box up above: they use a single, simple junction between n-type and p-type silicon layers, which are sliced from separate ingots. So an n-type ingot would be made by heating chunks of silicon with small amounts of phosphorus, antimony, or arsenic as the dopant, while a p-type ingot would use boron as the dopant. Slices of n-type and p-type silicon are then fused to make the junction. A few more bells and whistles are added (like an antireflective coating, which improves light absorption and gives photovoltaic cells their characteristic blue color, protective glass on front and a plastic backing, and metal connections so the cell can be wired into a circuit), but a simple p-n junction is the essence of most solar cells. It’s pretty much how all photovoltaic silicon solar cells have worked since 1954, which was when scientists at Bell Labs pioneered the technology: shining sunlight on silicon extracted from sand, they generated electricity.
Second-generation
Photo: A thin-film, second-generation solar panel. The power-generating film is made from amorphous silicon, fastened to a thin, flexible, and relatively inexpensive plastic backing (the substrate). Photo by Warren Gretz courtesy of NREL (image ID #6321083).
Classic solar cells are relatively thin wafers—usually a fraction of a millimeter deep (about 200 micrometers, 200μm, or so). But they’re absolute slabs compared to second-generation cells, popularly known as thin-film solar cells (TPSC) or thin-film photovoltaics (TFPV), which are about 100 times thinner again (several micrometers or millionths of a meter deep). Although most are still made from silicon (a different form known as amorphous silicon, a-Si, in which atoms are arranged randomly instead of precisely ordered in a regular crystalline structure), some are made from other materials, notably cadmium-telluride (Cd-Te) and copper indium gallium diselenide (CIGS). [4]
Because they’re extremely thin, light, and flexible, second-generation solar cells can be laminated onto Windows, skylights, roof tiles, and all kinds of substrates (backing materials) including metals, glass, and polymers (plastics). What second-generation cells gain in flexibility, they sacrifice in efficiency: classic, first-generation solar cells still outperform them. So while a top-notch first-generation cell might achieve an efficiency of 15–20 percent, amorphous silicon struggles to get above 7 percent, the best thin-film Cd-Te cells only manage about 11 percent, and CIGS cells do no better than 7–12 percent. [5] That’s one reason why, despite their practical advantages, second-generation cells have so far made relatively little impact on the solar market.
Third-generation
Photo: Third-generation plastic solar cells produced by researchers at the National Renewable Energy Laboratory. Photo by Jack Dempsey courtesy of NREL (image ID #6322357).
The latest technologies combine the best features of first and second generation cells. Like first-generation cells, they promise relatively high efficiencies (30 percent or more). Like second-generation cells, they’re more likely to be made from materials other than simple silicon, such as amorphous silicon, organic polymers (making organic photovoltaics, OPVs), perovskite crystals, and feature multiple junctions (made from multiple layers of different semiconducting materials). Ideally, that would make them cheaper, more efficient, and more practical than either first- or second-generation cells. [6] Currently, the world record efficiency for third-generation solar is 28 percent, achieved by a perovskite-silicon tandem solar cell in December 2018.
How much power can we make with solar cells?
The total solar energy that reaches the Earth’s surface could meet existing global energy needs 10,000 times over.
European Photovoltaic Industry Association/Greenpeace, 2011.
In theory, a huge amount. Let’s forget solar cells for the moment and just consider pure sunlight. Up to 1000 watts of raw solar power hits each square meter of Earth pointing directly at the Sun (that’s the theoretical power of direct midday sunlight on a cloudless day—with the solar rays firing perpendicular to Earth’s surface and giving maximum illumination or insolation, as it’s technically known).
In practice, after we’ve corrected for the tilt of the planet and the time of day, the best we’re likely to get is maybe 100–250 watts per square meter in typical northern latitudes (even on a cloudless day). That translates into about 2–6 kWh per day (depending on whether you’re in a northern region like Canada or Scotland or somewhere more obliging such as Arizona or Mexico). [11] Multiplying up for a whole year’s production gives us somewhere between 700 and 2500 kWh per square meter (700–2500 units of electricity). Hotter regions clearly have much greater solar potential: the Middle East, for example, receives around 50–100 percent more useful solar energy each year than Europe.
Unfortunately, typical solar cells are only about 15 percent efficient, so we can only capture a fraction of this theoretical energy: perhaps 4–10 watts per square meter. [7] That’s why solar panels need to be so big: the amount of power you can make is obviously directly related to how much area you can afford to cover with cells. A single solar cell (roughly the size of a compact disc) can generate about 3–4.5 watts; a typical solar module made from an array of about 40 cells (5 rows of 8 cells) could make about 100–300 watts; several solar panels, each made from about 3–4 modules, could therefore generate an absolute maximum of several kilowatts (probably just enough to meet a home’s peak power needs).
What about solar farms?
But suppose we want to make really large amounts of solar power. To generate as much electricity as a hefty wind turbine (with a peak power output of maybe two or three megawatts), you need about 500–1000 solar roofs. And to compete with a large coal or nuclear power plant (rated in the gigawatts, which means thousand megawatts or billions of watts), you’d need 1000 times as many again—the equivalent of about 2000 wind turbines or perhaps a million solar roofs. (Those comparsions assume our solar and wind are producing maximum output.) Even if solar cells are clean and efficient sources of power, one thing they can’t really claim to be at the moment is efficient uses of land. Even those huge solar farms now springing up all over the place produce only modest amounts of power (typically about 20 megawatts, or about 1 percent as much as a large, 2 gigawatt coal or nuclear plant). The UK renewable company Ecotricity has estimated that it takes about 22,000 panels laid across a 12-hectare (30-acre) site to generate 4.2 megawatts of power, roughly as much as two large wind turbines and enough to power 1,200 homes. [8]
Photo: The vast 91-hectare (225-acre) Alamosa Solar Generating Project in Colorado generates up to 30 megawatts of solar power using three cunning tricks. First, there are huge numbers of photovoltaic panels (500 of them, each capable of making 60kW). Each panel is mounted on a separate, rotating assembly so it can track the Sun through the sky. And each has multiple Fresnel lenses mounted on top to concentrate the Sun’s rays onto its solar cells. Photo by Dennis Schroeder courtesy of NREL (image ID #10895528).
Power to the people
Photo: A micro-wind turbine and a solar panel work together to power a bank of batteries that keep this highway construction warning sign lit up day and night. The solar panel is mounted, facing up to the sky, on the flat yellow lid you can see just on top of the display.
Some people are concerned that solar farms will gobble up land we need for real farming and food production. Worrying about land-take misses a crucial point if we’re talking about putting solar panels on domestic roofs. Environmentalists would argue that the real point of solar power is not to create large, centralized solar power stations (so powerful utilities can go on selling electricity to powerless people at a high profit), but to displace dirty, inefficient, centralized power plants by allowing people to make power themselves at the very place where they use it. That eliminates the inefficiency of fossil fuel power generation, the air pollution and carbon dioxide emissions they make, and also does away with the inefficiency of transmitting power from the point of generation to the point of use through overhead or underground power lines. Even if you have to cover your entire roof with solar panels (or laminate thin-film solar cells on all your Windows), if you could meet your entire electricity needs (or even a large fraction of them), it wouldn’t matter: your roof is just wasted space anyway. According to a 2011 report [PDF] by the European Photovoltaic Industry Association and Greenpeace, there’s no real need to cover valuable farmland with solar panels: around 40 percent of all roofs and 15 percent of building facades in EU countries would be suitable for PV panels, which would amount to roughly 40 percent of the total electricity demand by 2020.
It’s important not to forget that solar shifts power generation to the point of power consumption —and that has big practical advantages. Solar-powered wristwatches and calculators theoretically need no batteries (in practice, they do have battery backups) and many of us would relish solar-powered smartphones that never needed charging. Road and railroad signs are now sometimes solar powered; flashing emergency maintenance signs often have solar panels fitted so they can be deployed in even the remotest of locations. In developing countries, rich in sunlight but poor in electrical infrastructure, solar panels are powering water pumps, phone boxes, and fridges in hospitals and health clinics.
Why hasn’t solar power caught on yet?
The answer to that is a mixture of economic, political, and technological factors. From the economic viewpoint, in most countries, electricity generated by solar panels is still more expensive than electricity made by burning dirty, polluting fossil fuels. The world has a huge investment in fossil fuel infrastructure and, though powerful oil companies have dabbled in solar power offshoots, they seem much more interested in prolonging the lifespan of existing oil and gas reserves with technologies such as fracking (hydraulic fracturing). Politically, oil, gas, and coal companies are enormously powerful and influential and resist the kind of environmental regulations that favor renewable technologies like solar and wind power. Technologically, as we’ve already seen, solar cells are a permanent work in progress and much of the world’s solar investment is still based on first-generation technology. Who knows, perhaps it will take several more decades before recent scientific advances make the business case for solar really compelling?
One problem with arguments of this kind is that they weigh up only basic economic and technological factors and fail to consider the hidden environmental costs of things like oil spills, air pollution, land destruction from coal mining, or climate change—and especially the future costs, which are difficult or impossible to predict. It’s perfectly possible that growing awareness of those problems will hasten the switch away from fossil fuels, even if there are no further technological advances; in other words, the time may come when we can no longer afford to postpone universal adoption of renewable energy. Ultimately, all these factors are interrelated. With compelling political leadership, the world could commit itself to a solar revolution tomorrow: politics could force technological improvements that change the economics of solar power.
And economics alone could be enough. The pace of technology, innovations in manufacturing, and economies of scale continue to drive down the cost of solar cells and panels. Look what’s happened over the last decade or so. Between 2008 and 2009 alone, according to the BBC’s environment analyst Roger Harrabin, fell by about 30 percent, and China’s increasing dominance of solar manufacturing has continued to drive them down ever since. Between 2010 and 2016, the cost of large-scale photovoltaics fell by about 10–15 percent per year, according to the US Energy Information Administration; overall, the price of switching to solar has plummeted by around 90 percent in the last decade, further cementing China’s grip on the market. Six of the world’s top ten solar manufacturers are now Chinese; in 2016, around two thirds of new US solar capacity came from China, Malaysia, and South Korea.
Photo: Solar cells aren’t the only way to make power from sunlight—or even, necessarily, the best way. We can also use solar thermal power (absorbing heat from sunlight to heat the water in your home), passive solar (designing a building to absorb sunlight), and solar collectors (shown here). In this version, 16 mirrors collect sunlight and concentrate it onto a Stirling engine (the gray box on the right), which is an extremely efficient power producer. Photo by Warren Gretz courtesy of NREL (image ID #6323238).
Catching up fast?
The tipping point for solar is expected to arrive when it can achieve something called grid parity, which means that solar-generated electricity you make yourself becomes as cheap as power you buy from the grid. Many European countries expected to achieve that milestone by 2020. Solar has certainly posted very impressive rates of growth in recent years, but it’s important to remember that it still represents only a fraction of total world energy. In the UK, for example, the solar industry boasted of a milestone achievement in 2014 when it almost doubled the total installed capacity of solar panels from roughly 2.8 GW to 5 GW. But that still represents only a couple of large power stations and, at maximum output, a mere 8 percent of the UK’s total electricity demand of roughly 60 GW (factoring in things like cloudiness would reduce it to some fraction of 8 percent).
According to the US Energy Information Administration, in the United States, where photovoltaic technology was invented, in 2020, solar represented only 3 percent of the country’s total electricity generation. That’s about 2.3 times more than in 2017 (when solar was 1.3 percent), 3.3 times more than in 2016 (when the figure was 0.9 percent) and about 7.5 times as much as in 2014 (when solar stood at just 0.4 percent). [9] Even so, it’s still less than a third as much as coal and 26 times less than all fossil fuels. [10] Even a doubling in US solar would see it producing not much more than half as much electricity as coal does today (10 × 3 = 6 percent, compared to 10 percent for coal in 2020). It’s telling to note that two of the world’s major annual energy reviews, the BP Statistical Review of World Energy and the International Energy Agency’s Key World Energy Statistics, barely mention solar power at all, except as a footnote.
Chart: Solar power is making more of our electricity every year, but still nowhere near as much as coal (which is in steep decline). This chart compares the percentage of electricity generated in the United States by solar power (green line) and coal (red line). The position is better than this in some countries and worse in others. Drawn by explainthatstuff.com using historic and current data from US Energy Information Administration (historic data from that page is available from the Wayback Machine).
Will that change anytime soon? It just might. According to a 2016 paper by researchers from Oxford University, the cost of solar is now falling so fast that it’s on course to provide 20 percent of the world’s energy needs by 2027, which would be a step change from where we are today, and a far faster rate of growth than anyone has previously forecast. modestly, the US EIA predicts that solar will be providing 20 percent of all US electricity by 2050. Can the pace of growth possibly continue? Could solar really make a difference to climate change before it’s too late? Watch this space!
Find out more
On this website
- Climate change and global warming
- Electronics
- Energy
- Passive-solar energy
- Photoelectric cells
- Pyranometers (devices that measure sunlight)
- Renewable energy
- Wind turbines
Books for older readers
Books for younger readers
- Solar Power: Capturing the Sun’s Energy by Laurie Brearley. Scholastic, 2018. A 48-page introduction billed as suitable for grades 3–5, ages 8–10.
- Eyewitness Energy by Jack Challoner. New York/London, England: Dorling Kindersley, 2012: Explains the basic concepts of energy and the history of how people have harnessed it. Grades 4–6; ages 9–12.
- Energy by Chris Woodford. New York/London, England: Dorling Kindersley, 2007: My own colorful little book about energy in the modern world. Ages 9–12.
- Power and Energy by Chris Woodford. New York: Facts on File, 2004. Another of my books, this is a 100-page introduction to humankind’s efforts to harness energy. Suitable for grades 4–6; ages 9–12.
Articles
On other websites
- Solar Research: Lots of information on the latest from the US DOE’s National Renewable Energy Laboratory—home of cutting-edge research into sustainable power.
- Measuring solar insolation: Simple maps from NASA compare the amount of sunlight received by different regions of our planet.
Videos
- Energy 101: Solar PV: The US Department of Energy’s quick introduction explains how solar panels work and summarizes their advantages.
- How solar farms could work: The CSEM company of Switzerland have animated the idea of a solar farm that could work in the oceans or the desert.
- Suncatchers and Sterling Engines: Tessera Solar explain how solar power plants can use Stirling engines to convert thermal energy into electricity.
References
Please do NOT copy our articles onto blogs and other websites
Articles from this website are registered at the US Copyright Office. Copying or otherwise using registered works without permission, removing this or other copyright notices, and/or infringing related rights could make you liable to severe civil or criminal penalties.
Text copyright © Chris Woodford 2007, 2022. All rights reserved. Full copyright notice and terms of use.
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The Ultimate Guide to Solar Cell with Jackery
Whether the source is sunshine or artificial light, solar cells are referred to as photovoltaic. They serve as photodetector devices, such as infrared detectors, that can detect light or other electromagnetic radiation close to the visible range or measure light intensity. Solar cells are frequently grouped to create solar modules, which are then connected to solar panels, which are even larger units.
Some solar-powered gadgets don’t even have an off button and never require batteries. They operate indefinitely as long as there is sufficient sunlight. But how does solar energy use? Of course, the solar cell plays a part. You will discover what a solar cell is, how it functions, how it was developed, and how to choose the best solar panel with Jackery in this post.
What is A Solar Cell
The solar cell is a crucial component of photovoltaic energy conversion, which transforms light energy into electrical energy. Semiconductors are typically utilized as the material for solar cells. Converting energy entails charge carrier separation and the production of electron-hole pairs in a semiconductor from light’s photon energy absorption.
French scientist Edmond Becquerel initially showed the photovoltaic phenomenon in 1839. Based on fabrication methods, solar or photovoltaic technology can be divided into three generations. First-generation solar cells are constructed using silicon, which is both efficient and profitable. The original generation of silicon-based solar cells still accounts for 80% of today’s solar cell production. The first generation consists of monocrystalline silicon solar cells, polycrystalline, amorphous, and hybrid.
Source: Anthony Fernandez
What is Solar Photovoltaic Cell?
A photovoltaic (PV) cell, also known as a solar cell, can either reflect, absorb, or pass through a light that strikes it. The semiconductor material that makes up the PVPV cell can conduct electricity more effectively than an insulator but is less effective than a good conductor like a metal. In PVPV cells, a variety of semiconductor materials are employed.
When a semiconductor is exposed to light, the light’s energy is absorbed and transferred to the semiconductor’s negatively charged electrons. The additional energy enables the electrons to conduct an electrical current through the material. This current can be used to power your home and the rest of the electric grid by extracting it through conductive metal contacts, which are the grid-like lines on solar cells.
How is The Solar Cell Market Today?
The efficiency of solar cells has increased dramatically in recent years, going from reports of roughly 3% in 2009 to over 25% presently. Although solar cells have rapidly increased their efficiency, several obstacles must be overcome before they can be considered viable commercial technology.
Wafer-based PV and thin-film cell PVsPVs are the two primary divisions of photovoltaic technologies. The wafer-based PVsPVs include conventional crystalline silicon cells and gallium arsenide cells, with c-Si cells currently controlling the PVPV market with a market share of roughly 90% and GaAs having the highest efficiency.
What Are Solar Cells Made of
A layer of p-type silicon is sandwiched between a layer of n-type silicon to form a solar cell. There are too many electrons in the n-type layer and too many positively charged holes in the p-type layer. The electrons on one side of the junction (n-type layer) migrate into the holes on the opposite side, which is close to the intersection of the two layers (p-type layer). As a result, a region known as the depletion zone is formed surrounding the connection, where the electrons fill the holes.
The p-type side of the depletion zone now contains negatively charged ions, and the n-type side of the depletion zone now includes positively charged ions when all the holes in the depletion zone have been filled with electrons. These ions’ opposite charges provide an internal electric field that inhibits the n-type layer’s electrons from filling the p-type layer’s holes.
- Purify the Silicon:Silicon dioxide is put in an electric arc furnace, where oxygen is released using a carbon arc. Carbon dioxide and molten silicon are left, but even this is not pure enough to be used in solar cells. This silicon will produce one with just 1% impurities.
- Create Single Crystal Silicon:The Czochralski Method, in which a seed silicon crystal is dipped into molten polycrystalline silicon, is the most used technique for producing single-crystal silicon.
- Cut the Wafers:A circular saw is used to slice the second-stage boule into silicon wafers. The best raw material for this task is diamond, which produces silicon slices that can then be further cut to create squares or hexagons that are simpler to slot together into the surface of a solar cell.
- Doping:This technique, also known as doping, often entails firing phosphorous ions into the ingot using a particle accelerator.
- Add Electrical Contacts:Electrical contacts serve as a conduit for the current generated by solar cells and connect them. These connections, made of metals like palladium or copper, are thin so as not to prevent sunlight from reaching the cell.
- Add Anti-Reflective Coating:To lessen the quantity of sunlight lost through reflection, an anti-reflective coating is put on the silicon.
- Encapsulate the Cell:To complete the process, the solar cells are sealed in silicon rubber or ethylene vinyl acetate and mounted in an aluminum frame with a glass or plastic cover for added protection and a back sheet.
Source: US Energy Information Administration
How Does A Solar Cell Work
The solar cell is a technological innovation that directly converts light energy into electricity through the photovoltaic effect, creating electrical charges free to travel through semiconductors. All solar cells share a similar fundamental design. An optical coating or antireflection layer that reduces the quantity of light lost through reflection allows light to enter the system. As a result, the light is trapped and is more likely to reach the layers below that do energy conversion. Spin-coating or vacuum deposition creates this top antireflection layer, commonly an oxide of silicon, tantalum, or titanium.
Below the top antireflection layer are three energy conversion layers. These are the top junction layer, the absorber layer, and the back junction layer. Two additional electrical contact layers carry the electric current to an external load and then back to the cell to complete the electric circuit. A solar cell is a sandwich of n-type silicon and p-type silicon. It generates electricity by using sunlight to make electrons hop across the junction between the different flavors of silicon:
- Photons (light particles) pelt the cell’s upper surface when sunlight shines.
- The photons (yellow blobs) transport energy through the cell at a downward angle.
- In the lower p-type layer, photons transfer their energy to electrons (green blobs).
- With the help of this energy, the electrons can penetrate the barrier into the top n-type layer and break out into the circuit.
- As the electrons move across the circuit, the lamp begins to glow.
Source: Advanced Renewable Energy Systems
The Types of Solar Cells
The three main categories of solar cells are crystalline silicon-based, thin-film solar cells, and a more recent innovation that combines the other two. P-type and n-type silicon are two types of semiconductors used to make solar cells. Atoms with one fewer electron in their outer energy level than silicon, like boron or gallium, are added to create p-type silicon.
Crystalline Silicon Cells
Crystalline silicon (c-Si) wafers, cut from massive ingots manufactured in laboratories, make about 90% of solar cells. These nuggets can develop into single or numerous crystals and can take up to a month to grow. Monocrystalline solar panels are made from a single crystal, whereas polycrystalline are made from multiple crystals.
Thin Film Solar Cells
While thin-film solar cells, also known as thin-film photovoltaics, are around 100 times thinner than crystalline silicon cells, they are still produced from wafers that are only a tiny fraction of a millimeter deep (about 200 micrometers, or 200m). Amorphous silicon (a-Si), in which the atoms are randomly organized rather than in an ordered crystalline structure, is the material used to create these thin film solar panels and cells. These films can also be produced using organic photovoltaic (PVPV) materials, copper indium gallium diselenide (CIGS), and cadmium-telluride (Cd-Te).
Third Generation of Solar Cells
The most recent solar cell technologies combine the best aspects of thin-film and crystalline silicon solar cells to deliver high efficiency and enhanced usability. They frequently have several junctions made up of various semiconducting materials’ layers. Also, they are typically made of amorphous silicon, organic polymers, or perovskite crystals.
Solar Cell Development
Solar energy already offers consumers many advantages while reducing the harmful environmental effects of fossil fuel power generation. Switching to solar energy has benefits on a more local level and reduces air pollution and carbon dioxide emissions because it locates power generation at the point of use.
Smaller devices like watches and calculators may now operate without batteries, and road and train maintenance signs can now be powered by the sun so that they can be used in even the most remote regions. In some nations, solar energy is used to power telephone booths, water pumps, and even refrigeration systems in medical facilities. As the supply of fossil fuels declines, there will be a greater need to turn to renewable energy sources, such as solar.
Best Portable Solar Panels with Jackery
Jackery portable solar panels can be folded and strapped for easy carrying and use. One of the highest efficiency rates in the industry makes it possible to maximize the sun’s energy and transform it into clean energy. Use solar power and the Jackery rechargeable portable power stations to keep your equipment charged. For better backup power, it is the advanced off-grid solar generating system.
With mono crystalline solar cells and adjustable supports, Jackery portable solar panels have a charging efficiency of up to 25%. Make the most of solar energy’s potential. The solar panel can be easily connected to your power source. Connect the DCDC input of your portable power source to the DCDC interface.
Jackery SolarSaga 200W Solar Panel
The Jackery SolarSaga 200W solar panels are your best option if you want a solution that can power your entire home. Solar panels can generate more power under similar circumstances with a higher conversion rate of 24.3%. A Jackery Portable Power Station Explorer 2000 Pro can be fully charged in 2.5 hours using 6 SolarSaga 200. Additionally compatible with various Jackery power stations is the portable solar panel.
Compatible With
Recharging Time
Conversion Efficiency
Explorer 2000 Pro 6SolarSaga 200
What Is Photovoltaic Solar Energy and How Does it Work?
Nowadays, it’s not uncommon to find solar panels installed by a solar independent engineer on the roof of both residential and commercial buildings. These solar panels comprise small cells referred to as photovoltaic cells. These cells are the functional part of solar panels and generate electricity when exposed to sunlight. According to the U.S. Bureau of Labor Statistics, modern photovoltaic solar cells were invented in the 1940s and 1950s, and the technology has progressed significantly over the years. Photovoltaic cells work through a process called the photoelectric effect. The photoelectric effect is explained below.
How Does a Photovoltaic Cell Work?
Photons are particles of radiant solar energy that comprise sunlight. Photons contain varying quantities of energy. Some photons are absorbed, while others are reflected when they strike a solar cell. Electrons inside the solar cell material detach from their atoms when the substance absorbs enough photon energy. The electrons travel to the solar cell’s front surface, which has been designed to be more susceptible to free electrons. When a large number of electrons, each with a negative charge, flow toward the cell’s front surface, the ensuing charge imbalance between the front and rear surfaces provides a voltage potential, similar to the positive and negative terminals of a battery.
Electricity flows when an external load links the two surfaces. PV cells are usually joined in chains by a solar independent engineer to form bigger components, known as modules, to increase their power output. Individual modules can be utilized, or many modules can be combined to make arrays. As part of a comprehensive PV system, one or more arrays are subsequently linked to the electricity grid. PV systems can be developed to satisfy practically any electric power requirement, big or small, thanks to their modular construction.
What Are the Types of Solar Cells?
Monocrystalline and polycrystalline solar cells are today’s two primary solar cells. While there are numerous ways to create PV cells, the most popular household and commercial alternatives are monocrystalline and polycrystalline solar cells (made from silicon).
What Are Monocrystalline and Polycrystalline Cells?
A single silicon crystal is used to make a monocrystalline solar cell. On the other hand, polycrystalline silicon solar cells are formed by fusing several shards of silicon crystals. Monocrystalline solar cells are usually more efficient than polycrystalline cells. This is due to using a single, aligned silicon crystal, which allows for smoother electron transport. Polycrystalline solar panels, on the other hand, are generally less costly than monocrystalline choices. This is because a polycrystalline cell’s production process is simpler and involves less-specialized technologies.
Solar cells are an efficient way to generate electricity for residential and commercial purposes. It’s more environmentally sustainable, too, making it an attractive option for eco-conscious individuals. Need the installation of solar panels by a solar independent engineer? Don’t hesitate to reach out to us.