Solar cell facts for kids
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| Type | Active |
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| Working principle | Photovoltaic effect |
| First production | 1950s |
| Electronic symbol | |
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A solar cell, also called a photovoltaic cell (or PV cell), is a cool electronic device. It turns the energy from light directly into electricity. This happens thanks to something called the photovoltaic effect.
Think of a solar cell as a special kind of light sensor. Its electrical parts, like current and voltage, change when light hits it. Many small solar cells are put together to make larger solar panels.
Most solar cells you see today are made from crystalline silicon. This material makes up about 95% of the market! Some others use Cadmium telluride in a thin film form. A single silicon solar cell usually creates about 0.5 to 0.6 volts of electricity.
Solar cells can work with sunlight or even artificial light. Besides making solar power, they can also detect light. For example, they can be used in infrared detectors or to measure how bright a light is.
For a solar cell to work, three main things need to happen:
- It must absorb light. This creates tiny particles called electron-hole pairs.
- These electron-hole pairs need to be separated.
- The separated particles are then collected to create an electric current.
Many things can affect how much power a solar cell produces. These include temperature, the materials it's made from, weather, and how much sunlight hits it.
Solar cells are different from solar thermal collectors. Solar thermal collectors absorb sunlight to create heat. This heat can warm water directly or be used to spin turbines for making electricity. Solar cells, however, make electricity directly.
Many solar cells connected together form a solar module. Several modules then create a solar array. This array generates direct current (DC) electricity from the sun. Often, an inverter changes this DC power into alternating current (AC) for homes and businesses.
Contents
How Solar Cells Are Used
Solar Power for Vehicles
Cars that run on solar energy are called solar cars. They use solar panels to turn sunlight into electricity for their motors. Any extra energy is stored in batteries. These batteries are special. They are designed to power the car's electrical parts for a long time.
Solar cells were first used in vehicles in the mid-1900s. To promote solar transportation, Hans Tholstrup started the World Solar Challenge in 1987. This was a 3000 km race across Australia. Teams from companies and universities competed. General Motors won with their Sunraycer car, reaching speeds over 40 mph. Solar cars are actually one of the oldest types of alternative energy vehicles!
From Cells to Solar Systems
Many solar cells grouped together form a solar panel or module. These modules usually have a glass sheet on top. This glass lets light in and protects the delicate parts inside. Connecting solar cells in a series increases the total voltage. Connecting them in parallel increases the total current.
Solar modules often have special parts called bypass diodes. These diodes help if some cells get shaded. They let electricity flow around the shaded cells. This prevents power loss and protects the entire panel from damage.
You can connect many solar modules to create a large solar array. This array generates a lot of direct current (DC) electricity. Other devices, like MPPTs or microinverters, help manage this power. They make sure the system works as efficiently as possible.
Solar Power in Space
Solar cells first became famous when they powered the Vanguard satellite in 1958. They were an extra power source, helping the mission last longer. In 1959, the US launched Explorer 6. It had large, wing-shaped solar arrays. These became a common sight on satellites.
By the 1960s, solar cells were the main power source for most satellites orbiting Earth. They also powered many probes exploring the Solar System. This was because they were light and powerful. The demand for space solar power helped make solar cells more efficient.
Today, satellites use advanced multi-junction solar cells. These cells are made from special materials like gallium arsenide. They are lightweight, compact, flexible, and very efficient. They use different layers to capture more of the sun's energy spectrum.
Large satellites need big solar arrays. These arrays must fold up to fit inside the rocket. Once in space, they unfold into large panels. Newer satellites use flexible, rollable solar arrays. These are even lighter and take up less space. This helps reduce the cost of launching satellites.
In 2020, the United States Naval Research Laboratory tested solar power generation in a satellite. This was the PRAM experiment aboard the Boeing X-37.
History of Solar Cells
The photovoltaic effect was first shown by French physicist Edmond Becquerel. In 1839, when he was 19, he built the world's first photovoltaic cell. In 1876, William Grylls Adams and Richard Evans Day made the first solid state photovoltaic cell. Later, in 1883, Charles Fritts built another solid state cell. It used selenium coated with a thin layer of gold. This cell was only about 1% efficient.
Other important moments in solar cell history include:
- 1905 – Albert Einstein explained the photoelectric effect. He later won a Nobel Prize in Physics for this work.
- 1941 – Vadim Lashkaryov discovered p–n junctions in some early cells.
- 1954 – The first practical photovoltaic cell was shown at Bell Laboratories. Calvin Souther Fuller, Daryl Chapin, and Gerald Pearson were the inventors.
- 1958 – Solar cells became well-known when they were used on the Vanguard I satellite.
After the 1960s, solar cell prices slowly dropped, and their efficiency improved. In the early 1970s, Elliot Berman and his team at Solar Power Corporation (SPC) worked to make solar cells even cheaper. They found ways to simplify the manufacturing process.
After the 1970s, research into solar power for use on Earth became very important. Programs in the US funded studies to develop solar power for homes and businesses. The 1973 oil crisis also made oil companies invest in solar energy.
In the mid-1970s, a solar module cost about $96 per watt (adjusted for inflation). Thanks to better manufacturing and huge increases in production, this price dropped by over 99%. By 2018, it was about 30¢ per watt, and even as low as 20¢ per watt in 2020.
This huge price drop is often called Swanson's law. It's like Moore's Law for computers. It says that solar cell prices fall by 20% every time the industry's production capacity doubles.
Solar panel costs have fallen for many reasons:
- Larger silicon blocks: The semiconductor industry started making bigger silicon blocks. This made older equipment cheaper for solar cell makers.
- Bigger solar cells: As old equipment became available, solar cells themselves grew in size.
- Better glass: The rise of flat screen televisions led to more affordable, high-quality glass sheets for panels.
- Thinner cells: High silicon prices encouraged manufacturers to use less silicon by making cells thinner.
Falling costs are a major reason for the fast growth of renewable energy. Solar PV is growing fastest in Asia, with China and Japan leading the way. Between 2010 and 2021, the cost of solar electricity fell by about 85%. By 2019, solar cells generated about 3% of the world's electricity.
How Solar Cells Work
A solar cell is made from semiconducting materials like silicon. These materials are specially treated to create a p–n junction. This junction is made by adding tiny amounts of other elements, like boron (p-type) or phosphorus (n-type), to the silicon. This process is called "doping." Doping helps the cell turn light into electricity more easily.
When photons (tiny packets of light) from the sun hit the solar cell, the semiconductor absorbs them. This makes electrons jump to a higher energy level, creating "electron-hole pairs." If these pairs form near the p-n junction, an electric field pushes them apart. Electrons go to one side, and "holes" (missing electrons) go to the other.
If the solar cell is connected to an electrical device, these separated electrons flow through the circuit. This flow of electrons is the electricity we use.
Most solar cells use a large p–n junction made from silicon. Other types include organic solar cells and quantum dot solar cells. The side of the cell facing the sun usually has a clear, electrically conductive film. This film lets light in and collects the electricity produced.
Solar Cell Efficiency
The efficiency of a solar cell tells us how much of the sunlight's energy it can turn into electricity. This is called its power conversion efficiency.
Many factors affect efficiency, including how much light is reflected, how well the cell separates charges, and how easily electricity flows. The fill factor is a key measure. It compares the actual power a cell produces to its ideal maximum power. A high fill factor means less energy is lost inside the cell.
Single-junction silicon solar cells are getting very close to their theoretical maximum efficiency of 33.16%. This limit was set in 1961 by Shockley–Queisser. With many layers, the theoretical limit can be as high as 86% using concentrated sunlight.
In 2014, some companies achieved record efficiencies for silicon solar cells, over 25%. Panasonic, for example, moved electrical contacts to the back of the panel. This reduced shaded areas and improved efficiency.
In 2015, a special 4-junction solar cell achieved a record efficiency of 46.1% using concentrated sunlight. By 2017, researchers reported record efficiencies of 35.9% for triple-junction solar cells.
Materials Used in Solar Cells
Solar cells are named after the semiconducting material they are made from. Different materials absorb different parts of the sun's light spectrum best. Some cells are made for Earth, while others are optimized for space.
Solar cells are often grouped into three generations:
- First generation cells: These are the traditional cells made from crystalline silicon. This includes polysilicon and monocrystalline silicon. They are the most common type today.
- Second generation cells: These are thin film solar cells. They include amorphous silicon, CdTe, and CIGS cells. They are used in large solar farms and on buildings.
- Third generation cells: These are newer thin-film technologies, often still in research. Many use organic materials. They aim to be low-cost and highly efficient.
As of 2016, the most popular and efficient solar cells were those made from thin silicon wafers. This is also the oldest solar cell technology.
New Discoveries in Solar Cells
Perovskite Solar Cells
Perovskite solar cells use a special material called perovskite. These cells have rapidly improved in efficiency, from under 5% in 2009 to 25.5% in 2020. This makes them a very exciting new technology.
Perovskite solar cells are also expected to be very cheap to make on a large scale. However, most types haven't lasted long enough to be sold commercially yet. Researchers are working hard to solve this. Some efficient perovskite cells use lead, which is a toxic element. This is a challenge for their widespread use.
Bifacial Solar Cells
Bifacial solar cells can absorb light from both their front and back sides. This means they can produce more electricity than regular solar cells. The first patent for bifacial cells was filed in Japan in 1966. Russia used them in their space program in the 1970s.
In 1976, a research program in Spain began developing bifacial solar cells. In 1980, Andrés Cuevas showed that bifacial cells could produce 50% more power than regular ones when placed over a white surface. The company Isofoton started making these cells in 1981.
Due to lower manufacturing costs, companies started making commercial bifacial modules again around 2010. Experts predict that bifacial technology will grow a lot, from less than 5% of the market in 2016 to 30% by 2027.
Studies show that ground-mounted bifacial modules can give about 10% more electricity each year compared to regular ones. This gain can increase to about 30% if the modules are raised higher and placed over a very reflective surface. Bifacial panels also work better in snowy places.
Liquid Ink Solar Cells
In 2014, researchers found that using materials like kesterite and perovskite in liquid inks improved solar cell efficiency.
In 2022, MIT researchers created super lightweight fabric solar cells. These cells weigh 100 times less than traditional panels. They also generate 18 times more power per kilogram. These thin cells can be attached to many surfaces, like boat sails or drone wings. They use special electronic inks and can be printed.
Light-Absorbing Dyes
Dye-sensitized solar cells (DSSCs) are made from inexpensive materials. They don't need fancy equipment, so you could even make them yourself! They are much cheaper than older solid-state cells. DSSCs can be made into flexible sheets. Even though they are less efficient than the best thin-film cells, their low cost might make them competitive with fossil fuel electrical generation.
These cells use a special dye that absorbs light. This dye is placed on a thin film of titanium dioxide. When light hits the dye, it creates electrons. These electrons then move through the titanium dioxide to create electricity.
Quantum Dot Solar Cells
Quantum dot solar cells (QDSCs) are similar to dye-sensitized cells. But instead of dyes, they use tiny semiconductor nanoparticles called quantum dots. These dots are so small that their size changes how they absorb light. This allows scientists to fine-tune their properties.
Quantum dots can absorb light very well and can even create multiple electrons from a single photon. The efficiency of QDSCs has reached over 11%. Researchers have even made a "solar paint" using titanium dioxide and cadmium selenide. This paint can be applied to any conductive surface and has over 1% efficiency.
Organic and Polymer Solar Cells
Organic solar cells and polymer solar cells are made from very thin films of organic semiconductors. These include polymers and small-molecule compounds.
They can be made from liquid solutions. This means they could be produced using simple roll-to-roll printing, which could be very cheap and large-scale. These cells could also be useful for things that need to be flexible or disposable. However, their current efficiency is quite low.
In 2011, researchers developed transparent solar cells with about 2% efficiency. They were more than 65% clear to the human eye. This was done by absorbing only ultraviolet and near-infrared light. Later, similar polymer cells were made that were 70% transparent and 4% efficient. These lightweight, flexible cells could be used to make power-generating windows.
Adaptive Solar Cells
Adaptive cells can change how they absorb or reflect light based on the environment. For example, if light is very intense on one part of the cell, that part changes to let light in. Other parts stay reflective to keep absorbed light inside.
In 2014, a system was developed that combined an adaptive surface with a glass base. This system redirected absorbed light to a collector at the edges of the sheet. It also used lenses to concentrate light onto the adaptive surface.
Surface Texturing
When light hits a textured surface, it bounces around more inside the cell instead of reflecting away. This increases light absorption and makes the cell more efficient. Surface texturing is a way to reduce light loss, especially in thin-film solar cells.
By adding texture and anti-reflective coatings, solar cells can trap light rays more effectively. This means solar cells can be made thinner while still producing the same amount of power.
Scientists can create different textures. For example, etching silicon can create tiny pyramids on the surface. In 2012, MIT researchers showed that silicon films with nanoscale inverted pyramids could absorb as much light as much thicker flat silicon.
Encapsulation
Solar cells are usually covered in a clear plastic resin. This protects the delicate parts from moisture, dirt, ice, and other environmental damage. These covers are often made from polyvinyl acetate or glass. They help trap light inside the cell, increasing efficiency.
Researchers are also looking into making these covers even better. They are experimenting with roughened glass, prisms, and other shapes. These designs can further improve how much light the cell collects. Some coatings can even convert infrared light into visible light, boosting efficiency by 30%.
How Solar Cells Are Made
Making solar cells uses some of the same techniques as making other electronic devices. However, the rules for cleanliness and quality control are a bit more relaxed for solar cells. This helps keep costs down. Solar cells are commonly used in calculators, watches, and to power satellites.
To make a silicon solar cell, first, a thin slice of silicon (called a wafer) is cut. This wafer is usually treated to be "p-type." Then, the front side is treated to become "n-type." This creates the p-n junction, which is key to how the cell works.
Next, a special anti-reflection coating is added. This coating helps the cell absorb more light. Silicon nitride is a popular material for this. It also helps prevent electrons from getting lost at the surface.
Metal contacts are then added. A solid metal layer goes on the back. A grid of fine "fingers" and larger "bus bars" is printed on the front using silver paste. These contacts collect the electricity. To get the most sunlight, manufacturers use different ways to make the back contact:
- PERC (Passivated Emitter Rear Contact): Uses a solid aluminum back contact and a polymer film to capture light.
- TOPCon (Tunnel Oxide Passivated Contact): Adds an oxidation layer to the PERC film and uses a grid of smaller silver lines on the back.
- IBC (Interdigitated Back Contact): All contacts are on the back, leaving the front completely open to light.
After the metal contacts are made, the cells are heated. This helps the metal connect well with the silicon. Then, the solar cells are connected with wires and put together into modules or "solar panels." These panels have tempered glass on the front and a protective layer on the back.
The way solar panels are made and recycled affects their environmental impact. Scientists are studying how to make the most effective products for different uses and regions.
Disposing of Solar Panels
Solar cells lose their efficiency over time. In harsh climates, like deserts or polar regions, they can degrade faster due to strong UV light or heavy snow. Solar panels usually last about 25–30 years before they need to be taken out of service.
The International Renewable Energy Agency estimated that 43,500–250,000 metric tons of solar panel electronic waste were generated in 2016. This number is expected to grow a lot, possibly reaching 60–78 million metric tons by 2050.
Recycling Solar Panels
The most common solar cells are crystalline solar cells. After the Paris Agreement in 2016, many countries agreed to reduce carbon emissions. This means solar power will be a major source of electricity. So, there will be many solar panels to recycle after their useful life. Researchers are looking for ways to reuse silicon cells after recycling.
Solar cells also contain some elements that can be harmful if not disposed of properly. These include lead, cadmium, selenium, and barium. They also contain valuable materials like silicon, aluminum, silver, and copper.
There are different ways to recycle crystalline silicon cells. Mainly, heat and chemical methods are used. This usually happens in two steps:
- Separating parts: Heat is used to remove the protective layers. Then, materials like glass, aluminum frames, steel, copper, and plastics are separated.
- Cleaning cells: Unwanted layers (like anti-reflection coatings and metal) are removed from the silicon cells. This allows the silicon to be recovered and reused.
The first solar panel recycling plant opened in Rousset, France, in 2018. It was designed to recycle 1300 tonnes of solar panel waste per year. It can increase its capacity to 4000 tonnes.
See also
In Spanish: Célula fotoeléctrica para niños
- Anomalous photovoltaic effect
- Autonomous building
- Black silicon
- Electromotive force (solar cell)
- Energy development
- Flexible substrate
- Green technology
- Hot spot (photovoltaics)
- Inkjet solar cell
- List of solar engines
- List of types of solar cells
- Metallurgical grade silicon
- Microgeneration
- Nanoflake
- Photovoltaics
- Plasmonic solar cell
- Printed electronics
- Roll-to-roll processing
- Shockley-Queisser limit
- Solar cell research
- Solar Energy Materials and Solar Cells (journal)
- Solar module quality assurance
- Solar roof
- Solar shingles
- Solar tracker
- Spectrophotometry
- Standardization#Environmental protection
- Sustainable development
- Theory of solar cells
- Thermophotovoltaics
- Variable renewable energy
