Photovoltaics facts for kids

The Solar Settlement, a community of homes in Freiburg, Germany, that uses solar power.

A charging station in France that uses solar energy to power electric cars.

Solar panels on the International Space Station help power it in space.

Photovoltaics (say "foe-toe-VOL-tay-iks"), or PV, is a way to turn light directly into electricity. It uses special materials called semiconducting materials, which have a unique ability to create an electric current when light shines on them. This is known as the photovoltaic effect.

A photovoltaic system is made up of solar modules, which are like big panels. Each module contains many smaller solar cells. These cells work together to generate electrical power. You can find PV systems installed in many places: on the ground, on rooftops, on walls, or even floating on water! Some systems can even move to follow the sun across the sky, like a sunflower.

Solar PV technology is a great help in fighting climate change. It produces much less carbon dioxide than burning fossil fuels. Once a solar system is set up, it doesn't create any pollution or greenhouse gases while it's working. Solar power can be used for small needs or very large ones, and silicon, a main material for solar cells, is very common on Earth. However, making solar panels and setting them up does use some energy and create some pollution, but it's much less than what fossil fuels cause.

Photovoltaic systems have been used for a long time in special situations, like powering remote equipment. Since the 1990s, they have also been connected to main electricity grids. Solar modules started being mass-produced around 2000, partly because governments, like Germany's, supported their use. The cost of solar power has dropped a lot, making it a more popular energy choice. This is thanks to big investments, especially from China, and better manufacturing methods.

By 2022, enough solar PV systems were installed worldwide to generate over 1 terawatt (TW) of power, meeting almost two percent of the world's electricity needs. Solar PV is now the third largest renewable energy source globally, after hydro and wind power. In some sunny places, solar PV is even the cheapest way to get electricity!

What Does "Photovoltaic" Mean?

The word "photovoltaic" comes from two parts. "Photo" comes from the Greek word "phōs," which means "light." "Voltaic" comes from "volt," which is a unit for measuring electrical force. The "volt" was named after an Italian scientist named Alessandro Volta, who invented the battery. People have been using the term "photovoltaic" in English since 1849.

A Brief History of Solar Power

The idea of turning light into electricity isn't new!

In 1839, a French scientist named Edmond Becquerel noticed that a metallic solution produced an electric current when exposed to sunlight. This was the first time someone observed the photovoltaic effect.
In 1989, the German government started a program to help people put solar panels on their roofs.
Japan followed in 1994 with a similar program.

Since then, many countries have continued to develop and use solar power systems.

How Solar Cells Work

Solar cells turn sunlight directly into electricity.

This map shows how much electricity a 1 kWp solar panel can produce in different parts of the world.

Solar cells are best known for making electric power by changing energy from the sun into a flow of electrons. This is the photovoltaic effect in action!

Solar cells create direct current (DC) electricity from sunlight. This DC power can run equipment or recharge batteries. Early on, solar cells were used to power satellites and spacecraft. Today, most photovoltaic modules are connected to the main electricity grid to generate power for homes and businesses. For this, a device called an inverter changes the DC electricity into alternating current (AC), which is what most homes use. Some solar systems are also used in remote places, like for boats, recreational vehicles, or emergency phones.

Solar power systems use solar modules that contain many solar cells made from a special semiconductor material. Copper solar cables connect these modules. Because more and more people want renewable energy, the way solar cells and panels are made has improved a lot.

Solar cells need protection from the weather, so they are usually packed tightly inside solar modules.

The power of a solar module is measured in "W_p" (watts peak) under perfect test conditions. The actual power it produces can be different depending on where it is, the time of day, the weather, and other things.

Solar Cell Efficiency

The efficiency of a solar cell tells us how much of the sunlight hitting it is turned into electricity. Engineers are always working to make solar cells more efficient, so they can produce more power from the same amount of sunlight.

How Solar Panels Perform and Change Over Time

This chart shows how clouds can affect how much solar energy is produced.

Solar panels are usually tested under specific conditions, like a certain amount of sunlight and temperature. But in the real world, their performance changes. Factors like where you live, the time of day, the season, how much sun is shining, the angle of the panels, clouds, shadows, dirt, and temperature all affect how much electricity they produce.

For the best performance, all the solar panels in a system should be similar and face the same direction towards the sun. Special parts called bypass diodes help if one panel is broken or shaded, allowing electricity to keep flowing from the other panels.

Solar panels have different electrical features, like their maximum power (P_MAX, measured in W) and how much voltage they can produce when not connected (V_OC). The peak power rating (W_p) is the maximum power under standard test conditions. A typical solar panel, about 1 by 2 meters, might be rated from 75 W to 600 W, depending on how efficient it is.

How Temperature Affects Solar Panels

The temperature of a solar panel affects how well it works. Generally, when a solar panel gets hotter, it produces less power. This is because heat affects the way the semiconductor materials work inside the cell. Scientists use "temperature coefficients" to describe how much the power changes with temperature.

How Solar Panels Degrade

Solar modules are built to last and can handle rain, hail, heavy snow, and changes in heat and cold. Most panels are tested to make sure they are strong.

Over time, the power output of a solar panel can slowly decrease. This is called degradation and happens because of constant exposure to sunlight and other weather conditions. Engineers measure this with a "degradation index" to see how much power is lost each year. Different types of solar panels degrade at different rates. For example, crystalline silicon panels usually lose about 0.8% to 1.0% of their power each year. Some thin-film panels might degrade more at first, then stabilize.

One challenge for solar technology is the cost. Scientists are always looking for ways to make panels more efficient and cheaper. For example, adding tiny amounts of chemicals like boron to the silicon can help the panel convert more light into electricity.

How Solar Systems Are Made

Making solar panels is a fairly straightforward process, and because they don't have many moving parts, they can last a long time—from 10 to 30 years! To make more electricity, manufacturers simply add more solar components. This means that the more panels they make, the cheaper each one becomes.

Most solar panels today (about 90%) are made from crystalline silicon. Here's a simplified look at how they're made:

First, very pure silicon is made from quartz sand.
This pure silicon is melted and mixed with tiny amounts of other materials, like boron, to help it conduct electricity better.
Large blocks of this silicon are grown or cast, then sliced into very thin wafers.
These wafers are cleaned and treated.
A very thin layer of another material, like phosphorus, is added to the surface.
An anti-reflective coating is put on to help capture more sunlight, and electrical contacts are added.
Finally, these individual cells are connected together to form a solar module, ready for shipping and installation.

Environmental Impact of Manufacturing

Even though solar power is clean when it's used, making the panels does have an environmental impact. The production process uses energy and can create some greenhouse gas emissions. Materials are needed, and some toxic substances are used in small amounts. Scientists are working on better ways to recycle old solar panels.

One important idea is the "energy payback time" (EPBT). This is the amount of time a solar panel needs to operate to produce the same amount of energy that was used to make it. The lower the EPBT, the better for the environment. For example, making the pure silicon for panels uses a lot of energy. But engineers are constantly finding ways to use less silicon and make cells more efficient, which helps reduce the EPBT.

Different types of solar panels have different environmental impacts:

Crystalline Silicon Panels: These are the most common. They have an EPBT of about 1.5 to 2.7 years. This means that after about 2 years, a panel has produced more energy than it took to make it.
Cadmium Telluride (CdTe) Thin-Film Panels: These are a newer type that use very thin layers of material. They require less energy to produce and have a faster EPBT, sometimes less than a year. However, they use materials like cadmium, which needs careful handling.
Third-Generation PV: Scientists are developing even newer technologies that aim to be super-efficient and use materials that are common and not toxic. These are still mostly in labs but show great promise for the future.

The Cost of Solar Power

The cost of solar power has changed a lot over the years. It used to be very expensive, but now it's much more affordable. This is because of rapid improvements in technology, better manufacturing, and more companies making solar products.

Renewable energy technologies, especially solar and wind, have become much cheaper to build than power plants that use fossil fuels in many parts of the world.

How Much Does Solar Hardware Cost?

In 1977, a solar cell cost about $76.67 per watt. By 2011, prices had dropped below $1.00 per watt, and by 2024, they were as low as $0.11 per watt! This huge drop in price is sometimes called "Swanson's law," which suggests that solar panel prices fall by about 20% every time the amount of installed solar capacity doubles.

These prices are for the solar panels themselves. The total cost of a solar system also includes installation, inverters (which change DC to AC electricity), and other equipment. In some countries, like Germany, installing rooftop solar is cheaper than in others, like the US, due to different rules and policies.

The "True" Cost of Solar Electricity

A good way to compare the cost of different energy sources is the "levelised cost of electricity" (LCOE). This is the average cost per unit of electricity over the entire lifetime of a power plant. Solar LCOE has dropped dramatically. By 2017, solar farms in some places were selling electricity for as low as $0.03 per kilowatt-hour (kWh), which is very competitive with traditional power sources.

However, solar power isn't always available (the sun sets!), so there are extra costs for storing energy or having other power sources ready to fill in when needed. These extra costs are not always included in simple LCOE calculations.

Government Help and Funding

Many governments have offered financial help, like "feed-in tariffs," to encourage people to install solar panels. These programs pay solar owners for the electricity they produce. This help was very important for solar power to grow in its early days.

Sometimes, there are disagreements between countries about these subsidies. For example, some US companies have complained that Chinese government support has made solar panels cheaper, leading to trade discussions. However, many people believe that government support helps solar power become cheaper faster, eventually allowing it to compete without special help.

The Amazing Growth of Solar Power

Solar and wind power are growing faster than older ways of making electricity.

Solar power generation is growing very quickly around the world.

Solar power is growing incredibly fast! Scientists are doing a lot of research on it, and more and more solar systems are being installed. By April 2022, the world had enough solar panels to generate one terawatt of power, providing 2% of the world's electricity. Over 100 countries now use solar PV.

China has the largest solar power capacity in the world, with 1048 GW installed by 2024. Other big solar users include the United States, Japan, and Germany. In 2019, Honduras generated the highest percentage of its energy from solar (14.8%). Vietnam has also seen a huge boom in solar installations.

Scientists believe that by 2030, the world could have between 3,000 and 10,000 GW of solar power installed. This shows how important solar energy is becoming for our future!

Top 20 PV Countries in 2022 (Megawatts)

Installed and total solar power capacity in 2022 (MW)
#	Nation	Total capacity	Added capacity
1	China	393,000	86,100
2	United States	113,000	17,800
3	Japan	78,800	4,600
4	Germany	66,600	8,100
5	India	63,100	13,500
6	Australia	26,800	7,700
7	Italy	25,100	2,400
8	Brazil	24,100	9,900
9	South Korea	21,000	2,800
10	Spain	20,500	4,600
11	Netherlands	19,100	4,200
12	Vietnam	18,500	1,800
13	France	17,400	2,700
14	United Kingdom	14,400	720
15	Poland	11,200	4,900
16	Taiwan	9,700	2,000
17	Turkey	9,400	1,600
18	Mexico	9,000	2,000
19	Ukraine	8,100	0
20	Belgium	6,900	310

Data: IEA-PVPS Snapshot of Global PV Markets 2023 report, April 2023
Also see Solar power by country for a complete and continuously updated list

Where We Use Solar Power

Solar panels have many practical uses in almost every area of technology.

In farming, they can power irrigation systems.
In remote health clinics, they can keep medicines refrigerated.
They generate electricity for homes, businesses, and even entire power plants.
They are also built into homes and public buildings.

Photovoltaic Systems

A photovoltaic system is a setup designed to provide useful solar power. It includes:

Solar panels: To capture sunlight and turn it into electricity.
Solar inverter: To change the electricity from DC to AC.
Mounting, cabling, and other parts: To hold everything together and connect it.

PV systems can be small, like those on a rooftop, or very large, like huge solar power stations that generate hundreds of megawatts. Most PV systems today are connected to the main electricity grid, but some are "stand-alone" systems for places without grid access.

Photo Sensors

Solar cells are also a type of photo sensor. These are devices that detect light. A photo detector has a special part that turns light into an electric current. When light hits it, it creates tiny charged particles that move and make electricity. Photodiodes are examples of photo detectors. Solar cells are special because they convert a lot of the light energy into usable electrical energy.

New and Experimental Solar Technologies

While crystalline silicon solar cells are the most common, scientists are always working on exciting new technologies to make solar power even better.

One newer type is thin-film PV. These cells are made by putting very thin layers of special materials, like perovskite, onto a surface such as glass or steel. These layers are much thinner than silicon wafers. Perovskite solar cells are very efficient, but scientists are still working on making them for large areas. Thin-film technologies could be cheaper to make because they use less material.

CIGS Solar Cells

Copper indium gallium selenide (CIGS) is another type of thin-film solar cell. These cells are extremely thin, about 100 times thinner than traditional silicon cells! The materials needed to make CIGS cells are easy to find, and they are known for being very stable and not losing much performance over time.

Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSCs) are a unique type of thin-film cell that work very well in normal indoor light, not just bright sunshine. They use a special dye to absorb light, which then creates electricity. They are cheap to produce and don't degrade much in sunlight. However, they often use a liquid inside that can be tricky to work with and can be sensitive to temperature changes.

Organic Photovoltaics (OPVs)

Organic photovoltaics (OPVs) are a new area of research. These cells are made from organic (carbon-based) materials. They can be flexible, lightweight, and potentially very cheap to mass-produce, even using printing methods! They also use common, non-toxic elements. While their efficiency is currently lower than silicon cells, scientists are making rapid progress, and they could be very important for future solar applications.

Capturing Waste Heat

A Photovoltaic-Thermoelectric Generator (PV-TEG) is a clever hybrid system. Solar panels get hot when they work, and this heat can reduce their efficiency. A TEG is a device that can turn heat directly into electricity. By adding a TEG to a solar panel, it can capture some of that wasted heat and convert it into more electricity, making the whole system more efficient and helping the solar panel last longer.

Different Ways to Install Solar Panels

Solar panels can be installed in many creative ways:

Towers: Some systems mount panels vertically in a tower that can turn to follow the sun.
Ground-mounted: Panels can be placed on the ground, sometimes even combined with farming or grazing land.
Building-integrated: Panels can be built right into the roofs or walls of buildings.
Floating Solar: In 2008, a winery in California pioneered "floatovoltaic" systems by putting solar panels on pontoons floating on an irrigation pond. This helps keep the panels cooler (making them more efficient), reduces water evaporation, and stops algae from growing.
Concentrator Photovoltaics (CPV): These systems use lenses or curved mirrors to focus a lot of sunlight onto small, super-efficient solar cells. They often use trackers to follow the sun and cooling systems to keep the cells from overheating.

Improving Efficiency

Scientists are constantly working to make solar cells more efficient. In 2019, a world record was set with a solar cell that achieved 47.1% efficiency using special multi-junction concentrator cells.

One big problem for solar cells is overheating. A solar cell's efficiency can drop by about 0.5% for every degree Celsius it gets hotter. To solve this, engineers are developing "self-cooling" solar cells that use special shapes and materials, like silica pyramids, to reflect heat away while still letting sunlight reach the cells.

Some companies are also adding "power optimizers" to individual solar modules, creating "smart modules." These optimizers help each module work at its best, even if part of it is shaded, and can provide safety features.

Advantages of Solar Power

Solar power has many great benefits:

Plenty of Sunlight: The sun sends an enormous amount of energy to Earth—about 10,000 times more than humans use! This means solar energy could easily become our main energy source.
Clean Energy: Solar power produces no pollution or greenhouse gases while it's working. Using solar instead of fossil fuels can greatly reduce air pollution and save lives.
Long-Lasting and Low Maintenance: Solar panels usually come with a 25-year guarantee and need very little maintenance after they are installed. This means low operating costs over time.
Local Power: Rooftop solar panels can generate electricity right where it's needed, reducing energy loss during transmission.
Room for Improvement: Compared to other energy sources, not as much research money has been invested in solar cells yet. This means there's still a lot of potential for them to become even better and more efficient.
Financial Help: In some places, special programs help homeowners pay for solar panels, making it easier for more people to switch to solar.

Challenges of Solar Power

While solar power is amazing, it also has some challenges:

Impact on the Electricity Grid: When many homes have rooftop solar, electricity can flow both ways—from the grid to homes, and from homes back to the grid. Older electricity networks weren't designed for this, which can sometimes cause technical issues like too much voltage. Engineers are working on solutions, like smarter inverters and new control equipment.
The "Duck Curve": Solar power generates a lot of electricity during the middle of the day when the sun is highest. But as the sun goes down, solar production drops quickly, while people's electricity use often goes up (when they come home and turn on lights and appliances). This rapid change in demand for electricity from traditional power plants is called the "duck curve" because of how it looks on a graph. It means power companies need to quickly ramp up other power sources, which can be a challenge.