What are solar panels?

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Solar panels are devices that convert light into electricity. They are called “solar” panels because most of the time, the most powerful source of light available is the Sun, called Sol by astronomers. Some scientists call them photovoltaics which means, basically, “light-electricity.” A solar panel is a collection of solar cells. Lots of small solar cells spread over a large area can work together to provide enough power to be useful. The more light that hits a cell, the more electricity it produces, so spacecraft are usually designed with solar panels that can always be pointed at the Sun even as the rest of the body of the spacecraft moves around, much as a tank turret can be aimed independently of where the tank is going.

Solar cells and solar panels have lots of uses. They are in everyday things like calculators, watches, and flashlights. There are solar-powered toys, radios, and MP3 players. There are solar-powered cell phones and pagers. Using solar power with devices like these means you never have to worry about batteries. Solar panels are sometimes used to make the electricity to light up road signs and bus stops. They may make the electricity that makes roadside emergency phones or parking meters work. Even some ATM’s have solar panels. The ceiling lights and all kinds of machines and appliances used at home, school, and work get their electricity from the wires running through the building. Usually, this electricity comes to the building from the public power system, or grid. But solar panels can also be used along with power from the grid. People sometimes put solar panels on their homes. Large buildings may have them as well. They make it possible to use less of the grid’s costly electricity. In addition, they are a backup in case of a power failure, or blackout. In some areas the grid itself gets some power from solar panels.


The Sun constantly gives off energy. The energy is carried through space as electromagnetic radiation. There are several types of electromagnetic radiation. Light is one type. Radio waves are another. Electromagnetic radiation travels like waves in water. Like water waves, it is a series of ups and downs. One way various types of electromagnetic waves differ is in their wavelength. This is the distance between two ups (or two downs) in a row. The wavelengths of radio waves are longer than those of light. Among types of light, red has a longer wavelength than blue. Only part of the energy sent toward Earth by the Sun actually makes it to Earth’s surface. Some solar energy gets bounced back into space. Some gets absorbed by the air. Most of the solar energy that does make it to Earth’s surface is in the form of visible light. Solar cells can use the energy of this light to make electricity. But they don’t work equally well with all forms of light. Different types of solar cells use different wavelengths. This means a cell can use only some of the solar energy that it receives.

Russell Ohl was the first person to come up with a solar cell like the ones used today. He worked at Bell Laboratories in New Jersey. His cell was made of silicon (silicon is found in sand and in many types of rock). He called the cell a “light-sensitive electric device.” He filed for a patent on it in 1941. Five years later, he got the patent. In 1954, Bell Labs made the first practical solar cell. It was the first one to make enough electricity to run ordinary electrical devices. Still, early cells didn’t make much electricity. Also, they were very costly. Their first important use was in space satellites, starting in 1958. As cells became cheaper, they were used in other ways. The first power station able to make 1 megawatt of electricity with solar panels opened in Hesperia, California, in 1982.

Solar cells come in various sizes. Some are tinier than a stamp. Some are 5 inches (12 centimeters) across. The cells are made of a type of material known as a semiconductor. Often, they are made of silicon. Semiconductors can conduct, or carry, electricity. They don’t do this as well as metals, however. That is why they are called “semi.” Because they only “semi” conduct electricity, they can be used to control electric current. On their top and bottom they typically have metal contacts through which current can fl ow. A typical simple cell has two layers of silicon. One is known as n-type. The other is p-type. The layers are different from each other.

The process of making electricity begins when the silicon atoms absorb some light. The light’s energy knocks some electrons out of the atoms. The electrons fl ow between the two layers. The fl ow makes an electric current. The current can leave the cell through the metal contacts and be used. When light hits a solar cell, much of its energy is wasted. Some light bounces off or passes through the cell. Some is turned into heat. Only light with the right wavelengths, or colors, is absorbed and then turned into electricity. A single simple solar cell makes only a little electricity. For most purposes more is needed. For this reason, cells are often linked together in groups known as solar modules. A solar module has a frame that holds the cells. Some modules are several feet long and wide. They usually can produce up to a few hundred watts of electricity. If more power is needed, modules can be joined together to form a large solar array. Modules are sometimes called solar panels. Arrays are also sometimes called solar panels. Whatever you call a group of solar cells, the fact remains: the more cells you link together, the more electricity you make. With enough modules, huge amounts of power are possible. A good example is a new power plant being built at Moura in Portugal.The first phase of the project has 262,080 solar modules, each with 48 cells. They will produce up to 46 megawatts of electricity. Many experts think even bigger power plants using solar panels will be built in the coming years. Someday there may be solar plants able to make as much as 500 megawatts of power. That is about what a typical coal power plant produces today. Solar panels work best when they directly face the Sun. For this reason, the panels are often put on “trackers.” The trackers turn the panels so that they follow the Sun as it moves across the sky.