The photovoltaic conversion process is simple, solar panels transform sunlight (photons) into DC electric current that is then transformed into alternating current by means of an inverter.
When we talk about photovoltaic conversion we are talking about a process in which solar energy is converted into electricity. A necessary process to take advantage of an energy increasingly used and that we explain below to detail.
PHOTOVOLTAIC SOLAR ENERGY CONVERSION
The sun provides 1 kW / m 2 of free and non-polluting energy for several hours every day. Therefore we can take advantage , and each time, more people are doing it, thermal and photovoltaic systems that take advantage of the sun as well as biomass.
Coal, petroleum, vegetable ethanol and wood are all forms of stored solar energy. While each energy conversion process has a unique spectral response curve, most laboratory development work has focused on photovoltaic systems capable of converting stored energy into electricity in the process known as photovoltaic conversion.
HOW IS THE PHOTOVOLTAIC CONVERSION ORIGINATED?
When we talk about solar energy, we also do it with photovoltaic energy, which consists of the direct conversion of light into electricity at the atomic level .
Some materials exhibit a property known as the photoelectric effect that causes them to absorb photons of light and release electrons . When these free electrons are captured, an electric current is obtained that can be used as electricity.
The photoelectric effect was first observed by a French physicist, Edmund Bequerel , in 1839 , who discovered that certain materials were capable of producing small amounts of electric current when exposed to light.
In 1905, Albert Einstein described the nature of light and the photoelectric effect on which photovoltaic technology is based, a theory by which he later won a Nobel Prize in Physics.
The first photovoltaic module was built by Bell Labs in 1954 . It was advertised as a solar battery and was primarily a curiosity, since it was too expensive to obtain from it widespread use.
In the decade of the 60s, the space industry began to make the first serious use of technology to provide energy on board spacecraft. Through the space programs, the technology advanced , its reliability was established and the cost began to decrease .
HOW THE PHOTOVOLTAIC CONVERSION WORKS
Photovoltaic conversion occurs through what is known as a basic photovoltaic cell or also called a solar cell. Solar cells are made of the same type of semiconductor materials , such as silicon , which is used in the microelectronics industry.
For the operation of these solar cells , a thin semiconductor wafer is specially treated to form an electric field , which is positive on one side and negative on the other. When the energy of light hits the solar cell, the electrons are released from the atoms in the semiconductor material .
If the electrical conductors are connected to the positive and negative sides, forming an electrical circuit, the electrons can be captured in the form of an electric current , that is, electricity . This electricity can be used to feed a load, such as a light or a tool.
A number of solar cells electrically connected to each other and mounted on a supporting structure or frame is called a photovoltaic module. The modules are designed to supply electricity at a certain voltage , such as a common 12 volt system. The current produced depends directly on how much light hits the module.
Several modules can be connected together to form a matrix. In general, the larger the area of a module or matrix, the more electricity will be produced. The modules and photovoltaic arrays produce electricity from direct current (cd). They can be connected in series and parallel electrical configurations to produce any combination of current and voltage required.
HOW ARE THE PHOTOVOLTAIC MODULES THAT ARE USED?
The most common photovoltaic devices of today use a unique interface or union to create an electric field inside a semiconductor , such as a photovoltaic cell.
In a single-junction photovoltaic cell, only photons whose energy is equal to or greater than the band space of the cell material can release an electron for an electrical circuit and thus capture the energy.
In other words, the photovoltaic response of the single binding cells is limited to the portion of the spectrum of the sun whose energy is above the band space of the absorbing material, and no photons of lower energy are used.
One way to avoid this limitation is to use two (or more) different cells, with more than one band gap and more than one junction, to generate a voltage that then generates the conversion of the solar energy we want to use as electricity.
These are known as “multijunction” cells (also called “cascade” or “tandem” cells). The multifunction devices can achieve a higher total conversion efficiency because they can convert as much of the energy spectrum of light to electricity.
In reality, a device or multijunction cell is a stack of single junction cells in descending order of band gap (Eg). The upper cell captures the high energy photons and passes the rest of the photons to be absorbed by the low band cells.
Much of the current research in multi-functional cells focuses on gallium arsenide as one (or all) of the component cells. Such cells have reached efficiencies of around 35% under concentrated sunlight .
Other materials studied for multijunction devices have been the amorphous silicon and copper copper diselenide although at the moment they are not so used or should be studied more with them.
As an example we can add further that the conventional multijunctioning device uses an upper cell of indium and gallium phosphide, “a tunnel junction” , to help the flow of electrons between the cells, and a lower cell of gallium arsenide, thereby You can get the so-called photovoltaic conversion so necessary to take advantage of the sun and its energy.