How do solar panels and solar energy work?

How do photovoltaic solar panels work?  

Solar panels are the first component of a solar installation: they are devices that use solar energy to generate electricity or heat liquids depending on the type of radiation they absorb from the sun. A PV installation (derived from the English Photo-Voltaic) consists of three essential components: the solar panels, the inverter (s) and the electricity meters:

Solar panel are responsible for generating electricity under the influence of sunlight. A solar panel or PV panel consists of sixty photovoltaic solar cells (‘photo’ for light and ‘voltaic’ for electricity ). These plates with an area of ​​approximately 10 cm 2 are only 0.2 to 0.4 mm thick. It is important to note that these solar cells generate energy under the influence of sunlight, and not solar heat. This means that you often produce more electricity on a fresh, but sunny spring day than on a hot summer day.

How exactly do solar panel convert light into electricity? 

That has to do with its structure. Generally, solar panels consist of two layers of. When sunlight falls on the cells, an electrical voltage is created between the two silicon layers. The solar cells are mounted in series on a panel and the solar panels are also interconnected. In this way, the direct current generated can move from cell to cell and panel to panel, eventually reaching the second component of the solar installation – the inverter.

The origin of solar energy

To understand how solar or photovoltaic panels or panels work, we have to travel about 150 million kilometers to the center of our solar system, to find the origin of solar energy which is the sun . The sun is a medium-sized star that orbits the milky way. Like any star, the sun carries out a nuclear fusion reaction. 

Specifically, it fuses (unites) hydrogen atoms and transforms them into helium atoms. Approximately, it is estimated that the sun converts 4 million tons of hydrogen into 3 million tons of Helium every second. The missing million tons is transformed into energy

Sun Fusion Reaction

This energy, formed by particles called photons , escapes from the sun, travels to the earth, and is what we call solar energy. We feel solar energy as light and heat, plants absorb it for photosynthesis, animals like reptiles heat their blood and certain minerals and / or chemical elements change in the presence of solar energy.

Operation of solar panels, the photoelectric effect

It was these chemical changes, produced mostly in metals and semiconductors, that made the French physicist Edmond Becquerel realize , in 1839, that solar energy could be partially transformed into electricity, in what was later called the photoelectric effect.

The photoelectric effect occurs when the light photons, present in solar energy, index the atoms providing energy to the point that electrons are released from them. In principle, all atoms are susceptible to this phenomenon, but only in a few elements this effect is appreciable.  

Once the elements in which there is a greater number of electron release (metals and semiconductor elements) have been determined, we only have to indicate the way forward (electrical circuit), and we already have solar energy converted into electrical energy.

What are solar panels made of?

The first solar panel to produce electricity was made by Charles Fritts in 1883. It was made of selenium with a thin layer of gold. Apart from their low efficiency, around 1%, the high cost of these plates made their use to produce electricity in a significant way unfeasible.

In 1946, the American engineer Russell Ohl patented modern solar panels consisting of semiconductor silicon cells with pn junctions. And finally, in 1954 the inventors Daryl Chapin, Calvin Souther Fuller and Gerald Pearson, at Bell Labs, put Russel Ohl’s experiments into practice and built the first solar panel, like the ones we have today. These solar panels reached an efficiency of 5% in the 1960s.

How are solar panels manufactured?

Currently, the most used material to manufacture solar panels is crystalline silicon. Solar panels are basically made of two types of silicon joined in thin layers. These junctions are called pn junctions, where the type of silicon p has an electron spear and type n has an excess. When sunlight hits the junction, it causes the movement of electrons from one type to another, generating electricity. These plates have an efficiency between 12 and 25%.

Depending on the purity of the silicon crystals, we have monocrystalline and polycrystalline plates:

The monocrystalline plates are manufactured in long cylinders, in one piece, and cut into thin sheets. While this process consumes a lot of energy and uses more materials, it produces the most efficient cells. Modules made of single crystal cells can have efficiencies of up to 23 percent in laboratory tests. They are black, so they absorb more sunlight, generating electricity even on cloudy days, but being black they take more temperature which can be counterproductive. They are also somewhat more expensive than polycrystalline plates, because the crystals are purer.

The polycrystalline plates are made of ingot melted silicon and then cut into squares. While production costs are lower, cell efficiency is also lower. The efficiency of the modules is close to 20 percent. They are bluish in color and, although they are not as efficient as monocrystalline ones, as they do not get so hot, due to their color, their performance almost does not vary with temperature, making them ideal in places with lots of light or solar radiation. Polycrystalline plates represent about half of the global photovoltaic market.

To determine what type of plate suits us, we will have to make an average of the light / solar radiation that we have in our area throughout the year, the type of installation we want to do and our budget.

How do solar panels work?

To work, solar panel cells need to establish an electric field. Just like a magnetic field, which is produced due to the opposite poles, an electric field is produced when the positive / negative charges separate. To obtain this field, manufacturers “doped” the silicon with other materials, giving each layer of the joints a positive or negative electrical charge. Specifically, they add phosphorus in the top layer of silicon, which adds additional electrons, with a negative charge, to that layer. Meanwhile, the lower layer receives a dose of boron, resulting in fewer electrons or a positive charge. All this adds to an electric field at the junction between the silicone layers. Then, when a photon of sunlight releases an electron, the electric field will eject that electron from the silicon junction.
A couple of other cell components convert these electrons into usable energy. The metal conductive plates on the sides of the cell collect the electrons and transfer them to the wires. At that point, electrons can flow like any other source of electricity.

Parts of a solar panel

Each solar panel consists of smaller solar or photovoltaic cells linked together in series and parallel. The number of cells is what determines the tension and power of the plate. These cells in the monocrystalline plates are made of a single crystal while in the polycrystallines they are formed by several crystals. In turn, each cell is formed by layers, with pn-type silicon junctions in addition to protective layers (usually glass or transparent hard plastic). In the upper layer is the silicon of type n and in the lower one the one of type P. Except for some type of plaque, normally 12v plates have 36 cells, while 24v plates have 60 or 72 cells, depending on their use.

12v panel with 36 cells

The solar panels, in their great majority, bring a hard protection frame to be able to anchor them in their support, in addition to a crystal that protects the set of cells. Currently, flexible plates have also gone on the market, where the photovoltaic cells are between two plastic sheets.

Depending on the model, they will carry cables or plugs for their connections. There are models that also have a built-in electrical protection diode. 

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