What does a solar cell consist of? Production of photocells for solar panels
The basis of any installation in photovoltaics is always a photovoltaic module. A photovoltaic module is a combination of electrically interconnected photocells. The term photovoltaic consists of two words “photo” (from the Greek light) and “volt” (Alessandro Volta - 1745-1827, Italian physicist) - a unit of measurement of voltage in electrical engineering. Analyzing the term photovoltaic, we can say - this is.
A photovoltaic cell (PV cell) is used to generate electricity by converting solar radiation. A solar cell can be considered as a diode consisting of n-type and p-type semiconductors with a carrier depletion band formed, so an unilluminated photocell is similar to a diode and can be described as a diode.
For semiconductors having a bandgap between 1 and 3 eV, a maximum theoretical efficiency of 30% can be achieved. The band gap is the minimum photon energy that can lift an electron from the valence band to the conduction band. The most common industrially produced solar cells are.
Monocrystalline and polycrystalline silicon. Silicon today is one of the most common elements for the production of photovoltaic modules. However, due to the low absorption of solar radiation, silicon crystal solar cells are usually manufactured with a width of 300 microns. The efficiency of a photocell made from a single crystal of silicon reaches 17%.
If we take a solar cell made of polycrystalline silicon, then its efficiency is 5% lower than that of a single crystal of silicon. The grain boundary of a polycrystal is a center for the recombination of charge carriers. The size of a polycrystalline silicon crystal can vary from several mm to one cm.
Gallium arsenide (GaAs). Gallium arsenide solar cells have already shown an efficiency of 25% in laboratory conditions. Gallium arsenide, developed for optoelectronics, is difficult to produce in large quantities and for solar cells it is quite expensive. Solar cells made from gallium arsenide are also used for astronautics.
Thin film photocell technology. The main disadvantage of flint elements is their high price. Thin film cells are available that are made from amorphous silicon (a-Si), cadmium teluride (CdTe) or cuprum-indium diselinide (CuInSe 2). The advantage of thin-film solar cells is the savings in raw materials and cheaper production compared to silicon solar cells. Therefore, we can say that thin-film products have prospects for use in solar cells.
The downside is that some materials are quite toxic, so product safety and recycling play an important role. In addition, telluride is a finite resource compared to silicon. The efficiency of thin-film solar cells reaches 11% (CuInSe2).
In the early 1960s, solar cells cost approximately $1000/watt peak power and were manufactured primarily in space. In the 70s, serial production of photocells began, and their price dropped to $100/W. Further progress and reduction in the cost of photocells made it possible to use photocells for domestic needs. Especially for part of the population living far from power lines and standard electricity supply, photovoltaic modules have become a good alternative.
The photo shows the first silicon-based solar battery. It was created by scientists and engineers of the American company Bell Laboratories in 1956. A solar cell is a combination of electrically interconnected photovoltaic modules. The combination is selected depending on the required electrical parameters such as current and voltage. One cell of such a solar battery, which produced less than 1 watt of electricity, cost $250. The electricity generated was 100 times more expensive than from a conventional grid.
For almost 20 years, solar panels were used only for space. In 1977, the cost of electricity was reduced to $76 per 1 watt cell. Efficiency gradually increased: 15% in the mid-90s of the last century and 20% by 2000. Current most relevant data on this topic -
The production of solar cells from silicon can be divided into three main stages:
production of high-purity silicon;
production of thin silicon washers;
photocell assembly.
The main raw material for the production of high-purity silicon is quartz sand (SiO 2). By electrolysis of the melt it is obtained metallurgical silicon, which has a purity level of up to 98%. The process of silicon reduction occurs when sand interacts with carbon at a high temperature of 1800 °C:
This degree of purity is not sufficient for the production of a solar cell, so it must be further processed. Further purification of silicon for the semiconductor industry is carried out virtually throughout the world using technology developed by Siemens.
"Siemens process" is the purification of silicon by reacting metallurgical silicon with hydrochloric acid, resulting in trichlorosilane (SiHCl 3):
At a temperature of 30 °C, trichlorosilane (SiHCl 3) is in the liquid phase, so it is easily separated from hydrogen. Further, repeated distillation of trichlorosilane increases its purity to 10 -10%.
The subsequent process - pyrolysis from purified trichlorosilane - produces polycrystalline silicon of high purity. The resulting polycrystalline silicon does not quite meet the conditions for use in the semiconductor industry, however, the quality of the material is sufficient for the solar photovoltaic industry.
Polycrystalline silicon is the raw material for the production of monocrystalline silicon. Two methods are used to produce monocrystalline silicon: the Czochralski method and the zone melting method.
Czochralski method is energy-intensive and also material-intensive. A relatively small amount of polycrystalline silicon is placed in a crucible and melted in a vacuum. A small seed of monosilicon is lowered onto the surface of the melt and then, twisting, rises, pulling out a cylindrical ingot due to the force of surface tension.
Currently, the diameters of drawn ingots reach up to 300 mm. The length of ingots with a diameter of 100-150 mm reaches 75-100 cm. The crystal structure of the elongated ingot repeats the single-crystal structure of the seed. Increasing the diameter and length of the ingot, as well as improving the technology of sawing it, will reduce the amount of waste, thereby reducing the cost of the resulting solar cells.
Tape technology. The technological process developed by Mobil Solar Energy Corporation is based on drawing silicon strips from a melt and forming solar cells on them. The matrix is partially immersed in the silicon melt and, thanks to the capillary effect, the polycrystalline silicon rises, forming a ribbon. The melt crystallizes and is removed from the matrix. To increase productivity, equipment is designed that can produce up to nine tapes simultaneously. The result is a nine-sided prism.
The advantage of the tapes is that they have low waste due to the fact that the process of cutting the ingot is eliminated. In addition, rectangular-shaped solar cells can be easily obtained, while the round shape of monocrystalline wafers does not contribute to a good layout of the photovoltaic cell in a photovoltaic module.
The resulting polycrystalline or monocrystalline silicon rods must then be sawn into thin washers, 0.2 - 0.4 mm thick. When sawing a rod of monocrystalline silicon, about 50% of the material is lost. Next, the round washers are not always, but often, cut to obtain a square shape.
For a long time solar panels there were either bulky panels of satellites and space stations, or low-power photocells of pocket calculators. This was due to the primitiveness of the first monocrystalline silicon solar cells: they not only had low efficiency (no more than 25% in theory, in practice - about 7%), but also noticeably lost efficiency when the angle of incidence of light deviated from 90˚. Considering that in Europe in cloudy weather the specific power of solar radiation can fall below 100 W/m 2, too large areas of solar panels were required to obtain any significant power. Therefore, the first solar power plants were built only in conditions of maximum light output and clear weather, that is, in deserts near the equator.
A significant breakthrough in the creation of photocells has returned interest in solar energy: for example, the cheapest and most accessible polycrystalline silicon cells, although they have lower efficiency than monocrystalline ones, are also less sensitive to operating conditions. A solar panel based on polycrystalline wafers will produce enough stable voltage under partly cloudy conditions. More modern solar cells based on gallium arsenide have an efficiency of up to 40%, but are too expensive to make a solar cell yourself.
The video talks about the idea of building a solar battery and its implementation
Is it worth doing?
In many cases the solar panel will be very useful: for example, the owner of a private house or cottage located far from the power grid can even use a compact panel to keep his phone charged and connect low-power consumers like car refrigerators.For this purpose, ready-made compact panels are produced and sold, made in the form of quickly folded assemblies on a synthetic fabric base. In central Russia, such a panel measuring about 30x40 cm can provide power within 5 W at a voltage of 12 V.
A larger battery will be able to provide up to 100 watts of electrical power. It would seem that this is not so much, but it is worth remembering the principle of operation of small ones: in them the entire load is powered through a pulse converter from a battery of batteries, which are charged from a low-power windmill. This makes it possible to use more powerful consumers.
Using a similar principle when building a home solar power plant makes it more profitable than a wind turbine: in summer the sun shines most of the day, in contrast to the fickle and often absent wind. For this reason, the batteries will be able to charge much faster during the day, and the solar panel itself is much easier to install than one requiring a high mast.
There is also a point in using a solar battery solely as a source of emergency power. For example, if a gas heating boiler with circulation pumps is installed in a private house, when the power supply is turned off, you can power them through a pulse converter (inverter) from batteries that are kept charged from a solar battery, keeping the heating system operational.
TV story on this topic
Solar cells are parts of batteries that generate electric current. They appeared relatively recently, in the 19th century, and only now they have begun to be used as an inexpensive, but effective way extraction of energy resources. The principle of operation of solar panels is quite simple. They can be equipped with residential or non-residential premises. There are different types of these batteries. Let's look at them in more detail.
Solar cell elements
Often, the energy from a solar panel is used for the home and its needs. Produced electric current enough for a two-element boiler system, refrigerator, TV and other household appliances.
The sun's rays are an environmentally friendly “fuel”. After all, during operation, the solar battery module does not emit an abundance of harmful exhausts, carbon dioxide and does not consume irreplaceable natural resources.
It is worth understanding that solar panels are made up of many modules. And what we see on the roof of buildings or on the walls is only part of the system.
What does it consist of? solar system power supply:
- Solar cells folding into panels. These are the batteries visible to us that are mounted on the roof or walls.
- . This element in the system is necessary to accumulate excess energy, for example, on a clear day. In cloudy weather, when the batteries are not operating at full capacity, current for household needs is taken from the battery.
- regulates the battery charge, tells the system owner that there is not enough or too much charge. Excessive voltage is detrimental to the battery.
- Converter DC to AC () is necessary for the operation of household appliances. After all, not all of them are capable of operating on a constant flow of charged particles.
When connecting solar modules, you must initially decide on their location, type, quantity household appliances, the need for an ABK controller.
It is worth understanding that such a system is stackable, and you can easily install more than one solar module.
The principle of operation of solar panels
Humanity has learned to obtain energy from fossils, streams of water and gusts of wind, and has even come to the use of light rays. There are even solar modules that absorb the invisible infrared spectrum and work at night. All-weather batteries are effective in cloudy weather, fog, and rain.
The operating principle of any battery is to convert the sun's rays into an electrical impulse.
Solar modules often operate on silicon crystals, and there is an explanation for this. This metal is sensitive to the effects of rays, it is inexpensive to mine, and amounts to 17-25%. When exposed to sunlight, a silicon crystal produces a directed movement of electrons. With an average battery area of 1-1.5 m², an output voltage of 250 W can be achieved.
Currently, not only silicon is used, but also compounds of selenium, copper, iridium and polymers. But they are not widely used, even despite the efficiency of 30-50%. This is because they are very expensive. For the electrification of an ordinary country house or country house A silicon photovoltaic panel would work well.
Types of solar panels
Such batteries are constantly being modified. This area is being modified and subject to innovative solutions.
This is why there are many types of solar panels.
Monocrystalline
These batteries have good efficiency. Each cell is a separate silicon crystal. The surface of the battery is slightly convex and deep blue. Photovoltaic panels of this type have the most high price, which is determined by the complexity of the technology. After all, all the crystals are turned in the same direction.
Additional equipment will be needed that will deploy the complex of panels depending on the position of the Sun on the horizon. Due to the need for direct rays, such elements are installed in well-lit areas or hills.
The average service life is 25 years.
Polycrystalline (multi-Si)
Solar modules of this type have an unevenly saturated blue color due to the different orientations of the silicon crystals. They are cheaper than their analogues, have good efficiency, and do not need to be turned towards the sun. In cloudy or cloudy weather they show better results than the type described above.
The average service life without loss of quality is 15-20 years.
Amorphous (polymer solar cells)
In this case, not solid crystals are used, but silicon hydride. It is applied to a solid or flexible substrate. The advantages are low cost. In addition, the polymer solar cell can be applied to any flexible substrate. This means you can make the most of the roof slope and uneven surfaces.
The photovoltaic structure of polymer silicon allows it to absorb even scattered light. It is advantageous to install in northern conditions, short daylight hours, and in areas with aggressive atmospheric conditions.
There are other, rarer varieties.
Organic
These solar panels are just being studied. Active developments appeared in the last decade, so manufacturers do not have reliable data on the guaranteed service life. The solar cell uses an organic base - carbon compounds.
Some types of solar panels of this structure have good efficiency, they are plastic, environmentally friendly, easy to recycle and much cheaper than silicon analogues.
Silicon-free
Made from rare metals. Instead of silicon, compounds of tellurium, selenium, copper, and indium are used. These metals are rare and expensive, so the cost of batteries is very high. However, this type of panel can operate over a wide temperature range.
Comparison of efficiency of batteries of different types
How to choose a solar panel?
As you can see, the types of solar panels are different.
It is necessary to select a device based on many factors:
- degree of illumination of the territory;
- climate;
- room area;
- number of household appliances;
- financial budget;
- roof area;
- possibility of using stationary electrical networks;
- distance from a populated area.
Naturally, if you are going to install solar panels at your dacha, where you spend time only in the summer, you should worry about the safety of your property.
If you have long daylight hours and a well-lit area, then give preference to mono- and polycrystalline models. In cold latitudes, purchase polycrystalline or polymer solar cells.
Types of connection
You have already purchased photocells for solar panels, batteries and all other components. All that remains is to decide on the type of power supply for your home. They are:
- Autonomous. In this case, your house is powered only by solar panels and is in no way connected to general electricity.
- Adjacent. The panels are connected to a common network. If Appliances consume a small amount of energy, the landline network is not used, the current is taken from the battery. If demand exceeds, electricity is consumed from shared network. It is worth considering that without a network, the batteries themselves will not work.
- Combined similar to adjacent ones. But in this case, the excess electricity received by the panels does not go to the battery, but to the general network.
Which system and panels to choose is up to you. Before purchasing, consult several specialists, because such systems are purchased for more than one year. At correct connection they will delight you for a long time.
Effectively converting free rays of the sun into energy that can be used to power homes and other facilities is the cherished dream of many green energy apologists.
But the principle of operation of the solar battery and its efficiency are such that there is no need to talk about the high efficiency of such systems yet. It would be nice to have your own additional source of electricity. Is not it? Moreover, even today in Russia, with the help of solar panels, a considerable number of private households are successfully supplied with “free” electricity. Still don't know where to start?
Below we will tell you about the design and operating principles of a solar panel; you will learn what the efficiency of a solar system depends on. And the videos posted in the article will help you assemble a solar panel from photocells with your own hands.
There are quite a lot of nuances and confusion in the topic of “solar energy”. It is often difficult for beginners to understand all the unfamiliar terms at first. But without this, it is unreasonable to engage in solar energy, purchasing equipment for generating “solar” current.
Unknowingly, you can not only choose the wrong panel, but also simply burn it when connecting it or extract too little energy from it.
Image gallery
The maximum return from a solar panel can only be obtained by knowing how it works, what components and assemblies it consists of, and how it is all connected correctly
The second nuance is the concept of the term “solar battery”. Typically, the word “battery” refers to some kind of electrical storage device. Or a banal heating radiator comes to mind. However, in the case of solar batteries the situation is radically different. They do not accumulate anything in themselves.
