The principle of operation and design of a solar battery. Solar panels: how it works

In recent years, so-called “alternative energy” has become increasingly popular. Particular attention is paid to the use of solar radiation. This is quite natural, because if you create an element that is capable of converting light rays into electricity, you can get a free inexhaustible energy source. And such an element was created. It was called a “solar photocell” or “solar battery”, and how it works solar battery, it's pretty easy to figure out.

Operating principle

The main thing is not to confuse photovoltaic batteries with solar collectors (both are often called “solar panels”). If the principle of operation of collectors is based on heating the coolant, then photocells directly produce electricity. Their work is based on the photoelectric effect, which consists in generating current under the influence of sunlight in semiconductor materials.

Semiconductors are substances whose atoms either contain an excess number of electrons (n-type), or, conversely, lack them (p-type). And those areas of the structure of p-elements where electrons could potentially be located are called “holes”. Accordingly, a photocell based on semiconductors consists of two layers with different types of conductivity.

How do solar cells with this structure work? As follows. The inner layer of the element is made of a p-semiconductor, the outer, much thinner one, is made of an n-semiconductor. At the boundary of the layers, the so-called “zone p-n junction a”, formed due to the formation of positive volumetric charges in the n-layer and negative ones in the p-layer.

In this case, a certain energy barrier appears in the transition zone, caused by the difference in charge potentials. It prevents the penetration of major charge carriers, but freely allows minor ones to pass through, and in opposite directions. Under the influence of sunlight, some photons are absorbed by the surface of the element and generate additional “hole-electron” pairs. That is, electrons and holes move from one semiconductor to another, giving them an additional negative or positive charge. In this case, the initial potential difference between the n- and p-layers decreases, and an electric current is generated in the external circuit.

Features of the structure

Many modern photocells have only one p-n junction. In this case, freely transferring charge carriers are generated only by those photons whose energy is either greater than or equal to the width of the “gap” at the transition boundary. This means that photons with lower energy levels are simply not used, which in turn significantly reduces the efficiency of the cell. To overcome this limitation, multilayer (more often four-layer) photostructures were created.

They allow the use of a significantly larger part of the solar spectrum and have higher productivity. Moreover, the photocells are positioned in such a way that the rays hit the junction with the widest bandgap first. In this case, more “energy-intensive” photons are absorbed, while photons with less energy travel deeper and stimulate other elements.

What types of solar panels are there?

Solar cells, the operating principle of which is based on the photoelectric effect, have been created for a long time. The main difficulty in their production is the selection of materials capable of generating a sufficiently powerful current. The first experiments were carried out with selenium cells, but their efficiency was extremely low (about 1%). Nowadays, photovoltaic cells mainly use silicon; the productivity of such devices is about 22%. In addition, new cell samples are constantly being developed (for example, using gallium or indium arsenide) with more high efficiency. The maximum efficiency of solar panels today is 44.7%.

But such elements are very expensive and are so far produced only in laboratory conditions. Cells based on monocrystalline or polycrystalline silicon, as well as thin-film elements, have become widespread. Photobatteries based on monocrystals are more expensive, but have greater performance, while polycrystals are cheaper, but due to their heterogeneous structure, they are less efficient. In the production of thin-film cells, it is not crystals that are used, but silicon layers deposited on a flexible substrate.

Nowadays, almost everyone can assemble and have at their disposal their own independent source of electricity using solar batteries (in the scientific literature they are called photovoltaic panels).

Over time, expensive equipment is offset by the opportunity to receive free electricity. It is important that solar panels are an environmentally friendly source of energy. In recent years, prices for photovoltaic panels have fallen tens of times and they continue to decline, which indicates great prospects when using them.

In its classical form, such a source of electricity will consist of the following parts: directly, a solar battery (DC generator), a battery with a charge control device and an inverter that converts D.C. into variable.

Solar panels consist of a set of solar cells (photovoltaic converters) that directly convert solar energy into electrical energy.

Most solar cells are made from silicon, which is quite expensive. This fact will determine the high cost of electrical energy, which is obtained by using solar panels.

There are two common types of photovoltaic converters: those made of monocrystalline and polycrystalline silicon. They differ in production technology. The former have an efficiency of up to 17.5%, and the latter - 15%.

The most important technical parameter solar battery, which has a major impact on the efficiency of the entire installation, is its useful power. It is determined by voltage and output current. These parameters depend on the intensity of sunlight hitting the battery.

The electromotive force of individual solar cells does not depend on their area and decreases when the battery is heated by the sun, by approximately 0.4% per 1 g. C. The output current depends on the intensity of solar radiation and the size of the solar cells. The brighter sunlight, the more current is generated by the solar cells. The charging current and power output are sharply reduced in cloudy weather. This occurs by reducing the current supplied by the battery.

If a battery illuminated by the sun is connected to any load with resistance Rн, then an electric current I appears in the circuit, the magnitude of which is determined by the quality of the photoelectric converter, the intensity of illumination and the load resistance. The power Pн, which is released in the load, is determined by the product Pн = InUn, where Un is the voltage at the battery terminals.

The greatest power is released in the load at a certain optimal resistance Ropt, which corresponds to the highest efficiency of converting light energy into electrical energy. Each converter has its own Ropt value, which depends on the quality, size of the working surface and degree of illumination.

A solar cell consists of individual solar cells that are connected in series and parallel to increase the output parameters (current, voltage and power). At serial connection elements, the output voltage increases, and in parallel, the output current increases.

In order to increase both current and voltage, these two connection methods are combined. In addition, with this connection method, the failure of one of the solar cells does not lead to the failure of the entire chain, i.e. increases the reliability of the entire battery.

Thus, a solar battery consists of parallel-series connected solar cells. The maximum possible current supplied by the battery is directly proportional to the number of parallel connected ones, and electromotive force- series-connected solar cells. So, by combining connection types, a battery with the required parameters is assembled.

The solar cells of the battery are shunted by diodes. Usually there are 4 of them - one for each ¼ of the battery. Diodes protect parts of the battery from failure that for some reason are darkened, that is, if at some point in time the light does not fall on them.

The battery temporarily generates 25% less output power than with normal sun illumination of the entire surface of the battery.

In the absence of diodes, these solar cells will overheat and fail, since during darkening they turn into current consumers (the batteries are discharged through the solar cells), and when diodes are used, they are shunted and no current flows through them.

The resulting electrical energy is stored in batteries and then transferred to the load. Batteries are chemical sources of current. The battery is charged when a potential is applied to it that is greater than the battery voltage.

The number of solar cells connected in series and parallel must be such that the operating voltage supplied to the batteries, taking into account the voltage drop in the charging circuit, slightly exceeds the battery voltage, and the load current of the battery provides the required amount of charging current.

For example, to charge a 12 V lead battery, you need to have a solar battery consisting of 36 cells.

In weak sunlight, the battery charge decreases and the battery loses power electrical energy electrical receiver, i.e. Rechargeable batteries constantly operate in discharge and recharge mode.

This process is controlled by a special controller. Cyclic charging requires a constant voltage or constant charging current.

When there is good lighting, the battery is quickly charged to 90% of its rated capacity, and then at a slower charge rate to full capacity. Switching to a lower charging rate is performed by the charger controller.

The most effective use of special batteries is gel batteries (the battery uses sulfuric acid as an electrolyte) and lead batteries, which are made using AGM technology. These batteries do not require special installation conditions and do not require maintenance. The certified service life of such batteries is 10 - 12 years with a discharge depth of no more than 20%. Batteries should never be discharged below this value, otherwise their service life will be drastically reduced!

The battery is connected to the solar panel through a controller that controls its charge. When charging the battery to full power A resistor is connected to the solar panel, which absorbs excess power.

In order to convert DC voltage from the battery into alternating voltage, which can be used to power most electrical receivers, together with solar batteries, you can use special devices - inverters.

Without using an inverter, a solar battery can power electrical receivers operating on constant voltage, incl. various portable equipment, energy-saving light sources, for example, the same LED lamps.

Author of the text: Andrey Povny. The text was first published on the website Electrik.info. Reprinted with the consent of the editors.

Quite often, those who live in their own home have to face the fact that electricity is turned off due to technical reasons or due to emergency. Such problems cause not only discomfort, but also many problems, for example, food spoils, it is impossible to do work if this requires the use of electrical appliances. What to do in such a situation? It is worth installing solar panels, which allow you to solve this problem as quickly as possible and can only deliver benefits and nothing more.

A solar battery (or panel) is a battery (called a photoplate) that changes its conductivity and releases energy when exposed to sunlight. It is precisely this transformation that will enrich the residential structure necessary electricity. As a rule, solar panels have different types.

The following designs are available for sale:

Monocrystalline;
Polycrystalline;
Amorphous.

Each design has a certain performance, which directly determines the principle of operation and price. The plate with the minimum power is considered to be a battery made on the basis of monocrystals, and they also have the lowest price. Basically, they try to use them in conditions where a constant supply of electricity is not too important.

The owner of a private home and such batteries must carefully ensure that the photovoltaic panel is clean, since if it gets on its coating large number contaminants such as snow, bird droppings and even dry leaves, this will reduce the operating efficiency and reduce the voltage level supplied. A solar battery for a home works according to a special principle.

Namely:

The sun's energy is captured by a silicon-based plate.
When heated, energy is released.
Next, electrons are activated, which facilitates their movement along the conductor.
The conductors direct the current into the battery cavity, this forms a kind of recharging.
Through wired connection, current flows to household appliances.

The principle of operation of the installation is quite clear, but it is worth familiarizing yourself with the features of battery maintenance and whether it is required at all. Initially, it should be noted that the solar battery has no moving part at all, since these are stationary structures.

How to maintain a solar battery to work

As a rule, cleaning the coating should be done once every 7 days. Experts believe that this is quite enough to maintain the optimal condition of the plates in their pure form. It is also necessary to carry out a number of other procedures; this will allow the panels to be operated without problems, as well as to eliminate the formation of defects and malfunctions.

Mandatory:

External inspection to identify loose fasteners and the formation of cracks in the frame.
Cleaning the panel.
Check the power cable for exposed wires, which could cause a fire.
Monitoring and recording the state of automation and instrumentation indicators.
Battery charge level tracking.
Monitoring the condition of the structural components of the block to identify corrosive formations.
Inspecting the strength of the panel casing.

Adjustments to the position of the structure are also necessary, depending on the time of year, and tightening of each threaded connection. In addition, you can water the panels with a hose using ordinary running water, for which 4 procedures per year are enough.

You can assemble a safe and efficient wind generator with your own hands. All stages of work are described on the following page:

Efficiency of solar panels and other parameters

Solar panels are made from a material such as silicon, and when purchasing, you should pay attention to such features as the presence of an efficiency indicator, which should exceed 20%, high level resistance.

Availability tempered glass, resistance to the harshest weather conditions, polycrystalline coating is necessary if the product is installed in a region with hot temperatures.

Monocrystalline coating is important for areas with unfavorable climatic conditions. Modern silicon solar cookers have a number of advantages. Those who already use similar installations respond extremely positively.

The following products are recognized:

Autonomous;
Maximum cost-effective, as there is no need to pay for electricity;
Very convenient to use, as no adjustment is needed;
Profitable, since the resource is replenished automatically;
Environmental;
Safe;
Practical, as they can be used as a reserve or main;
Very durable.

There are some disadvantages, but against the backdrop of many positive qualities they can be called insignificant. These include high cost, low resistance to weather disasters, the need to prepare a site for the location of the structure, maintenance, decreased productivity in winter, the need for modernization, if necessary, increase power and, accordingly, productivity.

Types of solar panels

Monocrystalline products are recognized as the most affordable products for capturing solar energy, since they are made using the simplest technology and in terms of power they can be significantly inferior to other types of plates. Each type has its own characteristics, due to which their choice is made.

There are three types of solar cookers:

Monocrystalline;
Polycrystalline;
Amorphous.

Panels made from polycrystalline silicon are the most expensive products, as they can accumulate solar energy even in cloudy and cloudy weather. Their peculiarity is high performance, as well as slow cooling of the silicon melt. After the canvas has completely cooled, it is subjected to repeated heat treatment.

These plates are available in dark blue.

If amorphous silicon is used to make a slab, then these are products that are not produced in large quantities. These designs are at the stage of improvement and modernization, as some test models have gone on sale.

What are solar panels mainly made of?

Many owners think that if they have created such equipment on their own, then to do this they just need to follow the technology for assembling the system, but they must also meet the high requirements.

The composition of elements for capturing solar energy is very simple, since all structures consist of:

Solar module;
Controller;
Battery;
Inverter;
Primary converter;
Set of wires;
Devices capable of monitoring battery charge;
Devices for taking power from the battery.

In addition, the plates may contain polymer film roll coatings, which are needed to protect against exposure external factors. A solar panel is designed to capture the sun's rays and convert them into electricity.

Solar battery design and design nuances

As soon as all the necessary devices, as well as materials and equipment have been purchased, the actual construction can begin. Anyone who came up with and independently invented a solar battery necessarily began with a design that took into account important points.

Namely:

Location of the structure.
Product tilt angle.
Calculation of the load-bearing capacity of the roof if the installation will be carried out on the roof itself, and not on the walls or foundation of the house.

An aluminum corner is used for the frame, the thickness of which must be at least 35 mm. The volume of cells must completely match the number of photocells. For example, 835x690 mm. Holes for hardware are made in the frame. Apply 2 layers of sealant to the inside of the corner. The frame is filled with plexiglass, polycarbonate, plexiglass or any other material.

In order to seal the seams between the frame and the material sheet, you will need to carefully press the sheet along the entire perimeter.

The product is left outdoors until completely dry. The glass is fixed at 10 points, in pre-prepared holes, which should be located in the corner of the frame and on each side. Before attaching photocells, you need to clean the surface from dust. Next, the wire is soldered to the tile, for which the contacts are first wiped with an alcohol solution and placed under flux. When working with a crystal, you should be as careful as possible, as its structure is too fragile.

The busbar is laid along the entire length of the contact and slowly warmed up using a soldering iron. Next, the plates need to be turned over and the same actions performed. Then the photocells are laid out on the surface of the plexiglass in a frame, and they are fixed to the mounting tape. As a fixative, ordinary silicone glue can be used, which is applied in a dotted manner. One small drop is enough, as it is very durable.

The arrangement of the crystals should be with gaps between them of 3-5 mm, so that when heated under the influence of ultraviolet rays there is no deformation of the surface. It is imperative to connect the conductor along the edges of the photocells to the cavity of the common busbars. The soldering quality is tested using a special device. To seal the panel, sealant is applied between the panels. It is necessary to carefully press down the sheets to ensure maximum adhesion to the glass. The edges of the frame are also coated with sealant.

The side of the frame is equipped with a connecting connector for connecting Schottky diodes. The frame is covered with glass for protection and the joints are also sealed to prevent moisture from penetrating into the structure. The front side needs to be varnished. The panel is installed on the roof, walls or any other place designated in advance for it.

Solar Panel Efficiency

As already noted, there are different types solar panels and each of them has its own characteristics. It is worth noting that there are also hybrid designs for capturing solar energy, but their cost is much higher, and they are mainly used for industrial buildings.

Naturally, the quality and performance of any solar battery directly depends on the efficiency of its photocells, which can be influenced by factors such as:

Climatic conditions;
Weather;
Length of day and night;
Panel illumination uniformity;
Changes in air temperature;
Presence of dirt on the plastic;
Irreversible losses.

Basically, the efficiency or, in other words, the performance of solar panels directly depends on the uniformity of illumination of the structure. For example, if one of the solar cells of a structure has a low lighting intensity, unlike the others, this will cause an uneven distribution of the sun's rays when hitting the panel, which means there will be an overload and a decrease in the overall energy output.

To reduce the influence of such a factor, in some cases the photocell that fails is simply turned off.

To provide solar battery maximum performance, you should point it exactly at the sun, depending on the time of year. Some owners of such structures prefer to install special installations, through which it is possible to remotely control or, in other words, turn the structure in the desired direction. There are systems with automatic rotation depending on the location of the sun, which move independently during the day without outside help according to a given program.

In addition, the efficiency of the product can be affected by the presence of dust and dirt on the plate, since some solar cells darken and thus begin to unevenly distribute solar energy, as described earlier. There is a special composition on sale that can be used to coat the surface of a solar battery and thereby prevent the accumulation of various types of pollutants on it.

How a solar battery works (video)

A solar battery is an expensive piece of equipment, regardless of whether it is assembled yourself or purchased ready-made, and the need for constant maintenance can cause discomfort, but once you have invested in this product, you can be content with the constant presence of electricity and the absence of fees for a long time him.

All life on earth arose thanks to the energy of the sun. Every second, a huge amount of energy enters the surface of the planet in the form of solar radiation. While we burn thousands of tons of coal and petroleum products to heat our homes, countries located closer to the equator are sweltering in the heat. Using the energy of the sun for human needs is a task worthy of inquiring minds. In this article we will look at the design of a direct converter of sunlight into electrical energy - a solar cell.

The simplest design of a solar cell (SC) based on monocrystalline silicon is shown in the figure.

A thin wafer consists of two layers of silicon with different physical properties. The inner layer is pure monocrystalline silicon with “hole conductivity” (p-type). On the outside, it is coated with a very thin layer of “contaminated” silicon, for example with an admixture of phosphorus (n-type). (About p-, n- and p-n types see article on diodes). A continuous metal contact is applied to the back side of the plate. U n-and boundaries p-layers, as a result of charge flow, depleted zones are formed with an uncompensated volumetric positive charge in the n-layer and a volumetric negative charge in the p-layer. These zones together form a p-n junction.

The potential barrier (contact potential difference) that appears at the transition prevents the passage of the main charge carriers, i.e. electrons from the p-layer side, but freely allow minority carriers to pass in opposite directions. This property of p-n junctions determines the possibility of obtaining photo-emf when irradiating a solar cell with sunlight. When the SC is illuminated, the absorbed photons generate nonequilibrium electron-hole pairs. Electrons generated in the p-layer near the p-n junction approach the p-n junction and those existing in it electric field are transferred to the n-region.

Similarly, excess holes created in the n-layer are partially transferred to the p-layer (Fig. a). As a result, the n-layer acquires an additional negative charge, and the p-layer acquires a positive charge. The initial contact potential difference between the p- and n-layers of the semiconductor decreases, and voltage appears in the external circuit (Fig. b). The negative pole of the current source corresponds to the n-layer, and the p-layer to the positive one.

Most modern solar cells have a single pn junction. In such an element, free charge carriers are created only by those photons whose energy is greater than or equal to the band gap. In other words, the photovoltaic response of a unijunction cell is limited to the part of the solar spectrum whose energy is above the bandgap, and lower energy photons are not used. Multilayer structures of two or more solar cells with different band gaps can overcome this limitation. Such elements are called multi-junction, cascade or tandem. Because they work with a much larger portion of the solar spectrum, their photovoltaic conversion efficiency is higher. In a typical multijunction solar cell, single solar cells are arranged one behind the other in such a way that sunlight hits the cell with the largest bandgap first, and the highest energy photons are absorbed.

Photons transmitted by the top layer penetrate into the next element with a smaller bandgap, etc. The main direction of research in the field of cascade cells involves the use of gallium arsenide as one or more components. The conversion efficiency of such solar cells reaches 35%! For technological reasons, a single solar cell can only be manufactured in a small size, therefore, for greater efficiency, several cells are combined into batteries.

Solar batteries have proven themselves in space as a fairly reliable and stable source of energy, capable of very long time. The main danger to solar cells in space is cosmic radiation and meteor dust, which cause erosion of the surface of silicon cells and limit the life of the batteries. For small inhabited stations, this current source will apparently remain the only acceptable and sufficiently effective one.

Sunlight not only makes life on Earth possible, it may eventually also provide large quantity electricity, without which modern civilization is unthinkable. The use of sunlight may not be direct, but in the form of energy supply to turbines.

In this case, a set of mirrors focuses solar energy onto a heat exchanger, which evaporates water or any other liquid, producing steam to drive a conventional turbine connected to a generator. However, it is also possible to directly convert sunlight into electricity, for example using silicon solar cells.

A typical solar cell consists of six layers. The base (base) simultaneously serves as the negative pole of the element; the reflective layer retains light inside the working part of the element, increasing its electrical efficiency; two layers of enriched silicon (N-type and P-type) form the core of the solar cell. N-type silicon has free negative charges, while P-type silicon has free positive charges. In the absence of illumination, these charges accumulate in the contact zone of the layers; When sunlight hits an element, the charges move apart. This movement of charges creates a direct current if the solar cell is part of a closed circuit. On top, the silicon is protected by a transparent film on which a metal contact of the positive pole is placed.

How does a solar cell work?

Sunlight falling on a solar cell cell separates positive and negative charges, which accumulate in the contact zone between P-type and N-type silicon wafers. This separation creates a voltage, under the influence of which, when an element is connected to a closed circuit, an electric current begins to flow in it

Sectional solar panels

Solar panels (picture above text) produce direct current, which can be converted to alternating current at a power plant. Excess electricity generated by solar cells can be stored in batteries for later use.

Solar panels in space

For most space satellites, solar panels are the main source of energy. These batteries (picture on the right) are different from those used on Earth (picture on the left). If batteries installed near the earth's surface need protection from rain and dust, then those operating in space must be protected from hard cosmic radiation.

Solar Thermal Power Plant

Sunlight can provide heat to a steam turbine unit that drives a generator. A set of mirrors focuses sunlight onto the concentrator tower. The resulting light beam is so intense that it can convert sodium into vapor. Sodium vapor is used to convert water into steam, which then drives a turbine.