How solar panels work. Solar battery - how it works

Alternative energy sources that convert sunlight into electricity are becoming more and more popular in everyday life and industry. They are used in aviation, space development, electronics, and to create environmentally friendly transport. But the most promising branch is considered to be the power supply of buildings: power supply of household appliances and home heating systems, heating of hot water. The advantages include: independence from the season and utilities, the ability to accumulate energy reserves, reliability and long service life. But in order to achieve the maximum effect from the application, it is important to know the principle of operation of the batteries and observe the conditions for their installation and operation.

Photovoltaic converters or solar storage batteries are a plate with semiconductor properties that generates direct current when light rays strike it. The base can be silicon (the most common type) and its compounds with copper, gallium, cadmium, indium, amphora, organic or chemical solar cells, polymer film.

Each material has its own FEP coefficient of sunlight (from 5 to 30%) and, as a result, generates a certain power with an equal intensity of light flux. Much depends on the area of ​​the battery, a single semiconductor crystal produces a negligible amount of energy, on average, 1 m2 of a panel is required to obtain 0.15 kW. The exception is innovative multilayer polymer compounds (single crystals), their efficiency reaches 30%, but this technology is not yet available to the average consumer.

In addition to the plate, the solar battery circuit includes auxiliary devices (for transmission, distribution and storage of energy):

• Inverter or DC / DC converter.
• Storage for uninterrupted operation of the system at night or in cloudy weather.
• Voltage regulator.
• Controller for tracking charge.

Depending on the area, miniature low-power batteries (up to 10 W) or large stationary panels are used. The former are portable (popular for charging a laptop, calculator, mobile devices). The latter are more often used for power supply and heating of the house; they are usually located on the roof. Since the power of the batteries is fully proportional to the solar intensity, it became advisable to place tracking panels (changing the angle of the location, depending on the movement of the Sun). The thickness of the semiconductor options is insignificant (from 10 microns to 10 cm), but taking into account the auxiliary devices, the modules weigh more, which is taken into account when calculating the load on the rafters and the roof surface.

Photoelectric conversion principle

In order to understand how a solar battery works, one should recall the school physics course. When light hits a plate of two layers of semiconductors of different conductivity, the p-n transition effect occurs, electrons from the cathode leave their atoms and are captured at the level of the anode. When a load (battery) is connected to the circuit, they give up their positively charged energy and return to the n-layer. This phenomenon is better known as "external photoelectric effect" and the double layer plate as "photocell". Most often, the same material is used: a base semiconductor with a certain type of conductivity is covered with a layer with an opposite charge, but with a high concentration of dopants.

This principle of operation of solar cells has not changed since the discovery of the effect; it is at the boundary of the bands that the electron-hole transition occurs. When exposed to sunlight, the movement of differently charged particles passes in both directions; when the FEP circuit is closed, they work on the load. For a full-fledged transfer (collection and removal of electrons), a contact system is used (the outer side of the battery resembles a grid or comb, and the back is usually solid). The higher the p-n junction area and the photoelectric conversion factor of the semiconductor, the more power the device produces. The physical phenomenon and the principle of operation do not depend on the air temperature, only the intensity of sunlight is important. As a result, the panel's efficiency is influenced by weather conditions, climate, season, latitude.

Ways to Improve Battery Performance

Even in central Russia, the installation of solar batteries pays off in 3-5 years, because the rays are absolutely free and available all year round. But for full heating of a house of 100 m2 of usable area, about 30 m2 of panels will be required. To enhance the principle of the photoelectric effect, it is recommended to carry out the following work:

1. Place batteries on the south side at an angle of at least 30 °.
2. Do not mount solar panels under the shade of tall trees.
3. Clean the surface from dirt every 2 years.
4. Install solar tracking systems.

It is not worth completely abandoning external power supply, even modern complexes are not able to accumulate enough energy to fully supply the building during prolonged bad weather. It is best to use them as part of a combined system.

Sunlight not only makes life possible on Earth, it can, over time, also become a supplier of large amounts of electricity, without which modern civilization is unthinkable. The use of sunlight may not be direct, but in the form of supplying energy to the turbines.

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

A typical solar cell has six layers. The base (base) simultaneously serves as the negative pole of the element; the reflective layer keeps 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 unbound positive charges. In the absence of illumination, these charges accumulate in the contact zone of the layers; when sunlight falls on the element, the charges diverge to the sides. This movement of charges creates a constant current if the solar cell is part of a closed circuit. The top of the silicon is protected by a transparent film on which the metal contact of the positive pole is placed.

How the solar cell works

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

Sectional solar panels

Solar panels (picture above the text) generate direct current, which can be converted into alternating current in a power plant. Surplus 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 that operate in space must be protected from harsh cosmic radiation.

Solar thermal power plant

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

With constantly rising electricity prices, you will inevitably begin to think about using natural sources for power supply. One of these possibilities is solar panels for a home or summer cottage. If desired, they can fully meet all the needs of even a large house.

Solar Power System Design

Converting the energy of the sun into electricity - this idea did not let scientists sleep for a long time. With the discovery of the properties of semiconductors, this became possible. Solar cells use silicon crystals. When sunlight hits them, a directed movement of electrons is formed in them, which is called an electric current. When connecting a sufficient number of such crystals, we get quite decent currents: one panel with an area of ​​slightly more than a meter (1.3-1.4 m2 with a sufficient level of illumination can produce up to 270 W (voltage 24 V).

Since the illumination varies depending on the weather, time of day, it is impossible to directly connect the devices to solar panels. You need a whole system. In addition to solar panels, you need:

• Battery. During the daylight hours, under the influence of sunlight, solar panels generate electric current for the house, summer cottage. It is not always used in full, its surplus accumulates in the battery. The stored energy is wasted in inclement weather.
• Controller. Not an obligatory part, but a desirable one (with sufficient funds). Monitors the battery charge level to prevent over-discharge or over-charge. Both of these conditions are detrimental to the battery, so the presence of a controller extends the life of the battery. Also, the controller ensures optimal operation of solar panels.
• DC-to-AC converter (inverter). Not all devices are rated for direct current. Many operate on 220 volts alternating voltage. The converter makes it possible to obtain a voltage of 220-230 V.

Solar panels for home - only part of the system

By installing solar panels for your home or summer cottage, you can become completely independent from the official supplier. But for this you need to have a large number of batteries, a certain number of accumulators. A kit that generates 1.5 kW per day costs about $ 1000. This is enough to meet the needs of the summer cottage or part of the electrical equipment in the house. A set of solar panels for the production of 4 kW per day costs about $ 2200, for 9 kW per day - $ 6200. Since solar panels for a home are a modular system, you can buy an installation that will provide part of the needs, gradually increasing its performance.

Types of solar panels

With the rise in energy prices, the idea of ​​using solar energy to generate electricity is becoming more and more popular. Moreover, with the development of technologies, solar converters are becoming more efficient and, at the same time, cheaper. So, if you wish, you can provide your needs by installing solar panels. But they are of different types. Let's figure it out.

The solar battery itself is a number of photocells, which are located in a common housing, protected by a transparent front panel. For household use, solar cells are produced on the basis of silicon, since it is relatively inexpensive, and cells based on it have a good efficiency (about 20-24%). Monocrystalline, polycrystalline and thin-film (flexible) photocells are made on the basis of silicon crystals. A number of these photocells are electrically connected to each other (in series and / or in parallel) and brought out to terminals located on the body.

The photocells are installed in a closed housing. The solar cell body is made of anodized aluminum. It is lightweight and does not corrode. The front panel is made of durable glass, which must withstand snow and wind loads. In addition, it must have certain optical properties - have maximum transparency in order to transmit as many rays as possible. In general, due to reflection, a significant amount of energy is lost, so the requirements for the quality of the glass are high and it is also coated with an anti-reflective compound.

Types of solar cells

Solar panels for the home are made on the basis of three types of silicon cells;

If you have a pitched roof and the facade is turned to the south or east, it does not make sense to think too much about the occupied area. Polycrystalline modules can quite suit. With the same amount of energy produced, they cost a little less.

How to choose the right solar panel system for your home

There are common misconceptions that lead you to spend extra money on overpriced equipment. Below are recommendations on how to properly build a solar power system and not spend extra money.

What to buy

Not all components of a solar power plant are vital for operation. Some parts are quite possible to do without. They serve to improve reliability, but without them the system is functional. The first thing to remember is to buy solar panels in late winter, early spring. Firstly, the weather at this time is excellent, there are many sunny days, the snow reflects the sun, increasing the overall illumination. Secondly, discounts are traditionally announced at this time. Further tips are as follows:

If you use only these tips, and connect only appliances that operate on constant voltage, a solar panel system for your home will cost a much more modest amount than the cheapest kit. But that's not all. You can also leave some of the equipment "for later" or do without it altogether.

What you can do without

The cost of a set of solar panels for 1 kW per day is more than a thousand dollars. Considerable investment. Involuntarily you will wonder whether it is worth it and what the payback period will be. With current tariffs, it will take more than one year to wait until your money is repaid. But costs can be reduced. Not at the expense of quality, but at the expense of a slight decrease in the comfort of using the system and due to a reasonable approach to the selection of its components.

So, if the budget is limited, you can get by with a few solar panels and batteries, the capacity of which is 20-25% higher than the maximum charge of solar panels. For health monitoring, buy a car clock that still measures voltage. This saves you the need to measure the battery charge several times a day. Instead, you will need to look at the clock from time to time. That's all for the start. In the future, you can buy solar panels for your home, increase the number of batteries. If you wish, you can buy an inverter.

Determine the size and number of photocells

A good 12 volt solar cell should have 36 cells, and a 24 volt battery should have 72 photocells. This amount is optimal. With fewer photocells, you will never get the stated current. And this is the best option.

Do not buy dual solar panels - 72 and 144 cells, respectively. Firstly, they are very large, which is inconvenient for transportation. Secondly, at abnormally low temperatures, which we have periodically, they are the first to fail. The fact is that the laminating film greatly decreases in size during frost. On large panels, due to the high tension, it peels or even tears. Transparency is lost, performance drops catastrophically. The panel is being repaired.

Second factor. Large panels should have more thickness of the case and glass. After all, windage and snow loads increase. But this is not always done, since the price increases significantly. If you see a double panel, and the price for it is lower than the two "regular" ones, you better look for something else.

Once again: the best choice is a 12 volt solar panel for your home, consisting of 36 solar cells. This is the best option, proven by practice.

Specifications: what to look for

The certified solar panels always indicate the operating current and voltage, as well as the open circuit voltage and short-circuit current. It should be borne in mind that all parameters are usually indicated for a temperature of + 25 ° C. On a sunny day on the roof, the battery heats up to temperatures well above this figure. This explains the higher operating voltage.

Also pay attention to the open circuit voltage. In normal batteries, it is about 22 V. And all would be fine, but if you carry out work on the equipment without disconnecting the solar panels, the open circuit voltage will damage the inverter or other connected equipment that is not designed for such a voltage. Therefore, for any work - switching wires, connecting / disconnecting batteries, etc. and so on - the first thing you should do is turn off the solar panels (remove the terminals). After going through the circuit, connect them last. This procedure will save you a lot of nerves (and money).

Body and glass

Solar panels for home have an aluminum casing. This metal does not corrode, with sufficient strength it has a small mass. A normal body should be assembled from a profile in which at least two stiffeners are present. In addition, the glass must be inserted into a special groove, and not fixed from above. These are all signs of normal quality.

Even when choosing a solar panel, pay attention to glass. In normal batteries, it is textured rather than smooth. To the touch - rough, if you hold your nails, you can hear a rustle. In addition, it must have a high-quality coating that minimizes glare. This means that nothing should be reflected in it. If the reflections of the surrounding objects are visible at least from any angle, it is better to find another panel.

Selection of cable cross-section and subtleties of electrical connection

It is necessary to connect solar panels for the home with a single-core copper cable. The cross-section of the cable core depends on the distance between the module and the battery:

• distance less than 10 meters:
  • 1.5 mm2 per 100 W solar panel;
  • for two batteries - 2.5 mm2;
  • three batteries - 4.0 mm2;
• distance more than 10 meters:
  • to connect one panel, we take 2.5 mm2;
  • two - 4.0 mm2;
  • three - 6.0 mm2.

You can take a larger section, but not less (there will be big losses, but we don't need it). When buying wires, pay attention to the actual cross-section, since today the declared dimensions very often do not correspond to the actual ones. To check, you will have to measure the diameter and read the section (you can read how to do this).

When assembling the system, you can carry out the advantages of solar panels using a multicore cable of a suitable cross-section, and for a minus use one thick one. Before connecting to the batteries, we pass all the "pluses" through diodes or diode assemblies with a common cathode. This prevents the battery from shorting out (could cause a fire) if the wires between the batteries and the battery are shorted or broken.

Diodes use SBL2040CT, PBYR040CT types. If they are not found, they can be removed from the old power supplies of personal computers. There are usually SBL3040 or similar. It is desirable to pass through diodes. Do not forget that they get very hot, so you need to mount them on a radiator (you can use a single one).

The system also needs a fuse box. One for each consumer. We connect the entire load through this block. First, the system is safer this way. Secondly, if problems arise, it is easier to determine its source (by a blown fuse).

Recently, technologies for obtaining alternative energy have been actively developing. These are solar panels (SB), wind stations and a number of other devices. Particularly promising are SB or the so-called photovoltaic panels, because, given the almost eternal life of the sun, such energy is inexhaustible. Despite their still relatively high cost, they provide free and environmentally friendly energy. Nevertheless, the prices for SB are declining from year to year, which indicates that there are great prospects for their widespread implementation.

Solar array device

A solar battery is a system of semiconductor devices in the form of photoelectric converters that convert the sun's energy into direct electric current using the principle of the photoelectric effect.

1 - Controller
2 - Battery
3 - Inverter
4 - Module
5 - Electrical equipment

The solar cell includes the following elements:

• , consisting of two layers of materials with different conductivity. For example, it can be polycrystalline or monocrystalline silicon with the inclusion of other chemical compounds to create the principle of the pn junction photoelectric effect. That is, one material has a lack of electrons, while the other has an excess of them.
• , the thinnest layer of the element that resists the transition of electrons.
• ... When connected to the opposing layer, the barrier zone is easily overcome by electrons. As a result, an orderly movement of infected particles appears, that is, an electric current.
• ... Provides the accumulation and conservation of energy.
• ... Converts direct current from the solar panel into alternating current.
• ... Provides in the solar battery system the creation of a voltage of the required range.

Operating principle

• Sunlight in the form of photons of light hits the surface of the solar panel.
• When photons collide with the surface of the semiconductor, they transfer energy to the electrons of the semiconductor.
• The electrons knocked out of the semiconductor due to the impact, overcome the protective layer, having additional energy with them.
• As a result, negative electrons pass into conductor n from the p-conductor, and positive electrons perform the opposite maneuver. This transition is facilitated by the electric fields that are currently present in the conductors. Subsequently, they increase the difference and the strength of the charges.

If the battery, illuminated by the sun, is closed to a certain load with resistance R, then the appearance of an electric current I is observed. Its value is determined by the load resistance, the intensity of the illumination and the quality of the photoelectric converter. The power P released in the load is determined by the formula P = I * U, where U indicates the voltage at the battery terminals.

Kinds

Depending on the materials used, solar panels can be:

• Monocrystalline photovoltaic panels. They are effective, but more expensive, the efficiency is 14-16%. Monocrystalline elements have a polygonal shape, as a result of which it is difficult to fill the entire area;
• Amorphous silicon panels. Such batteries exhibit low efficiency in the range of 6-8%. But among silicon converter technologies, they have the cheapest electricity;
• Cadmium telluride panels are made on the basis of film technology. The semiconductor layer is applied in a layer of several hundred micrometers. The efficiency is 11%, but in comparison with silicon batteries, watts of power are tens of percent cheaper;
• Panels based on CIGS semiconductors, which are composed of selenium, gallium, indium and copper. The efficiency of such panels reaches 15%;
• Polymer panels. This is a type of thin-film battery that works like plant photosynthesis. Includes polymer layer, protective layer, flexible backing and aluminum electrodes. Efficiency 5-6%;
• Due to the optimal ratio of efficiency and price, the most common panels are made of polycrystalline photovoltaic cells. Their efficiency reaches 12-14%.

SB can also be conditionally divided into the following types:

• Thin film or flexible (based on cadmium telluride, crystalline and amorphous);
• Hard(from crystalline silicon, sometimes amorphous);
• Unilateral(absorb light on one side);
• Double-sided(absorb light on both sides).

Peculiarities

• The battery charge decreases in weak sunlight, giving electrical energy to the electrical receiver, that is, there is a constant operation in the charging and discharging mode. The control is carried out by a special controller.
• SB does not require any special maintenance work. Only dusting may be required.
• The panels can be used in winter as well, but productivity during this period decreases by one and a half to two times. To prevent snow accumulation on the panels, they should be installed at an angle of 70 degrees on an elevation.
• Solar panels are best suited for stand-alone systems in which there are many household energy-efficient electrical appliances that are not turned on all the time.

Application

Solar panels can be used almost everywhere:

• Electric vehicles.
• Portable electronics.
• Calculators, flashlights, players and so on, that is, wherever you need to recharge the batteries of various consumer electronics.
• Aviation. This is how the Solar Impulse, a solar-powered aircraft, was created.
• Power supply for homes, schools, airports and other buildings. Solar panels are widely used in subtropical and tropical regions where there are many sunny days. They are especially popular in the Mediterranean countries.
• Use in space. SB is placed on the ISS, installed on satellites, space and interplanetary vehicles, and much more.

Advantages and disadvantages

Among the advantages are:

• Environmental friendliness;
• Durability, photocells serve for several decades;
• Simple working principle. Due to this, there are practically no breakdowns in the solar battery;
• Silence;
• The possibility of permanent work;
• No fuel needed;
• General availability;
• The ability to change the power of the system.

Among the disadvantages are:

• Low efficiency. A large area of ​​batteries is needed to meet the needs of even a small family;
• Complexity of system assembly and commissioning;
• Quite high cost of solar panels, as well as low payback of the system.

Perspectives

Humanity's desire for environmental friendliness and the abandonment of oil will lead to the introduction of more and more energy-saving technologies. This means that solar panels will be used everywhere. And the creation of panels with a higher efficiency will allow:

• Equip most buildings with energy panels;
• Mount them in cars, roads, robots and numerous other devices;
• Install them in clothes and even implant them into a person. South Korean scientists have already created a subcutaneous solar cell that is 15 times thinner than a hair. It ensures the smooth operation of devices that are implanted into the body, for example, a pacemaker.

Nowadays, almost everyone can collect and get at their disposal their independent source of electricity on solar panels(in scientific literature they are called photovoltaic panels).

Over time, expensive equipment is compensated by the ability 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 dropped tenfold and they continue to decline, which indicates great prospects for their use.

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

Solar panels consist of a set solar cells (photovoltaic converters) which 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 using solar panels.

There are two types of photovoltaic converters, made from 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 of the solar battery, which has a major impact on the efficiency of the entire installation, is its net power... It is determined by voltage and output current. These parameters depend on the intensity of sunlight falling on the battery.

E.m.s. (electromotive force) of individual solar cells does not depend on their area and decreases when the battery is heated by the sun, by about 0.4% per 1 gram. C. The output current depends on the intensity of solar radiation and the size of the solar cells. The brighter the sunlight, the more current generated by the solar cells. The charging current and power output drop sharply in cloudy weather. It does this by reducing the current delivered by the battery.

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

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

Solar battery consists of individual solar cells that are connected in series and in parallel in order to increase the output parameters (current, voltage and power). When the elements are connected in series, the output voltage increases, with parallel - the output current. In order to increase both current and voltage, these two connection methods are combined. In addition, with such a connection method, the failure of one of the solar cells does not lead to failure of the entire chain, i.e. increases the reliability of the entire battery.

In this way, a solar battery consists of solar cells connected in parallel in series... The value of the maximum possible current given by the battery is directly proportional to the number of parallel connected, and the emf. - solar cells connected in series. Thus, by combining the types of connection, the battery is assembled with the required parameters.

The solar cells of the battery are shunted by diodes. Usually there are 4 of them - one for each ¼ part of the battery. Diodes protect the battery parts from failure, which for some reason turned out to be darkened, that is, if at some point in time the light does not fall on them. The battery temporarily generates 25% less power output than under normal sun exposure of the entire battery surface.

In the absence of diodes, these solar cells will overheat and fail, since they turn into current consumers during blackout (batteries are discharged through solar cells), and when using diodes, they are shunted and no current flows through them. Diodes should be low impedance to reduce the voltage drop across them. For these purposes, Schottky diodes have recently been used.

The resulting electrical energy is accumulated in batteries, and then transferred to the load. - chemical current sources. The battery is charged when a potential is applied to it, which is greater than the battery voltage.

The number of solar cells connected in series and in parallel should 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 battery load current provides the required charging current.

For example, to charge a 12V lead-acid battery, you need a 36-cell solar battery.

In weak sunlight, the battery charge decreases and the battery gives off electrical energy to the electrical receiver, i.e. rechargeable batteries constantly work in the discharge and recharge mode.

This process is monitored. Cyclic charging requires constant voltage or constant charging current.

In good lighting conditions, the battery is quickly charged to 90% of its nominal capacity, and then at a slower rate to full capacity. Switching to a lower charging rate is made by the charger controller.

The most effective use of special batteries - (sulfuric acid is used as an electrolyte in the battery) and lead batteries, which are made using AGM technology. These batteries do not require special installation conditions and require no maintenance. The passport service life of such batteries is 10 - 12 years with a discharge depth of no more than 20%. Batteries must 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 the battery is charged at full power, a resistor is connected to the solar panel and absorbs the excess power.

In order to convert the constant voltage from the storage battery into alternating voltage, which can be used to power most electrical receivers in conjunction with solar panels, you can use special devices -.

Without the use of an inverter, a solar battery can be used to power electrical consumers operating on constant voltage, incl. various portable equipment, energy-saving light sources, for example, the same LED lamps.