The principle of operation of solar panels. Solar panels (batteries) for home Solar batteries device and principle of operation

It would seem that just recently the solar battery was strongly associated with spaceships, orbital stations and lunar rovers. And now, a device capable of extracting electricity from light can be found in any calculator. Moreover, in sun-rich countries with hot summers and mild winters (scientists call them “high insolation countries”), such as Italy, Spain, Portugal, the southern states of the USA, etc. Solar energy is a significant way to save money on electricity and heat supply. Moreover, this saving occurs both on the private initiative of citizens and in the form of mandatory government regulations, such as in Spain.

Attempts to make the energy of the sun work for themselves have been made by mankind for a long time, so according to legend, Archimedes burned the Roman fleet, ordering many mirrors (in another version - shields polished to a shine) to focus sunlight on the sails of Roman galleys. But the attempts to harness the energy of the sun gave noticeable results only in the last century. What are the ways to use solar energy?

How to get electricity

The most obvious way is to convert the light energy of the sun into heat. Strictly speaking, this cannot even be called a transformation, because light and heat have the same nature and differ only in frequency; it would be more correct to talk about heat collection. To collect solar heat, devices are called - (“collector” literally means collector). The principle of their operation is extremely simple - the coolant (water, less often air) is heated in a radiator made of heat-absorbing material. Such devices are widely used for hot water supply to private homes.

Another interesting way to use the energy of the nearest star is suggested to us by nature. Over millions of years of evolution, plants have learned to convert the energy of the sun into the energy of chemical bonds, synthesizing a complex compound - glucose - from simple substances. Anyone who didn’t skip botany at school, of course, guessed that we were talking about photosynthesis. But not everyone thought about the energy essence of this process, which consists precisely in the accumulation of solar energy and its further use (including in winter) for “personal” purposes. That is, we are talking about bioenergy. The real one, and not the one that home-grown magicians talk about. The method of using solar energy according to this operating principle is still awaiting its application in man-made technology.

As mentioned above, the easiest way to use solar energy for personal purposes is to collect thermal energy. However, “easiest” does not always mean “best.” The fact is that thermal energy is, one might say, a “perishable product.” Try to “conserve” the heat or transfer it over long distances. Most likely, the costs will cover all possible benefits. The most convenient type of energy for accumulation and transportation is electricity. It can be assembled in batteries without any problems or transmitted via wires to the place where it will work, with minimal losses. This leads to the third, most common way of using sunlight - converting it into electrical energy.

How it works

The transformation of sunlight occurs in batteries (that is, series-connected groups) of photocells, which have acquired the name “solar batteries.” On what principle do solar panels work?

The heart of a photocell is a silicon crystal. We encounter silicon (more precisely, its oxides) every day - this is the familiar sand. Thus, we can say that a silicon crystal is a giant grain of sand grown in a laboratory. The crystals are cube-shaped and cut into platinum two hundred microns thick (about three to four times the thickness of a human hair).

A thin layer of phosphorus is applied to a silicon wafer on one side, and a thin layer of boron on the other side. Where silicon is in contact with boron, an excess of free electrons appears, and where silicon is in contact with phosphorus, on the contrary, electrons are in short supply, so-called “holes” appear. The junction of media with an excess and deficiency of electrons is called a p-n junction in physics. Photons of light bombard the surface of the plate and knock out excess phosphorus electrons to missing boron electrons. The ordered movement of electrons is electric current. All that remains is to “assemble” it by running metal tracks through the plate. This is how a silicon photocell works in principle.

The power of one photocell plate is quite modest; it is only enough to operate a flashlight bulb. Therefore, individual elements are assembled into battery systems. Theoretically, it is possible to assemble a battery of any power from the elements. The battery is placed on a metal substrate, reinforced to increase strength and covered with glass. It is important that the solar battery converts not only the visible part of the solar spectrum into electricity, but also the ultraviolet part of the solar spectrum, so the glass covering the battery must transmit ultraviolet radiation.

An important advantage of a solar battery is that it uses light, not heat, therefore, unlike a collector, a solar battery can work in winter, as long as clouds do not block the sunlight. There are projects to build huge fields of solar panels in the Arctic and Antarctic that will store energy during the six-month polar day, which occurs in the north in summer and in the south in winter, meaning two giant solar power plants will never be idle at the same time.

This is all in the long term, but you can benefit from the properties of a solar battery today by equipping your home with a miniature solar power plant. Such a station, of course, is unlikely to be able to fully satisfy the household’s electricity needs, but, without a doubt, it will become a sensitive factor in saving the family budget.

Solar batteries are already used to power a wide variety of equipment: from mobile gadgets to electric vehicles. You will learn from this article how they work, what they are and what modern solar batteries are capable of.

History of creation

Historically, solar panels are humanity’s second attempt to harness the limitless energy of the Sun and make it work for its own benefit. The first to appear were solar collectors (solar thermal power plants), in which electricity is generated by water heated to boiling point under concentrated sunlight.

Solar panels produce electricity directly, which is much more efficient. With direct transformation, significantly less energy is lost than with multi-stage transformation, as with collectors (concentration of solar rays, heating of water and release of steam, rotation of the steam turbine and only at the end the generation of electricity by a generator).

Modern solar panels consist of a chain of photocells - semiconductor devices that convert solar energy directly into electrical current. The process of converting solar energy into electrical current is called the photoelectric effect.

This phenomenon was discovered by the French physicist Alexandre Edmond Becquerel in the mid-19th century. The first working photocell was created half a century later by the Russian scientist Alexander Stoletov. And already in the twentieth century, the photoelectric effect was quantitatively described by Albert Einstein, who requires no introduction.

Principle of operation

A semiconductor is a material whose atoms either have extra electrons (n-type) or, conversely, lack them (p-type). Accordingly, a semiconductor photocell consists of two layers with different conductivities. An n-layer is used as a cathode, and a p-layer is used as an anode.

Excess electrons from the n-layer can leave their atoms, while the p-layer captures these electrons. It is the rays of light that “knock out” electrons from the atoms of the n-layer, after which they fly into the p-layer to occupy empty spaces. In this way, electrons run in a circle, leaving the p-layer, passing through the load (in this case, the battery) and returning to the n-layer.

The first photovoltaic material in history was selenium. It was with its help that photocells were produced at the end of the 19th and beginning of the 20th centuries. But given the extremely low efficiency (less than 1 percent), they immediately began to look for a replacement for selenium.

Mass production of solar cells became possible after the telecommunications company Bell Telephone developed a silicon-based solar cell. It still remains the most common material in the production of solar cells. True, purifying silicon is an extremely expensive process, and therefore little by little alternatives are being tried: compounds of copper, indium, gallium and cadmium.

It is clear that the power of individual photocells is not enough to power powerful electrical appliances. Therefore, they are combined into an electrical circuit, thereby forming a solar battery (another name is a solar panel).

Photocells are attached to the frame of the solar battery in such a way that in case of failure they can be replaced one at a time. To protect against external factors, the entire structure is covered with durable plastic or tempered glass.

Existing varieties

Solar batteries are classified according to the power of electricity generated, which depends on the area of the panel and its design. The power of the solar rays at the equator reaches 1 kW, while in our area in cloudy weather it can drop below 100 W. As an example, let's take the average figure (500 W) and in further calculations we will build on it.

Amorphous, photochemical and organic solar cells have the lowest photoelectric conversion coefficient. For the first two types it is approximately 10 percent, while for the latter it is only 5 percent. This means that with a solar flux power of 500 W, a solar panel with an area of one square meter will generate 50 and 25 W of electricity, respectively.

In contrast to the above-mentioned types of photocells, solar cells based on silicon semiconductors act. A photoelectric conversion coefficient of 20%, and under favorable conditions, even 25% is commonplace for them. As a result, the power of a meter solar panel can reach 125 W.

Only solutions based on gallium arsenide can compete in power with silicon solar batteries. Using this connection, engineers have learned to create multilayer solar cells with a PFC of over 30% (up to 150 W of electricity per square meter).

If we talk about the area of solar batteries, then there are both miniature “plates” with a power of up to 10 W (for frequent transportation), and wide “sheets” of 200 W or more (purely for stationary use).

The performance of solar panels can be negatively affected by a number of factors. For example, with increasing temperature, the coefficient of performance of photocells decreases. This is despite the fact that solar panels are installed in hot, sunny countries. It turns out to be a kind of double-edged sword.

And if you darken part of the solar panel, then the inactive photocells not only stop producing electricity, but also become an additional, harmful load.

Largest producers

The leaders in global solar cell production are Suntech, Yingli, Trina Solar, First Solar and Sharp Solar. The first three represent China, the fourth – the USA, and the fifth, as you might guess, is a division of the Japanese corporation Sharp.

The American company First Solar not only produces solar panels, but is also directly involved in the design and construction of solar power plants. , which is located in Arizona, USA, is the work of First Solar engineers.

The largest Ukrainian solar power plant, Perovo, was built and supplied with solar panels by the Austrian company Activ Solar.

The Chinese company Suntech became famous for preparing a football stadium called the “Bird's Nest” in Beijing for the 2008 Summer Olympics. The electricity generated throughout the day using solar panels is stored and then used to light the stadium, water the grass on the football field and operate telecommunications equipment.

conclusions

Just two decades ago, microcalculators with photocells seemed a curiosity, which made it possible not to change their “button battery” for years. Nowadays, mobile phones with a solar panel built into the back cover do not surprise anyone. But this is a small thing in comparison with cars and planes (even unmanned ones), which have learned to move using solar energy alone.

The future of solar panels appears to be as bright as the sun itself. I would like to believe that it is solar panels that will finally cure smartphones and tablets from “outlet dependence.”

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). (For p-, n- and p-n types, see the article on diodes). A continuous metal contact is applied to the back side of the plate. At the boundary of the n- and 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 are carried into the n-region by the electric field existing in it.

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 corresponds 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.

The 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 well in space as a fairly reliable and stable source of energy, capable of operating for a 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 elements and limit the life of the batteries. For small inhabited stations, this current source will apparently remain the only acceptable and sufficiently effective one.

Solar panels are considered a very efficient and environmentally friendly source of electricity. In recent decades, this technology has been gaining popularity around the world, motivating many people to switch to cheap renewable energy. The purpose of this device is to convert the energy of light rays into electric current, which can be used to power a variety of household and industrial devices.

Governments of many countries allocate enormous amounts of budgetary funds, sponsoring projects that are aimed at developing solar power plants. Some cities rely entirely on electricity from the sun. In Russia, these devices are often used to provide electricity to country houses and private homes as an excellent alternative to centralized energy supply services. It is worth noting that the principle of operation of solar panels for a home is quite complex. Next, let's take a closer look at how solar panels for the home work in detail.

The first attempts to use solar energy to generate electricity were made back in the mid-twentieth century. At that time, the leading countries of the world attempted to build efficient thermal power plants. The concept of a thermal power plant involves using concentrated sunlight to heat water into steam, which in turn rotates the turbines of an electrical generator.

Since such power plants used the concept of energy transformation, their efficiency was minimal. Modern devices directly convert the sun's rays into current thanks to the concept of the photoelectric effect.

The modern operating principle of a solar cell was discovered back in 1839 by a physicist named Alexandre Becquerel. In 1873, the first semiconductor was invented, which made it possible to put the principle of operation of a solar cell into practice.

Principle of operation

As stated earlier, the operating principle is based on the semiconductor effect. Silicon is one of the most efficient semiconductors known to mankind at the moment.

When the solar cell (the top silicon wafer of the converter block) is heated, electrons from the silicon atoms are released, after which they are captured by the atoms of the bottom wafer. According to the laws of physics, electrons tend to return to their original position. Accordingly, electrons from the lower plate move along conductors (connecting wires), giving up their energy to charge the batteries and returning to the upper plate.

The efficiency of solar cells created using the monocrystalline silicon deposition method is significantly higher, since in this situation the silicon crystals have fewer edges, which allows electrons to move in a straight line.

Device

The design of a solar battery is very simple.

The design of the device is based on:

panel body;
conversion blocks;
batteries;
additional devices.

The body performs solely the function of holding the structure together, having no other practical use.

The main elements are converter blocks. This is a photocell consisting of a semiconductor material, which is silicon. We can say that solar batteries, the structure and operating principle of which are always the same, consist of a frame and two thin layers of silicon, which can be applied to the surface using both monocrystalline and polycrystalline methods.

The cost of the battery, as well as its efficiency, depends on the method of applying silicon. If silicon is applied in a monocrystalline manner, then the battery efficiency will be as high as possible, as will the cost.

If we talk about how a solar battery works, then we should not forget about batteries. Typically, two batteries are used. One is the main one, the second is the backup one. The main one accumulates electricity, immediately sending it to the electrical network. The second accumulates excess electricity, and then sends it to the network when the voltage drops.

Additional devices include controllers that are responsible for distributing electricity in the network and between batteries. As a rule, they work on the principle of a simple rheostat.

Diodes are very important solar elements. This element is installed on every fourth part of the converter block, protecting the structure from overheating due to excess voltage. If diodes are not installed, then there is a high probability that after the first rain the system will fail.

How to connect

As mentioned earlier, the design of a solar battery is quite complex. The right solar panel layout will help you achieve maximum efficiency. It is necessary to connect converter units using a parallel-series method, which will allow you to obtain optimal power and the most efficient voltage in the electrical network.

Types of solar panels

There are several types of photocells for solar batteries, which differ in the structure of silicon crystals.

There are three types of photocells:

polycrystalline;
monocrystalline;
amorphous.

The first type of panel is cheaper, but less efficient, because if silicon is deposited in a polycrystalline manner, then electrons cannot move in a straight line.

Monocrystalline solar cells have a maximum efficiency that reaches 25%. The cost of such batteries is higher, but to obtain 1 kilowatt, a significantly smaller area of photocells is needed than when using polycrystalline panels.

Flexible solar cells are made from amorphous silicon, but their efficiency is the lowest and amounts to 4-6%.

Advantages and disadvantages

The main advantages of solar panels:

solar energy is absolutely free;
allow you to receive environmentally friendly electricity;
quickly pay for themselves;
simple installation and operating principle.

Flaws:

high cost;
to satisfy the electricity needs of a small family, a sufficiently large area of photocells is needed;
efficiency drops significantly in cloudy weather.

How to achieve maximum efficiency

When purchasing solar panels for your home, it is very important to choose a design that can provide your home with sufficient power. It is believed that the efficiency of solar panels in cloudy weather is approximately 40 W per 1 square meter per hour. In fact, in cloudy weather the light output at ground level is approximately 200 watts per square meter, but 40% of sunlight is infrared radiation, which solar panels are not sensitive to. It is also worth considering that battery efficiency rarely exceeds 25%.

Sometimes the energy from intense sunlight can reach 500 W per square meter, but when calculating, it is worth taking into account the minimum indicators, which will make the autonomous power supply system uninterrupted.

Every day the sun shines for an average of 9 hours, if we take the annual average. In one day, a square meter of converter surface is capable of generating 1 kilowatt of electricity. If the residents of a house consume approximately 20 kilowatts of electricity per day, then the minimum area of solar panels should be approximately 40 square meters.

However, such an indicator of electricity consumption is rare in practice. As a rule, residents will use up to 10 kW per day.

If we talk about whether solar panels work in winter, then it is worth remembering that at this time of year the duration of daylight hours is greatly reduced, but if you provide the system with powerful batteries, then the energy received per day should be sufficient, taking into account the presence of a backup battery.

When selecting a solar battery, it is very important to pay attention to the battery capacity. If solar panels are needed to operate at night, then the capacity of the backup battery plays a key role. The device must also be resistant to frequent recharging.

Despite the fact that the cost of installing solar panels can exceed 1 million rubles, the costs will pay off within a few years, since solar energy is absolutely free.