The process that generates solar energy. The principle of solar energy conversion, its application and prospects

Every day the amount of world reserves of coal, oil, gas, that is, everything that serves us as a source of energy today, is decreasing. And in the near future, humanity will come to the point where there will simply be no fossil fuels left. Therefore, all countries are actively seeking salvation from the catastrophe that is rapidly approaching us. And the first means of salvation that comes to mind is, of course, the energy of the sun, which has been used by people from time immemorial for drying clothes, lighting homes and cooking. This gave rise to one of the areas of alternative energy - solar energy.

The energy source for solar energy is the energy of sunlight, which is converted into heat or electricity using special structures. According to experts, in just one week, the earth’s surface receives an amount of energy from the sun that exceeds the energy of the world’s reserves of all types of fuel. And although the pace of development of this area of ​​alternative energy is steadily growing, solar energy still has not only advantages, but also disadvantages.

If the main advantages include accessibility, and most importantly the inexhaustibility of the energy source, then the disadvantages include:

• the need to accumulate energy received from the sun,
• significant cost of the equipment used,
• dependence on weather conditions and time of day,
• increase in atmospheric temperature above power plants, etc.

Numerical characteristics of solar radiation

There is such an indicator as the solar constant. Its value is 1367 W. This is exactly the amount of energy per 1 sq.m. planet Earth. But because of the atmosphere, about 20-25% less energy reaches the surface of the earth. Therefore, the value of solar energy per square meter, for example, at the equator is 1020 W. And taking into account the change of day and night, the change in the angle of the sun above the horizon, this figure decreases by about 3 times.

But where does this energy come from? Scientists first began to study this issue back in the 19th century, and the versions were completely different. Today, as a result of a huge number of studies, it is reliably known that the source of solar energy is the reaction of converting 4 hydrogen atoms into a helium nucleus. As a result of this process, a significant amount of energy is released. For example, the energy released during the transformation of 1 g. hydrogen is comparable to the energy released during the combustion of 15 tons of gasoline.

Solar Energy Conversion

We already know that the energy received from the sun must be converted into some other form. The need for this arises due to the fact that humanity does not yet have such devices that could consume solar energy in its pure form. Therefore, energy sources such as solar collectors and solar panels were developed. If the first is used to generate thermal energy, then the second produces electricity directly.

There are several ways to convert solar energy:

• photovoltaics;
• thermal air energy;
• solar thermal energy;
• using solar balloon power plants.

The most common method is photovoltaics. The principle of this conversion is the use of photovoltaic solar panels, or solar panels as they are also called, through which solar energy is converted into electrical energy. As a rule, such panels are made of silicon, and the thickness of their working surface is only a few tenths of a millimeter. They can be placed anywhere, there is only one condition - the presence of a large amount of sunlight. An excellent option for installing photographic plates on the roofs of residential buildings and public buildings.

In addition to the photographic plates discussed above, thin-film panels are used to convert the energy of solar radiation. They are distinguished by their even smaller thickness, which allows them to be installed anywhere, but a significant drawback of such panels is their low efficiency. It is for this reason that their installation will be justified only for large areas. Just for fun, the thin-film panel can even be placed on a laptop case or on a handbag.

In thermal air energy, solar energy is converted into the energy of air flow, which is then sent to a turbogenerator. But in the case of using solar balloon power plants, water vapor is generated inside the balloon. This effect is achieved by heating the surface of the balloon, on which a selective-absorbing coating is applied, by sunlight. The main advantage of this method is the sufficient supply of steam, which is enough to continue the operation of the power plant in bad weather and at night.

The principle of solar energy is to heat a surface that absorbs the sun's rays and focuses them for the subsequent use of the resulting heat. The simplest example is heating water, which can then be used for domestic needs, for example, to be supplied to sewers or batteries, while saving gas or other fuel. On an industrial scale, solar radiation energy obtained by this method is converted into electrical energy using heat engines. The construction of such combined power plants can last over 20 years, but the pace of development of solar energy is not decreasing, but, on the contrary, is steadily growing.

Where can solar energy be used?

Solar energy can be used in completely different areas - from the chemical industry to the automotive industry, from cooking to space heating. For example, the use of solar panels in the automotive industry dates back to 1955. This year was marked by the release of the first car that ran on solar batteries. Today, BMW, Toyota and other major companies produce such cars.

In everyday life, solar energy is used for heating rooms, for lighting and even for cooking. For example, solar ovens made of foil and cardboard, on the initiative of the UN, are actively used by refugees who were forced to leave their homes due to the difficult political situation. More complex solar furnaces are used for heat treatment and smelting of metals. One of the largest such furnaces is located in Uzbekistan.

The most interesting inventions on the use of solar energy include:

• A protective case for a phone with a photocell, which is also a charger.
• A backpack with a solar panel attached to it. It will allow you to charge not only your phone, but also your tablet and even your camera, in general, any electronics that has a USB input.
• Solar Bluetooth headphones.

And the most creative idea is clothes made from special fabric. A jacket, tie and even a swimsuit - all this can become not only an item in your wardrobe, but also a charger.

Development of alternative energy in the CIS countries

Alternative energy, including solar, is developing at a high rate not only in the USA, Europe or India, but also in the CIS countries, including Russia, Kazakhstan, and especially Ukraine. For example, the largest solar power plant in the former Soviet Union, Perovo, was built in Crimea. Its construction was completed in 2011. This power plant became the 3rd innovative project of the Austrian company Activ Solar. The peak power of Perovo is about 100 MW.

And in October of the same year, Activ Solar launched another solar power plant, Okhotnikovo, also in Crimea. Its power was 80 MW. Okhotnikovo also received the status of the largest, but in Central and Eastern Europe. We can say that alternative energy in Ukraine has taken a huge step towards safe and inexhaustible energy.

In Kazakhstan, the situation looks a little different. Basically, the development of alternative energy in this country occurs only in theory. The republic has enormous potential, but it has not yet been fully realized. Of course, the government is dealing with this issue, and even a plan has been developed for the development of alternative energy in Kazakhstan, but the share of energy obtained from renewable sources, in particular from the sun, will be no more than 1% in the country’s overall energy balance. By 2020, there are plans to launch only 4 solar power plants, the total capacity of which will be 77 MW.

Alternative energy in Russia is also developing at a considerable pace. But, as the Deputy Minister of Energy said, the focus in this area is mainly on the Far Eastern regions. For example, in Yakutia, the total output of 4 solar power plants operating in the most remote northern villages amounted to more than 50 thousand kWh. This allowed saving more than 14 tons of expensive diesel fuel. Another example of the use of solar energy is the multi-functional aviation complex under construction in the Lipetsk region. Electricity for its operation will be generated by the first solar power plant, also built in the Lipetsk region.

All this allows us to draw the following conclusion: today all countries, even not the most developed ones, strive to get as close as possible to the cherished goal: the use of alternative energy sources. After all, electricity consumption is growing every day, and the amount of harmful emissions into the environment is increasing every day. And many already understand that our future and the future of our planet depends only on us.

R. Abdullina

Ukraine relies on solar energy

People can no longer imagine life without electricity, and every year the need for energy is growing more and more, while reserves of energy resources such as oil, gas, and coal are rapidly declining. Humanity has no other options but to use alternative energy sources. One way to generate electricity is to convert solar energy using photocells. People learned that it is possible to use solar energy relatively long ago, but began to actively develop it only in the last 20 years. In recent years, thanks to ongoing research, the use of new materials and creative design solutions, it has been possible to significantly increase the performance of solar panels. Many believe that in the future humanity will be able to abandon traditional methods of generating electricity in favor of solar energy and obtain it using solar power plants.

Solar energy

Solar energy is one of the sources of generating electricity in a non-traditional way, therefore it is classified as an alternative energy source. Solar energy uses solar radiation and converts it into electricity or other forms of energy. Solar energy is not only an environmentally friendly source of energy, because... When converting solar energy, no harmful by-products are released, but solar energy is also a self-renewing source of alternative energy.

How solar energy works

Theoretically, it is not difficult to calculate how much energy can be obtained from the flow of solar energy; it has long been known that having traveled the distance from the Sun to the Earth and falling on a surface with an area of ​​1 m² at an angle of 90°, the solar flow at the entrance to the atmosphere carries an energy charge equal to 1367 W/ m², this is the so-called solar constant. This is an ideal option under ideal conditions, which, as we know, are practically impossible to achieve. Thus, after passing through the atmosphere, the maximum flux that can be obtained will be at the equator and will be 1020 W/m², but the average daily value that we can obtain will be 3 times less due to the change of day and night and the change in the angle of incidence of the solar flux. And in temperate latitudes, the change of day and night is also accompanied by a change of seasons, and with it a change in the length of daylight hours, so in temperate latitudes the amount of energy received will be reduced by another 2 times.

Development and distribution of solar energy

As we all know, in the last few years, the development of solar energy is gaining momentum every year, but let's try to trace the dynamics of development. Back in 1985, global solar capacity was only 0.021 GW. In 2005, they already amounted to 1.656 GW. The year 2005 is considered a turning point in the development of solar energy; it was from this year that people began to take an active interest in the research and development of electrical systems powered by solar energy. Further dynamics leave no doubt (2008-15.5 GW, 2009-22.8 GW, 2010-40 GW, 2011-70 GW, 2012-108 GW, 2013-150 GW, 2014-203 GW). The countries of the European Union and the United States hold the palm in the use of solar energy; more than 100 thousand people each are employed in the production and operational sphere in the United States and Germany alone. Also, Italy, Spain and, of course, China can boast of their achievements in the development of solar energy, which, if not a leader in the operation of solar cells, is how the manufacturer of solar cells is increasing the pace of production from year to year.

Advantages and disadvantages of using solar energy

Advantages: 1) environmental friendliness - does not pollute the environment; 2) availability - photocells are available for sale not only for industrial use, but also for creating private mini solar power plants; 3) inexhaustibility and self-renewability of the energy source; 4) constantly decreasing cost of electricity production.
Flaws: 1) the impact of weather conditions and time of day on productivity; 2) to conserve energy, it is necessary to accumulate energy; 3) lower productivity in temperate latitudes due to changing seasons; 4) significant heating of the air above the solar power plant; 5) the need to periodically clean the surface of photocells from contamination, and this is problematic due to the huge areas occupied by the installation of photocells; 6) we can also talk about the relatively high cost of equipment, although every year the cost is decreasing, so far there is no need to talk about cheap solar energy.

Prospects for the development of solar energy

Today, a great future is predicted for the development of solar energy; every year more and more new solar power plants are being built, which amaze with their scale and technical solutions. Also, scientific research aimed at increasing the efficiency of photocells does not stop. Scientists have calculated that if we cover the landmass of planet Earth by 0.07%, with an efficiency of photocells of 10%, then there will be enough energy to more than 100% meet all the needs of humanity. Today, photocells with an efficiency of 30% are already used. According to research data, it is known that the ambitions of scientists promise to bring it to 85%.

Solar power plants

Solar power plants are structures whose task is to convert solar energy flows into electrical energy. The sizes of solar power plants can vary, ranging from private mini power plants with several solar panels to huge ones, occupying areas of over 10 km².

What types of solar power plants are there?

Quite a lot of time has passed since the construction of the first solar power plants, during which many projects have been implemented and many interesting design solutions have been applied. It is customary to divide all solar power plants into several types:
1. Tower-type solar power plants.
2. Solar power plants, where solar panels are photovoltaic cells.
3. Dish solar power plants.
4. Parabolic solar power plants.
5. Solar power plants of the solar-vacuum type.
6. Solar power plants of mixed type.

Solar power plants of tower type

A very common type of power plant design. It is a tall tower structure on top with a reservoir of water painted black to better attract reflected sunlight. Around the tower there are large mirrors with an area of ​​over 2 m² located in a circle, they are all connected to a single control system that monitors the change in the angle of the mirrors so that they always reflect sunlight and direct it straight to the water tank located at the top of the tower. Thus, the reflected sunlight heats the water, which forms steam, and then this steam is supplied to the turbogenerator using pumps, where electricity is generated. The heating temperature of the tank can reach 700 °C. The height of the tower depends on the size and power of the solar power plant and, as a rule, starts from 15 m, and the height of the largest today is 140 m. This type of solar power plant is very common and is preferred by many countries for its high efficiency of 20%.

Solar power plants of photocell type

Photocells (solar batteries) are used to convert solar flux into electricity. This type of power plant has become very popular due to the possibility of using solar panels in small blocks, which allows the use of solar panels to provide electricity to both private homes and large industrial facilities. Moreover, the efficiency is growing every year and today there are already photocells with an efficiency of 30%.

Parabolic solar power plants

This type of solar power plant looks like huge satellite dishes, the inside of which is covered with mirror plates. The principle by which energy conversion occurs is similar to tower stations with a slight difference: the parabolic shape of the mirrors determines that the sun's rays, reflected from the entire surface of the mirror, are concentrated in the center, where the receiver is located with a liquid that heats up, forming steam, which in its turn The queue is the driving force for small generators.

Plate solar power plants

The operating principle and method of generating electricity are identical to tower and parabolic solar power plants. The only difference is the design features. A stationary structure, a bit like a giant metal tree, holds round flat mirrors that concentrate the sun's energy onto a receiver.

Solar power plants of solar-vacuum type

This is a very unusual way of using solar energy and temperature differences. The power plant structure consists of a glass-roofed, circular plot of land with a tower in the center. The tower is hollow inside; at its base there are several turbines that rotate thanks to the air flow arising from the temperature difference. Through the glass roof, the sun heats the ground and air inside the room, and the building communicates with the outside environment through a pipe, and since the air temperature outside the room is much lower, air draft is created, which increases with increasing temperature difference. Thus, at night the turbines generate more electricity than during the day.

Mixed solar power plants

This is when solar power plants of a certain type use, for example, solar collectors as auxiliary elements to provide objects with hot water and heat, or it is possible to use sections of photocells simultaneously at a tower-type power plant.

Solar energy is developing at a high pace, people are finally seriously thinking about alternative energy sources in order to prevent the inevitably approaching energy crisis and environmental disaster. Although the leaders in solar energy are still the United States and the European Union, all other world powers are gradually beginning to adopt and use the experience and technologies of production and use of solar power plants. There is no doubt that sooner or later solar energy will become the main source of energy on Earth.

The sun is an inexhaustible, environmentally friendly and cheap source of energy. As experts say, the amount of solar energy that reaches the Earth's surface during the week exceeds the energy of all the world's reserves of oil, gas, coal and uranium 1 . According to Academician Zh.I. Alferova, “humanity has a reliable natural thermonuclear reactor - the Sun. It is a star of the “F-2” class, very average, of which there are up to 150 billion in the Galaxy. But this is our star, and it sends enormous powers to Earth, the transformation of which makes it possible to satisfy almost any energy needs of humanity for many hundreds of years.” Moreover, solar energy is “clean” and does not have a negative impact on the ecology of the planet 2.

An important point is the fact that the raw material for the manufacture of solar cells is one of the most common elements - silicon. In the earth's crust, silicon is the second element after oxygen (29.5% by mass) 3 . According to many scientists, silicon is the “oil of the twenty-first century”: over 30 years, one kilogram of silicon in a photovoltaic plant produces as much electricity as 75 tons of oil in a thermal power plant.

However, some experts believe that solar energy cannot be called environmentally friendly due to the fact that the production of pure silicon for photo batteries is very “dirty” and very energy-intensive production. Along with this, the construction of solar power plants requires the allocation of vast lands, comparable in area to the reservoirs of hydroelectric power stations. Another disadvantage of solar energy, according to experts, is high volatility. Ensuring the efficient operation of the energy system, the elements of which are solar power plants, is possible provided that:
- the presence of significant reserve capacities using traditional energy sources, which can be connected at night or on cloudy days;
- carrying out large-scale and expensive modernization of electrical networks 4.

Despite this drawback, solar energy continues to develop around the world. First of all, due to the fact that radiant energy will become cheaper and in a few years will become a significant competitor to oil and gas.

Currently in the world there are photovoltaic installations, converting solar energy into electrical energy based on the direct conversion method, and thermodynamic installations, in which solar energy is first converted into heat, then converted into mechanical energy in the thermodynamic cycle of a heat engine, and converted into electrical energy in a generator.

Solar cells as an energy source can be used:
- in industry (aircraft industry, automotive industry, etc.),
- in agriculture,
- in the domestic sphere,
- in the construction industry (for example, eco-houses),
- at solar power plants,
- in autonomous video surveillance systems,
- in autonomous lighting systems,
- in the space industry.

According to the Institute of Energy Strategy, the theoretical potential of solar energy in Russia is more than 2,300 billion tons of standard fuel, the economic potential is 12.5 million tons of equivalent fuel. The potential of solar energy entering the territory of Russia within three days exceeds the energy of the entire annual electricity production in our country.
Due to Russia's location (between 41 and 82 degrees north latitude), the level of solar radiation varies significantly: from 810 kWh/m2 per year in remote northern regions to 1400 kWh/m2 per year in the southern regions. The level of solar radiation is also influenced by large seasonal fluctuations: at a width of 55 degrees, solar radiation in January is 1.69 kWh/m2, and in July - 11.41 kWh/m2 per day.

The solar energy potential is greatest in the southwest (North Caucasus, the Black and Caspian Seas) and in Southern Siberia and the Far East.

The most promising regions in terms of the use of solar energy: Kalmykia, Stavropol Territory, Rostov Region, Krasnodar Territory, Volgograd Region, Astrakhan Region and other regions in the southwest, Altai, Primorye, Chita Region, Buryatia and other regions in the southeast. Moreover, some areas of Western and Eastern Siberia and the Far East exceed the level of solar radiation in the southern regions. For example, in Irkutsk (52 degrees north latitude) the level of solar radiation reaches 1340 kWh/m2, while in the Republic of Yakutia-Sakha (62 degrees north latitude) this figure is 1290 kWh/m2. 5

Currently, Russia has advanced technologies for converting solar energy into electrical energy. There are a number of enterprises and organizations that have developed and are improving the technologies of photoelectric converters: both on silicon and multijunction structures. There are a number of developments in the use of concentrating systems for solar power plants.

The legislative framework to support the development of solar energy in Russia is in its infancy. However, the first steps have already been taken:
- July 3, 2008: Government Decree No. 426 “On the qualification of a generating facility operating on the basis of the use of renewable energy sources”;
- January 8, 2009: Order of the Government of the Russian Federation No. 1-r “On the Main Directions of State Policy in the Sphere of Improving Energy Efficiency of the Electric Power Industry Based on the Use of Renewable Energy Sources for the Period until 2020”

Targets were approved to increase the share of renewable energy sources in the overall level of the Russian energy balance to 2.5% and 4.5%, respectively, by 2015 and 2020 6 .

According to various estimates, at the moment in Russia the total volume of installed solar generation capacity is no more than 5 MW, most of which falls on households. The largest industrial facility in Russian solar energy is a solar power plant in the Belgorod region with a capacity of 100 kW, commissioned in 2010 (for comparison, the largest solar power plant in the world is located in Canada with a capacity of 80,000 kW).

Currently, two projects are being implemented in Russia: the construction of solar parks in the Stavropol Territory (capacity - 12 MW), and in the Republic of Dagestan (10 MW) 7 . Despite the lack of support for renewable energy, a number of companies are implementing small-scale solar energy projects. For example, Sakhaenergo installed a small station in Yakutia with a capacity of 10 kW.

There are small installations in Moscow: in Leontyevsky Lane and on Michurinsky Prospekt, the entrances and courtyards of several houses are illuminated using solar modules, which has reduced lighting costs by 25%. On Timiryazevskaya Street, solar panels are installed on the roof of one of the bus stops, which ensure the operation of a reference and information transport system and Wi-Fi.

The development of solar energy in Russia is due to a number of factors:

1) climatic conditions: this factor influences not only the year in which grid parity is achieved, but also the choice of the solar installation technology that is best suited for a particular region;

2)governmental support: the presence of legally established economic incentives for solar energy is critical to
its development. Among the types of government support that are successfully used in a number of countries in Europe and the USA, we can highlight: preferential tariffs for solar power plants, subsidies for the construction of solar power plants, various options for tax breaks, compensation for part of the costs of servicing loans for the purchase of solar installations;

3)cost of PVEU (solar photovoltaic installations): Today, solar power plants are one of the most expensive electricity generation technologies in use. However, as the cost of 1 kWh of generated electricity decreases, solar energy becomes competitive. Demand for solar power plants depends on the reduction in the cost of 1W of installed power of solar power plants (~$3000 in 2010). Cost reduction is achieved by increasing efficiency, reducing technological costs and reducing production profitability (the influence of competition). The potential for reducing the cost of 1 kW of power depends on the technology and ranges from 5% to 15% per year;

4) environmental standards: The solar energy market may be positively affected by tightening environmental standards (restrictions and fines) due to a possible revision of the Kyoto Protocol. Improving the mechanisms for selling emission quotas can provide a new economic incentive for the PVEM market;

5) balance of supply and demand for electricity: implementation of existing ambitious plans for the construction and reconstruction of generating and power grids
capacity of companies spun off from RAO UES of Russia during the industry reform will significantly increase the supply of electricity and may increase pressure on prices
on the wholesale market. However, the retirement of old capacity and a simultaneous increase in demand will entail an increase in prices;

6)presence of problems with technological connection: delays in the execution of applications for technological connection to the centralized power supply system are an incentive for the transition to alternative energy sources, including PVEU. Such delays are determined by both an objective lack of capacity and the ineffectiveness of organizing technological connection by grid companies or the lack of financing for technological connection from the tariff;

7) initiatives of local authorities: Regional and municipal governments can implement their own programs to develop solar energy or, more broadly, renewable/non-traditional energy sources. Today, such programs are already being implemented in the Krasnoyarsk and Krasnodar territories, the Republic of Buryatia, etc.;

8) development of own production: Russian production of solar power plants can have a positive impact on the development of Russian solar energy consumption. Firstly, thanks to our own production, the general awareness of the population about the availability of solar technologies and their popularity increases. Secondly, the cost of SFEU for end consumers is reduced by reducing intermediate links in the distribution chain and by reducing the transport component 8 .

Solar energy

Solar radiation parameters

First of all, it is necessary to assess the potential energy capabilities of solar radiation. Here, its total specific power at the Earth's surface and the distribution of this power over different radiation ranges are of greatest importance.

Solar radiation power

The radiation power of the Sun, located at the zenith, at the Earth's surface is estimated at approximately 1350 W/m2. A simple calculation shows that to obtain a power of 10 kW it is necessary to collect solar radiation from an area of ​​only 7.5 m2. But this is on a clear afternoon in a tropical zone high in the mountains, where the atmosphere is rarefied and crystal clear. As soon as the Sun begins to lean towards the horizon, the path of its rays through the atmosphere increases, and accordingly, the losses along this path increase. The presence of dust or water vapor in the atmosphere, even in quantities imperceptible without special instruments, further reduces the flow of energy. However, even in the middle zone on a summer afternoon, for every square meter oriented perpendicular to the sun’s rays, there is a flow of solar energy with a power of approximately 1 kW.

Of course, even light cloud cover dramatically reduces the energy reaching the surface, especially in the infrared (thermal) range. However, some energy still penetrates the clouds. In the middle zone, with heavy clouds at noon, the power of solar radiation reaching the Earth's surface is estimated at approximately 100 W/m2, and only in rare cases, with particularly dense clouds, can it fall below this value. Obviously, in such conditions, to obtain 10 kW it is necessary to completely, without losses and reflection, collect solar radiation not from 7.5 m2 of the earth's surface, but from an entire hundred square meters (100 m2).

The table shows brief averaged data on solar radiation energy for some Russian cities, taking into account climatic conditions (frequency and intensity of cloudiness) per unit of horizontal surface. Details of this data, additional data for panel orientations other than horizontal, as well as data for other regions of Russia and the countries of the former USSR are provided on a separate page.

A fixed panel, placed at an optimal angle of inclination, is capable of absorbing 1.2 .. 1.4 times more energy compared to a horizontal one, and if it rotates after the Sun, the increase will be 1.4 .. 1.8 times. This can be seen, broken down by month, for fixed panels oriented south at different angles of inclination, and for systems tracking the movement of the Sun. Features of the placement of solar panels are discussed in more detail below.

Direct and diffuse solar radiation

There are diffuse and direct solar radiation. To effectively perceive direct solar radiation, the panel must be oriented perpendicular to the flow of sunlight. For the perception of scattered radiation, orientation is not so critical, since it comes quite evenly from almost the entire sky - this is how the earth's surface is illuminated on cloudy days (for this reason, in cloudy weather, objects do not have a clearly defined shadow, and vertical surfaces, such as pillars and the walls of the houses practically do not cast a visible shadow).

The ratio of direct and diffuse radiation strongly depends on weather conditions in different seasons. For example, winter in Moscow is cloudy, and in January the share of scattered radiation exceeds 90% of the total insolation. But even in the Moscow summer, scattered radiation makes up almost half of all solar energy reaching the earth's surface. At the same time, in sunny Baku both in winter and summer, the share of scattered radiation ranges from 19 to 23% of total insolation, and about 4/5 of solar radiation, respectively, is direct. The ratio of diffuse and total insolation for some cities is given in more detail on a separate page.

Energy distribution in the solar spectrum

The solar spectrum is practically continuous over an extremely wide range of frequencies - from low-frequency radio waves to ultra-high-frequency x-rays and gamma radiation. Of course, it is difficult to capture such different types of radiation equally effectively (perhaps this can only be achieved theoretically with the help of an “ideal black body”). But this is not necessary - firstly, the Sun itself emits in different frequency ranges with different strengths, and secondly, not everything that the Sun emits reaches the Earth's surface - certain parts of the spectrum are largely absorbed by different components of the atmosphere - mainly ozone layer, water vapor and carbon dioxide.

Therefore, it is enough for us to determine those frequency ranges in which the greatest flux of solar energy is observed at the Earth’s surface, and use them. Traditionally, solar and cosmic radiation are separated not by frequency, but by wavelength (this is due to the exponents being too large for the frequencies of this radiation, which is very inconvenient - visible light in Hertz corresponds to the 14th order). Let's look at the dependence of the energy distribution on the wavelength for solar radiation.

The visible light range is considered to be the wavelength range from 380 nm (deep violet) to 760 nm (deep red). Anything that has a shorter wavelength has higher photon energy and is divided into ultraviolet, x-ray and gamma radiation ranges. Despite the high energy of photons, there are not so many photons themselves in these ranges, so the total energy contribution of this part of the spectrum is very small. Everything that has a longer wavelength has lower photon energy compared to visible light and is divided into the infrared range (thermal radiation) and various parts of the radio range. The graph shows that in the infrared range the Sun emits almost the same amount of energy as in the visible (the levels are smaller, but the range is wider), but in the radio frequency range the radiation energy is very small.

Thus, from an energy point of view, it is enough for us to limit ourselves to the visible and infrared frequency ranges, as well as near ultraviolet (somewhere up to 300 nm, shorter wavelength hard ultraviolet is almost completely absorbed in the so-called ozone layer, ensuring the synthesis of this very ozone from atmospheric oxygen) . And the lion's share of solar energy reaching the Earth's surface is concentrated in the wavelength range from 300 to 1800 nm.

Limitations when using solar energy

The main limitations associated with the use of solar energy are caused by its inconsistency - solar installations do not work at night and are ineffective in cloudy weather. This is obvious to almost everyone.

However, there is one more circumstance that is especially relevant for our rather northern latitudes - seasonal differences in day length. If for the tropical and equatorial zones the duration of day and night depends slightly on the time of year, then already at the latitude of Moscow the shortest day is almost 2.5 times shorter than the longest! I’m not even talking about the circumpolar regions... As a result, on a clear summer day, a solar installation near Moscow can produce no less energy than at the equator (the sun is lower, but the day is longer). However, in winter, when the need for energy is especially high, its production, on the contrary, will decrease several times. Indeed, in addition to the short daylight hours, the rays of the low winter sun, even at noon, must pass through a much thicker layer of the atmosphere and therefore lose significantly more energy on this path than in summer, when the sun is high and the rays pass through the atmosphere almost vertically (the expression “cold winter sun "has the most direct physical meaning). However, this does not mean that solar installations in the middle zone and even in much more northern areas are completely useless - although they are of little use in winter, during the period of long days, at least six months between the spring and autumn equinoxes, they are quite effective .

Particularly interesting is the use of solar installations to power the increasingly widespread, but very “gluttonous” air conditioners. After all, the stronger the sun shines, the hotter it gets and the more air conditioning is needed. But in such conditions, solar installations are also capable of generating more energy, and this energy will be used by the air conditioner “here and now”; it does not need to be accumulated and stored! In addition, it is not at all necessary to convert energy into electrical form - absorption heat engines use heat directly, which means that instead of photovoltaic batteries, you can use solar collectors, which are most effective in clear, hot weather. True, I believe that air conditioners are indispensable only in hot, waterless regions and in humid tropical climates, as well as in modern cities, regardless of their location. A competently designed and built country house, not only in the middle zone, but also in most of the south of Russia, does not need such an energy-hungry, bulky, noisy and capricious device.

Unfortunately, in urban areas, the individual use of more or less powerful solar installations with any noticeable practical benefit is possible only in rare cases of particularly fortunate circumstances. However, I do not consider a city apartment to be full-fledged housing, since its normal functioning depends on too many factors that are not available to the direct control of residents for purely technical reasons, and therefore in the event of failure of at least one of the life support systems for a more or less long time In a modern apartment building, the conditions there will not be acceptable for living (rather, an apartment in a high-rise building should be considered as a kind of hotel room, which the residents bought for indefinite use or rented from the municipality). But outside the city, special attention to solar energy can be more than justified even on a small plot of 6 acres.

Features of placement of solar panels

Choosing the optimal orientation of solar panels is one of the most important issues in the practical use of solar installations of any type. Unfortunately, this aspect is discussed very little on various sites dedicated to solar energy, although neglecting it can reduce the efficiency of panels to unacceptable levels.

The fact is that the angle of incidence of the rays on the surface greatly affects the reflection coefficient, and therefore the proportion of unreceptive solar energy. For example, for glass, when the angle of incidence deviates from perpendicular to its surface by up to 30°, the reflection coefficient practically does not change and is slightly less than 5%, i.e. more than 95% of the incident radiation passes inward. Further, the increase in reflection becomes noticeable, and by 60° the share of reflected radiation doubles - almost to 10%. At an incidence angle of 70°, about 20% of the radiation is reflected, and at 80° - 40%. For most other substances, the dependence of the degree of reflection on the angle of incidence is approximately the same.

Even more important is the so-called effective panel area, i.e. the cross section of the radiation flux it covers. It is equal to the real area of ​​the panel multiplied by the sine of the angle between its plane and the direction of flow (or, which is the same, by the cosine of the angle between the perpendicular to the panel and the direction of flow). Therefore, if the panel is perpendicular to the flow, its effective area is equal to its real area, if the flow has deviated from the perpendicular by 60°, it is half the real area, and if the flow is parallel to the panel, its effective area is zero. Thus, a significant deviation of the flow from perpendicular to the panel not only increases the reflection, but reduces its effective area, which causes a very noticeable drop in production.

Obviously, for our purposes, the most effective is a constant orientation of the panel perpendicular to the flow of solar rays. But this will require changing the position of the panel in two planes, since the position of the Sun in the sky depends not only on the time of day, but also on the time of year. Although such a system is certainly technically possible, it is very complex, and therefore expensive and not very reliable.

However, let us remember that at angles of incidence up to 30°, the reflection coefficient at the air-glass interface is minimal and practically unchanged, and over the course of a year, the angle of maximum rise of the Sun above the horizon deviates from the average position by no more than ±23°. The effective area of ​​the panel when deviating from the perpendicular by 23° also remains quite large - at least 92% of its actual area. Therefore, you can focus on the average annual height of the maximum rise of the Sun and, with virtually no loss of efficiency, limit yourself to rotation in only one plane - around the polar axis of the Earth at a speed of 1 revolution per day. The angle of inclination of the axis of such rotation relative to the horizontal is equal to the geographic latitude of the place. For example, for Moscow, located at a latitude of 56°, the axis of such rotation should be tilted north by 56° relative to the surface (or, which is the same thing, deviated from the vertical by 34°). Such rotation is much easier to organize, however, a large panel requires a lot of space to rotate smoothly. In addition, it is necessary either to organize a sliding connection that allows you to remove all the energy it receives from the constantly rotating panel, or to limit yourself to flexible communications with a fixed connection, but ensure automatic return of the panel back at night - otherwise, twisting and breakage of the energy-removing communications cannot be avoided . Both solutions dramatically increase the complexity and reduce the reliability of the system. As the power of the panels (and therefore their size and weight) increases, the technical problems become exponentially more complex.

In connection with all of the above, almost always the panels of individual solar installations are mounted motionlessly, which ensures relative cheapness and the highest reliability of the installation. However, here the choice of panel placement angle becomes especially important. Let's consider this problem using the example of Moscow.

Let's look at the insolation diagrams for various panel installation angles. Of course, the panel turning after the Sun is out of competition (orange line). However, even on long summer days, its efficiency exceeds the efficiency of fixed horizontal (blue) and tilted at an optimal angle (red) panels by only about 30%. But these days there is enough warmth and light! But during the most energy-deficient period from October to February, the advantage of a rotating panel over a fixed panel is minimal and almost imperceptible. True, at this time the company of the inclined panel is not a horizontal, but a vertical panel (green line). And this is not surprising - the low rays of the winter sun glide across the horizontal panel, but are well perceived by the vertical panel, which is almost perpendicular to them. Therefore, in February, November and December, the vertical panel is more effective than even the inclined one and is almost no different from the rotary one. In March and October, the days are longer, and the rotating panel is already beginning to confidently (though not very much) outperform any fixed options, but the effectiveness of the inclined and vertical panels is almost the same. And only during the period of long days from April to August, the horizontal panel is ahead of the vertical panel in terms of energy received and approaches the inclined one, and in June it even slightly exceeds it. The summer loss of the vertical panel is natural - after all, say, the day of the summer equinox lasts in Moscow for more than 17 hours, and in the front (working) hemisphere of the vertical panel the Sun can remain for no more than 12 hours, the remaining 5-plus hours (almost a third of the daylight hours!) is behind her. If we take into account that at angles of incidence of more than 60°, the proportion of light reflected from the surface of the panel begins to grow rapidly, and its effective area is reduced by half or more, then the time of effective perception of solar radiation for such a panel does not exceed 8 hours - that is, less than 50 % of the total length of the day. This is precisely what explains the fact that the performance of vertical panels stabilizes throughout the entire period of long days - from March to September. And finally, January stands somewhat apart - in this month the performance of panels of all orientations is almost the same. The fact is that this month in Moscow is very cloudy, and more than 90% of all solar energy comes from scattered radiation, and for such radiation the orientation of the panel is not very important (the main thing is not to direct it to the ground). However, a few sunny days, which still occur in January, reduce the production of a horizontal panel by 20% compared to the rest.

What angle of inclination should you choose? It all depends on when exactly you need solar energy. If you want to use it only in the warm season (say, in the country), then you should choose the so-called “optimal” tilt angle, perpendicular to the average position of the Sun during the period between the spring and autumn equinoxes. It is approximately 10° .. 15° less than the geographic latitude and for Moscow it is 40° .. 45°. If you need energy year-round, then you should “squeeze out” the maximum in the energy-deficient winter months, which means you need to focus on the average position of the Sun between the autumn and spring equinoxes and place the panels closer to the vertical - 5° .. 15° more than the geographic latitude (for Moscow it will be 60° .. 70°). If, for architectural or design reasons, it is impossible to maintain such an angle and you must choose between an angle of inclination of 40° or less or a vertical installation, you should prefer the vertical position. At the same time, the “shortage” of energy on long summer days is not so critical - during this period there is plenty of natural heat and light, and the need for energy production is usually not as great as in winter and in the off-season. Naturally, the tilt of the panel should be oriented to the south, although a deviation from this direction by 10° .. 15° to the east or west changes little and is therefore quite acceptable.

Horizontal placement of solar panels throughout Russia is ineffective and completely unjustified. In addition to too great a decrease in energy production in the autumn-winter period, dust intensively accumulates on horizontal panels, and also snow in winter, and they can only be removed from there with the help of specially organized cleaning (usually manually). If the slope of the panel exceeds 60°, then the snow on its surface does not linger much and usually quickly crumbles on its own, and a thin layer of dust is easily washed off by rain.

Since prices for solar equipment have been falling recently, it may be advantageous, instead of a single field of solar panels oriented to the south, to use two with a higher total power, oriented to adjacent (southeast and southwest) and even opposite (east and west) cardinal directions. This will ensure more uniform production on sunny days and increased production on cloudy days, while the rest of the equipment will remain designed for the same, relatively low power, and therefore will be more compact and cheaper.

And one last thing. Glass, the surface of which is not smooth, but has a special relief, is able to perceive side light much more efficiently and transmit it to the working elements of the solar panel. The most optimal seems to be a wavy relief with the orientation of protrusions and depressions from north to south (for vertical panels - from top to bottom) - a kind of linear lens. Corrugated glass can increase the production of a fixed panel by 5% or more.

Traditional types of solar energy installations

From time to time there are reports about the construction of another solar power plant (SPP) or desalination plant. Thermal solar collectors and photovoltaic solar panels are used all over the world, from Africa to Scandinavia. These methods of using solar energy have been developing for decades; many sites on the Internet are devoted to them. Therefore, here I will consider them in very general terms. However, one important point is practically not covered on the Internet - this is the choice of specific parameters when creating an individual solar power supply system. Meanwhile, this question is not as simple as it seems at first glance. An example of choosing parameters for a solar-powered system is given on a separate page.

Solar panels

Generally speaking, a “solar battery” can be understood as any set of identical modules that perceive solar radiation and are combined into a single device, including purely thermal ones, but traditionally this term has been assigned specifically to photoelectric converter panels. Therefore, the term “solar battery” almost always refers to a photovoltaic device that directly converts solar radiation into electric current. This technology has been actively developing since the middle of the 20th century. A huge incentive for its development was the exploration of outer space, where solar batteries can currently only compete with small-sized nuclear energy sources in terms of power produced and operating time. During this time, the conversion efficiency of solar batteries increased from one or two percent to 17% or more in mass-produced, relatively cheap models and over 42% in prototypes. Service life and operational reliability have significantly increased.

Advantages of solar panels

The main advantage of solar panels is their extreme design simplicity and the complete absence of moving parts. The result is a low specific weight and unpretentiousness combined with high reliability, as well as the simplest possible installation and minimal maintenance requirements during operation (usually it is enough to just remove dirt from the working surface as it accumulates). Representing flat elements of small thickness, they are quite successfully placed on a roof slope facing the sun or on the wall of a house, practically without requiring any additional space or the construction of separate bulky structures. The only condition is that nothing should obscure them for as long as possible.

Another important advantage is that the energy is generated immediately in the form of electricity - in the most universal and convenient form to date.

Unfortunately, nothing lasts forever - the efficiency of photovoltaic converters decreases over their service life. Semiconductor wafers, which usually make up solar panels, degrade over time and lose their properties, as a result of which the already not very high efficiency of solar cells becomes even lower. Prolonged exposure to high temperatures accelerates this process. At first I noted this as a drawback of photovoltaic batteries, especially since “dead” photovoltaic cells cannot be restored. However, it is unlikely that any mechanical electric generator will be able to demonstrate at least 1% efficiency after just 10 years of continuous operation - most likely it will require serious repairs much earlier due to mechanical wear, if not of bearings, then of brushes - and modern photoconverters are able to maintain their efficiency for decades. According to optimistic estimates, over 25 years the efficiency of a solar battery decreases by only 10%, which means that if other factors do not intervene, then even after 100 years almost 2/3 of the original efficiency will remain. However, for mass commercial photovoltaic cells based on poly- and monocrystalline silicon, honest manufacturers and sellers give slightly different aging figures - after 20 years one should expect a loss of up to 20% of efficiency (then theoretically after 40 years the efficiency will be 2/3 of the original, halved in 60 years, and after 100 years a little less than 1/3 of the original productivity will remain). In general, the normal service life for modern photoconverters is at least 25...30 years, so degradation is not so critical, and it is much more important to wipe off dust from them in a timely manner...

If the batteries are installed in such a way that natural dust is practically absent or is promptly washed away by natural rains, then they will be able to operate without any maintenance for many years. The ability to operate for such a long time in maintenance-free mode is another major advantage.

Finally, solar panels are capable of producing energy from dawn to dusk, even in cloudy weather when the solar thermal collectors are only slightly different from the ambient temperature. Of course, compared to a clear sunny day, their productivity drops many times, but something is better than nothing at all! In this regard, the development of batteries with maximum energy conversion in those ranges where clouds absorb solar radiation the least is of particular interest. In addition, when choosing solar photoconverters, you should pay attention to the dependence of the voltage they produce on illumination - it should be as small as possible (when illumination decreases, the current, not the voltage, should first drop, because otherwise, to obtain at least some useful effect in On cloudy days, you will have to use expensive additional equipment that forcibly increases the voltage to the minimum sufficient to charge the batteries and operate the inverters).

Disadvantages of solar panels

Of course, solar panels have many disadvantages. In addition to depending on the weather and time of day, the following can be noted.

Low efficiency. The same solar collector, with the correct choice of shape and surface material, is capable of absorbing almost all of the solar radiation that hits it in almost the entire spectrum of frequencies that carry noticeable energy - from the far infrared to the ultraviolet range. Solar batteries convert energy selectively - for the working excitation of atoms, certain photon energies (radiation frequencies) are required, therefore in some frequency bands the conversion is very effective, while other frequency ranges are useless for them. In addition, the energy of the photons captured by them is used quantumly - its “excess”, exceeding the required level, goes to heating the photoconverter material, which is harmful in this case. This is largely what explains their low efficiency.
By the way, if you choose the wrong protective coating material, you can significantly reduce the battery efficiency. The matter is aggravated by the fact that ordinary glass absorbs the high-energy ultraviolet part of the range quite well, and for some types of photocells this particular range is very relevant - the energy of infrared photons is too low for them.

Sensitivity to high temperature. As temperatures rise, the efficiency of solar cells, like almost all other semiconductor devices, decreases. At temperatures above 100..125°C, they may temporarily lose their functionality, and even greater heating threatens their irreversible damage. In addition, elevated temperatures accelerate the degradation of photocells. Therefore, it is necessary to take all measures to reduce the heating that is inevitable under the scorching direct rays of the sun. Typically, manufacturers limit the nominal operating temperature range of photocells to +70°..+90°C (this means heating of the elements themselves, and the ambient temperature, naturally, should be much lower).
Further complicating the situation is that the sensitive surface of rather fragile photocells is often covered with protective glass or transparent plastic. If an air gap remains between the protective cover and the surface of the photocell, a kind of “greenhouse” is formed, aggravating overheating. True, by increasing the distance between the protective glass and the surface of the photocell and connecting this cavity with the atmosphere above and below, it is possible to organize a convection air flow that naturally cools the photocells. However, in bright sunshine and at high outside temperatures, this may not be enough; moreover, this method contributes to accelerated dusting of the working surface of the photocells. Therefore, even a not very large solar battery may require a special cooling system. In fairness, it must be said that such systems are usually easily automated, and the fan or pump drive consumes only a small fraction of the generated energy. In the absence of strong sun, there is not much heating and no cooling is required at all, so the energy saved in driving the cooling system can be used for other purposes. It should be noted that in modern factory-made panels, the protective coating usually fits tightly to the surface of the photocells and removes heat outside, but in home-made designs, mechanical contact with the protective glass can damage the photocell.

Sensitivity to illumination unevenness. As a rule, to obtain a voltage at the battery output that is more or less convenient for use (12, 24 or more volts), photocells are connected in series circuits. The current in each such chain, and therefore its power, is determined by the weakest link - a photocell with the worst characteristics or with the lowest illumination. Therefore, if at least one element of the chain is in the shadow, it significantly reduces the output of the entire chain - the losses are disproportionate to the shading (moreover, in the absence of protective diodes, such an element will begin to dissipate the power generated by the remaining elements!). A disproportionate reduction in output can be avoided only by connecting all the photocells in parallel, but then the battery output will have too much current at too low a voltage - usually for individual photocells it is only 0.5 .. 0.7 V, depending on their type and load size.

Sensitivity to pollution. Even a barely noticeable layer of dirt on the surface of solar cells or protective glass can absorb a significant portion of sunlight and significantly reduce energy production. In a dusty city, this will require frequent cleaning of the surface of solar panels, especially those installed horizontally or at a slight angle. Of course, the same procedure is necessary after each snowfall and after a dust storm... However, far from cities, industrial zones, busy roads and other strong sources of dust at an angle of 45° or more, rain is quite capable of washing away natural dust from the surface of the panels, “automatically” maintaining them in a fairly clean condition. And the snow on such a slope, which also faces south, usually does not stay long even on very frosty days. So, far from sources of atmospheric pollution, solar panels can operate successfully for years without any maintenance at all, if only there was sun in the sky!

Finally, the last but most important obstacle to the widespread adoption of photovoltaic solar panels is their rather high price. The cost of solar battery elements is currently at least 1 $/W (1 kW - $1000), and this is for low-efficiency modifications without taking into account the cost of assembly and installation of panels, as well as without taking into account the price of batteries, charging controllers and inverters (converters of the generated low-voltage direct current). current to a household or industrial standard). In most cases, for a minimum estimate of real costs, these figures should be multiplied by 3-5 times when self-assembling from individual solar cells and by 6-10 times when purchasing ready-made equipment sets (plus installation costs).

Of all the elements of a power supply system using photovoltaic batteries, batteries have the shortest service life, but manufacturers of modern maintenance-free batteries claim that in the so-called buffer mode they will work for about 10 years (or they will work out the traditional 1000 cycles of strong charging and discharging - if you count one cycle per day, then in this mode they will last for 3 years). I note that the cost of batteries is usually only 10-20% of the total cost of the entire system, and the cost of inverters and charge controllers (both are complex electronic products, and therefore there is some probability of their failure) is even less. Thus, taking into account the long service life and the ability to work for a long time without any maintenance, photoconverters may well pay for themselves more than once during their life, and not only in remote areas, but also in populated areas - if electricity tariffs will continue to grow at the current pace!

Solar thermal collectors

The name “solar collectors” is assigned to devices that use direct heating by solar heat, both single and stackable (modular). The simplest example of a thermal solar collector is a black water tank on the roof of the above-mentioned country shower (by the way, the efficiency of heating water in a summer shower can be significantly increased by building a mini-greenhouse around the tank, at least from a plastic film; it is desirable that between the film and the walls of the tank on the top and sides there was a gap of 4-5 cm).

However, modern collectors bear little resemblance to such a tank. They are usually flat structures made of thin blackened tubes arranged in a lattice or snake pattern. The tubes can be mounted on a blackened heat-conducting substrate sheet, which traps solar heat entering the spaces between them - this allows the overall length of the tubes to be reduced without loss of efficiency. To reduce heat loss and increase heating, the top of the collector can be covered with a sheet of glass or transparent cellular polycarbonate, and on the reverse side of the heat-distributing sheet, a layer of thermal insulation prevents unnecessary heat loss - a kind of “greenhouse” is obtained. Heated water or other coolant moves through the tube, which can be collected in a thermally insulated storage tank. The coolant moves under the action of a pump or by gravity due to the difference in coolant densities before and after the thermal collector. In the latter case, more or less efficient circulation requires careful selection of slopes and pipe sections and placement of the collector itself as low as possible. But usually the collector is placed in the same places as the solar battery - on a sunny wall or on a sunny roof slope, although an additional storage tank must be placed somewhere. Without such a tank, during intensive heat recovery (say, if you need to fill a bath or take a shower), the collector capacity may not be enough, and after a short time slightly warmed water will flow from the tap.

Protective glass, of course, somewhat reduces the efficiency of the collector, absorbing and reflecting several percent of solar energy, even if the rays fall perpendicularly. When the rays hit the glass at a slight angle to the surface, the reflection coefficient can approach 100%. Therefore, in the absence of wind and the need for only slight heating relative to the surrounding air (by 5-10 degrees, say, for watering a garden), “open” structures can be more effective than “glazed” ones. But as soon as a temperature difference of several tens of degrees is required or if even a not very strong wind rises, the heat loss of open structures rapidly increases, and protective glass, with all its shortcomings, becomes a necessity.

An important note - it is necessary to take into account that on a hot sunny day, if not analyzed, the water may overheat above the boiling point, therefore, it is necessary to take appropriate precautions in the design of the collector (provide a safety valve). In open collectors without protective glass, such overheating is usually not a concern.

Recently, solar collectors based on so-called heat pipes have begun to be widely used (not to be confused with “heat pipes” used for heat removal in computer cooling systems!). Unlike the design discussed above, here each heated metal tube through which the coolant circulates is soldered inside a glass tube, and air is pumped out from the space between them. It turns out to be an analogue of a thermos, where due to vacuum thermal insulation, heat loss is reduced by 20 times or more. As a result, according to the manufacturers, when there is a frost of -35°C outside the glass, the water in the inner metal tube with a special coating that absorbs the widest possible spectrum of solar radiation is heated to +50..+70°C (a difference of more than 100°C) .Efficient absorption combined with excellent thermal insulation allows you to heat the coolant even in cloudy weather, although the heating power, of course, is several times less than in bright sunshine. The key point here is to ensure the preservation of the vacuum in the gap between the tubes, that is, the vacuum tightness of the junction of glass and metal, in a very wide temperature range, reaching 150 ° C, throughout the entire service life of many years. For this reason, in the manufacture of such collectors it is impossible to do without careful coordination of the coefficients of thermal expansion of glass and metal and high-tech production processes, which means that in artisanal conditions it is unlikely to be possible to make a full-fledged vacuum heat pipe. But simpler collector designs can be made independently without any problems, although, of course, their efficiency is somewhat less, especially in winter.

In addition to the liquid solar collectors described above, there are other interesting types of structures: air (the coolant is air, and it is not afraid of freezing), “solar ponds”, etc. Unfortunately, most research and development on solar collectors is devoted specifically to liquid models, therefore alternative types are practically not mass-produced and there is not much information about them.

Advantages of solar collectors

The most important advantage of solar collectors is the simplicity and relative low cost of manufacturing their quite effective options, combined with unpretentiousness in operation. The minimum required to make a collector with your own hands is a few meters of thin pipe (preferably thin-walled copper - it can be bent with a minimum radius) and a little black paint, at least bitumen varnish. We bend the tube like a snake, paint it with black paint, place it in a sunny place, connect it to the water main, and now the simplest solar collector is ready! At the same time, the coil can easily be given almost any configuration and make maximum use of all the space allocated for the collector. The most effective home-applied blackening that is also very resistant to high temperatures and direct sunlight is a thin layer of carbon black. However, soot is easily erased and washed off, so such blackening will definitely require protective glass and special measures to prevent possible condensation from entering the soot-covered surface.

Another important advantage of collectors is that, unlike solar panels, they are able to capture and convert up to 90% of the solar radiation that hits them into heat, and in the most successful cases, even more. Therefore, not only in clear weather, but also in light cloudy conditions, the efficiency of collectors exceeds the efficiency of photovoltaic batteries. Finally, unlike photovoltaic batteries, uneven illumination of the surface does not cause a disproportionate reduction in the efficiency of the collector - only the total (integrated) radiation flux is important.

Disadvantages of solar collectors

But solar collectors are more sensitive to weather than solar panels. Even in bright sunshine, a fresh wind can reduce the heating efficiency of an open heat exchanger many times over. Protective glass, of course, sharply reduces heat loss from the wind, but in the case of dense clouds it is also powerless. In cloudy, windy weather there is practically no use from the collector, but the solar battery produces at least some energy.

Among other disadvantages of solar collectors, I will first of all highlight their seasonality. Short spring or autumn night frosts are enough for the ice formed in the heater pipes to create a danger of their rupture. Of course, this can be eliminated by heating the “greenhouse” with a coil with a third-party heat source on cold nights, but in this case the overall energy efficiency of the collector can easily become negative! Another option - a double-circuit manifold with antifreeze in the external circuit - will not require energy consumption for heating, but will be much more complicated than single-circuit options with direct water heating, both in manufacturing and during operation. In principle, air structures cannot freeze, but there is another problem - the low specific heat capacity of the air.

And yet, perhaps, the main disadvantage of a solar collector is that it is precisely a heating device, and although industrially manufactured samples, in the absence of heat analysis, can heat the coolant to 190..200 ° C, the usually achieved temperature rarely exceeds 60..80 °C. Therefore, it is very difficult to use the extracted heat to obtain significant amounts of mechanical work or electrical energy. After all, even for the operation of the lowest temperature steam-water turbine (for example, the one that V.A. Zysin once described) it is necessary to overheat the water to at least 110°C! And energy directly in the form of heat, as is known, is not stored for a long time, and at temperatures below 100°C it can usually only be used in hot water supply and heating a house. However, taking into account the low cost and ease of manufacture, this may be quite a sufficient reason to acquire your own solar collector.

To be fair, it should be noted that the “normal” operating cycle of a heat engine can be organized at temperatures below 100 ° C - either if the boiling point is lowered by reducing the pressure in the evaporation part by pumping out steam from there, or by using a liquid whose boiling point lies between the temperature heating of the solar collector and ambient air temperature (optimally - 50..60°C). True, I can remember only one non-exotic and relatively safe liquid that more or less satisfies these conditions - ethyl alcohol, which under normal conditions boils at 78°C. Obviously, in this case, it will be necessary to organize a closed cycle, solving many related problems. In some situations, the use of externally heated engines (Stirling engines) may be promising. Interesting in this regard may also be the use of alloys with shape memory effect, which are described on this site in the article by I.V. Nigel - they only need a temperature difference of 25-30°C to operate.

Solar Energy Concentration

Increasing the efficiency of a solar collector primarily involves a steady increase in the temperature of the heated water above the boiling point. This is usually done by concentrating solar energy on a collector using mirrors. This is the principle that underlies most solar power plants; the differences lie only in the number, configuration and placement of the mirrors and collector, as well as in the methods of controlling the mirrors. As a result, at the focusing point it is quite possible to reach a temperature of not even hundreds, but thousands of degrees - at such a temperature, direct thermal decomposition of water into hydrogen and oxygen can already occur (the resulting hydrogen can be burned at night and on cloudy days)!

Unfortunately, the effective operation of such an installation is impossible without a complex control system for concentrating mirrors, which must track the constantly changing position of the Sun in the sky. Otherwise, within a few minutes the focusing point will leave the collector, which in such systems is often very small in size, and heating of the working fluid will stop. Even the use of paraboloid mirrors only partially solves the problem - if they are not periodically rotated after the Sun, then after a few hours it will no longer fall into their bowl or will only illuminate its edge - this will be of little use.

The easiest way to concentrate solar energy at home is to place a mirror horizontally near the collector so that the sun hits the collector most of the day. An interesting option is to use the surface of a specially created reservoir near the house as such a mirror, especially if it is not an ordinary reservoir, but a “solar pond” (although this is not easy to do, and the reflection efficiency will be much less than that of an ordinary mirror). A good result can be achieved by creating a system of vertical concentrating mirrors (this undertaking is usually much more troublesome, but in some cases it may be justified to simply install a large mirror on an adjacent wall if it forms an internal angle with the collector - it all depends on the configuration and location of the building and collector).

Redirecting solar radiation using mirrors can also increase the output of a photovoltaic battery. But at the same time, its heating increases, and this can damage the battery. Therefore, in this case, you have to limit yourself to a relatively small gain (by a few tens of percent, but not by several times), and you need to carefully monitor the battery temperature, especially on hot, clear days! It is precisely because of the danger of overheating that some manufacturers of photovoltaic batteries directly prohibit the operation of their products under increased illumination created with the help of additional reflectors.

Converting solar energy into mechanical energy

Traditional types of solar installations do not directly produce mechanical work. To do this, an electric motor must be connected to a solar battery on photoconverters, and when using a thermal solar collector, superheated steam (and for overheating it is unlikely to be possible without concentrating mirrors) must be supplied to the input of a steam turbine or to the cylinders of a steam engine. Collectors with relatively little heat can convert heat into mechanical motion in more exotic ways, such as using shape memory alloy actuators.

However, there are also installations that involve the conversion of solar heat into mechanical work, which is directly incorporated into their design. Moreover, their sizes and power are very different - this is a project for a huge solar tower hundreds of meters high, and a modest solar pump, which would belong on a summer cottage.

We live in the world of the future, although this is not noticeable in all regions. In any case, the possibility of developing new energy sources is being seriously discussed in progressive circles today. One of the most promising areas is solar energy.

At the moment, about 1% of the electricity on Earth is obtained from the processing of solar radiation. So why haven’t we given up other “harmful” methods yet, and will we give up at all? We invite you to read our article and try to answer this question yourself.

How solar energy is converted into electricity

Let's start with the most important thing - how the sun's rays are processed into electricity.

The process itself is called "Solar generation" . The most effective ways to ensure this are as follows:

• photovoltaics;
• solar thermal energy;
• solar balloon power plants.

Let's look at each of them.

Photovoltarics

In this case, the electric current appears due to photovoltaic effect. The principle is this: sunlight hits a photocell, electrons absorb the energy of photons (light particles) and begin to move. As a result, we get electrical voltage.

This is exactly the process that occurs in solar panels, which are based on elements that convert solar radiation into electricity.

The design of photovoltaic panels itself is quite flexible and can have different sizes. Therefore, they are very practical to use. In addition, the panels have high performance properties: they are resistant to precipitation and temperature changes.

And here's how it works separate solar panel module:

You can read about the use of solar panels as chargers, power sources for private homes, for urban improvement and for medical purposes.

Modern solar panels and power plants

Recent examples include the company's solar panels SistineSolar. They can have any shade and texture, unlike traditional dark blue panels. This means that they can be used to “decorate” the roof of the house as you please.

Another solution was proposed by Tesla developers. They launched not just panels, but full-fledged roofing material that processes solar energy. contains built-in solar modules and can also have a wide variety of designs. At the same time, the material itself is much stronger than ordinary roofing tiles; Solar Roof even has an endless guarantee.

An example of a full-fledged solar power plant is a station recently built in Europe with double-sided panels. The latter collect both direct solar radiation and reflective radiation. This allows you to increase the efficiency of solar generation by 30%. This station should generate about 400 MWh per year.

Of interest is also the largest floating solar power plant in China. Its power is 40 MW. Such solutions have 3 important advantages:

• there is no need to occupy large land areas, which is important for China;
• in reservoirs, water evaporation decreases;
• The photocells themselves heat up less and work more efficiently.

By the way, this floating solar power plant was built on the site of an abandoned coal mining enterprise.

Technology based on the photovoltaic effect is the most promising today, and according to experts, solar panels will be able to produce about 20% of the world's electricity demand in the next 30-40 years.

Solar thermal energy

Here the approach is a little different, because... solar radiation is used to heat a container containing liquid. Thanks to this, it turns into steam, which rotates a turbine, resulting in the generation of electricity.

Thermal power plants operate on the same principle, only the liquid is heated by burning coal.

The most obvious example of the use of this technology is Ivanpah Solar station in the Mojave Desert. It is the world's largest solar thermal power plant.

It has been operating since 2014 and does not use any fuel to produce electricity - only environmentally friendly solar energy.

The water boiler is located in the towers, which you can see in the center of the structure. Around there is a field of mirrors that direct the sun's rays to the top of the tower. At the same time, the computer constantly rotates these mirrors depending on the location of the sun.

Under the influence of concentrated solar energy, the water in the tower heats up and turns into steam. This creates pressure and the steam begins to rotate the turbine, resulting in the release of electricity. The power of this station is 392 megawatts, which can be easily compared with the average thermal power plant in Moscow.

Interestingly, such stations can also operate at night. This is possible by placing part of the heated steam in storage and gradually using it to rotate the turbine.

Solar balloon power plants

This original solution, although not widely used, still has a place.

The installation itself consists of 4 main parts:

• Aerostat – located in the sky, collecting solar radiation. Water enters the ball and quickly heats up, becoming steam.
• Steam pipeline - through it, steam under pressure descends to the turbine, causing it to rotate.
• Turbine - under the influence of a flow of steam, it rotates, generating electrical energy.
• Condenser and pump - the steam that has passed through the turbine is condensed into water and rises into the balloon using a pump, where it is again heated to a vapor state.

What are the advantages of solar energy

• The sun will continue to give us its energy for several more billion years. At the same time, people do not need to spend money and resources to extract it.
• Generating solar energy is a completely environmentally friendly process with no risks to nature.
• Autonomy of the process. Harvesting sunlight and generating electricity occurs with minimal human intervention. The only thing you need to do is keep your work surfaces or mirrors clean.
• Exhausted solar panels can be recycled and reused in production.

Problems of solar energy development

Despite the implementation of ideas to maintain the operation of solar power plants at night, no one is immune from the vagaries of nature. Cloudy skies for several days significantly reduce electricity production, but the population and businesses need an uninterrupted supply.

Construction of a solar power plant is not a cheap pleasure. This is due to the need to use rare elements in their design. Not all countries are ready to waste budgets on less powerful power plants when there are working thermal power plants and nuclear power plants.

To place such installations, large areas are required, and in places where solar radiation has a sufficient level.

How is solar energy developed in Russia?

Unfortunately, our country is still burning coal, gas and oil at full speed, and Russia will certainly be among the last to completely switch to alternative energy.

To date solar generation accounts for only 0.03% of the energy balance of the Russian Federation. For comparison, in Germany this figure is more than 20%. Private entrepreneurs are not interested in investing in solar energy because of the long payback period and not so high profitability, because gas is much cheaper in our country.

In the economically developed Moscow and Leningrad regions, solar activity is low. There, building solar power plants is simply not practical. But the southern regions are quite promising.