Introduction

The sun is known to be the primary and main source of energy for our planet. It warms the entire Earth, sets rivers in motion and imparts strength to the wind. Under its rays, 1 quadrillion tons of plants grow, feeding, in turn, 10 trillion tons of animals and bacteria. Thanks to the same Sun, the earth has accumulated reserves of hydrocarbons, that is, oil, coal, peat, etc., which we are now actively burning. In order for humanity today to be able to meet its energy needs, it takes about 10 billion tons of standard fuel a year. (The heat of combustion of the equivalent fuel is 7,000 kcal / kg).

Tasks:

Consider the main physical principles and phenomena;

· To form knowledge and skills, allowing to carry out a theoretical calculation of the main parameters;

Consider the advantages and disadvantages of using solar energy

Consider ways to obtain electricity and heat from solar radiation

Solar energy - the use of solar radiation to obtain energy in any form. Solar energy uses a renewable energy source and in the future can become environmentally friendly, that is, it does not produce harmful waste.

Solar radiation is practically inexhaustible source energy, it goes to all corners of the Earth, is "at hand" for any consumer and is an environmentally friendly and affordable source of energy.

The use of sunlight and heat is clean, simple, and natural way receiving all the forms of energy we need. Solar collectors can be used to heat or supply residential and commercial buildings hot water... Sunlight, concentrated by parabolic mirrors (reflectors), is used to generate heat (with temperatures up to several thousand degrees Celsius). It can be used for heating or for power generation. In addition, there is another way to generate energy using the sun - photovoltaic technology. Photovoltaic cells are devices that convert solar radiation directly into electricity.

SOLAR ENERGY

The energy of the Sun is the source of life on our planet. The sun heats the atmosphere and surface of the Earth. Thanks to solar energy winds blow, the water cycle in nature is carried out, the seas and oceans are heated, plants develop, animals have food. It is thanks to solar radiation that fossil fuels exist on Earth. Solar energy can be converted into heat or cold, propulsion and electricity.

Solar radiation

Solar radiation is electromagnetic radiation, concentrated mainly in the wavelength range of 0.28 ... 3.0 microns. The solar spectrum consists of:

Ultraviolet waves with a length of 0.28 ... 0.38 microns, invisible to our eyes and making up approximately 2% of the solar spectrum;

Light waves in the range 0.38 ... 0.78 µm, making up approximately 49% of the spectrum;

Infrared waves with a length of 0.78 ... 3.0 microns, which account for most of the remaining 49% of the solar spectrum. The rest of the spectrum plays a minor role in heat balance Earth.

How much solar energy hits the Earth?

The sun is radiating great amount energy - approximately 1.1x10 20 kWh per second. A kilowatt hour is the amount of energy required to operate a 100 watt incandescent light bulb for 10 hours. The outer layers of the Earth's atmosphere intercept approximately one millionth of the energy emitted by the Sun, or approximately 1,500 quadrillion (1.5 x 10 18) kWh annually. However, due to its reflection, scattering and absorption by atmospheric gases and aerosols, only 47% of all energy, or approximately 700 quadrillion (7 x 10 17) kWh, reaches the Earth's surface.

Solar radiation in the Earth's atmosphere is divided into the so-called direct radiation and scattered radiation, on particles of air, dust, water, etc., contained in the atmosphere. Their sum forms the total solar radiation.

The amount of energy falling per unit area per unit of time depends on a number of factors: the latitude of the local climate, the season of the year, and the angle of inclination of the surface in relation to the Sun.

Time and place

The amount of solar energy falling on the surface of the Earth changes due to the movement of the Sun. These changes depend on the time of day and time of year. Usually, more solar radiation hits the Earth at noon than in the early morning or late evening. At noon, the Sun is high above the horizon, and the length of the path for the Sun's rays through the Earth's atmosphere is shortened. Consequently, less solar radiation is scattered and absorbed, which means more reaches the surface.

The amount of solar energy reaching the Earth's surface differs from the average annual value: in winter time- less than 0.8 kWh / m2 per day in the North of Europe and more than 4 kWh / m2 per day in summer time in the same region. The difference decreases as you get closer to the equator.

The amount of solar energy also depends on the geographical location of the site: the closer to the equator, the more it is. For example, the average annual total solar radiation incident on a horizontal surface is: in Central Europe, Central Asia and Canada - approximately 1000 kWh / m2; in the Mediterranean - approximately 1700 kWh / m 2; in most desert regions of Africa, the Middle East and Australia - about 2200 kWh / m2.

Thus, the amount of solar radiation varies significantly depending on the season and geographic location... This factor must be taken into account when using solar energy.

Solar insolation Is a quantity that determines the amount of irradiation of the surface by the beam sun rays(even reflected or scattered by clouds). A surface can be anything, including a solar panel that converts the sun's energy into electrical energy... And this is how effective your natural power plant will be and determines the parameter of solar insolation. Insolation is measured in kW * h / m2, that is, the amount of solar energy received by one square meter of the surface during one hour. Naturally derived metrics are calculated for ideal conditions: complete absence clouds and sun rays falling on the surface at a right angle (perpendicular).

In simple words, solar insolation is the average number of hours per day that the sun shines on the calculated surface at a right angle in clear weather.

Quite often, people believe that if the sun rises at 6 am and sets at 7 pm, then the daily output of a solar panel should be considered as the product of its power by 13 hours while the sun was shining. This is fundamentally wrong, because there is cloudiness, but the main sun moves across the sky, casting rays onto the surface of the earth under different angles... Yes, you can certainly use special trackers that will rotate your solar panel towards the sun, but this is expensive and rarely economically justified. Trackers are used when it is necessary to increase the power per unit area.

Where does solar activity data come from?

The National Aeronautics and Space Administration (NASA) is studying solar activity in all regions of our planet. Satellites monitor the activity of the sun around the clock and enter the information received into tables. The calculations take into account the data of the last 25 years. An example of such a table for St. Petersburg (59.944, 30.323) you can see at the link https://eosweb.larc.nasa.gov/. This organization belongs to the US federal government and, unfortunately, their website is only available in English.

There is no need to decipher all the values ​​and coefficients in the table, because we are only interested in two - this is the actual value of solar insolation in certain months (OPT) and the value of the optimal angle of inclination of the solar panel (OPT ANG).

Calculation of the output of a solar power plant based on insolation values

Let's say we have a network solar power plant with a capacity of 5 kW in St. Petersburg and we want to calculate its output in June. Solar modules are installed at an optimal angle.

5 kW * 5.76 kW * h / m2 * 30 days = 864 kW * h

* The formula is simplified, so the calculation units in the formula will not match the answer. This is corrected by introducing parameters into the formula solar power plant and converting days into hours.

But in January, the same power plant will generate only 5 * 1.13 * 30 = 169.5 kW * h, so St. Petersburg solar panels are actively used only in summer.

For a year, such a solar power plant will be able to receive 5 * 3.4 * 365 = 6205 kW or 6.2 MW of clean electricity. Is it profitable? It's up to you, because the life of the grid power plant is more than 50 years, and the tariffs for industrial electricity are growing every year by at least 10%.

The intensity of sunlight that reaches the earth varies with the time of day, year, location, and weather conditions. The total amount of energy calculated per day or per year is called irradiation (or in other words, "the arrival of solar radiation") and shows how powerful the solar radiation was. Irradiation is measured in W * h / m² per day, or another period.

The intensity of solar radiation in free space at a distance equal to the average distance between the Earth and the Sun is called the solar constant. Its value is 1353 W / m². When passing through the atmosphere, sunlight is attenuated mainly due to the absorption of infrared radiation by water vapor, ultraviolet radiation by ozone and scattering of radiation by atmospheric dust particles and aerosols. The indicator of atmospheric influence on the intensity of solar radiation reaching the earth's surface is called "air mass" (AM). AM is defined as the secant of the angle between the Sun and the zenith.

Figure 1 shows the spectral distribution of the intensity of solar radiation in different conditions... The upper curve (AM0) corresponds to the solar spectrum outside the earth's atmosphere (for example, on board spaceship), i.e. at zero air mass. It is approximated by the distribution of the radiation intensity of an absolutely black body at a temperature of 5800 K. Curves AM1 and AM2 illustrate the spectral distribution of solar radiation on the Earth's surface when the Sun is at its zenith and at an angle between the Sun and the zenith of 60 °, respectively. In this case, the total radiation power is about 925 and 691 W / m², respectively. The average radiation intensity on Earth roughly coincides with the radiation intensity at AM = 1.5 (the Sun is at an angle of 45 ° to the horizon).

Near the surface of the earth, you can take average intensity of solar radiation 635 W / m². On a very clear sunny day, this value ranges from 950 W / m² to 1220 W / m². Average value is about 1000 W / m². Example: Intensity of total radiation in Zurich (47 ° 30 ′ N, 400 m above sea level) on a surface perpendicular to the radiation: 1 May 12:00 hrs 1080 W / m2; 21 December 12:00 hrs 930 W / m2 ...

To simplify the calculation of solar energy input, it is usually expressed in hours of sunshine at an intensity of 1000 W / m². Those. 1 hour corresponds to the arrival of solar radiation of 1000 W * h / m². This roughly corresponds to the period when the sun shines in the summer in the middle of a sunny cloudless day on the surface perpendicular to the sun's rays.

Example
The bright sun shines with an intensity of 1000 W / m² on a surface perpendicular to the sun's rays. For 1 hour, 1 kWh of energy falls per 1 m² (energy is equal to the product of power and time). Likewise, an average solar irradiance of 5 kWh / m² during the day corresponds to 5 peak hours of sunshine per day. Don't confuse peak hours with actual duration daylight hours... During the daylight hours the sun shines with different intensities, but in total it gives the same amount of energy as if it shone for 5 hours at maximum intensity. It is the peak hours of sunshine that are used in the calculations of solar power plants.

The arrival of solar radiation varies throughout the day and from place to place, especially in mountainous regions. Irradiation varies on average from 1000 kW * h / m2 per year for the North European countries, to 2000-2500 kW * h / m2 per year for deserts. Weather conditions and declination of the sun (which depends on the latitude of the area) also lead to differences in the arrival of solar radiation.

In Russia, contrary to popular belief, there are a lot of places where it is profitable to convert solar energy into electricity using. Below is a map of solar energy resources in Russia. As you can see, in most of Russia it can be successfully used in a seasonal mode, and in areas with more than 2000 hours of sunshine / year - all year round... Naturally, in winter period the generation of energy from solar panels is significantly reduced, but still the cost of electricity from a solar power plant remains significantly lower than from a diesel or gasoline generator.

It is especially advantageous to use it where there are no centralized electrical networks and power supply is provided by diesel generators. And there are a lot of such regions in Russia.

Moreover, even where there is a grid, the use of solar panels working in parallel with the grid can significantly reduce energy costs. With the current trend towards higher tariffs for Russia's natural energy monopolies, installing solar panels is becoming a smart investment.

A solar battery is a series of solar modules that convert solar energy into electricity and, using electrodes, transmit it further to other conversion devices. The latter are needed in order to make an alternating current out of direct current, which is able to perceive household electrical appliances... Direct current is obtained when solar energy is received by solar cells and the energy of photons is converted into electric current.

How many photons hit the photocell determines how much energy the solar battery gives. For this reason, battery performance is influenced not only by the material of the photocell, but also by the amount sunny days in a year, the angle of incidence of sunlight on the battery and other factors beyond the control of a person.

Aspects Affecting How Much Power a Solar Cell Generates

First of all, the performance of solar panels depends on the material of manufacture and production technology. From those on the market, you can find batteries with a performance ranging from 5 to 22%. All solar panels are divided into silicon and film.

Silicon module performance:

• Monocrystalline silicon panels - up to 22%.
• Polycrystalline panels - up to 18%.
• Amorphous (flexible) - up to 5%.

Film modules performance:

• Based on cadmium telluride - up to 12%.
• Based on meli-indium-gallium selenide - up to 20%.
• Polymer-based - up to 5%.

There are also mixed types panels, which, with the advantages of one type, allow covering the disadvantages of another, thereby increasing the efficiency of the module.

Also, how much energy the solar battery provides is affected by the number of clear days per year. It is known that if the sun in your area appears for a whole day in less than 200 days a year, then the installation and use of solar panels will hardly be profitable.

In addition, the heating temperature of the battery also affects the efficiency of the panels. So, when heated by 1̊C, the productivity drops by 0.5%, respectively, when heated by 10̊C, we have half the efficiency. To prevent such troubles, cooling systems are installed, which also require energy consumption.

To save high performance solar tracking systems are installed during the day, which help maintain a right angle of incidence of rays on solar panels. But these systems are quite expensive, not to mention the batteries themselves, so not everyone can afford to install them to power their home.

How much energy the solar battery generates also depends on the total area of ​​the installed modules, because each solar cell can receive a limited amount.

How to calculate how much energy a solar panel provides for your home?

Based on the above points that should be taken into account when buying solar panels, we can derive a simple formula by which we can calculate how much energy one module will produce.

Let's say you have chosen one of the most productive modules with an area of ​​2 m2. The amount of solar energy on a typical sunny day is approximately 1000 watts per m2. As a result, we get the following formula: solar energy (1000 W / m2) × productivity (20%) × module area (2 m2) = power (400 W).

If you want to calculate how much solar energy is perceived by a battery in the evening and on a cloudy day, you can use the following formula: amount of solar energy on a clear day × sine of the angle of sunlight and panel surface × percentage of energy converted on a cloudy day = how much solar energy eventually converts the battery. For example, let's say that in the evening the angle of incidence of the rays is 30̊. We get the following calculation: 1000 W / m2 × sin30̊ × 60% = 300 W / m2, and we use the last number as the basis for calculating the power.

The rise in energy prices in Russia is forcing interest in cheap energy sources. Solar energy is the most readily available. The energy of solar radiation falling on the Earth is 10,000 times higher than the amount of energy generated by mankind. Problems arise in the technology of energy collection and in connection with the uneven supply of energy to solar plants. Therefore, solar collectors and solar panels are used either in conjunction with energy storage devices or as a means of additional recharge for the main power plant.

Our country is vast and the picture of the distribution of solar energy over its territory is very diverse.

Average solar input data

Intensity of solar energy input

Areas of maximum solar radiation intensity. More than 5 kW is supplied per 1 square meter. hour. solar energy per day.

Along the southern border of Russia from Baikal to Vladivostok, in the Yakutsk region, in the south of the Republic of Tyva and the Republic of Buryatia, oddly enough, beyond the Arctic Circle in the eastern part of Severnaya Zemlya.

Solar energy input from 4 to 4.5 kW. hour for 1 sq. meter per day

Krasnodar region, North Caucasus, Rostov region, the southern part of the Volga region, the southern regions of Novosibirsk, Irkutsk regions, Buryatia, Tuva, Khakassia, Primorsky and Khabarovsk region, Amur Region, Sakhalin Island, vast territories from Krasnoyarsk Territory to Magadan, Severnaya Zemlya, northeast of the Yamalo-Nenets Autonomous District.

From 2.5 to 3 kW. hour per sq. meter per day

Along the western arc - Nizhny Novgorod, Moscow, St. Petersburg, Salekhard, the eastern part of Chukotka and Kamchatka.

From 3 to 4 kW. hour for 1 sq. meter per day

The rest of the country.

Duration of sunshine per year

The energy flow is most intense in May, June and July. During this period, in central Russia, 1 sq. meter of surface accounts for 5 kW. hour a day. The lowest intensity is in December-January, when 1 sq. meter of surface accounts for 0.7 kW. hour a day.

Installation features

If the solar collector is installed at an angle of 30 degrees to the surface, then it is possible to ensure the removal of energy in the maximum and minimum modes, respectively, 4.5 and 1.5 kWh per 1 sq. meter. in a day.

Distribution of solar radiation intensity in central Russia by months

Based on the given data, it is possible to calculate the area of ​​flat solar collectors required to provide hot water supply for a family of 4 in an individual house. Heating 300 liters of water from 5 degrees to 55 degrees in June can be provided by collectors with an area of ​​5.4 square meters, in December 18 square meters. meters. If more efficient vacuum collectors are used, the required collector area is approximately halved.

Solar DHW coverage

In practice, it is advisable to use solar collectors not as the main source of hot water supply, but as a device for heating the water entering the heating installation. In this case, fuel consumption is sharply reduced. This ensures uninterrupted supply hot water and saving money on hot water supply and heating of the house, if it is a house for permanent residence. At dachas, in the summer, to obtain hot water, they are used different kinds solar collectors. From factory-made collectors to homemade devices made from scrap materials. They differ, first of all, in terms of efficiency. Factory-made is more efficient, but more expensive. Almost free of charge, you can make a collector with a heat exchanger from an old refrigerator.

In Russia, the installation of solar collectors is regulated by RD 34.20.115-89 " Methodical instructions for the calculation and design of solar heating systems ", VSN 52-86 (in RTF format, 11 Mb)" Installations of hot solar water supply. Design standards ". There are recommendations for the use of non-traditional energy sources in animal husbandry, fodder production, peasant farms and the rural housing sector, developed at the request of the Ministry of Agriculture in 2002. GOST R 51595" Solar collectors. Technical requirements ", GOST R 51594" Solar energy. Terms and Definitions",

These documents describe in some detail the schemes of the solar collectors used and the most effective ways their application in various climatic conditions.

Solar collectors in Germany

In Germany, the state subsidizes the costs of installing solar collectors, so their use is growing steadily. In 2006, 1 million 300 thousand were installed square meters collectors. Of this amount, approximately 10% are more expensive and efficient vacuum collectors. The total area of ​​solar collectors installed to date is approximately 12 million square meters.

Materials and graphics provided by Viessmann