Calculation of a flat solar collector
Practice shows that an average of 900 W of thermal energy per square meter of a surface installed perpendicular to the bright rays of the sun (with a cloudless sky). We will calculate the SC on the basis of a model with an area of 1 m². The front side is matte, black (has close to 100% absorption of thermal energy). The back side is insulated with a 10 cm layer of expanded polystyrene. It is required to calculate the heat losses that occur on the reverse, shady side. Thermal insulation coefficient of expanded polystyrene - 0.05 W / m × deg. Knowing the thickness and assuming that the temperature difference on opposite sides of the material is within 50 degrees, we calculate the heat loss:
0.05 / 0.1 × 50 = 25 W.
Approximately the same losses are expected from the ends and pipes, that is, the total amount will be 50 watts. Cloudless skies are rare, and the effect of dirt deposits on the collector should also be taken into account. Therefore, we will reduce the amount of thermal energy per 1 m² to 800 W. Water used as a heat carrier in flat SCs has a heat capacity of 4200 J/kg × deg or 1.16 W/kg × deg. This means that in order to raise the temperature of one liter of water by one degree, it will take 1.16 W of energy. Given these calculations, we obtain the following value for our solar collector model of 1 m² of area:
We round for convenience up to 700 / kg × deg. This expression indicates the amount of water that can be heated in a collector (1 m² model) for an hour. This does not take into account the heat loss from the front side, which will increase as it warms up. These losses will limit the heating of the coolant in the solar collector within 70-90 degrees. In this regard, the value of 700 can be applied to low temperatures (from 10 to 60 degrees). The calculation of the solar collector shows that a 1 m² system is capable of heating 10 liters of water by 70 degrees, which is quite enough to provide a house with hot water. You can reduce the time of heating water by reducing the volume of the solar collector while maintaining its area. If the number of people living in the house requires a larger volume of water, several collectors of this area should be used, which are connected into one system. In order for sunlight to act on the radiator as efficiently as possible, the collector must be oriented at an angle to the horizon line equal to the latitude of the area. This has already been discussed in the article How to calculate the power of solar panels, the same principle applies. On average, 50 liters of hot water are needed to ensure the life of one person. Given that the water before heating has a temperature of about 10 °C, the temperature difference is 70 - 10 = 60 °C. The amount of heat needed to heat water is as follows:
W=Q × V × Tp = 1.16 × 50 × 60 = 3.48 kW of energy.
Dividing W by the amount of solar energy per 1 m² of surface in a given area (data from hydrometeorological centers), we get the collector area. The calculation of a solar collector for heating is carried out in a similar way. But the volume of water (coolant) is needed more, which depends on the volume of the heated room. It can be concluded that improving the efficiency of this type of water heating system can be achieved by reducing the volume and simultaneously increasing the area.
Ice technologies
A number of technologies are being developed where ice is produced during off-peak periods and later used for cooling. For example, air conditioning can be made more economical by using cheap electricity at night to freeze water and then using the cooling power of ice during the day to reduce the amount of energy required to maintain air conditioning. The storage of thermal energy using ice uses the high heat of fusion of water. Historically, ice was transported from the mountains to the cities to be used as a coolant. One metric (= 1 m3) ton of water can store 334 million joules (J) or 317,000 British thermal units (93 kWh).A relatively small storage unit can store enough ice to cool a large building for an entire day or week.
In addition to using ice for direct cooling, it is also used in heat pumps that power heating systems. In these areas, phase energy changes provide a very serious heat-conducting layer, close to the lower temperature threshold at which a heat pump using the heat of water can operate. This allows the system to handle the heaviest heating loads and increase the amount of time the energy source elements can return heat to the system.
Endothermic and exothermic chemical reactions
Salt hydrate technology
An example of an experimental energy storage technology based on the energy of chemical reactions is a technology based on salt hydrates. The system uses the energy of the reaction created in the case of hydration or dehydration of salts. It works by storing heat in a tank containing a 50% sodium hydroxide solution. Heat (for example, obtained from a solar collector) is stored due to the evaporation of water during an endothermic reaction. When water is added again, heat is released during the exothermic reaction at 50C (120F). At the moment, the systems operate with an efficiency of 60%. The system is especially effective for seasonal thermal energy storage, as dried salt can be stored at room temperature for a long time without energy loss. Containers of dehydrated salt can even be transported to different locations. The system has a higher energy density than the heat stored in water, and its capacity allows you to store energy for several months or even years.
In 2013, the Dutch technology developer TNO presented the results of the MERITS project for storing heat in a salt container. The heat that can be delivered from the solar collector to the flat roof evaporates the water contained in the salt. When water is added again, heat is released with virtually no loss of energy. A container with a few cubic meters of salt can store enough thermochemical energy to heat a house all winter long. With temperatures as in the Netherlands, an average heat-tolerant farm will require approximately 6.7 GJ of energy over the winter. To store that much energy in water (with a temperature difference of 70C) would require 23 m3 of water in an insulated tank, which is more than most homes can store. With the use of salt hydrate technology with an energy density of about 1 GJ/m3, 4-8 m3 would be sufficient.
As of 2016, researchers from several countries are conducting experiments to determine the best type of salt or mixture of salts. Low pressure inside the container seems to be the best for power transfer. Particularly promising are organic salts, the so-called "ionic liquids". Compared to lithium halide sorbents, they cause far fewer problems in resource-limited environments, and compared to most halides and sodium hydroxide, they are less caustic and have no negative impact through carbon dioxide emissions.
Molecular chemical bonds
At the moment, the possibility of storing energy in molecular chemical bonds is being investigated. An energy density equivalent to lithium-ion batteries has already been achieved.
Distribution of radiation at the boundary of the atmosphere
For climatology, the question of the distribution of the inflow and return of radiation over the globe is of significant interest. Consider first the distribution of solar radiation on a horizontal surface "at the boundary of the atmosphere." One could also say: "in the absence of an atmosphere." By this we assume that there is neither absorption nor scattering of radiation, nor its reflection by clouds. The distribution of solar radiation at the boundary of the atmosphere is the simplest.It really exists at an altitude of several tens of kilometers. This distribution is called the solar climate.
It is known how the solar constant changes during the year and, consequently, the amount of radiation coming to the Earth. If we determine the solar constant for the actual distance of the Earth from the Sun, then with an average annual value of 1.98 cal/cm2 min. it will be equal to 2.05 cal/cm2 min. in January and 1.91 cal/cm2 min. in July.
Therefore, the northern hemisphere during a summer day receives somewhat less radiation at the boundary of the atmosphere than the southern hemisphere during its summer day.
The amount of radiation received per day at the boundary of the atmosphere depends on the time of year and the latitude of the place. Under each latitude, the season determines the duration of the influx of radiation. But under different latitudes, the duration of the daytime part of the day at the same time is different.
At the Pole, the sun does not set at all in summer, and does not rise for 6 months in winter. Between the Pole and the Arctic Circle, the sun does not set in summer, and does not rise in winter for a period of six months to one day. At the equator, the daytime always lasts 12 hours. From the Arctic Circle to the equator, daylight hours decrease in summer and increase in winter.
But the influx of solar radiation on a horizontal surface depends not only on the length of the day, but also on the height of the sun. The amount of radiation arriving at the boundary of the atmosphere per unit of horizontal surface is proportional to the sine of the sun's height. And the height of the sun not only changes in each place during the day, but also depends on the time of year. The height of the sun at the equator varies throughout the year from 90 to 66.5°, in the tropics from 90 to 43°, in the polar circles from 47 to 0° and at the poles from 23.5 to 0°.
The sphericity of the Earth and the inclination of the equatorial plane to the plane of the ecliptic create a complex distribution of radiation influx over latitudes at the boundary of the atmosphere and its changes during the year.
In winter, the influx of radiation decreases very quickly from the equator to the pole, in summer it decreases much more slowly. In this case, the maximum in summer is observed in the tropic, and the influx of radiation somewhat decreases from the tropic to the equator. The small difference in the influx of radiation between the tropical and polar latitudes in summer is explained by the fact that although the heights of the sun in polar latitudes are lower in summer than in the tropics, the length of the day is long. On the day of the summer solstice, therefore, in the absence of an atmosphere, the pole would receive more radiation than the equator. However, near the earth's surface, as a result of the attenuation of radiation by the atmosphere, its reflection by clouds, etc., the summer influx of radiation in polar latitudes is significantly less than in lower latitudes.
At the upper boundary of the atmosphere outside the tropics, there is one annual radiation maximum at the time of the summer solstice and one minimum at the time of the winter solstice. But between the tropics, the influx of radiation has two maxima per year, attributable to those times when the sun reaches its highest noon height. At the equator, this will be on the days of the equinoxes, in other intratropical latitudes - after the spring and before the autumn equinox, moving away from the timing of the equinoxes, the greater the latitude. The amplitude of the annual variation at the equator is small, inside the tropics it is small; in temperate and high latitudes it is much larger.
Distribution of heat and light on Earth
The Sun is the star of the solar system, which is the source of a huge amount of heat and blinding light for the planet Earth. Despite the fact that the Sun is at a considerable distance from us and only a small part of its radiation reaches us, this is quite enough for the development of life on Earth. Our planet revolves around the sun in an orbit. If the Earth is observed from a spacecraft during the year, then one can notice that the Sun always illuminates only one half of the Earth, therefore, there will be day there, and at that time there will be night on the opposite half. The earth's surface receives heat only during the day.
Our Earth is warming unevenly. The uneven heating of the Earth is explained by its spherical shape, so the angle of incidence of the sun's ray in different areas is different, which means that different parts of the Earth receive different amounts of heat. At the equator, the sun's rays fall vertically, and they greatly heat the Earth.The farther from the equator, the angle of incidence of the beam becomes smaller, and consequently, these territories receive less heat. The same power beam of solar radiation heats a much smaller area near the equator, since it falls vertically. In addition, rays falling at a smaller angle than at the equator, penetrating the atmosphere, travel a longer path in it, as a result of which part of the sun's rays are scattered in the troposphere and do not reach the earth's surface. All this indicates that as you move away from the equator to the north or south, the air temperature decreases, as the angle of incidence of the sun's beam decreases.
The degree of heating of the earth's surface is also affected by the fact that the earth's axis is inclined to the plane of the orbit, along which the Earth makes a complete revolution around the Sun, at an angle of 66.5 ° and is always directed by the northern end towards the Polar Star.
Imagine that the Earth, moving around the Sun, has the Earth's axis perpendicular to the plane of the orbit of rotation. Then the surface at different latitudes would receive a constant amount of heat throughout the year, the angle of incidence of the sun's ray would be constant all the time, the day would always be equal to the night, there would be no change of seasons. At the equator, these conditions would differ little from the present. The inclination of the earth's axis has a significant influence on the heating of the earth's surface, and hence on the entire climate, precisely in temperate latitudes.
During the year, that is, during the complete revolution of the Earth around the Sun, four days are especially noteworthy: March 21, September 23, June 22, December 22.
The tropics and polar circles divide the Earth's surface into belts that differ in solar illumination and the amount of heat received from the Sun. There are 5 illumination zones: the northern and southern polar zones, which receive little light and heat, the tropical zone with a hot climate, and the northern and southern temperate zones, which receive more light and heat than the polar ones, but less than the tropical ones.
So, in conclusion, we can draw a general conclusion: uneven heating and illumination of the earth's surface are associated with the sphericity of our Earth and with the inclination of the earth's axis up to 66.5 ° to the orbit of rotation around the Sun.
Heat accumulation in hot rock, concrete, pebbles, etc.
Water has one of the highest heat capacities - 4.2 J / cm3 * K, while concrete has only one third of this value. Concrete, on the other hand, can be heated to much higher temperatures of 1200C by, for example, electrical heating and thus has a much higher overall capacity. Following from the example below, an insulated cube approximately 2.8 m across may be able to provide enough stored heat for one home to meet 50% of the heating demand. In principle, this could be used to store excess wind or photovoltaic thermal energy due to the ability of electrical heating to reach high temperatures.
At the county level, the Wiggenhausen-Süd project in the German city of Friedrichshafen attracted international attention. This is a 12,000 m3 (420,000 cu.ft.) reinforced concrete heat storage unit connected to a 4,300 m2 (46,000 sq.
ft.), covering half the need for hot water and heating for 570 homes. Siemens is building a heat storage facility near Hamburg with a capacity of 36 MWh, consisting of basalt heated to 600C and generating 1.5 MW of power. A similar system is planned for construction in the Danish city of Sorø, where 41-58% of the stored heat with a capacity of 18 MWh will be transferred to the district heating of the city, and 30-41% as electricity.
How to calculate the payback of solar heating
Using the table below, you can calculate how much your heating costs will be reduced when using solar collectors, how long this system can pay off and what benefits can be obtained over various periods of operation. This model was developed for Primorsky Krai, but can also be used to estimate the use of solar heating in Khabarovsk Krai, Amur Oblast, Sakhalin, Kamchatka and southern Siberia.In this case, solar collectors will have less effect in December-January at higher latitudes, but the overall benefits will be no less, given the longer heating season.
In the first table, enter the parameters of your house, heating system and energy prices. All fields that are marked green can be modified and simulate an existing or planned house.
First, enter the heated area of your house in the first column.
Then evaluate the quality of the building's thermal insulation and heating method by selecting the appropriate values.
Indicate the number of family members and the consumption of hot water - this will help to evaluate the benefits of hot water supply of solar collectors.
Enter prices for your usual heating energy source - electricity, diesel or coal.
Enter the value of the usual income of a family member who is engaged in heating in your household. This helps to estimate the labor costs for the heating season and plays a particularly important role for solid fuel systems, where it is necessary to bring and unload coal, throw it into the furnace, throw away ash, etc.
The price of the solar collector system will be determined automatically, based on the parameters of the building you specified. This price is approximate - the actual installation costs and parameters of solar heating equipment may differ and are calculated by specialists individually in each case.
In the "Installation Costs" column, you can enter the cost of equipment and installation of a traditional heating system - existing or planned
If the system is already installed, you can enter "0".
Pay attention to the amount of expenses for the heating season and compare with your usual expenses. If they are different, then try changing the settings.
In the column “Heating costs per season”, coal-fired heating systems take into account the monetary value of labor costs. If you do not want to take them into account, you can reduce the value of the income of a family member involved in heating. Labor costs are considered to a lesser extent for liquid fuel systems and are not taken into account for electric boiler systems. Adjustment of the solar collectors is carried out automatically and does not require constant attention.
In the "Lifetime" column, the default is 20 years - this is the usual life of solar heating systems with solar collectors. Depending on the operating conditions, solar collectors can last longer than this period. You can change the lifetime and the graph below will reflect the difference between installation and maintenance costs and the benefits of using solar collectors for heating. Thus, you will see how much the heating costs will be reduced and how long this difference will make it possible to recoup the costs of installing solar collectors.
The final results are approximate, but give a good idea of how much a solar heating system can cost and how long it can pay for itself.
Please note that heating season costs can be significantly reduced by using solar collectors, underfloor heating systems and improving the thermal insulation of the building. Also, heating costs can be reduced if the building is designed in advance for the use of solar heating and using eco-house technologies.
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What is solar heat
Since ancient times, people have been well aware of the role of the Sun in their lives. In almost all nations, it acted as the main or one of the main deities, giving life and light to all living things. Today, humanity has a much better idea of where the sun's heat comes from.
From the point of view of science, our Sun is a yellow star, which is the luminary for our entire planetary system.It draws its energy from the core - the central part of a huge hot ball, where thermonuclear fusion reactions of unimaginable power take place at a temperature measured in millions of degrees. The radius of the core is no more than a fourth of the total radius of the Sun, but it is in the core that radiant energy is generated, a small fraction of which is enough to support life on our planet.
The released energy enters the outer layers of the Sun through the convective zone and reaches the photosphere - the radiating surface of the star. The temperature of the photosphere is approaching 6,000 degrees, it is it that converts and emits into space the radiant energy that our planet receives. In fact, we live due to the gradual, slow burning of the stellar plasma that makes up the Sun.
Spectral composition of solar radiation
The wavelength interval between 0.1 and 4 microns accounts for 99% of the total energy of solar radiation. Only 1% remains for radiation with shorter and longer wavelengths, down to x-rays and radio waves.
Visible light occupies a narrow range of wavelengths, only from 0.40 to 0.75 microns. However, this interval contains almost half of all solar radiant energy (46%). Almost the same amount (47%) is in infrared rays, and the remaining 7% is in ultraviolet.
In meteorology, it is customary to distinguish between short-wave and long-wave radiation. Short-wave radiation is called radiation in the wavelength range from 0.1 to 4 microns. It includes, in addition to visible light, the ultraviolet and infrared radiation closest to it in wavelengths. Solar radiation is 99% such shortwave radiation. Long-wave radiation includes radiation of the earth's surface and atmosphere with wavelengths from 4 to 100-120 microns.
Intensity of direct solar radiation
Radiation coming to the earth's surface directly from the solar disk is called direct solar radiation, in contrast to radiation scattered in the atmosphere. Solar radiation propagates from the Sun in all directions. But the distance from the Earth to the Sun is so great that direct radiation falls on any surface on the Earth in the form of a beam of parallel rays emanating, as it were, from infinity. Even the globe as a whole is so small in comparison with the distance from the Sun that all solar radiation falling on it can be considered as a beam of parallel rays without noticeable error.
The influx of direct solar radiation to the earth's surface or to any higher level in the atmosphere is characterized by the intensity of radiation I, i.e., the amount of radiant energy entering per unit of time (one minute) per unit area (one square centimeter) perpendicular to the sun's rays.
Rice. 1. The influx of solar radiation to the surface perpendicular to the rays (AB), and on a horizontal surface (AC).
It is easy to understand that a unit area located perpendicular to the sun's rays will receive the maximum possible amount of radiation under given conditions. A unit of horizontal area will have a smaller amount of radiant energy:
I' = I sinh
where h is the height of the sun (Fig. 1).
All types of energy are mutually equivalent. Therefore, radiant energy can be expressed in units of any kind of energy, for example, in thermal or mechanical. It is natural to express it in thermal units, because measuring instruments are based on the thermal effect of radiation: radiant energy, almost completely absorbed in the device, is converted into heat, which is measured. Thus, the intensity of direct solar radiation will be expressed in calories per square centimeter per minute (cal/cm2min).
Power generation
Solar energy works by converting sunlight into electricity.This can happen either directly, using photovoltaics, or indirectly, using concentrated solar energy systems, in which lenses and mirrors collect sunlight from a large area into a thin beam, and a tracking mechanism tracks the position of the Sun. Photovoltaics converts light into electricity using the photoelectric effect.
Solar energy is projected to become the largest source of electricity by 2050, with photovoltaics and concentrated solar energy accounting for 16% and 11% of global electricity generation, respectively.
Commercial power plants using concentrated solar energy first appeared in the 1980s. After 1985, a 354 MW SEGS installation of this type in the Mojave Desert (California) became the largest solar power plant in the world. Other solar power plants of this type include SPP Solnova (English) (150 MW) and SPP Andasol (English) (100 MW), both in Spain. Among the largest photovoltaic power plants (English) are Agua Caliente Solar Project (250 MW) in the USA, and Charanka Solar Park (221 MW) in India. Projects over 1 GW are under development, but most photovoltaic installations up to 5 kW are small and rooftop. As of 2013, solar energy accounted for less than 1% of the electricity in the global grid.
Types of solar radiation
In the atmosphere, solar radiation on its way to the earth's surface is partially absorbed, and partially scattered and reflected from clouds and the earth's surface. Three types of solar radiation are observed in the atmosphere: direct, diffuse and total.
Direct solar radiation - radiation coming to the earth's surface directly from the disk of the sun. Solar radiation propagates from the Sun in all directions. But the distance from the Earth to the Sun is so great that direct radiation falls on any surface on the Earth in the form of a beam of parallel rays emanating, as it were, from infinity. Even the entire globe as a whole is so small in comparison with the distance to the Sun that all solar radiation falling on it can be considered a beam of parallel rays without noticeable error.
Only direct radiation reaches the upper boundary of the atmosphere. About 30% of the radiation incident on the Earth is reflected into outer space. Oxygen, nitrogen, ozone, carbon dioxide, water vapor (clouds) and aerosol particles absorb 23% of direct solar radiation in the atmosphere. Ozone absorbs ultraviolet and visible radiation. Despite the fact that its content in the air is very small, it absorbs all the ultraviolet radiation (about 3%)
Thus, it is not observed at the earth's surface at all, which is very important for life on Earth.
Direct solar radiation on its way through the atmosphere is also scattered. A particle (drop, crystal or molecule) of air, which is in the path of an electromagnetic wave, continuously “extracts” energy from the incident wave and re-radiates it in all directions, becoming an energy emitter.
About 25% of the energy of the total solar radiation flux passing through the atmosphere is dissipated by atmospheric gas molecules and aerosol and is converted in the atmosphere into diffuse solar radiation. Thus, scattered solar radiation is solar radiation that has undergone scattering in the atmosphere. Scattered radiation comes to the earth's surface not from the solar disk, but from the entire firmament. Scattered radiation differs from direct radiation in spectral composition, since rays of different wavelengths are scattered to different degrees.
Since the primary source of diffuse radiation is direct solar radiation, the flux of diffuse radiation depends on the same factors that affect the flux of direct radiation. In particular, the flux of scattered radiation increases with the increase in the height of the Sun and vice versa.It also increases with an increase in the number of scattering particles in the atmosphere, i.e. with a decrease in the transparency of the atmosphere, and decreases with height above sea level due to a decrease in the number of scattering particles in the overlying layers of the atmosphere. Cloudiness and snow cover have a very great influence on diffuse radiation, which, due to the scattering and reflection of the direct and diffuse radiation incident on them and their re-scattering in the atmosphere, can increase the diffuse solar radiation by several times.
Scattered radiation significantly supplements direct solar radiation and significantly increases the flow of solar energy to the earth's surface. Its role is especially great in winter at high latitudes and in other regions with high cloudiness, where the fraction of diffuse radiation may exceed the fraction of direct radiation. For example, in the annual amount of solar energy, scattered radiation accounts for 56% in Arkhangelsk and 51% in St. Petersburg.
Total solar radiation is the sum of the fluxes of direct and diffuse radiation arriving on a horizontal surface. Before sunrise and after sunset, as well as in the daytime with continuous cloudiness, the total radiation is completely, and at low altitudes of the Sun it mainly consists of scattered radiation. In a cloudless or slightly cloudy sky, with an increase in the height of the Sun, the proportion of direct radiation in the composition of the total rapidly increases and in the daytime its flux is many times greater than the flux of scattered radiation. Cloudiness on average weakens the total radiation (by 20-30%), however, with partial cloudiness that does not cover the solar disk, its flux may be greater than with a cloudless sky. The snow cover significantly increases the flux of total radiation by increasing the flux of scattered radiation.
The total radiation, falling on the earth's surface, is mostly absorbed by the upper layer of soil or a thicker layer of water (absorbed radiation) and turns into heat, and is partially reflected (reflected radiation).
Thermal belts
Depending on the amount of solar radiation entering the Earth's surface, 7 thermal zones are distinguished on the globe: hot, two moderate, two cold and two zones of eternal frost. The boundaries of thermal zones are isotherms. The hot belt is limited by the average annual isotherms of +20°C from the north and south (Fig. 9). Two temperate zones to the north and south of the hot zone are limited from the equator side by an average annual isotherm of +20 ° С, and from the side of high latitudes by an isotherm of +10 ° С (the average air temperature of the warmest months is July in the Northern and January in the Southern Hemispheres) . The northern border coincides approximately with the border of forest distribution. The two cold zones north and south of the temperate zone in the Northern and Southern Hemispheres lie between the +10°C and 0°C isotherms of the warmest month. The two belts of eternal frost are bounded by the 0°C isotherm of the warmest month from the cold belts. The realm of eternal snow and ice extends to the North and South Poles.
Measurement results of direct solar radiation
With the transparency of the atmosphere unchanged, the intensity of direct solar radiation depends on the optical mass of the atmosphere, i.e., ultimately on the height of the sun. Therefore, during the day, solar radiation must first increase rapidly, then more slowly from sunrise to noon, and at first slowly, then quickly decrease from noon to sunset.
But the transparency of the atmosphere during the day varies within certain limits. Therefore, the curve of the daytime course of radiation, even on a completely cloudless day, shows some irregularities.
Differences in radiation intensity at noon are primarily due to differences in the sun's noon height, which is lower in winter than in summer. The minimum intensity in temperate latitudes occurs in December, when the sun is at its lowest. But the maximum intensity is not in the summer months, but in the spring.The fact is that in the spring the air is the least clouded by condensation products and little dusty. In summer, dusting increases, and the content of water vapor in the atmosphere also increases, which somewhat reduces the intensity of radiation.
The maximum direct radiation intensity values for some points are as follows (in cal/cm2min): Tiksi Bay 1.30, Pavlovsk 1.43, Irkutsk 1.47, Moscow 1.48, Kursk 1.51, Tbilisi 1.51, Vladivostok 1, 46, Tashkent 1.52.
It can be seen from these data that the maximum values of the radiation intensity grow very little with decreasing geographic latitude, despite the increase in the height of the sun. This is explained by an increase in moisture content, and partly by air dusting in southern latitudes. At the equator, the maximum values of radiation do not greatly exceed the summer maxima of temperate latitudes. In the dry air of subtropical deserts (Sahara), however, values up to 1.58 cal/cm2 min were observed.
With height above sea level, the maximum values of radiation increase due to a decrease in the optical mass of the atmosphere at the same height of the sun. For every 100 m of altitude, the radiation intensity in the troposphere increases by 0.01-0.02 cal/cm2 min. We have already said that the maximum values of radiation intensity observed in the mountains reach 1.7 cal/cm2 min and more.