How much solar energy hits the earth? Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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The sun radiates a huge amount of energy - approximately 1,1x1020 kWh per second. A kilowatt hour is the amount of energy required to run a 100 watt incandescent light bulb for 10 hours. The Earth's outer atmosphere intercepts approximately one millionth of the energy emitted by the Sun, or approximately 1500 quadrillion (1,5 x 1018) kWh annually. However, due to reflection, scattering and absorption by atmospheric gases and aerosols, only 47% of all energy, or approximately 700 quadrillion (7 x 1017) kWh, reaches the Earth's surface.

Solar radiation in the Earth's atmosphere is divided into the so-called direct radiation and scattered by 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 time depends on a number of factors:

• latitude
• local climate season of the year
• the angle of inclination of the surface with respect to the sun.

Time and geographic location

The amount of solar energy falling on the Earth's surface changes due to the movement of the Sun. These changes depend on the time of day and season. Usually more solar radiation hits the Earth at noon than early in the morning or late in the evening. At noon, the Sun is high above the horizon, and the length of the path of the Sun's rays through the Earth's atmosphere is reduced. 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 - less than 0,8 kWh / m2 per day in Northern Europe and more than 4 kWh / m2 per day in summer in this same region. The difference decreases as you get closer to the equator.

(click to enlarge)

The amount of solar energy also depends on the geographical location of the site: the closer to the equator, the greater 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 / m2; in most desert regions of Africa, the Middle East and Australia, approximately 2200 kWh/m2.

Thus, the amount of solar radiation varies significantly depending on the time of year and geographical location (see table). This factor must be taken into account when using solar energy.

The influence of clouds on solar energy

The amount of solar radiation reaching the Earth's surface depends on various atmospheric phenomena and on the position of the Sun both during the day and throughout the year. Clouds are the main atmospheric phenomenon that determines the amount of solar radiation reaching the Earth's surface. At any point on the Earth, solar radiation reaching the Earth's surface decreases with increasing cloud cover. Consequently, countries with predominantly cloudy weather receive less solar radiation than deserts, where the weather is mostly cloudless.

The formation of clouds is influenced by the presence of local features such as mountains, seas and oceans, as well as large lakes. Therefore, the amount of solar radiation received in these areas and the regions adjacent to them may differ. For example, mountains may receive less solar radiation than adjacent foothills and plains. Winds blowing towards the mountains cause part of the air to rise and, cooling the moisture in the air, form clouds. The amount of solar radiation in coastal areas may also differ from those recorded in areas located inland.

The amount of solar energy received during the day is largely dependent on local atmospheric phenomena. At noon with a clear sky, the total solar

radiation falling on a horizontal surface can reach (for example, in Central Europe) a value of 1000 W/m2 (in very favorable weather conditions this figure can be higher), while in very cloudy weather it is below 100 W/m2 even at noon.

Effects of Atmospheric Pollution on Solar Energy

Anthropogenic and natural phenomena can also limit the amount of solar radiation reaching the Earth's surface. Urban smog, smoke from forest fires and airborne volcanic ash reduce the use of solar energy by increasing the dispersion and absorption of solar radiation. That is, these factors have a greater influence on direct solar radiation than on the total. With severe air pollution, for example, with smog, direct radiation is reduced by 40%, and the total - only by 15-25%. A strong volcanic eruption can reduce, and over a large area of ​​the Earth's surface, direct solar radiation by 20%, and total - by 10% for a period of 6 months to 2 years. With a decrease in the amount of volcanic ash in the atmosphere, the effect weakens, but the process of complete recovery may take several years.

The potential of solar energy

The sun provides us with 10 times more free energy than is actually used worldwide. The global commercial market alone buys and sells just under 000 trillion (85 x 8,5) kWh of energy per year. Since it is impossible to follow the whole process, it is not possible to say with certainty how much non-commercial energy people consume (for example, how much wood and fertilizer is collected and burned, how much water is used to produce mechanical or electrical energy). Some experts estimate that such non-commercial energy accounts for one-fifth of all energy used. But even if this is true, then the total energy consumed by mankind during the year is only approximately one seven thousandth of the solar energy that hits the surface of the Earth in the same period.

In developed countries, such as the USA, energy consumption is approximately 25 trillion (2.5 x 1013) kWh per year, which corresponds to more than 260 kWh per person per day. This is the equivalent of running more than 100 33W incandescent bulbs daily for a full day. The average US citizen consumes 13 times more energy than an Indian, XNUMX times more than a Chinese, two and a half times more than a Japanese and twice as much as a Swede.

The amount of solar energy reaching the Earth's surface is many times greater than its consumption, even in countries such as the United States, where energy consumption is huge. If only 1% of the country's territory was used to install solar equipment (photovoltaic panels or solar hot water systems) operating at a 10% efficiency, then the US would be fully supplied with energy. The same can be said about all other developed countries. However, in a certain sense, this is unrealistic - firstly, due to the high cost of photovoltaic systems, and secondly, it is impossible to cover such large areas with solar equipment without harming the ecosystem. But the principle itself is correct.

It is possible to cover the same area by dispersing installations on the roofs of buildings, on houses, along roadsides, on predetermined areas of land, etc. In addition, in many countries already more than 1% of the land is allocated for the extraction, conversion, production and transportation of energy. And, since most of this energy is non-renewable at the scale of human existence, this kind of energy production is much more harmful to the environment than solar systems.

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