What is Solar Radiation

An image depicting solar radiation in the solar system.
What are the types of solar radiation?

Solar radiation is the energy emitted by the sun in the form of radiation – electromagnetic waves. This energy is emitted by the photosphere, the outermost layer of the sun, which is approximately 300 km long.

It is a source of energy for the planet, and is responsible for heating it up. It is also fundamental in determining the Earth’s climate.

The volume of radiation varies according to the region of the globe: the areas that receive the most radiation are those near the Equator. The lowest levels of radiation are found in extreme areas.

How does solar radiation reach the Earth?

Solar radiation passes through the atmosphere and reaches the Earth’s surface, heating it. A good part of the radiation received is absorbed, and this part is responsible for the heating of the planet. Another fraction – the infrared – is reflected and does not reach the Earth.

The radiation that reaches the surface is influenced by the atmosphere, which filters it in different ways, according to the length of the waves.

Part of the solar radiation that reaches the Earth (ultraviolet) is absorbed by the ozone layer, a layer formed by ozone gas (O3) that lies around the Earth. It is this layer that prevents high levels of radiation from reaching the planet.

Types of solar radiation

Solar radiation is divided into three types, which are classified according to wavelengths and intensity:

  • Visible
  • Ultraviolet
  • Infrared

Visible radiation

Visible radiation gets its name because it is visible to human beings. It is the simplest form of electromagnetic radiation.

Visible radiation
Visible light

As we see in the image, it is composed of a spectrum of the following colors:

  • Red
  • Orange
  • Yellow
  • Green
  • Blue
  • Violet

Color wavelengths vary between 380 nm (violet) and 750 nm (red).

Ultraviolet radiation

Ultraviolet UV Radiation.
Ultraviolet UV Radiation.

UV (Ultraviolet) radiation contains the least amount of solar energy. Its wavelength is shorter and for this reason it is not visible.

It has three classifications, according to wavelength:

  • UVA (between 400 nm and 315 nm)
  • UVB (between 315 nm and 280 nm)
  • UVC (between 280 nm and 100 nm)

UVA radiation accounts for almost all of the ultraviolet radiation that reaches the earth. To a lesser extent, UVB radiation also reaches the surface. Both of these can cause sunburn.

UVC radiation, on the other hand, does not reach the earth’s surface due to its shorter wavelength and is completely absorbed by the atmosphere.

Infrared radiation

Picture of Infrared radiation from solar radiation.
Solar Radiation – Infrared radiation

The infrared radiation contains the largest part of the solar energy with almost 50 % and is also not visible for humans. Its length varies between 780 nm and 1 mm.

It has the property of generating large thermal motion. Therefore, this radiation can cause lesions in human tissues that consist of many water molecules, as is the case with the eyes.

Solar radiation as an energy source

Solar radiation reaching the Earth can be used for the production of energy. The result of this process is called photovoltaic energy. The generation happens by means of solar panels, formed by small silicon structures (voltaic cells).

The panels are installed in areas of high solar radiation exposure, and the energy is generated from a reaction between the photons present in the radiation and the cells composed of silicon.

The system has many advantages:

  • It is not polluting
  • Does not require much maintenance
  • Highly durable

The disadvantages are:

  • The high cost of installing the panels
  • Instability of energy production, which varies according to local climate conditions

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