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A modern pyranometer, here model SR20

A pyranometer (from Greek  πῦρ pyr "fire" and οὐρανός ouranós "sky") is used to measure the incoming solar radiation . In other words, a pyranometer is a sensor that measures the sun's irradiance (in watts per square meter) with a 180 degree field of view.

Pyranometers are widely used in meteorology , climatology , building physics and in research on solar energy . They are used in meteorological stations, mostly mounted horizontally and next to solar cells, mostly parallel to the surface of the solar cell. The ISO 9060 standard , which is also recognized by the World Meteorological Organization , exists for pyranometers . This standard distinguishes between three classes. The best class is called the “secondary standard”, the second best “first class” and the last “second class”.

Measuring principle

Potsdam , 1973: Measurements with "Bellani spherical pyranometers"

Pyranometers normally detect the radiation arriving from the half-space above the sensor. This radiation around the visible wavelength range of the sunlight spectrum is called global radiation and consists of direct solar radiation ( direct radiation ) and diffuse sky radiation ( diffuse radiation ). The incidence of radiation is usually measured on a horizontal surface. The pyranometer consists of a cover that protects it from environmental influences and a blackened thermopile . Using a calibration factor, the output signal is directly proportional to the irradiance , which is measured in watts per square meter.

For a heat flux density or irradiation measurement, the directional behavior is proportional to the cosine of the angle of incidence , so the maximum response is obtained for perpendicular radiation.


Drawing of a pyranometer with essential parts: (1) cable, (3) and (5) glass domes, (4) black sensor element, (6) sunshade, (7) drying indicator, (9) leveling feet, (10) level, (11) Connectors

Pyranometer (standard)

The main components of a pyranometer are:

  • A thermopile with a black housing. This sensor absorbs all solar radiation in a wavelength range from 0.3 µm to 5 µm. The response is almost proportional to the cosine of the zenith angle.
  • The glass dome limits the spectral range to 0.3 µm to 2.8 µm (the range above 2.8 µm is filtered out). The glass dome also protects the thermopile from convection .

The black coating of the thermopile absorbs the solar radiation and converts it into heat. The heat is conducted through the sensor into the housing of the pyranometer. The thermopile emits an electrical voltage proportional to the radiation.

A pyranometer is an active measuring device; so it does not require an external energy source.

Shadow ring pyranometer

A shadow ring pyranometer is a pyranometer supplemented by a thin, often semicircular cover for measuring diffuse radiation. The shadow ring shields the sensors from direct solar radiation so that they only measure the diffuse short-wave radiation. The direct radiation can be calculated from measured diffuse radiation and global radiation.

The shadow ring must be carried along with the course of the sun . Because the shadow ring also prevents diffuse irradiation from the shielded area of ​​the sky, the measurement results must be subsequently corrected by a value for this area.

Albedometer or dual pyranometer

An albedometer for measuring the short-wave solar radiation from above and the short-wave radiation reflected from below is a double pyranometer. It basically consists of two interconnected star pyranometers: On the back of the upward-facing pyranometer there is another downward-facing pyranometer. The pyranometer, rotated horizontally by 180 °, is used to measure the reflected solar radiation. From the ratio of the two radiation fluxes, the albedo , i.e. H. calculate the reflectivity of the surfaces under the albedometer.

See also

Web links

Individual evidence

  1. ISO 9060: 1990. Solar energy - Specification and classification of instruments for measuring hemispherical solar and direct solar radiation
  2. a b Pyranometer - measurement of global and diffuse radiation. German Weather Service, accessed on May 14, 2020 .
  3. Albedometer. In: Spectrum Lexicon of Geosciences. Retrieved May 14, 2020 .