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A pyrheliometer is an instrument for measurement of direct beam
A pyrheliometer is an instrument for measurement of direct beam solar irradiance
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
. Sunlight enters the instrument through a window and is directed onto a thermopile
A thermopile is an electronic device that converts thermal energy into electrical energy. It is composed of several thermocouples connected usually in series or, less commonly, in parallel. Such a device works on the principle of the thermoele ...
which converts heat to an electrical signal that can be recorded. The signal voltage is converted via a formula to measure watts per square metre.
Standards
Pyrheliometer measurement specifications are subject toInternational Organization for Standardization
The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Art ...
(ISO) and World Meteorological Organization
The World Meteorological Organization (WMO) is a specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology and geophysics.
The WMO originated from the Internat ...
(WMO) standards.
Comparisons between pyrheliometers for intercalibration are carried out regularly to measure the amount of solar energy received.
The aim of the International Pyrheliometer Comparisons, which take place every 5 years at the World Radiation Centre in Davos
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Davos (, ; or ; rm, ; archaic it, Tavate) is an Alpine resort town and a municipality in the Prättigau/Davos R ...
, is to ensure the world-wide transfer of the World Radiometric Reference.
During this event, all participants bring their instruments, solar-tracking and data acquisition systems to Davos to conduct simultaneous solar radiation measurements with the World Standard Group.
Applications
Typical pyrheliometer measurement applications include scientific meteorological and climate observations, material testing research, and assessment of the efficiency of solar collectors and photovoltaic devices.Usage
Pyrheliometers are typically mounted on asolar tracker
A solar tracker is a device that orients a payload toward the Sun. Payloads are usually solar panels, parabolic troughs, fresnel reflectors, lenses or the mirrors of a heliostat.
For flat-panel photovoltaic systems, trackers are used to mini ...
. As the pyrheliometer only 'sees' the solar disk, it needs to be placed on a device that follows the path of the sun.
See also
*Actinometer
Actinometers are instruments used to measure the heating power of radiation. They are used in meteorology to measure solar radiation as pyranometers, pyrheliometers and net radiometers.
An actinometer is a chemical system or physical device which ...
* Active cavity radiometer
* Bolometer
* Pyrometer
A pyrometer is a type of remote-sensing thermometer used to measure the temperature of distant objects. Various forms of pyrometers have historically existed. In the modern usage, it is a device that from a distance determines the temperature of ...
* Solar constant
The solar constant (''GSC'') is a flux density measuring mean solar electromagnetic radiation (total solar irradiance) per unit area. It is measured on a surface perpendicular to the rays, one astronomical unit (au) from the Sun (roughly the d ...
References