Pyranometer
Encyclopedia
A pyranometer is a type of actinometer
used to measure broadband solar irradiance on a planar surface and is a sensor that is designed to measure the solar radiation flux density (in watts per metre square) from a field of view of 180 degrees. The name pyranometer stems from Greek, "pyr - πῦρ" meaning "fire" and "ano - ἄνω" meaning "above, sky".
A typical pyranometer does not require any power to operate.
extends approximately from 300 to 2,800 nm. Pyranometers usually cover that spectrum with a spectral sensitivity that is as “flat” as possible.
To make a measurement of irradiance
, it is required by definition that the response to “beam” radiation varies with the cosine of the angle of incidence, so that there will be a full response when the solar radiation hits the sensor perpendicularly (normal to the surface, sun at zenith, 0 degrees angle of incidence), zero response when the sun is at the horizon (90 degrees angle of incidence, 90 degrees zenith angle), and 0.5 at 60 degrees angle of incidence. It follows that a pyranometer should have a so-called “directional response” or “cosine response” that is close to the ideal cosine characteristic.
The black coating on the thermopile sensor absorbs the solar radiation. This radiation is converted to heat. The heat flows through the sensor to the pyranometer housing. The thermopile sensor generates a voltage output signal that is proportional to the solar radiation.
, climatology
, solar energy studies and building physics. They can be seen in many meteorological stations - typically installed horizontally and next to solar panel
s - typically mounted with the sensor surface in the plane of the panel.
(WMO). This standard discriminates three classes. The best is (confusingly) called "secondary standard," the second best "first class" and the last one "second class."
Calibration is typically done relative to World Radiometric Reference (WRR). This reference is maintained by PMOD in Davos
, Switzerland
.
Actinometer
Actinometers are instruments used to measure the heating power of radiation. They are used in meteorology to measure solar radiation as pyrheliometers.An actinometer is a chemical system or physical device which determines the number of...
used to measure broadband solar irradiance on a planar surface and is a sensor that is designed to measure the solar radiation flux density (in watts per metre square) from a field of view of 180 degrees. The name pyranometer stems from Greek, "pyr - πῦρ" meaning "fire" and "ano - ἄνω" meaning "above, sky".
A typical pyranometer does not require any power to operate.
Explanation
The solar radiation spectrumSpectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
extends approximately from 300 to 2,800 nm. Pyranometers usually cover that spectrum with a spectral sensitivity that is as “flat” as possible.
To make a measurement of irradiance
Irradiance
Irradiance is the power of electromagnetic radiation per unit area incident on a surface. Radiant emittance or radiant exitance is the power per unit area radiated by a surface. The SI units for all of these quantities are watts per square meter , while the cgs units are ergs per square centimeter...
, it is required by definition that the response to “beam” radiation varies with the cosine of the angle of incidence, so that there will be a full response when the solar radiation hits the sensor perpendicularly (normal to the surface, sun at zenith, 0 degrees angle of incidence), zero response when the sun is at the horizon (90 degrees angle of incidence, 90 degrees zenith angle), and 0.5 at 60 degrees angle of incidence. It follows that a pyranometer should have a so-called “directional response” or “cosine response” that is close to the ideal cosine characteristic.
Design of pyranometers
In order to attain the proper directional and spectral characteristics, a pyranometer’s main components are:- A thermopileThermopileA 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....
sensor with a black coating. This sensor absorbs all solar radiation, has a flat spectrum covering the 300 to 50,000 nanometer range, and has a near-perfect cosine response.
- A glass dome. This dome limits the spectral response from 300 to 2,800 nanometers (cutting off the part above 2,800 nm), while preserving the 180 degrees field of view. Another function of the dome is that it shields the thermopile sensor from convection.
The black coating on the thermopile sensor absorbs the solar radiation. This radiation is converted to heat. The heat flows through the sensor to the pyranometer housing. The thermopile sensor generates a voltage output signal that is proportional to the solar radiation.
Usage
Pyranometers are frequently used in meteorologyMeteorology
Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...
, climatology
Climatology
Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences...
, solar energy studies and building physics. They can be seen in many meteorological stations - typically installed horizontally and next to solar panel
Photovoltaic module
A solar panel is a packaged, connected assembly of solar cells, also known as photovoltaic cells...
s - typically mounted with the sensor surface in the plane of the panel.
Standardisation
Pyranometers are standardised according to the ISO 9060 standard, that is also adopted by the World Meteorological OrganizationWorld Meteorological Organization
The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...
(WMO). This standard discriminates three classes. The best is (confusingly) called "secondary standard," the second best "first class" and the last one "second class."
Calibration is typically done relative to World Radiometric Reference (WRR). This reference is maintained by PMOD in Davos
Davos
Davos is a municipality in the district of Prättigau/Davos in the canton of Graubünden, Switzerland. It has a permanent population of 11,248 . Davos is located on the Landwasser River, in the Swiss Alps, between the Plessur and Albula Range...
, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
.
See also
- Heat flux sensorHeat flux sensorA heat flux sensor is a transducer that generates an electrical signal proportional to the total heat rate applied to the surface of the sensor. The measured heat rate is divided by the surface area of the sensor to determine the heat flux....
- Net radiometerNet radiometerA net radiometer is a type of actinometer used to measure net radiation at the Earth's surface in meteorological applications.The name net radiometer reflects the fact that it is supposed to measure incoming minus upwelling radiation...
- PyrgeometerPyrgeometerA pyrgeometer is a device that measures the atmospheric infra-red radiation spectrum that extends approximately from 4.5 µm to 100 µm.- Pyrgeometer components :A pyrgeometer consists of the following major components:...
- PyrheliometerPyrheliometerA pyrheliometer is an instrument for direct measurement of solar irradiance. Sunlight enters the instrument through awindow and is directed onto a thermopile which converts heat to an electrical signal that can be recorded. The signal voltage is converted via a formula to measure watts per square...
- RadiometerRadiometerA radiometer is a device for measuring the radiant flux of electromagnetic radiation. Generally, the term radiometer denotes an infrared radiation detector, yet it also includes detectors operating on any electromagnetic wavelength....
- Sun pathSun pathSun path refers to the apparent significant seasonal-and-hourly positional changes of the sun as the Earth rotates, and orbits around the sun. The relative position of the sun is a major factor in the heat gain of buildings and in the performance of solar energy systems...