What is a Pyranometer? - Definition, Types, and Applications

A pyranometer is a type of radiation thermometer used to measure the solar irradiance (insolation) from the sun. It is designed to measure the total solar radiation (both visible and invisible) that reaches the Earth's surface, and is commonly used in meteorology, agriculture, and solar energy applications.

The term "pyranometer" was coined by Sir George Gabriel Stokes in 1880, derived from the Greek words "pyre" meaning fire and "meter" meaning measure. The instrument consists of a flat, black surface with a small opening that allows sunlight to enter and be measured. The pyranometer is calibrated to produce a voltage output that is proportional to the amount of solar radiation it receives.

Pyranometers are available in different types, including:

1. Pyranometer with a single thermopile: This is the most common type, which consists of a flat black surface with a small opening and a thermopile (a stack of thermocouples) underneath. The thermopile converts the absorbed solar radiation into an electrical voltage.
2. Pyranometer with a multi-thermopile: This type has multiple thermopiles to increase the sensitivity and accuracy of the measurements.
3. Pyranometer with a silicon photodiode: This type uses a silicon photodiode to convert the absorbed solar radiation into an electrical current.
4. Pyranometer with a pyroelectric detector: This type uses a pyroelectric detector to measure the changes in temperature caused by the absorption of solar radiation.

Pyranometers are widely used in various applications, including:

1. Solar energy monitoring: To measure the amount of solar energy available for solar power generation.
2. Agricultural research: To study the effects of solar radiation on crop growth and development.
3. Climate monitoring: To measure the amount of solar radiation that reaches the Earth's surface and contribute to climate models.
4. Satellite remote sensing: To measure the amount of solar radiation reflected by the Earth's surface from space.