Difference Between Pyranometer and Pyrheliometer

Solar radiation measurement is essential in solar energy systems, meteorology and climate research. Two important instruments used for this purpose are the Pyranometer and the Pyrheliometer. While both devices measure solar irradiance, they differ in the type of radiation they detect and their operating methods.

Pyranometer

It is an instrument which measures global solar radiation (i.e. total sunlight energy) received on a horizontal surface. It measures both direct solar radiation and diffuse radiation from the sky. There are two main types viz. thermopile and photodiode sensor based pyranometers. Most of the pyranometers work based on thermoelectric effect. Small amount of voltage is produced based on solar radiation intensity.

Pyrheliometer

It is an instrument used to measure direct beam solar radiation coming straight from the sun. It does not measure diffuse radiation from the sky. Let us understand its working operation.

• The instrument has a long collimating tube that allows only direct sunlight to reach the sensor.
• The tube is pointed directly toward the sun.
• Solar radiation enters the tube and strikes a thermopile sensor.
• The absorbed energy creates a temperature difference that generates electrical voltage.
• The voltage is proportional to the direct solar irradiance.

Difference Between Pyranometer and Pyrheliometer

Following table mentions comparison between these two solar instruments.

Conclusion

In summary, Pyranometer measures total solar radiation from the sky where as Pyrheliometer measures direct sunlight coming straight from the sun. Understanding the difference between a pyranometer and a pyrheliometer helps researchers, engineers and solar energy professionals accurately analyze solar radiation data and optimize solar power system performance.