Operating Principle:

Pyranometers measure solar radiation by utilizing a thermopile sensor that generates a voltage proportional to the temperature difference between a blackened surface and the instrument's body, caused by the absorption of sunlight. This voltage output is calibrated to provide an accurate measurement of solar irradiance. 

• Advantage: Pyranometers are simple, widely applicable, provide real-time data, portable, and cost-effective.

• Disadvantage: Only measures solar irradiance

• Uncertainty: Sensitive to solar angles and weather interference

Operating Principle:

Pyrheliometers measure direct beam solar irradiance by tracking the sun in the sky. Sunlight enters the instrument through a window and is directed onto a thermopile which converts heat to an electrical signal that can be recorded.

• Advantage: Extremely accurate in direct solar irradiance measurements

• Disadvantage:  Requires precise alignment with the sun, making an unobstructed environment necessary for accurate measurements

• Limitations: It cannot measure diffuse radiation.

Operating Principle:

Pyrgeometers measures downward longwave infrared radiation through change in resistance. Its resistance changes proportionally to the amount of energy transferred.

• Advantage: Accurate measurements of downward longwave infrared radiation

• Disadvantage: Is sensitive to environmental interference and does not measure shortwave radiation 

• Uncertainty: Measurements are easily affected by nearby reflections and obstructions.