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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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What are pyrheliometers?
Instruments measures beam radiations
Diffuse radiations
Direct radiations only
None of the above
Instruments measures beam radiations
Quick Summary: A pyrheliometer is a precision instrument designed specifically to measure the intensity of direct solar radiation (beam radiation) falling on a surface held normal to the sun's rays. It uses a collimator tube to restrict the field of view, ensuring that only direct beam radiation from the solar disc and a small surrounding sky area reaches the sensor.
A pyrheliometer is a precision instrument designed specifically to measure the intensity of direct solar radiation (beam radiation) falling on a surface held normal to the sun's rays. It uses a collimator tube to restrict the field of view, ensuring that only direct beam radiation from the solar disc and a small surrounding sky area reaches the sensor.
Ibeam=SV — Intensity of beam radiation, where V is output voltage and S is sensitivity constant
FOV≈5° — Typical field of view aperture angle for solar tracking
The sensor, typically a thermopile, is placed at the base of a narrow tube (collimator) with a small aperture angle. This aperture allows the instrument to ignore diffuse or scattered radiation from the sky, measuring only the collimated beam of sunlight. The absorbed radiant energy creates a temperature difference across the thermopile junctions, generating an electromotive force (EMF) proportional to the irradiance, defined by I=KV, where V is the output voltage and K is the calibration constant.
Measures direct beam irradiance at normal incidence.
Requires a solar tracker to follow the sun's movement accurately throughout the day.
Used for calibration of other solar instruments like pyranometers.
Essential for evaluating solar concentrator (CSP) performance.
High accuracy for direct normal irradiance (DNI) measurements
Essential for Concentrated Solar Power (CSP) site assessment
Cannot measure diffuse or global horizontal irradiance
Requires complex, active solar tracking systems
Solar research and meteorology
Performance testing of solar thermal collectors and PV concentrators
Option B refers to a Pyranometer (in diffuse mode with a shadow band) or a Diffusiometer.
Option C is technically a subset of Option A; however, 'Beam radiation' is the standardized technical terminology used in instrumentation standards like ISO 9060.
A is correct — A pyrheliometer is specifically calibrated and designed to measure the direct beam component of solar radiation at normal incidence.
Always remember: Pyrheliometers measure Beam (Direct) radiation, while Pyranometers measure Global or Diffuse radiation by capturing the entire hemisphere of the sky.