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Solar Radiation Research Laboratory Photographs

The Solar Radiation Research Laboratory (SRRL) houses more than 70 instruments to analyze and record solar radiation and surface meteorology data. Learn more about this equipment by exploring the photographs below. Click on a thumbnail to view the full image.

Photo of researcher working on an instrument platform in front of the SRRL building.

The SRRL is located on South Table Mountain in Golden, Colorado, at 39.74° N, 105.18° W, and 1,829 m AMSL.


Photo of four researchers working on equipment atop the SRRL instrument deck.

The SRRL's instrument deck is 96 ft long and 16 feet wide.


Photo of two pyrheliometers mounted to an automatic sun-tracking base.

These two SRRL pyrheliometers are mounted to automatically track the sun for continuous monitoring of direct-normal solar irradiance. These thermopile-based radiometers have a uniform spectral response of 280–2,800 nm and a 5.7° field of view.


Photo of a typical pyranometer on a blue background.

This pyranometer is used to measure total hemispheric solar irradiance from 280 to 2,800 nm as part of the SRRL Baseline Measurement System.


Photo of a nearly 360° view of the sky framed in the lens of a camera.

This all-sky photograph was taken at the SRRL under partly cloudy conditions. The 8-mm camera lens approximates the 2p steradian field of view of a pyranometer.


Photo of a pyranometer mounted on a base with an automatic shading disk, a long metal arm that casts a shadow on the measurement equipment.

This pyranometer is mounted under an automatic shading disk to measure diffuse horizontal solar irradiance.


Photo of a pyranometer and shading disk with the sun in the background.

A shading disk blocks the direct-normal irradiance from a pyranometer receiver to create a measurement of diffuse horizontal or sky irradiance.


Photo of a pyranometer mounted on a platform with a shading band, a large horshoe-shaped band that creates shadows across the instrument.

This pyranometer is mounted under an adjustable shading band to measure diffuse horizontal solar irradiance.


Close-up photo of a pyranometer shaded by the shadow of a shading band.

Shading bands are adjusted daily for the changing solar declination angle to match the path of the sun across the sky. A shadowband correction factor must be applied to pyranometer measurements to account for the portion of the sky blocked by the band.


Photo of two pyranometers, one with a shadow band, and a pyrheliometer mounted on a single platform.

These pyranometers and pyrheliometer are positioned in a typical arrangement for independent measurements of global, direct, and diffuse solar irradiance. Note that the global pyranometer is not obstructed by the other instruments.


Photo of two pyranometers mounted on a single platform. One pyranomter has a colored filter.

The SRRL Baseline Measurement System collects direct normal and global horizontal solar irradiance from instruments with red Schott glass filters. These colored filters have a cut-on wavelength at 780 nm. The difference between filtered and unfiltered data can be used to estimate the atmospheric precipitable water vapor content.


Photo of a single pyranometer mounted on a platform at a 40° angle.

The SRRL Baseline Measurement System collects the global irradiance on a south-facing surface tilted 40° from horizontal. These data are used to estimate the energy available to a fixed flat-plate solar collector positioned for optimal annual performance.


Photo of a platform with a pyranometer mounted upside-down on an extending arm to measure irradiance reflected from the ground below.

The SRRL Baseline Measurement System collects the reflected solar irradiance from an inverted pyranometer 1.5 m above the surface. Previous research support included the irradiance distributions on vertical surfaces for model evaluations.


Photo of a radiometer mounted on a solar tracker with a view-limiting tube.

The SRRL Baseline Measurement System collects 5-minute averages of the total ultraviolet portion (295–385 nm) of the solar spectrum. Here, a total ultraviolet radiometer is mounted on a solar tracker and fitted with a view-limiting tube to measure the direct-normal component (a 5.7° full angle). A second photometer (not shown) is mounted on a fixed, horizontal surface for the total hemispheric measurement of ultraviolet radiation.


Photo of a researcher making adjustments to a pyranometer on the SRRL instrument deck.

A pyranometer mounted on an automatic solar tracker provides measurements of the global-normal solar irradiance to estimate the performance of a tracking flat-plate collector.


Photo of a group of table-mounted pyranometers on the equipment deck of the SRRL.

Broadband Outdoor Radiometer Calibration is routinely performed at the SRRL. All types of pyranometers and pyrheliometers are calibrated to the World Radiometric Reference maintained by the World Radiation Center in Davos, Switzerland.


Photo of an absolute cavity radiometer in the SRRL outdoor test area.

An absolute cavity radiometer is used to transfer the World Radiometric Reference to all radiometers calibrated at the SRRL. This electrically self-calibrating instrument is one of several used by NREL to maintain calibration traceability to the World Radiometric Reference.


Photo of an absolute cavity radiometer receiver displayed in a glass tube.

The receiver of an absolute cavity radiometer is carefully constructed and characterized to allow a measurement uncertainty of less than 0.5%. This is the basis of the World Radiometric Reference.


Photo of a pyranometer and shadow band covered in snow and ice.

Daily maintenance of all instruments in the SRRL Baseline Measurement System ensures research-quality data. Weather conditions and maintenance activities are recorded for reference and the assessment of data quality.


Photo of rotating shadowband radiometer mounted on the SRRL equipment deck.

A rotating shadowband radiometer uses a fast-response, silicon-based detector to measure the global and diffuse irradiance and compute the direct-normal component.