Rotating Platform

The AZTRAK (AZimuthal TRAcKing) Rotating Platform system was originally designed and installed at Sandia during the early 1980s to enable more accurate and rapid thermal performance testing of parabolic concentrators. When a parabolic concentrator (or any other solar collecting device) is equipped with an elevation tracker and mounted on the rotating platform, the solar position of the collector can be continuously maintained at any desired orientation.

The High Temperature Fluid Loop was designed in conjunction with the AZTRAK system to supply heated fluid to the collector inlet, at steady-state fluid temperatures up to 375°C, to evaluate the thermal performance of a parabolic concentrator at system operating temperatures.

The rotating platform and the high temperature fluid loop are a unique national facility:

• Ability to track sun in azimuth at 0 degrees incidence angle (eliminate off-axis cosine affects), but can track at any desired incident angle.
• Azimuth tracking: Resolution of 0.09 deg., accuracy of 0.30 deg.
• Elevation tracking: Resolution of 0.04 deg.; accuracy of 0.08 deg.
• Heat transfer fluid thermal stability at the test device of 0.2C at temperatures up to 375C at a flow rate of 550.2 l/min for a 15 to 20 minute test window
• Solar averaged mirror specular reflectivity measured before each test
• Documented collector mirror and receiver alignment

To cover the temperature range of near ambient temperatures up to 375 used for trough testing two different fluids are used. Water is used for testing where the fluid temperatures are near ambient. The high temperature fluid loop contains oil, Syltherm 800, and is used from 70°C up to 375°C.

SEGS LS-2 trough undergoing test on Sandia’s rotating platform

Precision Measurement System Used For Trough Testing at Sandia National Labs

• Meteorological weather station for ambient air temperatures, wind speed and direction, and DNI (Direct Normal Insolation) measurement for solar radiation
• Inlet and outlet temperatures for the trough receivers taken with precision 4-wire RTDs and Thermistors
• Flow measurements for the trough receivers taken with two turbine flow meters
• Collector module mirror alignment using distant observer technique with digital imaging and analysis
• Trough module efficiency measurement uncertainty typically ± 3 to 5 percent

Minimizing measurement uncertainty is not a trivial task!!
All instruments are calibrated with NIST traceability. NIST traceability obtains statistically defensible and reproducible data. Accuracy and traceability of measurement uncertainty becomes more important as receiver performance improves.

Tests that can be performed on the rotating platform for trough modules:

• Steady-state Efficiency vs. ∆T
• Out-of-Focus Heat Loss vs. ∆T during nighttime clear sky conditions
• Incident Angle Efficiency vs. ∆T where ∆T = average collector fluid temperature above ambient

The rotating platform can also be used for testing flat plate collectors for either commercial or residential applications that are used for heating fluids.