National Solar Thermal Test Facility

Operated by Sandia National Laboratories for the U.S. Department of Energy (DOE), the National Solar Thermal Test Facility (NSTTF) is the only test facility of this type in the United States. The NSTTF’s primary goal is to provide experimental engineering data for the design, construction, and operation of unique components and systems in proposed solar thermal electrical plants planned for large-scale power generation.

In addition, the site was built and instrumented to provide test facilities for a variety of solar and nonsolar applications. The facility can provide:

  • high heat flux and temperatures for materials testing or aerodynamic heating simulation;
  • large fields of optics for astronomical observations or satellite calibrations;
  • a solar furnace; and
  • a rotating platform for parabolic trough evaluation.

The NSTTF welcomes all users. Several mechanisms are available for non-Sandia researchers to contract with Sandia to use the facility. Previous users include government contractors and agencies, research institutes, universities, and private companies.

Download the NSTTF Fact Sheet (PDF).

Take a virtual tour of the National Solar Thermal Test Facility.

The heliostat field has 218 individual heliostats. This capability directly supports SunShot goals by providing flux levels of greater than 300 W/cm2 and total power in excess of 6 MWt. Each heliostat has two motors and two drives (one azimuth and one elevation), one 480 V power box, one electronics box, and one control box and associated cabling. The total reflective area on each heliostat is 37 m2. The reflectivity on the recently replaced facets is 96%.

The molten salt test loop directly supports SunShot goals by providing development for thermal energy storage costs ≤$15/kWhth and allowing greater collection efficiencies and higher-temperature operation for linear Fresnel and trough systems through utilization of molten salt HTF. The facility also provides a means of performing accelerated lifetime testing on components, thus reducing the risk of the technology. Though operating below 600°C, many of the lessons learned at this facility will be directly applicable to molten salt systems operating in the SunShot temperature range ≥ 650°C.

The NSTTF Apartment Complex was designed to facilitate high-temperature experiments within controlled environments. To date, many of the experiments performed in this facility have consisted of materials studies within the molten salt test pots, located in three of the four test cells, as well as sodium, which has been tested within heat pipes in the remaining test cell. Each test cell is equipped with chemical and fire detection sensors and related instrumentation, as well as a customized ventilation system. Fire extinguishing powder and other ES&H engineering controls are also found at this facility to allow for sodium and NaK experiments. The facility also has a respective heater instrumentation and controls for high-temperature operation, where experiments have been performed up to temperatures as high as 850°C./p

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 parts of 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 0.2°C at temperatures up to 375°C 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

    Two different fluids are used for trough testing to cover the temperature range of near ambient temperatures up to 375°C. 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.

  • SNL’s Photovoltaic and Distributed Systems Integration department and NSTTF staff worked with SunPower to install 110 kWe of SunPower’s new C7 low-concentration PV systems at the NSTTF. This was the first demonstration of a utility-size CPV test at SNL. The PV Reliability group worked closely with SunPower during the development and early implementation stage to support design optimization. SNL uses the systems data to evaluate the reliability of this low-concentration system. SunPower uses the site to test new components in side-by-side comparisons. The groups work together to improve performance models specific to this technology.

    The Concentrating photovoltaic array is located at the NSTTF. Hardware is provided and operated by SunPower Corporation.

    Test Cell 1

    This testing area is primarily configured to establish the overall performance of a heat-powered engine, including its efficiency, power output, and reliability. To date, research has been conducted both on externally heated Stirling, organic Rankine, and steam Rankine engines, and on the devices that generate the thermal input to these engines.

    The capabilities of Test Cell 1 include a fuel/air combustion skid for energy input; cooling systems for heat removal; 130 kW eddy-current dynamometer for precision power measurements; and instrumentation, system protection, and power control channels. To measure the thermal output of fuel-fired thermal energy systems, such as a gas-fired, liquid-metal evaporator for Stirling engines, Test Cell 1 offers a gas-gap calorimeter, which simulates the engine by allowing the liquid metal to condense at operating temperatures.

    Test Cell 2

    Test Cell 2 is currently set up to test bench-scale solar receivers, which are devices that absorb the concentrated solar energy from the sun and transfer it to a heat engine. In the testing area, the solar input is simulated by quartz lamp banks and their associated power control systems. Power is absorbed using gas-gap calorimeters.

    This test cell also supports bakeout and fills operations on liquid-metal heat-transfer devices. For these operations, portable heat trace and heat-trace control systems are available, as are portable vacuum systems and residual gas analyzers.

    Data/Control Room

    The Engine Test Facility offers a well-equipped control room for personnel to monitor tests. The data acquisition system (DAS) measures, displays, and stores the data from each data channel in the system. The HP3852 DAS is controlled by a personal computer with LabView software. Additional personal computers are also available for data reduction and other applications.

    Color video cameras are provided to capture the tests on film. The video lines are routed into the control room, are displayed on high-resolution monitors, and can be stored on 8-mm tape.

    Maintenance/Assembly Bay

    A maintenance and assembly bay is situated next to the test cells for test preparations. This bay includes the following conveniences:

    • 14-ft. ceiling
    • 10-ft. doors
    • Overhead crane
    • Electrical power
    • Compressed air
    • Workbenches
    • Parts Cleaner

    Optical equipment located in this lab space and tools developed, using DOE funds, allows for optical characterization of heliostat and dish facets. These flexible analytical tools, along with the on-site expertise, currently support the evaluation and development of low-cost, high-performance heliostat facets. The tools are also applicable to assembly/production line environments. In addition, field support for characterization and alignment of CSP systems is provided. SOFAST, a highly accurate fringe-reflection-based measurement tool, is used to characterize and set the focus heliostat facets in the laboratory. H-FACET is an optical-based alignment tool that is used to efficiently re-align the facets after re-attaching them to the heliostat. AIMFAST is used to characterize dish facets and align dish systems.

    This area of the site allows industry partners to install full-scale solar dishes for long-term reliability testing and evaluation. There are currently 10 Stirling Energy Systems (SES) dishes and six Infinia dishes at this location. The site also includes two SNL-developed solar dishes that are available for research. Solar dishes can be used for the high-temperature portions of the SunShot goals.

    A solar furnace uses a heliostat that tracks the sun to direct sunlight onto a mirrored parabolic dish. Because the focal point of the dish does not move, it is simple to install experiments. The power level of the furnace is adjusted using an attenuator that works like a venetian blind located between the heliostat and the dish.

    The Test Facility has a small solar furnace with:

    • High-temperature solar thermochemical water-spitting experiments
    • A heliostat that is 95 m²
    • A dish that is 6.7056 meters in diameter

    This furnace provides:

    • 16 kW total thermal power
    • Peak flux up to 500 W/cm²

    The furnace has a power control to simulate nuclear and other thermal transients.

    Applications include:

    • Investigating the thermophysical properties of materials in concentrated sunlight, including thermal expansion, thermal conductivity and diffusivity, specific heat, mechanical properties, and spectral emissivity and absorptivity
    • Simulation of thermal effects of nuclear explosions on materials and components
    • Determining the performance and failure thresholds of high-temperature ceramic and refractory materials

    The High-Flux Solar Simulator with Automated Sample Handling & Exposure System (ASHES) is a one-of-a-kind tool which can be used 24/7 with metal-halide lamps. ASHES provides accelerated lifetime aging tests for materials under high-temperature/high-flux conditions. A robotic sample-handling system can be used to move multiple coupons automatically into and out of the concentrated flux sequentially to expose the samples to predetermined temperatures, fluxes, and/or durations. The peak irradiance is ~1.1 MW/m2 with an average irradiance of ~0.9 MW/m2 over a spot size of ~1 inch (2.5 cm).