NREL: Concentrating Solar Power Research

To research, develop, and test a variety of concentrating solar power technologies, NREL features the following laboratory capabilities:

High-Flux Solar Furnace (HFSF)

NREL's High-Flux Solar Furnace.

The power generated at NREL's High-Flux Solar Furnace (HFSF) can be used to expose, test, and evaluate many components—such as receivers, collectors, and reflector materials—used in concentrating solar power systems.

The 10-kilowatt HFSF consists of a tracking heliostat and 25 hexagonal mirrors to concentrate solar radiation. The solar furnace can nominally provide flux at 2,500 suns, but, when required, can use specialized secondary optics to generate significantly higher concentrations (greater than 20,000 suns). Flux levels and distributions can also be tailored to the needs of a particular research activity.

The operational characteristics and size of the facility make it ideal for testing over a wide range of technologies with a diverse set of experimental requirements. The high heating rates make the HFSF an ideal tool for testing high-temperature materials, coatings on metals and ceramics, and other materials-related applications. Perhaps the most exciting use of the facility is to provide a platform for testing prototype advanced converters and chemical reactors for solar electric and solar chemistry applications. Researchers can also use the HFSF to evaluate and develop state-of-the-art measurement systems for the extreme solar environment.

The HFSF is available to industrial, university, and government researchers. We can provide experienced staff to operate the facility for a variety of experimental objectives.

For more information about the HFSF, contact Carl Bingham, Staff Engineer, 303-384-7477.

NREL's Large Payload Solar Tracker.

Large Payload Solar Tracker

NREL recently acquired a multipurpose, large payload tracker to support testing of solar components that require tracking the sun in elevation and azimuth. Concentrating collectors require 2-axis tracking to focus sunlight on a thermal or photovoltaic (PV) receiver. For flat-plate collectors, flat-plate PV, or solar hot water, this would imply tracking to minimize variation in solar resource during on-sun testing. As applicable, the site can be used to supplement metrology activities that require 2-axis tracking for simultaneous calibration of a large number of solar radiation measurement instrumentation. The large payload tracker is capable of carrying a maximum vertical load of 9,000 pounds with a tracking accuracy of 1 milliradian.

Advanced Optical Materials Laboratory

NREL's Advanced Optical Materials Laboratory provides substantial analytical and measurement capabilities for developing and testing optical materials used in concentrating solar power systems.

NREL's Advanced Optical Materials Laboratory.

The laboratory has many tools and instruments that allow measurement of optical properties and performance. We can measure a wide range of feature sizes (from nanometers to meters) and sample sizes (from millimeters to tens of meters) traceable to the National Institute of Standards and Technology.

We offer three types of exposure testing capabilities for optical materials, which include:

An international network of instrumented, outdoor exposure test sites
Accelerated laboratory-controlled exposure chambers
An ultra-accelerated, natural sunlight exposure testing facility.

For more information about NREL's capabilities in this area, see our information about optical analysis and modeling.

Advanced Thermal Storage Materials Laboratory

An NREL scientist works in the Advanced Thermal Storage Materials Laboratory. Credit: Warren Gretz

The Thermal Storage Materials Laboratory supports NREL's research and development of advanced heat transfer fluids for the next generation of parabolic trough systems. Our goal is to identify fluids with thermal and oxidative stabilities that can withstand extreme operating conditions, such as temperatures up to 425°C while remaining liquid at or below 0°C, and that can function as advanced thermal storage media.

To develop these heat transfer fluids, we use a synthetic chemistry laboratory that combines a work area for basic wet chemistry with extensive thermal and spectroscopic analysis capabilities. We can synthesize fluids in gram quantities and immediately evaluate their thermal behavior. To evaluate thermal behavior, we use NREL's molecular-beam mass spectrometry system to study the thermal degradation mechanisms by which newly synthesized fluids decompose at elevated temperatures.

Optical Testing Laboratory and Beam Characterization System

To develop and test concentrators for concentrating solar power systems, NREL researchers use VSHOT (Video Scanning Hartmann Optical Test) and a beam characterization system.

An NREL researcher uses VSHOT to test a parabolic trough concentrator.

VSHOT

We use VSHOT, developed by the U.S. Department of Energy's SunLab, to characterize the optical performance of point-focus and line-focus optical concentrators. The system uses laser ray tracing combined with fast video imaging to mathematically describe mirror concentrator surfaces and compare them to desired surfaces. It reports slope errors of the actual surface relative to the desired surface and provides plots of error location, magnitude, and direction. The surface slope data and mathematical surface description produced by VSHOT can be input into ray trace models to predict flux distributions on receivers.

And VSHOT is fast. It allows us to thoroughly test a solar thermal concentrator in 2 to 3 minutes or less. When detailed data isn't needed, VSHOT can test mirrors in even less time. SunLab continues to improve the speed and functionality of VSHOT, extending its capabilities as a field instrument for concentrator installation and alignment. The system has been used extensively both in the laboratory and in the field to quantify parabolic dish and parabolic trough optical performance, providing developers with valuable information in their efforts to deploy cost effective, high performance concentrating solar power technology.

Beam Characterization System

This image, developed by the beam characterization system, helps NREL researchers measure the distribution of concentrated sunlight on a target.

We use a beam characterization system to measure the distribution of concentrated sunlight on a target. The portable system acquires and processes images reflected from a diffuse, or Lambertian, target. These images are proportional to the incident flux. The system consists of:

The Beamview Digital Laser Beam Diagnostic System from Coherent, Inc. comprises the camera, frame grabber, and software. The beam characterization system allows us to measure the solar flux incident at the focal plane of thermal or concentrating photovoltaic receiver. The instrument is used extensively at the High-Flux Solar Furnace. However, because the beam characterization system is portable, it is used periodically to support field measurements at the request of our industry partners.

Receiver Test Laboratory

NREL's receiver thermal loss test stand

With NREL's parabolic trough receiver test stand, researchers can analyze the steady-state off-sun thermal losses of receivers used in solar parabolic trough power plants. First, electric heaters and thermocouples are placed inside the receiver being tested. Then, the heater power use is recorded at a desired absorber temperature. This routine is repeated for several different absorber temperatures, generating heat loss curves for a receiver.

Research continues to help reduce collector optical losses, as well as to further reduce receiver heat loss at elevated temperatures. For more information on receiver heat loss testing, visit TroughNet.

Heat Collection Element (HCE) Temperature Survey

NREL's non-disruptive, automated method records HCE glass temperatures in a parabolic trough power plant solar field. Occasional HCE temperature surveys can document the condition of HCEs over extended periods of time and locate those with unacceptable heat losses.

In this method, a vehicle with an infrared (IR) camera and Global Positioning System (GPS) receiver is driven down each solar field row. A data acquisition system uses the IR camera to photograph HCE glass temperatures and processes them automatically. The glass temperatures of about 6000 HCEs can be determined in one day. During this time, the solar plant operates normally.

Image from NREL's infrared method showing two adjacent parabolic trough receiver tubes in front of dark-blue-colored mirror facets in background. The left-hand receiver appears as an orange stripe, indicating a glass surface temperature of 300 degrees Fahrenheit. The right-hand receiver appears as a red stripe, indicating a glass surface temperature of 150 degrees Fahrenheit. The blue mirrors are at about 50 degrees Fahrenheit.

Infrared image of two adjacent receivers using NREL's IR technique shows a much higher glass temperature for the receiver on the left. Mirror facets are the blue background behind the receivers.

The glass temperature indicates how well the HCE is working. The cooler the HCE glass temperature for a given air temperature, wind speed, and internal heat-transfer fluid (HTF) temperature, the less the heat lost to the environment — leaving more heat to increase the temperature of the internal HTF. HCEs that have lost their vacuum or have hydrogen in their annuli show significantly increased glass temperatures (~300°F) and heat losses relative to evacuated HCEs.