scholarly journals A Flux Mapping Method for Central Receiver Systems

2011 ◽  
Author(s):  
Clifford K. Ho ◽  
Siri S. Khalsa
Keyword(s):  
Ccd Camera ◽  
Mapping Method ◽  
Test Facility ◽  
The Novel ◽  
Additional Information ◽  
Thermal Test ◽  
Central Receiver ◽  
Direct Normal Irradiance ◽  
Beam Characterization ◽  
Pixel Value

A new method is described to determine irradiance distributions on receivers and targets from heliostats or other collectors for concentrating solar power applications. The method uses a CCD camera, and, unlike previous beam characterization systems, it does not require additional sensors, calorimeters, or flux gauges on the receiver or target. In addition, spillage can exist (the beam does not need to be contained within the target). The only additional information required besides the digital images recorded from the CCD camera is the direct normal irradiance and the reflectivity of the receiver. Methods are described to calculate either an average reflectivity or a reflectivity distribution for the receiver using the CCD camera. The novel feature of this new PHLUX method is the use of recorded images of the sun to scale both the magnitude of each pixel value and the subtended angle of each pixel. A test was performed to evaluate the PHLUX method using a heliostat beam on the central receiver tower at the National Solar Thermal Test Facility in Albuquerque, NM. Results showed that the PHLUX method was capable of producing an accurate flux map of the heliostat beam with a relative error in the peak flux of 2%.

A Photographic Flux Mapping Method for Concentrating Solar Collectors and Receivers

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Clifford K. Ho ◽  
Siri S. Khalsa
Keyword(s):  
Digital Camera ◽  
Mapping Method ◽  
Test Facility ◽  
The Novel ◽  
Error Sources ◽  
Additional Information ◽  
Direct Normal Irradiance ◽  
Beam Characterization ◽  
Pixel Value ◽  
Relative Errors

A new method is described to determine irradiance distributions on receivers and targets from heliostats or other collectors for concentrating solar power applications. The method uses a digital camera, and, unlike previous beam characterization systems, it does not require additional sensors, calorimeters, or flux gauges on the receiver or target. In addition, spillage can exist and can also be measured (the beam does not need to be contained within the target). The only additional information required besides the images recorded from the digital camera is the direct normal irradiance and the reflectivity of the receiver. Methods are described to calculate either an average reflectivity or a reflectivity distribution for the receiver using the digital camera. The novel feature of this new photographic flux (PHLUX) mapping method is the use of recorded images of the sun to scale both the magnitude of each pixel value and the subtended angle of each pixel. A test was performed to evaluate the PHLUX method using a heliostat beam on the central receiver tower at the National Solar Thermal Test Facility in Albuquerque, NM. Results showed that the PHLUX method was capable of producing an accurate flux map of the heliostat beam on a Lambertian surface with a relative error in the peak flux of ∼2% when the filter attenuation factors and effective receiver reflectivity were well characterized. Total relative errors associated with the measured irradiance using the PHLUX method can be up to 20%–40%, depending on various error sources identified in the paper, namely, uncertainty in receiver reflectivity and filter attenuation.

Operation of Large-Scale Pumps and Valves in Molten Salt

1994 ◽  
Vol 116 (3) ◽  
pp. 137-141 ◽  
Author(s):  
D. C. Smith ◽  
E. E. Rush ◽  
C. W. Matthews ◽  
J. M. Chavez ◽  
P. A. Bator
Keyword(s):  
Molten Salt ◽  
Power Plants ◽  
Large Scale ◽  
Solar Power ◽  
Test Facility ◽  
Plant Design ◽  
Thermal Test ◽  
Central Receiver ◽  
Solar Power Plants ◽  
Careful Design

The molten salt pump and valve (P&V) test loops at Sandia National Laboratories (SNL) National Solar Thermal Test Facility (NSTTF) operated between Jan. 1988 and Oct. 1990. The purpose of the P&V test was to demonstrate the performance, reliability, and service life of full-scale hot and cold salt pumps and valves for use in commercial central receiver solar power plants. The P&V test hardware consists of two pumped loops; the “Hot Loop” to simulate the hot (565°C) side of the receiver and the “Cold Loop” to simulate the receiver’s cold (285°C) side. Each loop contains a pump and five valves sized to be representative of a conceptual 60-MWe commercial solar power plant design. The hot loop accumulated over 6700 hours of operation and the cold loop over 2500 hours of operation. This project has demonstrated that standard commercial scale pump and valve designs will work in molten salt. The test also exposed some pitfalls that must be avoided in specifying such equipment. Although certainly not all of the pitfalls were discovered, careful design and specification should result in reliable or at least workable equipment.

scholarly journals On-Sun Evaluation of the PHLUX Method for Heliostat Beam Characterization

2016 ◽  
Author(s):  
Julius Yellowhair ◽  
Clifford K. Ho
Keyword(s):  
Focal Length ◽  
Digital Camera ◽  
Total Power ◽  
Neutral Density ◽  
Additional Information ◽  
Direct Normal Irradiance ◽  
Beam Characterization ◽  
Peak Flux ◽  
And Performance ◽  
Solar Field

Flux distributions from solar field collectors are typically evaluated using a beam characterization system, which consists of a digital camera with neutral density filters, flux gauge or calorimeter, and water-cooled Lambertian target panel. The pixels in camera image of the flux distribution are scaled by the flux peak value measured with the flux gauge or the total power value measured with the calorimeter. An alternative method, called PHLUX developed at Sandia National Laboratories, can serve the same purpose using a digital camera but without auxiliary instrumentation. The only additional information required besides the digital images recorded from the camera are the direct normal irradiance, an image of the sun using the same camera, and the reflectivity of the receiver or target panel surface. The PHLUX method was evaluated using two digital cameras (Nikon D90 and D3300) at different flux levels on a target panel. The performances of the two cameras were compared to each other and to measurements from a Kendall radiometer. For consistency in comparison of the two cameras, the same focal length lenses and same number of neutral density filters were used. Other camera settings (e.g., shutter speed, f-stop, etc.) were set based on the aperture size and performance of the cameras. The Nikon D3300 has twice the number of pixels as the D90. D3300 provided higher resolution, however, due to the smaller pixel sizes the images were noisier, and the D90 with larger pixels had better response to low light levels. The noise in the D3300, if not corrected, could result in gross overestimation of the irradiance calculations. After corrections to the D3300 flux images, the PHLUX results from the two cameras showed they agreed to within 8% for a peak flux level of 1000 suns on the target, and less than 10% error in the peak flux when compared to the Kendall radiometer.

Heliostat Canting and Focusing Methods: An Overview and Comparison

2010 ◽  
Author(s):  
Julius Yellowhair ◽  
Clifford K. Ho
Keyword(s):  
Laser Beam ◽  
Test Facility ◽  
The Sun ◽  
Alignment Method ◽  
Advantages And Disadvantages ◽  
The Past ◽  
Thermal Test ◽  
Central Receiver ◽  
Look Back ◽  
The Individual

A central receiver power tower system consists of a field of heliostats that focus the sunlight onto the receiver on the tower. Heliostats typically consist of an array of mirror facets that track the sun throughout the day. To obtain the optimal concentrated solar flux on the receiver, the individual heliostat facets must be properly canted and focused. Several different methods have been used in the past for facet canting and focusing. These demonstrated methods and some new alignment concepts are under consideration for development and alignment of the 218 heliostats at the Sandia National Laboratories National Solar Thermal Test Facility in Albuquerque, NM. In this paper, we provide an overview and comparison of the different methods. The methods we consider are the gauge blocks, inclinometers, photogrammetry, fringe reflection, imaging with theoretical image overlays, laser beam projections, camera look-back, and target reflection methods. The advantages and disadvantages of each alignment method are identified based on several prescribed criteria for aligning the heliostats. Recommendations regarding the alignment method’s potential for efficiently and accurately aligning heliostat fields are provided.

scholarly journals The Development of the Heliostat Focusing and Canting Enhancement Technique: An Optical Heliostat Alignment Tool for the National Solar Thermal Test Facility

2011 ◽  
Author(s):  
Evan Sproul ◽  
Kyle Chavez ◽  
Julius Yellowhair
Keyword(s):  
Solar Thermal ◽  
Optical Methods ◽  
Test Facility ◽  
Moving Frame ◽  
Beam Diameter ◽  
Stationary Target ◽  
Enhancement Technique ◽  
Thermal Test ◽  
Central Receiver ◽  
Alignment Tool

A heliostat array is a field of heliostats that focuses sunlight continuously on a central receiver in a power tower solar concentration system. Each heliostat consists of a structurally mounted mirror surface capable of reflecting sunlight onto a given target throughout the day. Typically, most heliostats are actually a group of individual mirror facets on a single moving frame. To achieve highly concentrated solar flux on a central receiver, each heliostat mirror facet has to be properly aligned (both canted and focused) when attached to the heliostat frame. In order to accurately evaluate and correct heliostat facet alignment, Sandia National Laboratories (SNL) and New Mexico Tech (NMT) have developed the Heliostat Focusing and Canting Enhancement Technique (H-FACET), a new and unique heliostat alignment tool that allows technicians to make fast and effective adjustments to facet canting and focusing. H-FACET uses a high resolution digital camera mounted on top of a receiver tower to observe the image of a stationary target reflected by a heliostat. Custom image processing software compares specific measurement points on the actual target reflection image with the corresponding measurement points on an ideally reflecting heliostat. Deviations between the actual and ideal reflection points reveal facet misalignments. Additionally, a live image of the ideal and theoretical points provides real-time feedback during the alignment correction process. SNL has implemented H-FACET at the National Solar Thermal Test Facility (NSTTF). Technicians have used the canting portion of the software to successfully cant a large section of the SNL NSTTF heliostat field. Visual inspections of reflected heliostat beam patterns have demonstrated noticeable improvements in beam size and shape resulting from the use of H-FACET. Preliminary quantitative analyses of H-FACET have shown beam diameter reductions of up to fifty percent. The beam reductions resulting from the use of H-FACET will assist in minimizing beam spillage and increasing flux densities. As a result, H-FACET may be a valuable tool in increasing the annual performance of a heliostat field. This paper details the computational algorithms used in H-FACET. These algorithms include accurate models of heliostat field geometries, sun position, facet orientations and facet shapes. This paper also discusses the optical methods used to determine the orientations and surface shapes of ideally aligned facets. Lastly, it investigates probable sources of error and ways to improve H-FACET.

Sign in / Sign up

Export Citation Format

Share Document