The Ivanpah Solar Electric Generating System (ISEGS), located on I - 15 about 40 miles (60 km) south of Las Vegas, NV, consists of three power towers 459 ft (140 m) tall and over 170,000 reflective heliostats with a rated capacity of 390 MW. Reports of glare from the plant have been submitted by pilots and air traffic controllers and recorded by the Aviation Safety Reporting System and the California Energy Commission since 2013. Aerial and ground - based surveys of the glare were conducted in April, 2014, to identify the cause and to quantify the irradiance and potential ocular impact s of the glare . Results showed that the intense glare viewed from the airspace above ISEGS was caused by he liostats in standby mode that were aimed to the side of the receiver. Evaluation of the glare showed that the retinal irradiance and subtended source angle of the glare from the heliostats in standby were sufficient to cause significant ocular impact (pot ential for after - image) up to a distance of %7E6 miles (10 km), but the values were below the threshold for permanent eye damage . Glare from the receivers had a low potential for after - image at all ground - based monitoring locations outside of the site bound aries. A Letter to Airmen has been issued by the Federal Aviation Administration to notify pilots of the potential glare hazards. Additional measures to mitigate the potential impacts of glare from ISGES are also presented and discussed. This page intentionally left blank
ASME 2014 8th International Conference on Energy Sustainability, ES 2014 Collocated with the ASME 2014 12th International Conference on Fuel Cell Science, Engineering and Technology
Solar optical modeling tools are valuable for modeling and predicting the performance of solar technology systems. Four optical modeling tools were evaluated using the National Solar Thermal Test Facility heliostat field combined with flat plate receiver geometry as a benchmark. The four optical modeling tools evaluated were DELSOL, HELIOS, SolTrace, and Tonatiuh. All are available for free from their respective developers. DELSOL and HELIOS both use a convolution of the sunshape and optical errors for rapid calculation of flux profiles on the receiver surfaces. SolTrace and Tonatiuh use ray-tracing methods to determine reflected solar rays on the receiver surfaces and construct flux profiles. We found the raytracing tools, although slower in computation speed, to be more flexible for modeling complex receiver geometries, whereas DELSOL and HELIOS were limited to standard receiver geometries. We provide an example of using SolTrace for modeling non-conventional receiver geometries. We also list the strengths and deficiencies of the tools to show tool preference depending on the modeling and design needs.
Solar thermal receivers absorb concentrated sunlight and can operate at high temperatures exceeding 600°C for production of heat and electricity. New fractal-like designs employing light-trapping structures and geometries at multiple length scales are proposed to increase the effective solar absorptance and efficiency of these receivers. Radial and linear structures at the micro (surface coatings and depositions), meso (tube shape and geometry), and macro (total receiver geometry and configuration) scales redirect reflected solar radiation toward the interior of the receiver for increased absorptance. Hotter regions within the interior of the receiver also reduce thermal emittance due to reduced local view factors in the interior regions, and higher concentration ratios can be employed with similar surface irradiances to reduce the effective optical aperture and thermal losses. Coupled optical/fluid/thermal models have been developed to evaluate the performance of these designs relative to conventional designs. Results show that fractal-like structures and geometries can reduce total radiative losses by up to 50% and increase the thermal efficiency by up to 10%. The impact was more pronounced for materials with lower inherent solar absorptances (< 0.9). Meso-scale tests were conducted and confirmed model results that showed increased light-trapping from corrugated surfaces relative to flat surfaces.
ASME 2014 8th International Conference on Energy Sustainability, ES 2014 Collocated with the ASME 2014 12th International Conference on Fuel Cell Science, Engineering and Technology
The use of an air curtain blowing across the aperture of a falling-particle receiver has been proposed to mitigate convective heat losses and to protect the flow of particles from external winds. This paper presents experimental and numerical studies that evaluate the impact of an air curtain on the performance of a falling particle receiver. Unheated experimental studies were performed to evaluate the impact of various factors (particle size, particle mass flow rate, particle release location, air-curtain flow rate, and external wind) on particle flow, stability, and loss through the aperture. Numerical simulations were performed to evaluate the impact of an air curtain on the thermal efficiency of a falling particle receiver at different operating temperatures. Results showed that the air curtain reduced particle loss when particles were released near the aperture in the presence of external wind, but the presence of the air curtain did not generally improve the flow characteristics and loss of the particles for other scenarios. Numerical results showed that the presence of an air curtain could reduce the convective heat losses, but only at higher temperatures (>600°C) when buoyant hot air leaving the aperture was significant.
ASME 2014 8th International Conference on Energy Sustainability, ES 2014 Collocated with the ASME 2014 12th International Conference on Fuel Cell Science, Engineering and Technology
Cavity receivers have been an integral part of Concentrated Solar Power (CSP) plants for many years. However, falling solid particle receivers (SPR) which employ a cavity design are only in the beginning stages of on-sun testing and evaluation. A prototype SPR has been developed which will be fully integrated into a complete system to demonstrate the effectiveness of this technology in the CSP sector. The receiver is a rectangular cavity with an aperture on the north side, open bottom (for particle collection), and a slot in the top (particle curtain injection). The solid particles fall from the top of the cavity through the solar flux and are collected after leaving the receiver. There are inherent design challenges with this type of receiver including particle curtain opacity, high wall fluxes, high wall temperatures, and high heat losses. CFD calculations using ANSYS FLUENT were performed to evaluate the effectiveness of the current receiver design. The particle curtain mass flow rate needed to be carefully regulated such that the curtain opacity is high (to intercept as much solar radiation as possible), but also low enough to increase the average particle temperature by 200°C. Wall temperatures were shown to be less than 1200°C when the particle curtain mass flow rate is 2.7 kg/s/m which is critical for the receiver insulation. The size of the cavity was shown to decrease the incident flux on the cavity walls and also reduced the wall temperatures. A thermal efficiency of 92% was achieved, but was obtained with a higher particle mass flow rate resulting in a lower average particle temperature rise. A final prototype receiver design has been completed utilizing the computational evaluation and past CSP project experiences.