Tim Wendelin

SolTRACE: A New Optical Modeling Tool for Concentrating Solar Optics

SolTRACE, a new optical modeling code developed by researchers at the National Renewable Energy Laboratory (NREL) is currently being used to model solar power optical systems and analyze their performance. Although originally intended for solar optical applications, the code can also be used to model and characterize general optical systems. The creation of the code evolved out of a need to model more complex optical systems than could be modeled with existing tools. In addition, previous codes were based on outdated operating systems that significantly limited data presentation and output capabilities. SolTRACE is written specifically for the Windows® 2000 operating environment. Ray tracing methods coupled with the memory capabilities and the speed of the Windows® 2000 operating environment provide for accurate and rapid results. Output data presentation allows scatter plots, flux maps and performance graphs to be rapidly displayed and saved. SolTRACE has enabled Department of Energy (DOE) SunLab researchers to model and predict the performance of new, complex solar optical designs that previously could not be modeled. This paper describes the code and presents a comparison of SolTRACE results with measured and earlier modeled data.Copyright

Durability studies of solar reflector materials exposed to environmental stresses

Methods that allow accurate prediction of service lifetimes need to be developed and demonstrated to spur the commercialization of solar reflector materials and systems. Without confident knowledge of service lifetimes, uncertainties in life cycle cost and warranty projections will significantly limit the economic viability of solar concentrators. To assure general and robust usefulness, methods should be based on correlations between accelerated, laboratory-controlled environmental stress factors and actual deployment conditions for a variety of applicable geographical locations. Accelerated experiments have identified the key stress factors of UV radiation, temperature, and relative humidity, and their effect on loss of performance, for a particular class of reflector materials. A model is proposed that allows prediction of the time dependent degradation of such materials as an analytic function of combined applied stresses. The model is shown to provide excellent agreement with measured performance data and provides a strong basis for future comparisons with data collected in field tests.

Video Scanning Hartmann Optical Testing of State-of-the-Art Parabolic Trough Concentrators

This paper describes the Video Scanning Hartmann Optical Test System (VSHOT) used to optically test parabolic trough designs by both Solargenix and Industrial Solar Technology.

Thermal Modeling of a Multi-Cavity Array Receiver Performance for Concentrating Solar Power Generation

Concentrating solar power (CSP) plants can provide dispatchable power with the thermal energy storage (TES) capability for greater renewable-energy grid penetration. To increase the market competitiveness, CSP technology needs to increase the solar-to-electric efficiency and reduce costs in the areas of solar collection from the heliostat field to the receiver, energy conversion systems, and TES. The current state-of-the-art molten-salt systems have limitations regarding both the potential for cost reduction and improvements in performance. Even with significant improvements in operating performance, these systems face major challenges to satisfy the performance targets, which include high-temperature stability (>650°C), low freezing point ( 650°C) at a reduced cost. The fluidized-bed CSP (FB-CSP) plant being developed by the National Renewable Energy Laboratory (NREL) has the potential to overcome the above issues with substantially lower cost. The particle receiver is a critical component to enable the FB-CSP system.This paper introduces the development of an innovative receiver design using the blackbody design mechanism by collecting solar heat with absorber tubes that transfer the radiant heat to flowing particles. The particle and receiver materials can withstand temperatures of >1000°C because the receiver can use low-cost materials, such as ceramics and stainless steel, and the solid particles can be any low-cost, stable materials such as sand or ash for particle containment and TES. The heated particles can be stored in containers for TES or supply heat for power generation. This study investigated the performance of convection, reflection, and infrared (IR) re-radiation losses on the absorber solar receiving side. We developed a flux model to predict the reflection losses from the absorber tubes based on the NREL SolTrace program, and conducted thermal modeling by using the Fluent Software. This paper presents the thermal modeling and results on the receiver performance. The receiver configuration may have broad applications for different heattransfer fluids (HTFs), including gas, liquid, or the solid particle-based system in our receiver development.Copyright

Optical Evaluation of Composite-Based Reflector Facets for Parabolic Trough Concentrators

As a possible alternative to glass mirrors, the use of composite-based reflector facets has been investigated for use on parabolic trough concentrators. The approach evaluated here is a composite-based parabolic facet (steel and fiberglass) with a separately attached reflector. This paper describes the basic design of these structural facets and reports on the optical tests that have been used to determine the optical accuracy of the facets.Copyright

Performance Evaluation and Outlook of Utility-Scale Linear Fresnel Technology

As one of the viable concentrating solar power (CSP) technologies, linear Fresnel collectors differ from parabolic troughs by virtue of their low-profile mirror arrays and fixed receiver assemblies. This technology is capable of achieving high concentration ratios and so is applicable to high-temperature solar power plant designs. In addition, its low wind profile and linear nature lead to low system and operation and maintenance (O&M) costs.In this report two linear Fresnel solar plant configurations, namely a direct steam generation (DSG) system and a direct high-temperature molten-salt plant, are examined via a levelized cost of electricity (LCOE) analysis. By treating LCOE as a function of the annual investment energy return (IER, or the ratio of annual net electricity to the total direct system cost) under various assumptions of O&M cost, a few plant scenarios employing high-temperature linear Fresnel technology are carefully configured to meet the aggressive LCOE goals of 8 cents/kWh and 6 cents/kWh. The latter is the Department of Energy (DOE) SunShot Initiative goal aimed at making CSP cost competitive in the current energy market. In particular, a linear Fresnel scenario with the potential to meet the SunShot goal is featured with a collector cost of

Tools to Address Glare and Avian Flux Hazards from Solar Energy Systems.

100/m2, an annual system energy efficiency of 18%, a storage system cost of

A simple planar focusing collector for concentrated solar power applications

15/kWh-th, and an O&M cost of

History, current state, and future of linear Fresnel concentrating solar collectors

7.5/MWh. One of the most aggressive assumptions is an advanced power block with about 52% cycle efficiency and a turbine inlet temperature of 700°C.This work addresses unanswered questions regarding linear Fresnel cost and performance and identifies future research and development directions for linear Fresnel technology, including economic optimization of collectors and receivers, development of physical plant performance models, development of automated O&M mechanisms and sophisticated plant control software.Copyright

SolarPILOT: A power tower solar field layout and characterization tool

This report describes software tools that can be used to evaluate and mitigate potential glare and avian-flux hazards from photovoltaic and concentrating solar power (CSP) plants. Enhancements to the Solar Glare Hazard Analysis Tool (SGHAT) include new block-space receptor models, integration of PVWatts for energy prediction, and a 3D daily glare visualization feature. Tools and methods to evaluate avian-flux hazards at CSP plants with large heliostat fields are also discussed. Alternative heliostat standby aiming strategies were investigated to reduce the avian-flux hazard and minimize impacts to operational performance. Finally, helicopter flyovers were conducted at the National Solar Thermal Test Facility and at the Ivanpah Solar Electric Generating System to evaluate the alternative heliostat aiming strategies and to provide a basis for model validation. Results showed that the models generally overpredicted the measured results, but they were able to simulate the trends in irradiance values with distance. A heliostat up-aiming strategy is recommended to alleviate both glare and avian-flux hazards, but operational schemes are required to reduce the impact on heliostat slew times and plant performance. Future studies should consider the tradeoffs and collective impacts on these three factors of glare, avian-flux hazards, and plant operations and performance.