Zhiwen Ma

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

Feasibility Studies of Encapsulated Particles With Heat Absorbing Medium at 800–1300°C for Concentrating Solar Power Technology

The feasibility of using liquid Al or B2O3 encapsulated in SiC particles was studied by using thermodynamic analysis and fluid-solid analysis at temperatures ranging from 800 to 1300°C. Alloy melts of the Al-Si and Fe-Al-Si systems were considered for absorbing and desorbing energy for a high temperature energy storage (TES) unit incorporated in a concentrating solar power scheme. Boria was also evaluated instead of metallic melts and compared with the traditional NaNO3-KNO3 molten salt as a TES medium. In addition to determining the enthalpies for sensible heat and phase transformations, the phase equilibrium was determined for possible reactions at the liquid Al/SiC and B2O3/SiC interfaces by calculating their thermodynamic stability. The transport of encapsulated SiC particles within a fluid and their effect on the thermal conductivity is discussed toward the efficacy of the thermal energy storage.Copyright