Ty Neises

Thermodynamic Study of Advanced Supercritical Carbon Dioxide Power Cycles for High Performance Concentrating Solar Power Systems

In 2011, the U.S. Department of Energy (DOE) initiated a “SunShot Concentrating Solar Power R&D” program to develop technologies that have the potential for much higher efficiency, lower cost, and/or more reliable performance than existing CSP systems. The DOE seeks to develop highly disruptive Concentrating Solar Power (CSP) technologies that will meet 6¢/kWh cost targets by the end of the decade, and a high-efficiency, low-cost thermal power cycle is one of the important components to achieve the goal. Supercritical CO2 (s-CO2) operated in a closed-loop Brayton cycle offers the potential of equivalent or higher cycle efficiency versus superheated or supercritical steam cycles at temperatures relevant for CSP applications. Brayton-cycle systems using s-CO2 have a smaller weight and volume, lower thermal mass, and less complex power blocks versus Rankine cycles due to the higher density of the fluid and simpler cycle design. The simpler machinery and compact size of the s-CO2 process may also reduce the installation, maintenance and operation cost of the system.Copyright

Structural Design Considerations for Tubular Power Tower Receivers Operating at 650°C

Research of advanced power cycles has shown supercritical carbon dioxide power cycles may have thermal efficiency benefits relative to steam cycles at temperatures around 500–700°C. To realize these benefits for CSP, it is necessary to increase the maximum outlet temperature of current tower designs. Research at NREL is investigating a concept that uses high-pressure supercritical carbon dioxide as the heat transfer fluid to achieve a 650°C receiver outlet temperature. At these operating conditions, creep becomes an important factor in the design of a tubular receiver and contemporary design assumptions for both solar and traditional boiler applications must be revisited and revised. This paper discusses lessons learned for high-pressure, high-temperature tubular receiver design. An analysis of a simplified receiver tube is discussed, and the results show the limiting stress mechanisms in the tube and the impact on the maximum allowable flux as design parameters vary. Results of this preliminary analysis indicate an underlying trade-off between tube thickness and the maximum allowable flux on the tube. Future work will expand the scope of design variables considered and attempt to optimize the design based on cost and performance metrics.© 2014 ASME

Simulation of Direct Steam Power Tower Concentrated Solar Plant

Power tower concentrated solar plants have the potential to reach temperatures higher than those achievable by a parabolic trough plant. These higher temperatures allow for greater power cycle efficiencies and therefore make power towers an attractive option and a growing topic of research. One common design is to pump water through the tower such that it boils and returns to the power cycle as saturated or superheated vapor. One option to increase power cycle efficiency for a direct steam system is to send the steam exiting the high pressure turbine through a committed reheat receiver section and then through a low pressure turbine.This paper details a new semi-empirical, first-principles thermal model of a direct steam receiver consisting of dedicated boiler, superheater, and reheater sections. This thermal model — integrated with a regression power cycle model and a heliostat field model in SAM — is used to simulate the performance of a direct steam power tower concentrated solar plant and the analysis results are presented.© 2012 ASME

Development of a Thermal Model for Photovoltaic Modules and Analysis of NOCT Guidelines

The temperature of a photovoltaic module is typically required as an input to models that predict the module’s performance. Some common models use the nominal operating cell temperature (NOCT), as by the manufacturer. This paper develops a thermal model and uses it to analyze NOCT testing standards. Specifically, the standard correction factor charts found in the ASTM E1036 and IEC 61215 standards are evaluated. Results show that the correction charts were likely created assuming laminar flow correlations, while validation efforts and the fact that wind is often characterized by turbulence even at low wind speeds suggest that turbulent flow models may be more appropriate. In addition, the results presented in this paper show that the standard NOCT charts do not account for the backside insulation of photovoltaic (PV) arrays. These results suggest that the standard correction charts are inaccurate for any mounting types that differ from the open rack configuration. The paper concludes with recommendations to improve the usefulness of the NOCT. [DOI: 10.1115/1.4005340]

General Performance Metrics and Applications to Evaluate Various Thermal Energy Storage Technologies

The solution proposed in this paper presents a new modeling approach that integrates a generalized thermal storage performance model into a concentrating solar power (CSP) plant. The overall performance, including round trip efficiency, for a thermal energy storage system is highly dependent on the operating parameters and operation strategy of the complete power plant. Previous methods used for analysis of thermal storage have followed one of two approaches: The first requires time-intensive customized detailed performance models of the thermal storage system and the power cycle to account for the effects of charging and discharging storage on conversion efficiency and heat transfer fluid (HTF) return temperature to the solar field. The second method uses a simple energy balance with “derate” factors that do not accurately predict the effects of storage on other plant components. In this paper, we develop a generalized method based on efficiency metrics and discuss the application in TES sizing and performance evaluation for an early concept study. The method is an integral approach and complements the detailed models that simulate yearly operation of a CSP plant.Copyright