Trnsys Modeling of the Segs Vi Parabolic Trough Solar Electric Generating System

A detailed performance model of the 30 MWe SEGS VI parabolic trough plant was created in the TRNSYS simulation environment using the Solar Thermal Electric Component model library. Both solar and power cycle performance were modeled, but natural gas-fired hybrid operation was not. Good agreement between model predictions and plant measurements was found, with errors usually less than 10%, and transient effects such as startup, shutdown, and cloud response were adequately modeled. While the model could be improved, it demonstrates the capability to perform detailed analysis and is useful for such things as evaluating proposed trough storage systems. TRNSYS AND THE STEC LIBRARY The TRNSYS simulation environment (Solar Energy Laboratory, 2000) was selected for use in modeling solar thermal power systems for a number of reasons, including modularity, flexibility, and ease of use. Commercially available power cycle modeling codes have many standard components, but fxrequently limit the user’s ability to create new components, tend to be quite expensive, and are not capable of modeling annual performance using weather file data as input. The latest update of TRNSYS, Version 15, was used for this work. It has a number of improvements to the graphical user interface that were found to be very useful. A library of Solar Thermal Electric Component (STEC) models for both solar and conventional power cycle elements was created for TRNSYS (Pitz-Paal and Jones, 1998). The component models are linked together to form the desired system, thereby permitting flexibility in modeling different configurations such as standard solar plants or combined fossil-solar (hybrid) designs. The STEC library components are typically detailed steadystate models formulated in thermodynamic quantities such as temperature, pressure, and enthalpy. This high level of modeling detail can be valuable in many cases. For example, the ability of a solar steam generation system to handle startup transients could be analyzed. Of current interest is the evaluation of thermocline storage concepts for trough power plants. To evaluate these concepts, their performance and operational issues associated with startup, shutdown, and cloud transients must be studied on an annual basis. While annual system performance can be modeled in TRNSYS using these detailed state property components, it is also possible to create less complex component models based on a simple energy balance formulation. This would result in a similar model to SOLERGY (Stoddard et al., 1987), but would be more easily adaptable to different configurations such as hybrid plants. SOLERGY is a public-domain software tool frequently used for annual solar plant performance analysis. The ability in TRNSYS to create and share with others new component and system models also helps provide consistency in modeling efforts undertaken by different organizations around the world, and makes their results more comparable. Four other parabolic trough power plant models, none in the public domain, should be mentioned. The Luz System Performance Model (Kearney and Gilon, 1988) was used in the design of the SEGS plants and is generally less detailed than the TRNSYS model. KJC Operating Company has improved the Luz model for use in evaluating plant performance. The FLAGSOL model (Price et al., 1995) is also derived from the Luz model. It has a less detailed simulation of the power cycle than the TRNSYS model and does not provide cycle process data. These models are not modular like the TRNSYS model. The EASY simulation environment was also used for