A Parabolic Trough Solar Power Plant Simulation Model: Preprint

As interest for clean renewable electric power technologies grows, a number of parabolic trough power plants of various configurations are being considered for deployment around the globe. It is essential that plant designs be optimized for each specific application. The optimum design must consider the capital cost, operations and maintenance cost, annual generation, financial requirements, and time-of-use value of the power generated. Developers require the tools for evaluating tradeoffs between these various project elements. This paper provides an overview of a computer model that is being used by scientists and developers to evaluate the tradeoff between cost, performance, and economic parameters for parabolic trough solar power plant technologies. An example is included that shows how this model has been used for a thermal storage design optimization. INTRODUCTION The National Renewable Energy Laboratory (NREL) currently leads the research and develoment (R&D) efforts on parabolic trough solar power technology within the U.S. Department of Energy’s (DOE) Concentrating Solar Power (CSP) program. DOE supports the use of systems-driven analysis for evaluation of technologies and supporting R&D decisions. NREL has developed a parabolic trough simulation model that allows a detailed performance, cost, and economic assessment of design and technology variations. NREL uses this model to help direct R&D efforts in the parabolic trough program. This paper provides an overview of this model and presents an example of its use. 1 NREL is part of the SunLab collaboration with Sandia National Laboratories that jointly support the DOE CSP program. Performance Prediction Because solar plants rely on an intermittent fuel supply— the sun—it is necessary to model the plant’s performance on an hourly (or finer resolution) basis to understand what the annual performance will be. A number of proprietary computer performance simulations have been developed for modeling the performance of parabolic trough plants. Luz International Limited developed an hourly simulation model that was used to help design the SEGS plants [1]. Flabeg Solar International (FSI, known as Pilkington Solar International and Flagsol before 1995) developed a performance simulation model to market parabolic trough plants and conduct design studies for clients [2]. KJC Operating Company (KJCOC), the operator of SEGS III–VII, has developed an hourly simulation code for assessing the performance of its plants [3]. This model is very specific to the 30-MWe plants at Kramer Junction and the needs of the operating company. As a result, it has limited capability for modeling different plant configurations. The German research laboratory Deutsches Zentrum fur Luft-und Raumfahrt e.V (DLR) has also developed a performance model for parabolic trough plants [4]. All of these codes are proprietary and are not generally available to the general public. DLR and Sandia National Laboratories (SNL) have developed a special library for use with the TRNSYS thermal simulation software, to model parabolic trough solar power plants [5]. TRNSYS is a commercially available software package and is very suited for modeling complex systems, such as parabolic trough power plants. Unfortunately, TRNSYS requires very detailed input data to get results that accurately reflect expected plant performance. In addition, TRNSYS only calculates plant performance, thus economic trade-off studies must be iterated between TRNSYS and a separate economics model.