Modeling Simulation and Performance Evaluation of Parabolic Dish Solar Power Plant By Aklilu Tesfaye A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN SCHOOL OF MECHANICAL ENGINEERING (Thermal Engineering Stream) Advisor Dr.-Ing. Abebayehu Assefa Addis Ababa University January 2011 ADDIS ABABA UNIVERSITY SCHOOL OF GRADUATE STUDIES Modeling, Simulation and Performance Evaluation of Parabolic Dish Solar Power Plant By Aklilu Tesfaye Faculty of Technology Approved by Board of Examiners 1. Dr.-Ing. Edessa Dribssa _________________ Chairman Dep.’s Graduate Committee Signature 2. Dr.-Ing. Abebayehu Assefa ___________________ Advisor Signature 3. Dr. Tesfaye Dama _________________ Internal Examiner Signature 4. Dr.-Ing. Edessa Dribssa _________________ External Examiner Signature Abstract A solar parabolic dish electric power generation system is one option for a high temperature solar concentrator that is capable to achieve a high system performance. This results from the fact that it combines an excellent concentrator, a very efficient cavity receiver and a high performance heat engine. The Stirling dish system produces electricity using concentrated solar thermal energy to drive a Stirling engine. The system utilizes a parabolic mirror equipped with dual-axis tracking to concentrate solar radiation onto a thermal receiver integrated in the Stirling engine. The receiver consists of a heat exchanger designed to transfer the absorbed solar energy to the working fluid, typically, hydrogen. The Stirling engine then converts the absorbed thermal energy to mechanical power by expanding the gas in a piston-cylinder in a manner similar to a gas or diesel engine. The linear motion is converted to a rotary motion to turn a generator to produce electricity. The electrical output of the system is proportional to the size of the reflector, its optical losses and the efficiencies of the Stirling engine and the generator. This thesis outlines the theory and models for the collector, receiver, and Stirling engine, the parasitic power. An energy prediction model was created for solar Stirling dish systems to predict the location dependent long term performance of these systems. The model analyzes the performance of the parabolic mirror, receiver, Stirling engine, and the parasitic power consumption to predict the net power produced. The power plant analyzed in this paper has a capacity of generating 10MW electric power. The performance prediction models were implemented in EES and TRNSYS and include location dependent properties that affect the performance based on the direct normal insolation, ambient temperature, density of air (altitude), sun elevation angle, and the wind speed. The cost and financial analysis is made for the Dish System. Solar Advisor Model is used to make this analysis under Kombolcha weather condition. This analysis is used to determine the different costs associated with the power plant. The cash flow for the 30 years of operation of the power plant is also shown. I Acknowledgement I am heartily thankful to my advisor, Dr.-Ing. Abebayehu Assefa, whose encouragement, guidance and support from the initial to the final level enabled me to develop an understanding and ability to prepare this thesis. I owe my deepest gratitude to Habtamu Tkubet, Mekuanint Mesfin and friends who are always beside me and played part a great role in the completion of my work. I also want to appreciate all of my instructors / colleague in the Department of Mechanical Engineering, Addis Ababa University for their continuous encouragement. Finally, I would like to thank my family for the everlasting confidence, constant support and endless love. Aklilu Tesfaye II TABLE OF CONTENT Abstract ........................................................................................................................................ I Acknowledgement ...................................................................................................................... II Nomenclature ......................................................................................................................... XIV CHAPTER ONE ............................................................................................................................. 1 1.1 Introduction ...................................................................................................................... 1 1.2 Solar Collectors ................................................................................................................ 2 1.2.1 Concentrating Solar Collectors ...................................................................................... 3 1.2.1.1 Parabolic Trough ................................................................................................................... 3 1.2.1.2 Solar Power Tower ................................................................................................................ 4 1.2.1.3 Solar Dish .............................................................................................................................. 5 1.3 Concentrating Solar Power............................................................................................... 7 1.4 Status of CSP .................................................................................................................... 8 1.5 Background of the Study .................................................................................................. 8 1.6 Objective of the Thesis ................................................................................................... 12 1.7 Methodology .................................................................................................................. 13 1.8 Outline of the Thesis ...................................................................................................... 13 CHAPTER TWO .......................................................................................................................... 14 Stirling Dish System Component Modeling ................................................................................. 14 2.1 Introduction .................................................................................................................... 14 2.2 Sizing and Structural Design of Parabolic Solar Dish ................................................... 15 2.2.1 Concentrators ............................................................................................................... 15 2.2.2 Parabolic Concentrator Property .................................................................................. 17 2.2.3 Collector Design Criteria ............................................................................................. 18 2.2.3.1 Intercept Factor .................................................................................................................. 18 III 2.2.3.2 Beam Spread ....................................................................................................................... 18 2.2.4 Analysis of Solar Dish Data ......................................................................................... 19 2.2.4.1 Direct Normal Radiation from SEWERA Data ..................................................................... 19 2.2.4.2 Sizing of the Collector ......................................................................................................... 21 2.2.4.3 Focal Point Depth ................................................................................................................ 22 2.2.4.4 Length of a Parabolic Segment ........................................................................................... 24 2.2.4.5 Surface Area of a Parabolic Reflector ................................................................................. 24 2.2.4.6 Concentration Ratio ............................................................................................................ 25 2.2.5 Power at Focal Point (Receiver) and Efficiency of the Collector ................................ 26 2.2.6 Concentrator Performance ........................................................................................... 28 2.2.7 Supporting Structure .................................................................................................... 28 2.2.8 Tracking Mechanism ................................................................................................... 28 2.3 Receiver Integrated in the Stirling Engine ....................................................................... 29 2.3.1 Types of Receivers Used in Dish/Stirling System ....................................................... 30 2.3.2 Cavity Receivers Heat Loss ......................................................................................... 33 2.3.3 Heat Input to Stirling Engine ....................................................................................... 36 2.4 Stirling Engine and Working Principle ............................................................................ 37 2.4.1 Basic Theory of the Stirling Engine ............................................................................. 38 2.4.2 Heat Engine versus Stirling Engine ............................................................................. 41 2.4.3 Power Control .............................................................................................................. 41 2.4.4 Regenerator .................................................................................................................