THE DISS PROJECT : DIRECT STEAM GENERATION IN PARABOLIC TROUGHS OPERATION AND MAINTENANCE EXPERIENCE UPDATE ON PROJECT STATUS
The DISS (DIrect Solar Steam) project is a complete R+TD program aimed at developing a new generation of solar thermal power plants with direct steam generation (DSG) in the absorber tubes of parabolic trough collectors. During the first phase of the project (1996-1998), a life-size test facility was implemented at the Plataforma Solar de Almería (PSA) to investigate under real solar conditions the basic DSG processes and evaluate the open technical questions concerning this new technology. This paper updates DISS project status and explains O&M-related experience (e.g. main problems faced and solutions applied) with the PSA DISS test facility since January 1999. NOMENCLATURE DAS Data acquisition system DISS Direct solar steam (the project) DSG Direct steam generation (the process) PSA Plataforma Solar de Almería P Pressure T Temperature INTRODUCTION Solar thermal power plants based on parabolic trough collectors are presently the most successful solar technology for electricity generation, as demonstrated by the SEGS plants in California. Direct steam generation in the absorber tubes is seen as a promising option to further the competitiveness of this technology. Replacement of the oil by direct steam generation results in lower investment and operating costs, as well as reduced environmental risk and fire hazards in case of leaks. Simultaneously, the performance can be improved by avoiding the thermodynamic losses associated with the oil water/steam heat exchanger of the SEGS plants. In combination with further improvements of the collector field and overall system integration, a 26% reduction in the electricity cost seems to be achievable (Langenkamp, 1998). Taking into consideration this expected benefit, a group of German and Spanish partners, with the financial support of the European Commission JOULE Programme, started in 1996 the DISS (Direct Solar Steam) project, which is an R+D program aimed at developing a new generation of solar thermal power plants with parabolic trough collectors. Expected improvements are based on three main factors: 1. Development and implementation of improved components for parabolic trough collectors (e.g. new, more economical absorber tubes with good optical and thermal properties; cheaper sun-tracking systems; better mirrors, etc...). 2. Development of the Direct Steam Generation (DSG) process to eliminate the oil used at the existing solar thermal plants as a heat carrier from the solar field to the power block. Since the DSG process is a promising way
Control of Solar Energy Systems
Abstract This work deals with the main control problems found in solar power systems and the solutions proposed in literature. The paper first describes the main solar power technologies, its development status and then describes the main challenges encountered when controlling solar power systems. While in other power generating processes, the main source of energy can be manipulated, in solar energy systems, the main source of power which is solar radiation cannot be manipulated and furthermore it changes in a seasonal and on a daily base acting as a disturbance when considering it from a control point of view. Solar plants have all the characteristics needed for using industrial electronics and advanced control strategies able to cope with changing dynamics, nonlinearities and uncertainties.
Direct Solar Steam Generation in Parabolic Troughs: Thermal Stress due to Variations in Irradiation
The Californian parabolic trough power plants belong to the most successful systems for producing solar electricity. In order to improve the efficiency of these power plants, the research activities in direct steam generation (DSG) have been initiated. The aim is to avoid the necessity of a single phase thermooil used as heat transfer fluid (HTF) in the absorber pipes of the solar collectors. Instead, the feedwater of the steam cycle should be evaporated and superheated directly in the absorber pipes, thus eliminating the need for the second cycle and the heat exchanger. This demands the knowledge of the thermohydraulics of a two-phase flow in the absorber pipes. Since the characteristic parameters differ significantly from those typical of conventional steam generators, the basic relations describing heat transfer and pressure losses had to be investigated. Experimental data was gained using a electrically heated test-section. Based on the experiments, simulation tools for the design of DSG-systems have been developed. As a result, the feasibility of direct steam generation in stationary operation mode was proven. The collectors can cope with the thermal stress resulting from a circumferrentially varying solar irradiation provided the mass flow in the absorber tubes is sufficient. The performance can be optimized in order to guarantee an adequate cooling of the absorbersO wall while minimizing the pressure losses. Based on the results of the first stage of DSG-research, the first test facility for steam generation by solar energy was designed. This test facility was completed in 1999 at Almeria, Spain.