Browsing by Author "Laubscher, Hendrik Frederik"
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- ItemDeveloping and testing a cost effective thermal rock bed storage system.(Stellenbosch : Stellenbosch University, 2017-12) Laubscher, Hendrik Frederik; Dinter, Frank; Von Backstrom, Theodor Willem; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: In the concentrating solar power industry, thermal energy storage is an attractive solution for storing excess energy for the periods with insufficient solar resource. Energy storage in the form of sensible heat is a mature and practical method of storing energy for later use. Current thermal energy storage technologies are expensive and alternative solutions are needed. The ultimate goal of a more cost effective thermal storage for concentrating solar power is to decrease the levelized cost of electricity. Other than the potential for capital cost reduction, it is also adding value to concentrating solar power in industry compared to other renewable technologies. With thermal energy storage, a renewable energy electricity production plant can deliver electricity on demand and support the national grid. Thermal energy storage is a well-proven concept that can meet the need for more cost effective alternatives. The development of a novel cost effective thermal energy storage for air at 600° C with a unique system layout is covered in this project. This novel thermal energy storage concept has potential to reduce the specific installation cost per kWh installed. A test facility was constructed in this project for testing the feasibility of a specific concept of a packed bed thermal energy storage. The packed bed consist of a conical rock pile as a storage medium and air as the heat transfer fluid. The test facility has a scalable design of a specific concept of a packed rock bed for thermal energy storage system. An inverted thermocline is implemented in this concept where the heat is stored at the bottom of the packed bed. A cost effective layout is presented, with each component and subsystem optimized to reduce the installation cost of the thermal energy storage test facility. Design considerations focus on the constructability of the design, ease of assembling the structure on site and selection of the most suitable construction materials. Operational strategies are developed to ensure that the outlet temperature, the temperature of the heat transfer fluid trough the fan and also the temperature distribution through the rock pile do agree with the design specifications of the materials and the equipment used. Thermoclines defining the distribution of the temperature in the packed bed, round-the-clock cycle efficiency and characteristics of an idling storage system are investigated in this project. Commissioning and experimental testing of various operational strategies are conducted in this project in order to find a suitable operational strategy that can be used for this specific thermal energy storage that can make it feasible to use on a large scale. The experimental results with the operation strategies implemented show that the thermal energy storage concept can be used for short term energy storage with a usable energy recovery efficiency of 60%. The overall performance of the thermal energy storage system indicates that the concept under consideration in this project still needs to be improved to find an improved solution for a low-cost thermal energy storage that is a viable option to utilize in industry. Current challenges to improve the volume efficiency of the packed bed of rocks and the energy recovery efficiency are identified in this project for future research.