Thermal storage optimization of Solar Tower Thermal Power Plants

MSc student: Wouter de Lille

Modern solar tower thermal power plants use molten salt for thermal storage. These systems are limited to a temperature of 565˚C due to the properties of the molten salt. The heat from the molten salt is used to generate steam which drives a steam turbine achieving conversion efficiencies in the order of 40%. Solar power towers have a high capital cost, mainly due to the large heliostat field which is required to deliver the power. As indicated by the Carnot efficiency, increasing the highest temperature of the system increases the overall system efficiency. Higher conversion efficiency indicates that less power input is required. This thesis investigates whether it is possible to increase the temperature of the system to be able to use more efficient power cycles such as combined cycles - which can achieve conversion efficiencies up to 60% - to reduce the required size and thus cost of the heliostat field.

To be able to deliver electricity continuously, thermal storage is required. Since molten salt cannot cope with the required operational temperatures, a solution to the thermal storage needs to be obtained. A commonly used method to store high temperature energy is the use of Cowper stoves or regenerators. Optimization of these systems is performed to meet the requirements for solar power towers.

Finally, an economic evaluation is performed to determine whether it is beneficial to use higher temperatures to provide sustainable thermal solar energy or whether it is better to continue the development of molten salt solar towers.

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