Assessment of Improved Molten Salt Solar Tower Plants

Abstract

The temperature level increase of molten salt solar tower plants is one important task on the development schedule to increase the system’s overall efficiency. In the conventional power plant technology, modern supercritical steam power plants work with life steam temperatures near 620°C. To apply these modern power blocks in molten salt solar tower plants, salt temperatures near 650°C are required. Today’s molten salt tower plants reach salt temperatures of 565°C. To follow the positive development tendencies of fossil power plants, in the present work the combination of supercritical steam power plants with solar towers is analyzed. As stated in recent literature (Kolb, Kelly, Singer), the state of the art tubular central receiver concept coupled with increased steam parameters of the power block (300 bar / 600°C / 610°C) shows a marginal potential to decrease LEC. The identification of future concept innovations with significant cost reduction potential in the field of molten salt tower plants, the enhancement of the receiver efficiency as well as the assessment of critical aspects related to their feasibility is the task of this paper. Therefore this work first focuses on the state of the art molten salt tower technology and related improved oncepts with molten salt. The selected improvements follow on the one hand the aim to increase the receiver’s maximum temperature level to approximately 650°C to be able to feed modern supercritical power blocks, on the other hand the aim to require a low development effort. After the reference concept is characterized, the objective is the systematic comparison of receiver technologies, which show a potential of improved thermal efficiencies. The assessed receiver candidates are tubular and direct absorption receivers, either external or located in a cavity. The analyzed power level is 125 MWel, while the steam process parameters are varied from low temperature level (550°C) and subcritical steam to high temperature level (620°C) and supercritical steam. With this, selected molten salt power plants were specified and then modeled with different sizes of solar fields and different storage capacities and analyzed on an annual basis. The results show, that the assessed concept options close to the state of the art require drastically decreased investment costs to end up with significant LEC reduction and cost-competitiveness. The increase in overall efficiency of these improved concepts is compensated by their higher financial effort. Results of further concept assessments as well as the sensitivity analysis of parameters and costs are described.