Lukas Feierabend M.S. Graduate Student Mechanical Engineering Thesis: Model Development and Simulation of Central Receiver Systems for Solar Towers

Model Development and Simulation of Central Receiver Systems for Solar Towers L. Feierabend, S.A. Klein, D.T. Reindl

Technology Overview The heliostat field, evenly distributed on the northern hemicycle (PS10) around the tower, tracks the position of the sun and reflects radiation onto the central receiver. Heat transfer fluid (HTF) (e.g. molten salt, steam, air) flows through tubes on the receiver surface and absorbs incident solar radiation. This cycle converts thermal energy into electricity with a nominal output of 11 MW (PS10). Thermal energy is stored in large units to compensate for times when there is little or no solar radiation and during peak loads. The HTF is routed into a heat exchanger to deliver heat for a steam cycle (Rankine, Brayton). Process flow diagram of the PS10 solar tower power plant. [1]

Heat transfer fluid tubes are welded together to form a cylindrical surface area. Solar radiation is incident on the entire receiver circumference, therefore the heliostat field can be extended to cover the ground area completely around the tower. However, one has to consider that the costs for the heliostat field account for about a third of the total investment costs. The cylinder surface is completely exposed to the surroundings, thus the convective and radiative heat losses are high. Reflected radiation enters the cavity through a north-facing aperture. The heliostat field is built exclusively within the range of possible incidence angles onto the receiver. The geometry of the cavity-type receiver reduces radiative and convective heat losses, although forced convection losses depend significantly on the wind direction. Additionally, the radiation flux incident from the southern part of the field is low compared to the radiation reflected from the northern mirrors. The receiver cavity is formed by welded tubes, which contain the heat transfer fluid. The receiver face approximates a semicircular cylinder shape. Cylindrical Receiver Cavity Receiver Cylindrical receiver on top of the Solar Two Power Tower in Barstow, CA. [2] PS10 cavity-type receiver. [3]

Project Objectives Improvement of existing correlations for convective heat losses from receiver surfaces with numerical modeling of air flow around different receiver geometries. Development of a TRNSYS model for cavity-type central solar receivers for future incorporation into the “Solar Analysis Model”. References: [1]Romero, M., Buck, R. and Pacheco J. E. (2002). An Update on Solar Central Receiver Systems, Projects, and Technologies, Journal of Solar Energy Engineering, Vol. 124, pg [2] [3]