Energy and exergy analysis and performance optimization of a solar power tower system

Renewable energy is collected from resources which are naturally replenished and almost infinite in terms of human timescale. There are many forms of renewable energy which mostly depends on sunlight for producing heat and electricity. One of the methods to produce heat and electricity from solar energy is solar tower power plants. A solar tower power plant converts sunlight first to heat, then mechanical and ultimately electrical energy. The technology utilizes hundreds even thousands of sun-tracking mirrors which are called heliostats. They focus sunlight to a receiver which is usually constructed at the top of a tower. A heat transfer fluid that is the molten salt, is heated in the receiver. Then it is used to transfer its heat to the working fluid in the steam generator in order to generate steam. Finally, the steam is used in a conventional Rankine cycle to produce electricity. In this study, a base solar power tower system with a cavity receiver with molten salt is analyzed according to First and Second Laws of Thermodynamics by using parameters which are taken from the literature. Then, the effects of direct normal irradiation, heliostat field area, the emissivity of the receiver, the reflectivity of the receiver, receiver tube diameter, view factor and concentration ratio on the energy and exergy efficiencies of the system, receiver surface temperature and receiver total heat loss are investigated. Furthermore, a performance optimization of the system is carried out by modeling a Carnot-like heat engine of the system. For this purpose, the necessary equations are obtained by means of MATHEMATICA program. Then, these equations are solved by codes written in MATLAB program. Finally, the optimum parameters depending on max power and max power density generated by the system are obtained. Anahtar Kelimeler: Güneş enerjisi, yoğunlaştırılmış termal güneş enerjisi santralleri, güneş enerji kule sistemleri, birinci yasa analizi, ikinci yasa analizi, performans optimizasyonu.