Optimization of a Dish Stirling system working with DIR-type receiver using multi-objective techniques

Stirling engine driven by solar energy for thermal to electricity conversion is one of the most promising solution of renewable technologies to reduce the dependency from fossil fuels. Unfortunately, the lack of data about the performance and some operational parameters of this technology limited its detailed characterization and sizing. This paper presents a modeling and simulation of a Dish Stirling system working with DIR receiver (Directly Illumined Receiver), to determine its energy production and efficiency, having Itajuba a city in MG/Brazil, as case of study. Mathematical model allows determine the influence of concentrator's parameters on overall system efficiency. Opto-geometric and transfer processes, in concentrator-receiver system are modeled in detail, and this analysis is used to develop a thermal balance of the Dish Stirling system, to determine operation parameters like: operating temperature of receiver, receiver thermal heat losses, receiver efficiency, global thermal efficiency and electrical power generated by the system. Also procedure described in this article allows to develop a sensitivity analysis for some parameters as: solar irradiation, collector diameter, wind speed and tilt angle of the cavity. Multi-objective optimization based on NSGA-II algorithm has been employed to optimize the power and the efficiency of the system, by means of integration of Dish Stirling mathematical model in Modefrontier. Numerical results show that for low wind speed the radiation heat losses have more influence over system performance, representing 96.06% of total heat losses; when wind speed is greater than 8 m/s convection heat loss (45.27% of the total heat losses) becomes larger than emitted and reflected radiation. Pareto optimal front has been obtained for dual objective, and a final optimal solution has been selected using a decision-making approach by Simple Additive Weighting of decision variables (output electrical power and heat losses). Multi-objective optimization shows a way to obtain an output power of 11.1 kW, with an overall efficiency of 21%, with a significant decrease in heat loss, for the weather conditions of Itajuba-MG. Model gives consistent results confirmed by experimental data used in the validation, showing also that for regions with similar environmental condition like Itajuba, it is more interesting to improve the system material, reducing radiation heat losses. (C) 2017 Elsevier Ltd. All rights reserved.