# Sustainable Energy Systems: Optimization and Efficiency
###### Abstract
Thus, regarding this topic, several papers are published in this Issue. In [11], the authors present a simplified analytical approach to optimal planning of DG in electrical distribution networks. Distinct parameters of DG were taken into account and evaluated, in order to achieve a high loss reduction in the electrical distribution networks. The authors concluded that the proposed approach could provide an adequate solution, through a simple algorithm, without resorting to an intensive process of power flow computation. A multi-objective optimization of accommodation capacity for distributed generation, based on a mixed-strategy Nash equilibrium, considering distribution network flexibility, was presented in [12]. In this publication, a comprehensive learning particle swarm optimization (CLPSO) algorithm is employed to solve this multi-objective optimization model, and it is applied in a real example of a Chinese distribution network. Through this model, while taking into account multiple objectives, the authors reach the optimal solution. In [13], an energy management scheme for virtual power plants is proposed by considering DG sizing and pricing. In this study, the effect on simulations of distinct types of DG units was considered. The simulations are performed for three cases, and compared using the software HOMER in order to validate the capability of the proposed model. Meanwhile, in [14], the authors present a study addressing the incorporation of concentrated solar power into a highly renewables-penetrated power system, through chance-constrained stochastic unit commitment analysis. The results of this study show a reliable economic value of the concentrating of solar power stations on the improvement of unit commitment schedules. Finally, in [15]s the authors propose a study addressing the impact of demand-response programs on reducing the emissions and cost of a neighborhood home microgrid. Since several generation units are present, the Taguchi orthogonal array testing (TOAT) method was used. The results showed an increase in profits and a decrease in emissions if the proposed algorithm is used. Still on the topic of DG, protection relay issues are addressed in a study that focuses on the impact of recloser on protecting the blind areas of distribution networks in the presence of DG [16]. In this study, the simulations are made with the help of DIgSILENT software. The case study is based on realistic data of a distribution network, in which the DG comprises two generators with a capacity of 4 MW. The authors show that with this strategy, the protection of blind areas was achieved by the recloser relay, which improves the distribution network's reliability. As mentioned in the Abstract, the second section of the Special Issue addresses a wide range of topics. Since solar irradiation is intermittent and suffers from swift fluctuations [17], a PV Tracking design methodology based on an orientation efficiency chart is presented in [18], which, according to the authors, by being based on an orientation efficiency chart, can be applied to the construction or control of other types of solar tracker systems. Two parametric studies were published in this issue. A thermoeconomic modelling and parametric study of a simple orc, for the recovery of waste heat from a 2 MW gas engine under different working fluids, was presented in [19], and a parametric numerical study of the airflow and thermal performance of a real data center, for improving sustainability by reducing the thermal load [20]. The predictions and analysis of the combustion characteristics of a non-premixed oxy-flame, by applying a hybrid filtered Eulerian stochastic field/flamelet progress variable approach, was addressed in [21]. Comparisons with experimental data, in terms of temperature, scalar distributions and scatter plots, were made, and satisfactory results were obtained.