The fast depletion of fossil fuels and the growing awareness of the need for environmental protection have led us to the energy crisis. Positive development has been achieved since the last decade by the collective effort of scientists. In this regard, renewable energy sources (RES) are being deployed in the power system to meet the energy demand. The microgrid concept (AC, DC) is introduced, in which distributed energy resources (DERs), the energy storage system (ESS) and loads are interconnected. DC microgrids are appreciated due to their high efficiency and reliability performance. Despite its significant growth, the DC microgrid is still relatively novel in terms of grid architecture and control systems. In this context, an energy management system (EMS) is essential for the optimal use of DERs in secure, reliable, and intelligent ways. Therefore, this paper strives to shed light on DC microgrid architecture, control structure, and EMS. With an extensive literature survey on EMSs’ role, different methods and strategies related to microgrid energy management are covered in this article. More attention is centered on the EMS for DC microgrids in terms of size and cost optimization. A very concise analysis of multiple optimization methods and techniques has been presented exclusively for residential applications.

We report large and nonmonotonic dependences of the electro-optic (EO) coefficient ${{r}}_{22}$ and the corresponding dielectric permittivity in pure ${\mathrm{LiNbO}}_3$ on the concentration of intrinsic defects related to the deviation from the stoichiometry of the crystal. This variation is caused mainly by the electro-mechanical contribution. A stoichiometric crystal possesses both large EO properties and resistance to optical damage which renders it much more suitable for use in laser Q-switching than the congruent crystal.

International audienceZnO thin films are widely used as antireflection layer in solar cells and can be grown by various techniques implemented at various temperatures. In this contribution, we present the morphological and optical properties of ZnO thin films prepared by spray pyrolysis on glass substrates at various growth temperatures from 350 to 550 °C. The surface morphology of the films, analysed by scanning electron microscopy SEM, is modified with substrate temperature. Optical characterizations of ZnO films as a function of temperature were carried out by transmittance and photoluminescence (PL) measurements. Main optical properties are as follow: All the films are highly transparent in the visible region of the electromagnetic spectrum. The average transmission in the visible range (400–800 nm) was greater than 80%. The band gap of ZnO films increases with increasing substrate temperatures attributed to the increase of the grain size of thesample.PL spectrum of ZnO films can be divided into the UV emission and the visible broadband emission attributed to the near band edge emission (NBE) and to the deep level emissions (DLE), respectively. The biggest ratio of UV emission on visible emission of the PL intensity is observed for the ZnO thin film deposited at 550 °C by the spray pyrolysis technique. Therefore, we suggest that this original result indicate the most suitable growing conditions for obtaining high quality sprayed ZnO thin films with higher luminescence performances

We present a band structure approach in connection with a molecular dynamics cluster optimization that accounts for various structural modifications related to the nonstoichiometry of ${\mathrm{LiNbO}}_3$ crystals. Variation of optical properties with the deviation from the stoichiometric composition can be understood within this approach. The particular role of the electron-phonon contributions to the electro-optic coefficient is shown. Model calculations yield a large dependence of the electro-optic coefficient $r_{22}$ on the crystal composition, in agreement with the experimental data. The observed minimum of the $r_{22}$ coefficient versus nonstochiometry is explained within a microscopic approach. The $r_{33}$ tensor component shows substantially different behavior versus the stoichiometry.