The characteristics of power produced from photovoltaic (PV) and Wind systems are based on the weather condition. Both the system are very unreliable in itself without sufficient capacity storage devices like batteries or back-up system like conventional engine generators. The reliability of the system significantly increases when two systems are hybridized with the provision of storage device. Even in such case, sufficient battery bank capacity is required to provide power to the load in extended cloudy days and non-windy days. Therefore the optimal sizing of system component represents the important part of hybrid power system. This paper summarizes recent trends of energy usage from renewable sources. It discusses physical modeling of renewable energy systems, several methodologies and criteria for optimization of the Hybrid Renewable Energy System (HRES). HRES is getting popular in the present scenario of energy and environmental crises. In this paper, we present a comprehensive review on the current state of optimization techniques specifically suited for the small and isolated power system based on the published literatures. The recent trend in optimization in the field of hybrid renewable energy system shows that artificial intelligence may provide good optimization of system without extensive long term weather data.

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As a renewable energy harvesting method, interest in piezoelectric energy harvesting has increased significantly. Despite the piezoelectric energy-harvesting technology expanding its area to the flexible (elastic, amendable) devices, striking use or application of the technology is hardly found in the market. Here, we report a novel flexible piezoelectric energy harvester fabricated by using an additive manufacturing process, which enables both effective and customized manufacturing technique. By taking advantages of additive manufacturing, further application of the piezoelectric energy-harvesting technology is highly expected. Particles of BaTiO 3 , a ceramic with a large piezoelectric constant, were mixed with polyether block amide elastomer to form a flexible piezoelectric composite. The energy harvester was fabricated using an additive manufacturing process, by printing the piezoelectric composite on a laser-patterned flexible Indium-tin-oxidecoated polyethylene terephthalate substrate. Performance of fabricated energy harvester was evaluated by applying a mechanical stress to the energy harvester; voltage and current output were 2 V and 40 nA, respectively. An analytical model of the piezoelectric energy harvester was developed and discussed to explain the form of the voltage waveforms in response to the applied stress.

We investigate wave mixing effects in a phononic crystal that couples the wave dynamics of two channels -primary and control ones -via a variable stiffness mechanism. We demonstrate analytically and numerically that the wave transmission in the primary channel can be manipulated by the control channel's signal. We show that the application of control waves allows the selection of a specific mode through the primary channel. We also demonstrate that the mixing of two wave modes is possible whereby a modulation effect is observed.A detailed study of the design parameters is also carried out to optimize the switching capabilities of the proposed system. Finally, we verify that the system can fulfill both switching and amplification functionalities, potentially enabling the realization of an acoustic transistor.