Optimal operation and hydro storage sizing of a wind–hydro power plant

Ambitious targets for renewable power production have been defined for the electric power systems in Europe. The accomplishment of these targets requires the increase in renewable energy production, namely from wind power generation. However, the intermittent nature of wind creates several problems to the power system operation and new approaches based on the combined use of wind power and energy storage technologies need to be developed. In this paper, the concept of the combined use of wind power production and hydro storage/production is exploited, through the development of an operational optimisation approach applied to a wind generator park with little water storage ability. The optimisation model defines the operational strategy to be followed for the hours ahead by a pump station and an hydraulic generator embedded in a wind/hydro pumping facility, using the Portuguese energy remuneration rules. The proposed methodology leads to considerable yearly profits for the wind generator production.     

High efficiency CIGS based solar cells with electrodeposited ZnO:Cl as transparent conducting oxide front contact

In this paper high efficiency (up to 15.8%) Mo/Cu(In,Ga)Se₂/CdS/i‐ZnO solar cells terminated with an electrodeposited ZnO:Cl window layer are reported. The optoelectronic properties of these cells are comparable to reference cells terminated with standard sputtered ZnO:Al. The use of an electrochemical step, a low cost and easily up‐scalable method, in the fabrication process of this type of solar cell, opens the possibility to lower their production price and make them more competitive. The optimization involves a soft annealing treatment (T ≤ 150°C) under atmospheric conditions after the electrodeposition which improves the transparency of the ZnO:Cl layers in the infrared region, the short circuit current and the fill factor of the I–V curve. These changes are related to the increase of one order of magnitude (up to 5 × 10² Ω⁻¹·cm⁻¹) of the lateral conductivity of the electrochemical layer due to an improvement of the free carrier mobility. Copyright © 2010 John Wiley & Sons, Ltd.     

Stochastic modeling of asphaltenes deposition and prediction of its influence on friction pressure drop

Abstract

When dealing with heavy and extra-heavy crude oils, petroleum industry faces the deposition and incrustation of solids on pipelines walls during fluids transportation. Such a deposition phenomenon is supposed to be caused by asphaltenes aggregation. In this work, is presented a stochastic model that predicts the behavior of friction pressure drop with respect to asphaltenes concentration and the deposition and detaching velocities through the principles of fractal geometry and differential fractional calculus. Results show that at higher values of asphaltenes total concentration and deposition velocity, the friction pressure losses are also increased, which is an expected behavior because of the thickness and morphology of the asphaltenes deposited layer.     

Secondary phase formation in Zn‐rich Cu2ZnSnSe4‐based solar cells annealed in low pressure and temperature conditions

Zn‐rich Cu₂ZnSnSe₄ (CZTSe) films were prepared by a two‐step process consisting in the DC‐magnetron sputtering deposition of a metallic stack precursor followed by a reactive anneal under a Se + Sn containing atmosphere. Precursor composition and annealing temperature were varied in order to analyze their effects on the morphological, structural, and optoelectronic properties of the films and solar cell devices. Raman scattering measurements show the presence of ZnSe as the main secondary phase in the films, as well as the presence of SnSe at the back absorber region of the films processed with lower Zn‐excess values and annealing temperatures. The ZnSe phase is found to accumulate more towards the surface of the absorber in samples with lower Zn‐excess and lower temperature annealing, while increasing Zn‐excess and annealing temperature promote its aggregation towards the back absorber region of the devices. These measurements indicate a strong dependence of these process variables in secondary phase formation and accumulation. In a preliminary optimization of both the composition and reactive annealing process, a solar cell with 4.8% efficiency has been fabricated, and potential mechanisms limiting device efficiency in these devices are discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Impact of several variables on the microwave extraction of Chenopodium Quinoa willd saponins

Despite their possible applications in diverse fields, saponins are still considered to be industrial waste. The use of saponins, however, would make seed processing more profitable and reduce the pollution of watercourses. In this work, the microwave extraction method of Chenopodium quinoa Willd saponins was investigated. The effects of variables such as temperature, time of microwave application, solvent composition and solvent/mass seed ratio were investigated. Solvent mixtures (ethanol–water and isopropanol–water) were used for the extraction. The Taguchi design methodology was employed to determine the number of experiments and the optimal conditions for different extractions. The efficiency of each assay was determined and the results agreed with the best conditions provided by the Taguchi experimental design for both solvent mixtures. The isopropanol–water mixture efficiency was 91.8% in one extraction step, and for ethanol–water mixture, it was 57.1%, clearly showing the advantage of the first one.     

Structural and Electronic Properties of Zr x Al1−x N in Cubic Phase Using First Principles

We calculate the structural and electronic properties of the Zr _x Al_1?x N in cubic phase using first-principles total energy calculations. The study is based on the functional density theory, DFT, with Augmented Plane Wave Plus Local Orbitals method for Calculating Crystal Properties (FP-LAPW). Determination of the crystal lattice constant, the volume of the unit cell, the bulk modulus for concentrations x=0.25,0.50,0.75, is carried out. In addition, we also study the electronic properties for each x. The study consists of the analysis of the electrons energy versus the wave vector, in some directions of the first Brillouin zone, and the Density of States (DOS) as a function of the energy. The results show that the lattice constant increases with x, but the functional relations are not linear. On the other hand, the electronic properties vary substantially with x, and a possible semiconductor metal transition is predicted for any x<0.25.     

Pressure Induced Transition from NaCl to Wurtzite Phases of the New Hard Coating Zr x Al1−x N

We have carried out first-principles calculations to investigate the structural stability of the Zr _x Al_1?x N for several x values in sodium chloride and wurtzite structures. The Density Functional Theory (DFT), such as is implemented in the wien2k code was used and its is found that for x<0.5, a transition phase induced by pressure exists. The pressures that induce the transition are about 13.3, 6.0, and 0.67 GPa for x=0, 1/4, and 1/2, respectively. However, for x>0.5, such transition does not exist. Graphs of Density of States (DOS) for pressures across the transition are obtained and relevant electronic features are discussed.     

Geothermal Energy Potential of Active Northern Underground Mines: Designing a System Relying on Mine Water

Mine Water and the Environment - Mines in northern regions must heat underground workings, surface buildings, or process water due to frigid weather conditions. Mining companies commonly use fossil...