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This work presents a new and useful method to dimension wind turbines and control systems and to optimize their mechanical design. This method allows determining the principal curves for characterizing a small capacity wind turbine designed with a Permanent Magnet Synchronous Generator (PMSG). For the wind turbine characterization it was considered the losses in the process of energy transformation in the wind rotor, electric generator and in the bridge rectifier. The equivalent electric model of the synchronous generator was used to determine the electric parameter performance. The work of the wind rotor was considered in its maximum power curve and the PMSG performance in the linear region of its magnetization curve. This leads to develop a new methodology for the complete wind turbine characterization from the nominal parameters of the wind rotor and the electric generator. This method also allows obtaining the power curves and the parameters of voltage, current and efficiency around the wind speed domain and angular speed in the wind rotor. The method was tested for small-capacity wind turbine (1 kW and 10 kW) performances and the numerical and experimental results are described.

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Irreversible losses and heat transport in a magnetohydrodynamic flow of a viscous, steady, incompressible, and fully developed couple stress Al 2 O 3-water nanofluid through a sloping permeable wall channel with porous medium and under the effect of radiation heat flux and slip were analyzed. The fundamental equations were solved numerically by using Runge-Kutta together with the shooting technique and the results were in qualitative agreement with an exact solution obtained for a limit case. The impacts of couple stress, Darcy number, solid nanoparticle concentrations, conduction-radiation parameter, Hartmann number and hydrodynamic slip on flow, temperature, heat transport, and entropy production were examined. It was possible to achieve values of minimum entropy production not yet reported in previous studies. In this way, optimal values of couple stress and slip were obtained. The heat transport was also explored and optimal values of slip flow and conduction-radiation parameter with maximum heat transfer were found. Finally, in addition to the alumina, the distributions of velocity, temperature, and entropy generation in TiO 2-water and Cu-water were presented for different solid nanoparticle concentrations. It was obtained that the local entropy of TiO 2-water was lower than Cu-water and Al 2 O 3-water in the channel bottom region while it was greater in the upper region.

SUMMARY This paper compares some important parameters obtained in the hydrogen production between the photosynthetic microorganisms Spirulina maxima 2342 and Scenedesmus obliquus 39. It is also reported the employment of hydrogen produced in this study (m3 s−1) in a proton exchange membrane fuel cell (PEMFC) for electricity production. A comparison is also made between the electric current generated and the final dry biomass (mA mg−1) under specific experimental conditions. In this study, the electric current generated in the PEMFC for a period of 200 min under the light intensity of 150 µE m−2 s−1 and agitation was monitored. With the average current generated by the fuel cell the hydrogen produced by each microorganism is determined. The chromatography method was used to confirm the presence of hydrogen produced by each microorganism which was fed to the PEMFC. Copyright © 2011 John Wiley & Sons, Ltd.

SUMMARY This study presents a selection of optimal energy alternatives for electrical self‐sufficiency in a rural university (Universidad del Istmo, UNISTMO), located in the state of Oaxaca, Mexico and for the electricity supply for a rural community (Gran Piedra) in Santiago, Cuba. The analysis follows a multicriteria approach. It uses a method called compromise programming and takes into account the technical, economical, environmental and social criteria. The hybrid optimization model for electric renewables (HOMER) software was used to generate alternative energy sets through enumerative search, with which decisional matrices were built for each case study. The influence of weighting for each criterion was assessed. In the case of self‐sufficiency in UNISTMO, when the decision‐making center has a preference for the minimization of equivalent emissions in the life cycle (ESLC), a wind system is suitable. On the other hand, when there is a preference for the minimization of levelized cost of energy, a photovoltaic (PV) system is suitable; both systems connected to the national electrical grid. Obviously, a preference for the minimization of capital cost led to keeping the power supply from the grid. In the case of Gran Piedra, a diesel generator‐based system is suitable when the criterion ‘capital cost’ absorbs 70% or more of the preferences of the decision‐making centers. When the preference is less than 70% regardless of the weighting given to other criteria, the best alternatives are those involving renewable technologies, reaching renewable fractions of 75% and 94% in two potential configurations of energetic systems. Copyright © 2013 John Wiley & Sons, Ltd.

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