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J. Sol. Energy Eng. 2019;141(6):061001-061001-7. doi:10.1115/1.4043615.

The importance of statistical analysis in the field of energy for environmental engineering is shown in this research paper, in which the adequacy of the data sets of clarity index with the model of “best” probability (based on the criteria used) was studied. In Campo Grande which is the capital of the Brazilian state of Mato Grosso do Sul, located in the Center-West region of the country, there is a predominance of the atmospheric conditions of low cloudiness, with a high frequency of days with a clear sky and in consequence a low-frequency of days with cloudy sky. The aerosols resulting from the burning of sugarcane influence the sky conditions in Campo Grande thus reducing the frequency of the clear sky.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 2019;141(6):061002-061002-10. doi:10.1115/1.4043633.

To meet the increasing energy demand and to shave the peak, the Kingdom of Saudi Arabia (KSA) is currently planning to invest more on renewable energy (RE) seeking diversity of energy resources. Through the integration of demand-side management measures and renewable energy distributed generation (DG) systems, the study outlined in this paper aims at investigating the potential of hybrid renewable energy systems in supplying energy demands for residential communities in an oil-rich country. The residential community considered in this study, located in the eastern region of KSA, has an annual electrical usage of 1174 GWh and an electrical peak load of 335 MW that are met solely by the grid. The results of the analyses indicated that the implementation of cost-effective energy efficiency measures (EEMs) reduced the electricity usage by 38% and peak demand by 51% as well as CO2 emissions by 38%. Although the analysis of the hybrid systems showed that purchasing electricity from the grid is the best option with a levelized cost of energy (LCOE) of $0.1/kWh based on the current renewable energy market and economic conditions of KSA, RE systems can be cost-effective to meet the loads of the residential communities under specific electricity prices and capital cost levels.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 2019;141(6):061003-061003-6. doi:10.1115/1.4043657.

The work presented in this paper used rigorous 3D flow-field analysis combined with multi-objective constrained shape design optimization for the design of complete blade + bladelet configurations for a three-blade horizontal-axis wind turbine. The fluid flow analysis in this work was performed using Openfoam software. The 3D, steady, incompressible, turbulent flow Reynolds-Averaged Navier–Stokes equations were solved in the rotating frame of reference for each combination of wind turbine blade and bladelet geometry. The free stream uniform wind speed in all cases was assumed to be 9 m s−1. The three simultaneous design optimization objectives were as follows: (a) maximize the coefficient of power, (b) minimize the coefficient of thrust force, and (c) minimize twisting moment around the blade axis. The bladelet geometry was fully defined by using a small number of parameters. The optimization was carried out by creating a multidimensional response surface for each of the simultaneous objectives. The response surfaces were based on radial basis functions, where the support points were designs analyzed using the high-fidelity computational fluid dynamics (CFD) analysis of the full blade + bladelet geometry. The response surfaces were then coupled to an optimization algorithm in modefrontier software. The predicted values of the objective functions for the optimum designs were then again validated using Openfoam high-fidelity analysis code. Results for a Pareto-optimized bladelet on a given blade indicate that more than 4% increase in the coefficient of power at minimal thrust force penalty is possible at off-design conditions compared to the same wind turbine rotor blade without a bladelet.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 2019;141(6):061004-061004-10. doi:10.1115/1.4043658.

The present work is focused on the development of a simulation model for an existing cogeneration power plant, which utilizes a solar thermal field with parabolic trough solar collectors coupled to an Organic Rankine Cycle engine. The power plant is modeled in the trnsys v.17 software package and its performance has been validated with real operating conditions. The simulated system (concentrated solar power (CSP) field and ORC engine) is the main part of a hybrid power plant located near “Ziloti” village of the Municipality of Xanthi, in northeastern Greece. The construction of the hybrid power plant was funded by the Strategic Co-Funded Project of the European Territorial Cooperation Program Greece–Bulgaria 2007–2013 with the acronym ENERGEIA. The power plant simulated in this paper includes a 234 kWth solar parabolic trough collector (PTC) field, a 5 m3 thermal energy storage tank, and a 5 kWe ORC engine for the production of thermal and electrical energies. The results of the simulations present small deviation in contrast to the real operating data of the CSP power plant coupled with the ORC engine, therefore the simulation model is considered as reliable.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 2019;141(6):061005-061005-17. doi:10.1115/1.4043514.

A comprehensive aero-hydro-structural analysis is conducted for a 5 MW offshore wind turbine system in this study. Soil–structure interaction under complex aero-hydro loading is analyzed to provide a suitable foundation design with high safety. With consideration of the wind turbine size and water depth, the monopile foundation design by the National Renewable Energy Laboratory (NREL) is selected in the current study. Both aerodynamic loading for the 5 MW wind turbine rotor defined by NREL and hydrodynamic loading on the foundation are simulated under different flow conditions using high-fidelity computational fluid dynamics methods. Structural dynamic analysis is then carried out to estimate the stress field in the foundation and soil. Results from the comprehensive analysis indicate that the Morison equation is conservative when looking at the stress field in the monopile foundation and underestimates the stress field in soil. A similar analysis strategy can be applied to other types of foundations such as jacket foundations and lead to more economical and reliable designs of foundations.

Commentary by Dr. Valentin Fuster

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