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Review Article

J. Sol. Energy Eng. 2019;141(4):040801-040801-12. doi:10.1115/1.4042244.

Buildings' energy consumption has a great energetic and environmental impact worldwide. The architectural design has great potential to solve this problem because the building envelope exerts influence on the overall system performance, but this is a task that involves many objectives and constraints. In the last two decades, optimization studies applied to energy efficiency of buildings have helped specialists to choose the best design options. However, there is still a lack of optimization approaches applied to the design stage, which is the most influential stage for building energy efficiency over its entire life cycle. Therefore, this article presents a multi-objective optimization model to assist designers in the schematic building design, by means of the Pareto archived evolutionary strategies (PAES) algorithm with the EnergyPlus simulator coupled to evaluate the solutions. The search process is executed by a binary array where the array components evolve over the generations, together with the other building components. The methodology aims to find optimal solutions (OSs) with the lowest constructive cost associated with greater energy efficiency. In the case study, it was possible to simulate the process of using the optimization model and analyze the results in relation to: a standard building; energy consumption classification levels; passive design guidelines; usability and accuracy, proving that the tool serves as support in building design. The OSs reached an average of 50% energy savings over typical consumption, 50% reduction in CO2 operating emissions, and investment return less than 3 years in the four different weathers.

Commentary by Dr. Valentin Fuster

Research Papers

J. Sol. Energy Eng. 2019;141(4):041001-041001-7. doi:10.1115/1.4042314.

To improve the solar energy utilization in the photovoltaic power, the sun ray double axis tracking device is designed and its tracking method is introduced. Using the finite element method, the parameterized analysis model is built and the static calculation is performed in different conditions for the device. The design feasibility of the device is verified by evaluating the stress. The lightweight of the device is made on the premise that the design satisfies the intensity and this provides the basis for manufacturing the prototype. The sun's rays tracing experiment is carried out by the prototype. Results show that the device design is reasonable and meets the design requirements; the key working conditions for the solar tracking design are found; the lightweight is obvious and the weight is reduced by 14%; the average errors of azimuth angle and height angle are within 5 deg; compared with the fixed device, the increasing proportion of solar energy one day is up to 52.6%; and the device works steadily and has good mechanical properties.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 2019;141(4):041002-041002-13. doi:10.1115/1.4042315.

Along with the upscaling tendency, lighter and so more flexible wind turbine blades are introduced for reducing material and manufacturing costs. The flexible blade deforms under aerodynamic loads and in turn affects the flow field, arising the aeroelastic problems. In this paper, the impacts of blade flexibility on the wind turbine loads, power production, and pitch actions are discussed. An advanced aeroelastic model is developed for the study. A free wake vortex lattice model instead of the traditionally used blade element momentum (BEM) method is used to calculate the aerodynamic loads, and a geometrically exact beam theory is adopted to compute the blade structural dynamics. The flap, lead-lag bending, and torsion degrees-of-freedom (DOFs) are all included and nonlinear effects due to large deflections are considered. The National Renewable Energy Laboratory (NREL) 5 MW reference wind turbine is analyzed. It is found that the blade torsion deformations are significantly affected by both the aerodynamic torsion moment and the sectional aerodynamic center offset with respect to the blade elastic axis. Simulation results further show that the largest bending deflection of the blade occurs at the rated wind speed, while the torsion deformation in toward-feather direction continuously increases along with the above-rated wind speed. A significant reduction of the rotor power is observed especially at large wind speed when considering the blade flexibility, which is proved mainly due to the blade torsion deformations instead of the pure-bending deflections. Lower pitch angle settings are found required to maintain the constant rotor power at above-rated wind speeds.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 2019;141(4):041003-041003-6. doi:10.1115/1.4042245.

The solar energy is a renewable source that has a great potential for conversion into thermal energy or for generation of electric power through photovoltaic panels in Brazil. Concerns about environmental impacts and the fossil resources scarcity have motivated the technological development of renewable alternatives to fill out the energy matrix. The flat-plate solar water heater is an equipment used for domestic or commercial applications to heat fluids, which can minimize the demand for electric energy and, consequently, decrease the electrical bill. However, the development of technologies to increase the conversion of solar energy into thermal energy remains a challenge in order to increase the efficiency of these devices. Thus, passive techniques to enhance heat transfer have been applied and those results seem to be promissory. Among them, delta-winglet longitudinal vortex generator (VG) is a consolidated passive technique currently applied on compact heat exchangers, although few works have been applied this technique on the solar water heater. By a computational fluid dynamics approach, in this work, we analyze the augmentation of heat transfer through delta-winglet longitudinal vortex generator inside a tube of a flat-plate solar water heater. For the Reynolds numbers 300, 600, and 900, the better ratio between the heat transfer and the pressure drop penalty is found for the attack angle of the delta-winglet of 30 deg, while the highest heat transfer was to the attack angle of 45 deg. Moreover, the first vortex generators showed significant impact only on the friction factor and could be eliminated of the solar water heater with no penalty to the heat transfer.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 2019;141(4):041004-041004-18. doi:10.1115/1.4042203.

The installation of solar power plants is currently having a notable expansion. The results presented show that the Argentinean Andes range, from the central to northern latitudes, is an excellent region for the placement of these plants, due to the sum of different positive factors: very high mean annual solar irradiation, low ambient temperature and relative humidity, low precipitable water content, normal wind speeds, and extremely low aerosol content of the atmosphere. The proposed regions are nearby San Antonio de los Cobres and El Leoncito and are compared with two important locations where large solar power plants have been (or will be) built: a site in Africa (Ouarzazate, Morocco) and one in Asia (Dubai, Arab Emirates). We present the results of the possible production of electricity, supplying a total of about 21,000 GWh, which is 15.6% of the 2015 Argentinean electric consumption and, consequently, could reduce the emission of greenhouse gases in a total mass of 11.2 × 106 tons of CO2eq. The installation of this type of renewable power plant will contribute significantly to the Argentinean population due to frequent (mainly summer) cutoff of electric power supply and, in particular, to isolated (low income) populations leaving in the Argentinean Andes range.

Commentary by Dr. Valentin Fuster

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