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Optical system design has a significant impact on solar power plant efficiency. It can be advantageous to be able to very precisely adapt mirror shapes in order to improve energy yield. In this article it is investigated whether it is feasible to use non-uniform rational Beziers splines (NURBS) to describe mirrors. Algorithms and equations to evaluate optical performance by ray tracing are lined out. A parameterization scheme is given that reduces the degrees of freedom to a level suitable for automatic processing. To prove feasibility, a secondary reflector based on a NURBS surface and a compound parabolic concentrator (CPC) are designed for a specific test application and compared to each other. It is found that the suggested design method is feasible on contemporary personal computers and that the NURBS based surface performs well compared to the CPC.

202306 bcww ; Not applicable ; RGC ; Published ; 24 months

Abstract Ever-growing energy demands and unacceptable emissions from fossil fuel combustion are major driving forces for expanding alternative, green energy sources. Hydro-power is one promising ecological alternative to meet these energy requirements. Such systems do not require any weir or dam and, thus, can be employed with minimum ecological impact. However, available designs are not yet suitable as efficient water energy converters, in particular for conditions corresponding to low water speeds (as mostly found in practice), due to low power output. Savonius turbines are particularly robust and cost-efficient, but show a poor efficiency. This article aims at maximizing the output power of a hydraulic Savonius turbine by modifying the blade profile. The main difference in this work compared to previous studies is that the blade shape of the concave and convex sides evolve independently from each other (no constant blade thickness). Twelve geometrical parameters are involved during shape optimization. To obtain optimal conditions, many transient computational fluid dynamics (CFD) simulations are performed using the industrial flow simulation code Star-CCM+, driven by the in-house optimization library OPAL++ relying on evolutionary algorithms. The optimization process takes into account the output power coefficient ( C p ) as a target function. Compared to the traditional Savonius turbine, a relative increase of C p by almost 12% is obtained at a tip speed ratio of 1.1. The performance of the optimal geometry was compared to the standard design over the whole range of operation. This comparison revealed additionally that the performance was improved by almost 15% at a tip speed ratio of 1.2. The performance of the optimal design is superior for the whole range of operation, particularly at a tip speed ratio exceeding 0.8. Finally, it was checked that the optimal design is still self-starting.

Access to a reliable source of electricity is a basic need for any community as it can improve the living standards characterized via the improvement of healthcare, education, and the local economy at large. There are two key factors to consider when assessing the appropriateness of a micro-grid system, the cost-effectiveness of the system and the quality of service. The tradeoff between cost and reliability of the system is a major compromise in designing hybrid systems. In this way, optimization of a Hybrid Micro-Grid System (HMGS) is investigated. A hybrid wind/PV system with battery storage and diesel generator is used for this purpose. The power management algorithm is applied to the load, and the Multi-Objective Particle Swarm Optimization (MOPSO) method is used to find the best configuration of the system and for sizing the components. A set of recent hourly wind speed data from three meteorological stations in Iran, namely: Nahavand, Rafsanjan, and Khash, are selected and tested for the optimization of HMGS. Despite design complexity of the aforementioned systems, the results show that the MOPSO optimization model produces appropriate sizing of the components for each location. It is also suggested that the use of HMGS can be considered as a good alternative to promote electrification projects and enhance energy access within remote Iranian areas or other developing countries enjoying the same or similar climatic conditions.

While previous studies focused on managing charging demand for private electric vehicles (EVs), we investigate ways of supporting the upgrade of an entire public urban electric taxi (ET) system. Concerning the coexistence of plugin charging stations (CSs) and battery swap stations (BSSs) in practice, it thus requires further efforts to design a holistic charging management especially for ETs. By jointly considering the combination of plug-in charging and battery swapping, a hybrid charging management framework is proposed in this paper. The proposed scheme is capable of guiding ETs to appropriate stations with time-varying requirements depending on how emergent the demand will be. Through the selection of battery charging/swap, the optimization goal is to reduce the trip delay of ET. Results under a Helsinki city scenario with realistic ETs and charging stations show the effectiveness of our enabling technology, in terms of minimized drivers’ trip duration, as well as charging performance gains at the ET and station sides.

Abstract The vertical pipe intake-outlet plays an important role in the pumped hydro energy storage (PHES), and its main parameters included the orifice height ratio (H∗), the diffuser short semi-axis ratio (a∗), the diffuser long semi-axis ratio (b∗) and the cover plate radius ratio (Rc∗). The aim of this study was to analyse effects of the parameters and obtain the optimal design. An integration method combining computational fluid dynamics (CFD), response surface methodology (RSM) and genetic algorithm was proposed. To evaluate grid independency, the grid converge index was introduced. Based on the validation for the baseline design (H∗ = 0.577, a∗ = 1.087, b∗ = 4.231 and Rc∗ = 1.635), a reliable CFD model was developed to obtain results of sample points. Then RSM models were constructed and assessed, and contribution and interactions of the parameters were analyzed. Finally, the optimal design (H∗ = 0.422, a∗ = 1.177, b∗ = 5.363 and Rc∗ = 2.115) was obtained. The CFD results show that the overall head loss coefficient, the inflow and the outflow velocity distribution coefficient are reduced by 4.687%, 11.765% and 38.596%, respectively. Especially, the negative velocity at the trashrack section in the pump mode is eliminated. The improvement demonstrates that the proposed method achieves significant superiority over the trial-and-error method traditionally adopted in the intake-outlet design.

Abstract The hydrothermal geothermal heating depends heavily on the existence of hot water reservoir and the shallow ground source heat pump occupies large area. Here a single well geothermal heating (SWGH) technology is shown, which does not depend on the existence of hot water reservoir. An experimental research on SWGH is carried out and a mathematical model describing the heat transfer through surrounding rock to well tube as well as inside the geothermal well is developed. The mathematical model validated by experimental data is then used to predict the performance of SWGH. It is found that the average extracted thermal output is respectively 448.49 and 413.63 kW in the first and tenth heating seasons. By changing the injection water temperature and velocity, SWGH system can meet the requirement of building heating load varying with the outdoor air temperature and adjust the imbalance of the extracted thermal output among different heating seasons. Understanding these will enable us to better apply SWGH technology.

Abstract In this work, the reaction pathways of hemicellulose were investigated for a complete understanding of the mechanism of biomass pyrolysis in thermal plasma. Energies of the possible reaction pathways of three model compounds of hemicellulose, xylose, O-acetyl xylose and 4-O-MeGlcA, in hydrogen plasma were estimated through density functional theory (DFT), and the most favorable reaction routes were proposed. Combining with our previous work, the effects of the biomass composition on their pyrolysis behavior in hydrogen plasma were discussed, and the production distribution was predicted. The reaction mechanism of biomass pyrolysis in hydrogen plasma was clarified finally, which indicated that active H in plasma played a very important role in dehydrogenation reactions.