The hybrid wind-based pumped hydro storage system that absorbs the wind curtailment due to grid limitations is considered to be a solution to improve wind energy penetration and the cost-effectiveness of wind farms. An offshore wind-pumped hydro storage hybrid power system connected to thermal supplied main grid is proposed in this paper. The contribution of this paper can be summarized as follows: (1) a multi-objective dynamic economic optimization model for the proposed system based on evolutionary algorithms is established to optimize size for offshore wind-based pumped hydro storage system; (2) design parameters include the capacity of pump, turbine and reservoirs, and the key financial parameters such as wind power feed-in tariff and capacitor price of pumped hydro storage power station are also taken into account; and (3) examine the attainability of various objectives to analyze the influence on the operation and economic effectiveness. The results show that the optimizing size study is importance to test the economic feasibility of the system. The case study presented in this paper provides decision makers with the flexibility to choose the appropriate capacity installation under different expectations.
Liquid air energy storage system using Kapitza cycle is thermodynamically optimized with selected critical process variables by partial enumeration. With this method, the contour maps for the independent variables are illustrated, that give intuition to the behavior of the LAES systems. The Interaction between the variables can be found and thermodynamically analyzed. The optimized thermodynamic efficiency 40.0%, 48.8%, and 51.2% when compression pressure is set at 40 bar, 80 bar, and 120 bar, respectively.
In this paper, an AC/DC hybrid microgrid with PET is firstly modeled, and then a two-layer optimization model is established with the objective of minimizing the operating cost of AC/DC hybrid microgrid. Finally, the above two-layer optimization model is converted to a single-layer optimization model through KKT method for solving. According to the analysis of the case, the scheduling method based on two-layer optimization considers the cost of purchasing the PET in the upper layer and the operating cost of the different microgrids in the lower layer, and realizes the flexible scheduling between the main grid and microgrids through PET. Compared with the AC/DC hybrid microgrid with AC/DC converter, the hybrid microgrid with PET has flexible power regulation characteristics, and has advantages in reducing operating costs, fully absorbing and efficiently utilizing the renewable energy.
The rapid development of modern electronic devices urges an increasing need for better heat transfer techniques. Pool boiling heat transfer has great potential as it can provide high heat transfer capacity during the phase change of the working fluid. With the help of additive manufacturing technology, complex designs of pool boiling heat sinks can be achieved with selective laser melting (SLM) and they have shown great performances. In this study, heat sinks with one-layer and two-layer porous fin arrays are manufactured by SLM method using AlSi12 alloy powders and heat treated at 450℃ in nitrogen. Their pool boiling performances have shown great enhancement compared with plain copper heat sinks and the heat treated heat sinks have shown the best result both in heat transfer coefficient (HTC) and critical heat flux (CHF). The visualization data is collected during the experiments and used to analyze the heat transfer mechanism.
The growing global population and the resulting excess use of fossil fuels have brought the urgency for climate change mitigation leading to focus on renewable energy resources. Biomass is one of the earliest natural sources of energy, which has the potential to substitute for primary energy resource. However, commercial production of biofuel is still constrained by uncertainties such as biofuel demand. In this study, a two-stage stochastic mixed integer linear programing is formulated for biofuel supply chain based on macroalgae resource under uncertainties. The objective function in this formulation is total annual cost to be minimized. The approach is illustrated through a bioethanol supply chain case study in Korea, where macroalgae are among the dominant biomass resources.
In this paper, a data-driven approach is explored to evaluate the impact of weather conditions on the reliability of urban distribution system. The severity of power outages is divided into two levels according to the number of days with outages in one week. The actual outage records from the local utility are used for the analysis in this study. First, the difference of weather conditions under the two outage levels are intuitively described with the Kernel Density Estimation (KDE). Then, an extreme gradient boosting algorithm is applied to build a classification model for evaluating the outage levels of the local distribution system under given weather conditions. The importance of weather features on the outage level is discussed with the built model. Finally, the performance of the proposed data-driven model is assessed with the Receiver Operating Characteristic (ROC) curve.
Using conventional processes, biodiesel production is necessarily accompanied by the use of excess alcohol and production of a low value glycerol-rich co-product. There is currently a substantial worldwide surplus of this coproduct. While recovery of the alcohol is associated with high capital cost and energy requirement. This work tend to reduce the alcohol usage during biodiesel production and in situ convert the crude glycerol to an added valued product. The biodiesel was produced batch-wise at 130 – 160 oC with sulfuric acid as the catalyst. The effects of reaction temperature, catalyst concentration and molar ratio of triglyceride to methanol were studied. Approximately 100% conversion of the triglyceride was achieved. The glycerol conversion increased with increasing temperature and decreasing molar ratio. This represents proof-of-concept not only for reducing the excess methanol requirement, but also for combining production of fatty acid methyl esters with other added value products, whilst reducing glycerol production.
Polygeneration technology is an important way to realize clean and efficient coal utilization. Coal-steam gasification technology with thermochemical regenerative process is effective to enhance cold gas efficiency of coal gasification. In this paper, a novel methanol-electricity polygeneration system based on coal-steam gasification is proposed. In this novel polygeneration system, the component adjustment is cancelled and unreacted syngas partially recycled is adopted. The Aspen Plus software is selected to simulate the polygeneration systems. As a result, the energy efficiency of the novel polygeneration system based on coal-steam gasification is 53.5% when chemical to power output ratio is 1.1, while energy efficiency of polygeneration system based on traditional gasification is 47.3%. Furthermore, the energy saving effects of system integration method and gasification process improvement are distinguished.
Most of phase change materials have an obvious density change during solid-liquid phase change, which is along with the volume change of phase change materials, and results in the formation or disappearance of the void cavities based on the encapsulation methods. Void cavities play ignorable roles in the phase-change process, while their influence in the composite porous phase change materials were hardly taken into account in the literatures. In this work, the effect of void cavities on the heat transfer of the porous phase change material has been studied for the first time by a two-dimensional lattice Boltzmann method. The high thermal diffusion coefficient and low conductivity of void cavities show significant influence on not only the temperature distribution but also the energy storage performance. This simulation model gets closer to the real application, which holds great promising for being applied in the guidance on the thermal management system design.
Contactless slip-ring provide a safe, non-contact, high efficiency, wear-free and reliable power transfer solution with low maintenance for rotary applications. In this paper, a novel magnetic coupler of wireless power transfer (WPT) system is designed. Compared with the traditional slip ring power supply, it can be applied to the rotating condition. To realize light-weight and small-volume of the WPT, the magnetic coupler and circuit have been optimized from both compensation topology and coil configuration. Experimental results are demonstrating that transfer power is 280W at efficiency of 91.7%.