Abstract

In this study, a novel method that integrates the detailed channel two-phase flow into the 3D (threedimensional) model of PEMEC (proton exchange membrane electrolyzer cell) is proposed. We explored the effect of L/GDL (liquid/gas diffusion layer) wettability on the two-phase flow and performance of PEMEC. The results show that in the hydrophilic contact angle range, the more hydrophilic contact angle will deteriorate the performance and hinder the discharge of bubbles to the channel. The novel gradient type L/GDL will further promote the flow of water and gas due to the gradient effect of its wettability. In addition, adding MPL also can improve the two-phase management.

Abstract

Recently, it is found that cracks are generated on the micro-porous layer (MPL) surface during the fabrication, and these cracks may act as the main transport paths for liquid water to enter the gas diffusion layer (GDL) from the catalyst layer. In this study, the effects of MPL cracks on liquid behavior in GDL were investigated through a three-dimensional two-phase volume-of-fluid model with reconstructed fibrous structure. Meanwhile, the overlap tructure of MPL and GDL fiber was considered in this study. The results showed that the overlap between the racks and the GDL fibers had a significant influence on the formation of the liquid water breakthrough path. In contrast, cracks shape had less influence on the two-phase flow.

Abstract

The Photovoltaic (PV) hosting capacity of a low-voltage (LV) grid is generally limited by voltage swing issues, and the massive building thermal energy storage can be applied for relieving voltage fluctuations and increasing this capacity. Current voltage control methods (regulators and shunt capacitors) are originally design for conventional grid. New measures like battery storage still face economic controversies. This paper aims to empower air conditioning systems in residential houses for voltage regulation under high PV penetration.
First, two voltage stability issues under high PV penetration condition are revealed by simulation. Then, a temperature priority-based controller is designed for building air conditioning systems, which is categorized as passive thermal energy storage (TES), and a proactive schedule-based controller is designed for active TES – ice storage devices. Finally, A four-node test feeder populated with 360 single-phase PV-equipped residential houses was simulated to illustrate the effectiveness of the two control schemes for voltage regulation. We concluded that demand response (DR) is an effective way for LV grid voltage control. Air conditioning systems can be exploited for voltage control without sacrificing occupant comfort. Active thermal energy storage can effectively increase the DR potentials to regulate the voltage to acceptable levels.

Abstract

Various types of degradations and failures occur in photovoltaic (PV) modules during their outdoor operation, such as cell cracks and an increase in series resistance. Sensitive detection of them is essential to improve the efficiency and reliability of the PV modules and systems. Previous detection techniques such as the I–V curve measurement had a problem because they needed to interrupt the maximum power point tracking (MPPT) operation of the PV system. This study proposes a new method to detect those degradations and failures without interrupting the MPPT operation by using the time-series data of the voltage and current at the maximum power point (Vmp and Imp, respectively). The Vmp and Imp are corrected for temperature using recently developed temperature correction formulas, and are analyzed as the Imp–Vmp curves. It is shown that the existence of a cracked cell in a PV module can be sensitively detected from the Imp–Vmp curve, since the decrease in the photocurrent of a cracked cell tends to shift a part of the Imp–Vmp curve of the module toward high voltage. The experimental and simulation results indicate that a small cell crack less than 10% of a cell area can be detected. In addition, the simulation results also reveal that the increase in series resistance can be detected by the distortion of the Imp–Vmp curve toward a lower voltage in the high Imp, or high irradiance, region. These simulation results indicate that the present method is very powerful for detecting the degradation and failure of PV modules and systems.

Abstract

For the stable operation of proton exchange membrane fuel cells, measurements are made using sensors, and the controls are designed to detect, identify, and avoid defects based on the measured values. In this study, the control index using overpotential was calculated by the curve-fitting method. This method can increase the in-service operation and lower the cost because the sensors and measurement system are not used. The effectiveness of the proposed method for biased data is demonstrated, and the results are described.

Abstract

According to the Renewable Energy 3020 Implementation Plan announced in 2017 by the South Korean administration, the electricity share of renewable energy will be expanded to 20% of the total electricity generation by 2030. Given the intermittency of electricity generation from renewable energy, the realization of such a plan implies potentially large excess electricity generation in certain situations. The purpose of this study is to propose a model to accurately simulate the effects of excess energy generation from renewables which would arise during the transition to South Korea’s 8th Basic Plan for Long-term Electricity Supply and Demand. Our results show that the existence of excess power is highly likely when significant increases in generating capacity from PV and wind capacity are introduced, specifically in spring and fall. In addition, the planned ability to ramp down LNG plants will not be sufficient to cope with the excess energy produced by renewable intermittency. In this case, the role of coal-fired power plants through daily load-following operations could be essential to provide the grid system with additional operational flexibility. In addition, the role of nuclear energy would be vital to achieving both CO2 emissions and electricity cost reductions as an alternative to the fossil fuel generation capacity (i.e., LNG and Coal) outlined in the 8th Basic Plan.

Abstract

A three-dimensional model is applied in this paper to simulate the falling film flow on shell-side of the spiral wound heat exchangers (SWHEs), the flow behavior is simulated with winding angle varied from 0° to 20°. The falling film process of the spiral tube is analyzed and film thickness is measured in axial and circumferential direction. Meanwhile the dimensionless parameter of maldistribution is defined to evaluate the thickness distribution deviating from the ideal condition and the maldistribution is calculated with the simulated results. Results show that the winding angle can influence the flow behavior. The maximum film thickness decreases with the increase of the winding angle at the same circumferential angle. The ascending flow region reduces and the declining flow region enlarges with the winding angle increasing. The maldistribution declines with the winding angle increasing.

Abstract

With declining cost of renewable energy technologies, new form of urban energy systems can be established in a cost-effective way. Urban environments consist of various areas such as residential area and urban district with different energy consumption patterns and building structures. Cost effectiveness of the technologies can be different in different parts of urban environments and different time. To evaluate these differences, we performed techno-economic analyses of renewable energy technologies (PV, battery, and EV) for a residential area in Shinchi, Fukushima and a central district of Kyoto, Japan. We found that high electricity demands in the central Kyoto provide higher cost reduction through renewable energy than that of the residential area in Shinchi in 2018. PV only system has the highest cost reduction in 2018. By 2030, “PV EV” provides the highest cost reduction for both environments, but the Shinchi area with relatively larger number of EVs exhibits the higher cost reduction than that of Kyoto. These differences have important implications for strategies of urban decarbonization for coming decades.

Abstract

Shale pore-seepage parameters are the basic data for evaluating the seepage ability of shale formation. Due to the low-seepage characteristics of shale, only pulse attenuation method can be used to accurately test shale permeability.Various experimental results show that shale has distinct dual-pore characteristics, and conventional pulse attenuation method can only test the overall permeability and total porosity of shale.Based on the dual-hole characteristics of shale, this paper establishes a non-steady seepage model in shale matrix-natural cracks, solves it by Laplace transformation and fits it by genetic algorithm, and obtains an interpretation method for both shale matrix and natural fracture pore-seepage parameters by a set of data.This method can be used not only for the forward analysis of the pulse attenuation pressure response characteristics, but also for testing the pore and seepage parameters of natural fractures in shale core matrix by fitting experimental data.The correlation coefficients R2 of the two groups of experimental data were 0.9953 and 0.9996 respectively, and the fitting results were good.

Abstract

Since the current technologies for capturing CO2 are still too energy intensive, to develop new materials that can capture CO2 reversibly with acceptable energy costs are still needed. In this presentation, (i) by combining ab initio thermodynamic calculations with database mining, we demonstrate a high-throughput screening methodology to identify most promising candidates of CO2 sorbents from material databank; (ii) we show theoretical ways to synthesize new sorbents which could fit the needs of practical capture technologies; and (iii) we analyze some sorbents which possess dual-functionalities: as catalyst to oxidize CO to CO2 and as sorbent to capture CO2.