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As a form of solar energy utilization, photovoltaic/thermal (PV/T) modules generate heat and electricity at the same time. Relative to individual photovoltaic or photothermal, it has a higher efficiency. In this paper, a simulation process coupling optical, electrical and thermal models for a water based low-concentration photovoltaic/thermal module is established. The optical characteristics of the module are simulated by Monte Carlo method. The electrical and thermal characteristics are numerically simulated using the finite volume method. The simulated values of outlet water temperature, output current and output power are fit well with experimental values, which verifies the reliability of the simulation process. The effects of water inlet velocity, solar irradiation, water inlet temperature, ambient temperature and wind speed on the energy and exergy performances of the module are analyzed. Results show that the direct contact of the HTF with the backside of the solar panel and the use of bifacial solar cells give the module good electrical efficiency and an overall efficiency of over 65% in all simulations. By connecting modules in series, and the application scenario can be extended.

High coulombic efficiency (CE) usually indicates a long battery cycle life. However, the relationship between long-term CE evolution and battery degradation is not fully understood yet. This paper explores the behavior of long-term CE and clarifies its relationship with capacity degradation. Cycle life tests are conducted on two types of mainstream commercial lithium-ion batteries. An incremental capacity (IC) analysis is then employed to identify battery aging mechanisms. Experimental observations along with in-depth discussions are presented regarding battery degradation, aging mechanisms, and CE evolution. From the experimental results, two typical degradation patterns are recognized. From the IC analysis, we observed that, in addition to a loss of lithium inventory, a loss of active material accelerates battery degradation and brings down CE values. From an electrochemical perspective, this paper establishes the relationship between CE evolution and capacity degradation. This relationship can help develop battery degradation models, estimate battery health states, and provide early failure warnings for a battery management system.

This study explores suitability of battery electric vehicles in the United States by considering their potential market share and operations costs as well as the state-specific variations in electricity generation profiles, given current government policies and the social acceptability of the technology. A performance assessment is developed to compare each state and identify major policy efforts that are needed to increase the environmental and economic competitiveness of electric vehicles. A novel multi-criteria decision-support framework, integrating Life Cycle Assessment, Data Envelopment Analysis, and Agent Based Modeling, is developed. To this end, the environmental and economic impacts of battery electric vehicles are calculated based on three scenarios: an average electricity generation mix, a marginal electricity generation mix, and a solely renewable energy mix with 100% solar. The states are classified, each requiring different policy strategies, in accordance with their performance scores. The results provide important insights for advancing transportation policies and a novel framework for multi-criteria decision-making in the future analyses.

The integration of wind energy in the electricity sector and the adoption of electric vehicles in the transportation sector both have the potential to significantly reduce greenhouse gas emissions individually as well as in tandem with Vehicle-to-Grid technology. This study aims to evaluate the greenhouse gas emission savings of mitigating intermittency resulting from the introduction of wind power through Vehicle-to-Grid technologies, as well as the extent to which the marginal electricity consumption from charging an electric vehicle fleet may weaken this overall environmental benefit. To this end, the comparisons are conducted in seven independent system operator regions. The results indicate that, in most cases, the emission savings of a combination of wind power and Vehicle-to-Grid technology outweighs the additional emissions from marginal electricity generation for electric vehicles. In addition, the fluctuations in newly-integrated wind power could be balanced in the future using EVs and V2G technology, provided that a moderate portion of EV owners is willing to provide V2G services. On the other hand, such a combination is not favorable if the Vehicle-to-Grid service participation rate is less than 5% of all electric vehicle owners within a particular region.

In cascaded latent heat storage (CLHS) systems, the phase change processes of phase change materials (PCMs) can hardly sync due to different parameters in each stage. Hence, the thermodynamic analyses based on the static state hypothesis have limitations. In this study, a dynamic heat transfer model, which can describe the transient variation of the PCM temperature, was developed. Based on the model, six objective functions were defined to evaluate the CLHS system performance. The differential evolution (DE) algorithm was used to optimize the melting temperatures and mass of PCMs under different conditions. The results indicate that the objective functions based on the discharging process are superior to those based on the charging process, and they can be selected as optimization criteria according to specific design purposes. The switching operation can effectively improve the CLHS system performance for the unsteady heat sources that include a drop in temperature. The more extensive the temperature fluctuation range, the more significant the improvement. Furthermore, the stage number and the maximum discharging time have an important impact on the system efficiencies, and the former should be longer than the maximum charging time. This study provides theoretical guidance for practical applications of CLHS systems.

The vehicle-to-grid system is an approach utilizing the idle battery capacity of electric vehicles while they are parked to provide supplementary energy to the power grid. As electrification continues in light duty vehicle fleets, the application of vehicle-to-grid systems for commercial delivery truck fleets can provide extra revenue for fleet owners, and also has significant potential for reducing greenhouse gas emissions from the electricity generation sector. In this study, an economic input–output based hybrid life cycle assessment is conducted to analyze the potential greenhouse gas emissions emission savings from the use of the vehicle-to-grid system, as well as the possible emission impacts caused by battery degradation. A Monte Carlo simulation was performed to address the uncertainties that lie in the electricity exchange amount of the vehicle-to-grid service as well as the battery life of the electric vehicles. The results of this study showed that extended range electric vehicles and battery electric vehicles are both viable regulation service providers for saving greenhouse gas emissions from electricity generation if the battery wear-out from regulation services is assumed to be minimal, but the vehicle-to-grid system becomes less attractive at higher battery degradation levels.

Public transportation is one of the most promising transportation modes to reduce the environmental emissions of the transportation sector in the U.S. In order to mitigate the environmental impacts brought by the transit bus system, new energy buses are introduced into the vehicle market. The goal of this study is to find an optimal bus fleet combination for different driving conditions to minimize life cycle cost, greenhouse gas emissions, and conventional air pollutant emission impacts. For this purpose, a Multi-Objective Linear Programming approach is used to select the optimum bus fleet combinations. Given different weight scenarios, this method could effectively provide solutions for decision makers with various budget constraints or emission reduction requirements. The results indicate that in heavily congested driving cycles such as the Manhattan area, the battery electric bus is the dominant vehicle type, while the hybrid bus has more balanced performances in most scenarios because of its lower initial investment comparing to battery electric buses. Petroleum powered buses have seldom been selected by the model. The trade-off analysis shows that the overall greenhouse gas impact performance is sensitive to the life cycle cost after certain points, which could provide valuable information for the bus fleet combination planning.

The latent thermal energy storage (LTES) system, which uses phase change materials (PCMs), has received a great deal of attention as an effective means of storing thermal energy. However, because of the low thermal conductivity of most PCMs, there is still an urgent need to develop efficient heat transfer enhancement techniques. In this study, a novel combination of heat pipe-fins-copper foam (HP-Fin-CF) has been proposed, and its performance was evaluated via comparisons to the performances of HP-Fin and HP-CF combinations. The effective heat capacity method and thermal resistance network are used in numerical modeling. The results indicate that the HP-Fin combination has better melting performance, whereas the HP-CF combination leads to better solidification. Compared with the basic HP configuration, the total time for melting and solidification can be reduced by 82.70%, 89.03%, and 93.34% for the HP-Fin, HP-CF, and HP-Fin-CF combinations, respectively. The evolution of melting rates suggests that natural convection accelerates the melting of the PCM with the HP-Fin and HP-Fin-CF combinations, but may extend the complete melting time of the PCM in the HP-CF combination under some specific conditions. Also, the exergy analysis was performed to study the thermodynamic properties of the three combinations.

In-situ coal seam is generally under the stress constraint condition. However, the powder coal is often adopted to study gas diffusion dynamics in the laboratory, in this case, the stress cannot be imposed on the coal sample. So the question is, can the laboratory test results with the powder coal reflect the gas diffusion behaviors in the in-situ coal seam? Does the confining stress affect the gas diffusion behaviors in fractured coal? To address these questions, in this work, we first investigated the effect of coal size on gas diffusion dynamics with powder coal and lump coal under unconstrained conditions. The results show that there exists an obvious scale effect for gas diffusion in coal, and a critical value of coal size has been found for the scale effect. When the coal particle size is smaller than the critical value, the effective diffusivity decreases with an increase of the particle size; and when the particle size is larger than the critical value, no obvious change can be found in the effective diffusivity. The critical value for gas diffusion corresponds to the size of the coal matrix. The essential reason for the existence of the scale effect is the differences among the pore structures of coals with various sizes. Based on the research results under the unconstrained conditions, a coal core was selected to study the effect of confining stress and pore pressure on gas diffusion under constraint condition. The results indicated that the confining stress and pore pressure have significant impact on gas diffusion in fractured coal. With an increase of the confining stress and a decrease of the pore pressure, the effective diffusivity reduces gradually. Therefore, to get an accurate understanding of the gas diffusion behavior in in-situ coal seam, during the test in the lab, both the scale effect and confining stress should be considered. The research results obtained in this work have important guiding significance to reveal gas migration in in-situ coal seams during CBM depletion, CO2-ECBM and geological sequestration of CO2.

The dynamic behavior of the PEM (proton exchange membrane) fuel cell stack has great effect on the safety and effective operation of its applications. In this paper, a self-designed bulb-array is used to simulate the various loading conditions and study the dynamic behavior of a 2 kW PEM fuel cell stack. An evaluation index, including oscillation rate, pressure variation and dynamic resistance factor, is used to analyze the transient response of the PEM fuel cell stack. It is observed that the stack current increases about 8.6%, and the Oscillation rate decreases more rapidly after activation. In the step-up load stage, the oscillation rate and the dynamic resistance decrease more rapidly as the external load increases. Due to the periodic anodic purge process, a periodic voltage fluctuation can be seen. In addition, when the stack works in the open-loop state (working without the external load), the transient response of the stack current is significantly affected by the hydrogen humidity and the charge double-layer.

The objective of this paper is to investigate the performance characteristics of μDMFC (micro direct methanol fuel cell) using a novel concept of self-adaptive anode feeding pattern, which can be controlled by detecting the operating current. A comprehensive analysis, including polarization curve, methanol permeation current, mass transport efficiency and CO 2 volume fraction, is conducted to investigate the characterization of anode flow rate in different current regions. A metal-based μDMFC with the active area of 0.64 cm 2 is designed, fabricated and tested. Also, the circuit implementation is proposed. The results reveal that the cell with self-adaptive flow rate represents better stability and responding ability compared to the μDMFC with the constant flow rate.

Frost accumulation on evaporator decreased cooling capacity and COP (coefficient of performance) of cold storage refrigeration system, so timely and effective defrost was significant to cold storage energy-saving operation. The EHD (electric heat defrosting) method was commonly used in cold storages, however, defrost efficiency of the traditional EHD is rather low, and defrost operation usually caused an unfavorable storage temperature fluctuation, which is harmful to storage quality and shelf-life of stored products. In order to solve the problems existing in the traditional EHD method, a novel defrost method with air bypass circulation and electric heater was proposed for the first time in this paper. Five practical cases of this new method with different defrost heaters and air circulation modes were comparatively studied. The results showed that the case with heater embedded in evaporator fins and air circulating through bypass channel was the optimum implementation way of the new method. Compared with the traditional EHD method, the defrost time of this new method was shortened by 62.1%, defrost energy consumption was reduced by 61.0%, and storage temperature fluctuation was decreased by 70.1%. In addition, the defrost efficiency was up to 77.6%, which was 2.93 times of the traditional EHD method.

A start-up ignition burner has been proposed to reduce oil fuel consumption during the firing-up process and partial-load operation. To investigate the influence of different excess air ratios on bituminous coal combustion in the start-up ignition burner, full-scale reacting-flow experiments were performed for an experiment setup. The ignition burner was identical to that normally used in an 800 MWe utility boiler. Gas temperature distributions in the burner were obtained for excess air ratios of 0.56, 0.75, 0.98 and 1.14 (corresponding to primary air velocities of 17, 23, 30 and 35 m/s). Coal burnout and the release of C and H were observed at the exit of the burner nozzle. Gases such as O 2 and CO were measured at the center of the burner. A change in resistance was obtained within the burner.

This paper analyzes the properties of wavelet transform and its potential application in detecting the leakage location of gas pipeline. An entity-part method, which is proposed for the accurate leaking point, has been proved valid in the stimulation experiment. In addition, method of Romberg and Dichotomy Searching are also adopted for the computational analysis of leaking point. In detail, the effect of gas velocity is taken into consideration in the location formula and we propose to consider the average velocities of two parts caused by the leaking point, respectively. Finally, we test these three methods in a real gas pipeline experiment and the result shows the improvement to some extent in contrast to the traditional approach.

Thermodynamic properties and refrigerating performance for the alternative R32/134a mixtures in water-to-water heat pumps have been analyzed. Also, its dynamic model and flammability during the leakage process have been investigated. The results show that R32/134a (30/70) is a good alternative for water-to-water heat pumps. But the possibility of burning and explosive accidents during the leakage process cannot be excluded.

We describe a new air-conditioning and heat-pump system, which may be used to separate a refrigerant mixture efficiently and adjust the composition in the system with cooling- or heating-load changes. A dynamic model has been developed to analyze the transient behavior of the capacity-control system. An air conditioner equipped with a small distillation circuit has been tested. Increases in the SEERs (seasonal energy efficiency ratios) for the new composition-controlled system are 28.3 and 17.7% and capacity changes 57.3–91.8% and 71.5–101%, respectively, for R22/142b and R23/124.

The R22 alternatives R32/125/152a and R290 and their mixtures have been analyzed and evaluated in a room air conditioner. The cooling capacities, energy efficiencies, compressor-discharge temperatures, and pressures of alternatives have been compared with R22. R32/125/152a mixtures were found to be the most effective coolants.

A heat-pump system for heat recovery at substations is analysed. The analysis and test results show that the system yields substantial energy savings and reduces pollution.