Hydrogen supply chain architecture for bottom-up energy systems models. Part 1: Developing pathways

The integration of hydrogen energy systems in the overall energy system is an important and complex subject for hydrogen supply chain management. The efficiency of the integration depends on finding optimum pathways for hydrogen supply. Accordingly, energy systems modelling methods and tools have been implemented to obtain the best configuration of hydrogen processes for a defined system. The appropriate representation of hydrogen technologies becomes an important stage for energy system modelling activities. This study, split in consecutive parts, has been conducted to analyse how representative hydrogen supply pathways can be integrated in energy systems modelling. The current paper, the first part of a larger study, presents stylised pathways of hydrogen supply chain options, derived on the basis of a detailed literature review. It aims at establishing a reference hydrogen energy system architecture for energy modelling tools. The subsequent papers of the study will discuss the techno-economic assumptions of the hydrogen supply chain components for energy modelling purposes.     

A review of computer tools for analysing the integration of renewable energy into various energy systems

This paper includes a review of the different computer tools that can be used to analyse the integration of renewable energy. Initially 68 tools were considered, but 37 were included in the final analysis which was carried out in collaboration with the tool developers or recommended points of contact. The results in this paper provide the information necessary to identify a suitable energy tool for analysing the integration of renewable energy into various energy-systems under different objectives. It is evident from this paper that there is no energy tool that addresses all issues related to integrating renewable energy, but instead the ‘ideal’ energy tool is highly dependent on the specific objectives that must be fulfilled. The typical applications for the 37 tools reviewed (from analysing single-building systems to national energy-systems), combined with numerous other factors such as the energy-sectors considered, technologies accounted for, time parameters used, tool availability, and previous studies, will alter the perception of the ‘ideal’ energy tool. In conclusion, this paper provides the information necessary to direct the decision-maker towards a suitable energy tool for an analysis that must be completed.     

Spatial development of hydrogen economy in a low-carbon UK energy system

Hydrogen technologies and infrastructures might play a significant role in meeting ambitious climate and energy policy goals of the UK Government. Nonetheless, studies on hydrogen are either limited in scope in that they do not take into account the relationships with the wider energy system drivers and constraints or do not consider how a hydrogen network might develop geographically. This paper presents a framework where a spatially explicit hydrogen module is embedded in the UK MARKAL Energy System model to explore energy system trade-offs for the production, delivery and use of hydrogen at the sub-national level. A set of illustrative scenarios highlight the competitiveness of hydrogen related infrastructures and technologies as well as imported liquid hydrogen against a stringent emissions reduction target; the effect of emissions reduction trajectory on the development of hydrogen network; the intense resource competition between low carbon hydrogen production and electricity generation, and the importance of economies of scale in hydrogen supply and distribution.     

Molecular diffusion effects in LES of a piloted methane–air flame

Molecular diffusion effects in LES of a piloted methane–air (Sandia D) flame are investigated on a series of grids with progressively increased resolution. The reacting density, temperature and chemical composition are modeled based on the mixture fraction approach combined with a steady flamelet model. With a rationale to minimize interpolation uncertainties that are routinely introduced by a flamelet table look-up, quadratic splines relationships are employed to represent thermochemical variables. The role of molecular diffusivity in effecting spatial transport is studied by drawing a comparison with the turbulent diffusivity and analyzing their statistics conditioned on temperature. Statistical results demonstrate that the molecular diffusivity in the near-field almost always exceeds the turbulent diffusivity, except at low temperatures (less than 500 K). Thus, by altering the jet near-field, molecular transport plays an important role in the further downstream jet development. Molecular diffusivity continues to dominate in the centerline region throughout the flow field. Overall, the results suggest the strong necessity to represent molecular transport accurately in LES studies of turbulent reacting flows.     

Generation of typical meteorological years using genetic algorithm for different energy systems

Computer simulation plays an important role in investigating the thermal/energy performance of buildings and energy systems. In order to reduce the computational time and provide a consistent form of weather data, simulation run with multi-year weather files is generally avoided. In contrast, representative weather data is widely adopted. For developing typical meteorological year (TMY) weather files, Sandia method is one of the commonly adopted approaches. During the generation of TMY, different weighting factors are assigned to some key climatic indices. Currently, the values of weighting factors mainly depend on the researchers' judgement. As these weighting factors can express the relative importance of impact of a particular climatic index on the thermal/energy performance of an energy system, computer simulation using different TMYs may lead to different conclusions. Therefore, it is inappropriate to apply one single TMY for all energy systems. In this study, a novel TMY weather file generator has been developed to link up an optimization algorithm and an energy simulation program. Through four application examples (one air-conditioned building and three renewable energy systems), this weather file generator demonstrated its capability to search optimal/near optimal combinations of weighting factors for generating appropriate TMY for computer simulations of different energy systems.     

Large Eddy Simulation of NO Formation in Non-Premixed Turbulent Jet Flames with Flamelet/Progress Variable Approach

To improve the NO modelling in turbulent flames,the flamelet/progress variable(FPV)model is extended by introducing NO mass fraction into the progress variable and incorporating an additional NO transport equation.Two sets of flamelet databases are tabulated with progress variables based on major species and NO mass fraction,respectively.The former is used for the acquisition of the main thermochemical variables,while the latter is employed for NO modelling.Moreover,an additional transport equation is solved to obtain the NO mass fraction,with the source term corrected using the scale similarity method.Model assessments are first conducted on laminar counterflow diffusion flames to identify lookup-related errors and assess the suitability of progress variable definitions.The results show that the progress variables based on major species and NO could correctly describe the main thermochemical quantities and NO-related variables,respectively.Subsequently,the model is applied to the large eddy simulation(LES)of Sandia flames.The results indicate that the extended FPV model improves the NO prediction,with a mean error for NO prediction at 55％,significantly lower than those of existing FPV models(130％and 385％).The LES with the extended FPV model quantitatively captures NO suppression in the mid-range of Reynolds numbers from 22 400(Flame D)to 33 600(Flame E),but underestimates the NO suppression at higher Reynolds numbers from 33 600 to 44 800(Flame F).This underprediction is primarily attributed to the underestimation of local extinction levels in flames with high Reynolds numbers.     

A new weighted-sum-of-gray-gases model for CO2–H2O gas mixtures

Decoupled radiative transfer calculations of Sandia Flame D are performed employing experimental measurements of temperature and gas compositions and the discrete ordinates method. Turbulence radiation interactions are accounted for employing temperature variance measurements. The spatial variations in the mean H₂O/CO₂ ratios within the flame are seen to vary widely and sometimes fall outside the range of the weighted-sum-of-gray-gases model (WSGGM) parameters reported in the literature. Therefore, parameters for a new WSGGM are computed from total emissivity correlations encompassing the range of the H₂O/CO₂ ratios encountered within the flame. Predictions from the new model compare favorably against the spectral-line-based WSGGM and existing benchmarks.     

Dynamic modeling and simulation of a small wind–fuel cell hybrid energy system

This paper describes dynamic modeling and simulation results of a small wind–fuel cell hybrid energy system. The system consists of a 400 W wind turbine, a proton exchange membrane fuel cell (PEMFC), ultracapacitors, an electrolyzer, and a power converter. The output fluctuation of the wind turbine due to wind speed variation is reduced using a fuel cell stack. The load is supplied from the wind turbine with a fuel cell working in parallel. Excess wind energy when available is converted to hydrogen using an electrolyzer for later use in the fuel cell. Ultracapacitors and a power converter unit are proposed to minimize voltage fluctuations in the system and generate AC voltage. Dynamic modeling of various components of this small isolated system is presented. Dynamic aspects of temperature variation and double layer capacitance of the fuel cell are also included. PID type controllers are used to control the fuel cell system. SIMULINK^TM is used for the simulation of this highly nonlinear hybrid energy system. System dynamics are studied to determine the voltage variation throughout the system. Transient responses of the system to step changes in the load current and wind speed in a number of possible situations are presented. Analysis of simulation results and limitations of the wind–fuel cell hybrid energy system are discussed. The voltage variation at the output was found to be within the acceptable range. The proposed system does not need conventional battery storage. It may be used for off-grid power generation in remote communities.     

空气/水双冷型PV/T一体化组件实验与模拟研究

提出一种空气/水双冷型PV/T一体化组件,搭建2套测试平台开展PV/T组件的空冷、水冷、空气-水复合冷却实验,研究不同工作模式下组件的性能表现。实验结果表明：3种工作模式均可对光伏组件进行有效冷却,空冷、水冷、复合冷却模式组件综合效率分别为76.05%、74.51%、84.83%,其吸热板温度较无工质冷却模块分别可降低19.08、27.58和35.16℃。为进一步分析设计参数对PV/T组件电热特性的影响,利用ANSYS构建组件的三维数值模型,并通过实验数据验证模型的准确性。模拟显示：采用双风道翅片式结构可有效提升组件电热性能;随着环境温度的升高（10～40℃）,组件的综合效率由61.85%增至80.31%。     

Energy efficient building strategies for school buildings in Oman

In this paper hour-by-hour computer simulations of cooling load for a public building were carried out under local weather conditions using TRNSYS building computer simulation software. Different passive measures to reduce the cooling load were investigated. These include the envelope insulation, space ventilation, shading, glazing, artificial lighting variation, and evaporative cooling of the structure. The results show as high as 43% reductions in peak cooling load can be achieved using a combination of well-established passive cooling techniques and technologies. The significance of these results stems from the fact that they were obtained under local weather conditions, a matter of importance to building architects, designers, contractors, and builders as well as air-conditioning equipment manufacturers. Although this work was undertaken to improve the thermal performance of school buildings the results were extended to cover the summer school vacation months so that they will benefit public buildings as well. Copyright © 2002 John Wiley & Sons, Ltd.     

Renewable energy strategies for sustainable development

This paper discusses the perspective of renewable energy (wind, solar, wave and biomass) in the making of strategies for a sustainable development. Such strategies typically involve three major technological changes: energy savings on the demand side, efficiency improvements in the energy production, and replacement of fossil fuels by various sources of renewable energy. Consequently, large-scale renewable energy implementation plans must include strategies for integrating renewable sources in coherent energy systems influenced by energy savings and efficiency measures. Based on the case of Denmark, this paper discusses the problems and perspectives of converting present energy systems into a 100% renewable energy system. The conclusion is that such development is possible. The necessary renewable energy sources are present, and if further technological improvements of the energy system are achieved the renewable energy system can be created. Especially technologies of converting the transportation sector and the introduction of flexible energy system technologies are crucial.     

Energy and thermal performance of heat pipe/cooling coil systems in hot‐humid climates

The objective of this study is to evaluate the magnitude of reduction in cooling and reheat energy when a heat pipe system is incorporated with the cooling coil of an air‐conditioning system. The heat pipe/cooling coil (HP/CC) system performance is determined by several parameters that are related to both the air‐conditioner cooling coil and the heat pipe physical characteristics as well as the condition of the air entering and leaving the system. In order to appreciate the impact of these parameters and their relative influence on energy consumption and the required indoor air conditions, a simple mathematical model incorporating the parameters of HP/CC is formulated. The model describes the overall system performance at varying entering and leaving air conditions. The model is then applied to a case study as an example of an application to investigate these relationships for a better understanding of the system behaviour and the influencing design parameters. It is evident that due to the coupling nature of the heat pipe and the cooling coil actions, a unique system performance will be obtained for each combination of heat pipe effectiveness and cooling coil by‐pass factor. A proper selection of both the heat pipe and the cooling coil characteristics is found to be necessary for a satisfactory performance under the given operating conditions. Copyright © 2000 John Wiley & Sons, Ltd.