Transmission, Distribution & Storage

Compact-tension (CT) specimens made of low alloy 30CrMo steels were hydrogen-charged and then subjected to the fracture toughness test. The experimental results revealed that the higher crack propagation and the lower crack growth resistance (CTOD-R curve) are significantly noticeable with increasing hydrogen embrittlement (HE) indexes. Moreover the transition in the microstructural fracture mechanism from ductile (microvoid coalescence (MVC)) without hydrogen to a mixed quasi-cleavage (QC) fracture and QC + intergranular (IG) fracture with hydrogen was observed. The hydrogen-enhanced decohesion (HEDE) mechanism was characterized as the dominant HE mechanism. According to the experimental testing the coupled problem of stress field and hydrogen diffusion field with cohesive zone stress analysis was employed to simulate hydrogen-assisted brittle fracture behavior by using ABAQUS software. The trapezoidal traction-separation law (TSL) was adopted and the initial TSL parameters from the best fit to the load-displacement and J-integral experimental curves without hydrogen were calibrated for the critical separation of 0.0393 mm and the cohesive strength of 2100 MPa. The HEDE was implemented through hydrogen influence in the TSL and to estimate the initial hydrogen concentration based on matching numerical and experimental load-line displacement curves with hydrogen. The simulation results show that the general trend of the computational CTOD-R curves corresponding to initial hydrogen concentration is almost the same as that obtained from the experimental data but in full agreement the computational CTOD values being slightly higher. Comparative analysis of numerical and experimental results shows that the coupled model can provide design and prediction to calculate hydrogen-assisted fracture behavior prior to extensive laboratory testing provided that the material properties and properly calibrated TSL parameters are known.

The present work addresses the modelling control and simulation of a microgrid integrated wind power system with Doubly Fed Induction Generator (DFIG) using a hybrid energy storage system. In order to improve the quality of the waveforms (voltages and currents) supplied to the grid instead of a two level-inverter the rotor of the DFIG is supplied using a three-level inverter. A new adaptive algorithm based on combined Direct Reactive Power Control (DRPC) and fuzzy logic controls techniques is applied to the proposed topology. In this work two topologies are proposed. In the first one the active power injected into the grid is smoothened by using an economical hybrid battery and supercapacitor energy storage system. However in the second one the excess wind energy is used to produce and store the hydrogen and then a solid oxide fuel cell system (SOFC) is utilized to regenerate electricity by using the stored hydrogen when there is not enough wind energy. To avoid overcharging deep discharging of batteries to mitigate fluctuations due to wind speed variations and to fulfil the requirement of the load profile a power management algorithm is implemented. This algorithm ensures smooth output power in the first topology and service continuity in the second. The modelling and simulation results are presented and analysed using Matlab/Simulin.

Electrochemical energy storage is a key enabling technology for further integration of renewables sources. Redox flow batteries(RFBs) are promising candidates for such applications as a result of their durability efficiency and fast response. However deployment of existing RFBs is hindered by the relatively high cost of the (typically vanadium-based) electrolyte. Manganese is an earth-abundant and inexpensive element that is widely used in disposable alkaline batteries. However it has hitherto been little explored for RFBs due to the instability of Mn(III) leading to precipitation of MnO2 via a disproportionation reaction. Here we show that by combining the facile hydrogen negative electrode reaction with electrolytes that suppress Mn(III) disproportionation it is possible to construct a hydrogen/manganese hybrid RFB with high round trip energy efficiency (82%) and high power and energy density (1410 mW cm−2 33 Wh l−1 ) at an estimated 70% cost reduction compared to vanadium redox flow batteries.

Liquid hydrogen is the main fuel of large-scale low-temperature heavy-duty rockets and has become the key direction of energy development in China in recent years. As an important application carrier in the large-scale storage and transportation of liquid hydrogen liquid hydrogen cryogenic storage and transportation containers are the key equipment related to the national defense security of China’s aerospace and energy fields. Due to the low temperature of liquid hydrogen (20 K) special requirements have been put forward for the selection of materials for storage and transportation containers including the adaptability of materials in a liquid hydrogen environment hydrogen embrittlement characteristics mechanical properties and thermophysical properties of liquid hydrogen temperature which can all affect the safe and reliable design of storage and transportation containers. Therefore it is of great practical significance to systematically master the types and properties of cryogenic materials for the development of liquid hydrogen storage and transportation containers. With the wide application of liquid hydrogen in different occasions the requirements for storage and transportation container materials are not the same. In this paper the types and applications of cryogenic materials commonly used in liquid hydrogen storage and transportation containers are reviewed. The effects of low-temperature on the mechanical properties of different materials are introduced. The research progress of cryogenic materials and low-temperature performance data of materials is introduced. The shortcomings in the research and application of cryogenic materials for liquid hydrogen storage and transportation containers are summarized to provide guidance for the future development of container materials. Among them stainless steel is the most widely used cryogenic material for liquid hydrogen storage and transportation vessel but different grades of stainless steel also have different applications which usually need to be comprehensively considered in combination with its low temperature performance corrosion resistance welding performance and other aspects. However with the increasing demand for space liquid hydrogen storage and transportation the research on high specific strength cryogenic materials such as aluminum alloy titanium alloy or composite materials is also developing. Aluminum alloy liquid hydrogen storage and transportation containers are widely used in the space field while composite materials have significant advantages in being lightweight. Hydrogen permeation is the key bottleneck of composite storage and transportation containers. At present there are still many technical problems that have not been solved.

In the course of the energy transition distributed hybrid energy systems such as the combination of photovoltaic (PV) and battery storages is increasingly being used for economic and ecological reasons. However renewable electricity generation is highly volatile and storage capacity is usually limited. Nowadays a new storage component is emerging: the power-to-gas-to-power (PtGtP) technology which is able to store electricity in the form of hydrogen even over longer periods of time. Although this technology is technically well understood and developed there are hardly any evaluations and feasibility studies of its widespread integration into current distributed energy systems under realistic legal and economic market conditions. In order to be able to give such an assessment we develop a methodology and model that optimises the sizing and operation of a PtGtP system as part of a hybrid energy system under current German market conditions. The evaluation is based on a multi-criteria approach optimising for both costs and CO2 emissions. For this purpose a brute-force-based optimal design approach is used to determine optimal system sizes combined with the energy system simulation tool oemof.solph. In order to gain further insights into this technology and its future prospects a sensitivity analysis is carried out. The methodology is used to examine the case study of a German dairy and shows that PtGtP is not yet profitable but promising.

Hydrogen has been identified as a fuel of choice for providing clean energy for transport and other applications across the world and the development of materials to store hydrogen efficiently and safely is crucial to this endeavour. Hydrogen has the largest scattering interaction with neutrons of all the elements in the periodic table making neutron scattering ideal for studying hydrogen storage materials. Simultaneous characterisation of the structure and dynamics of these materials during hydrogen uptake is straightforward using neutron scattering techniques. These studies will help us to understand the fundamental properties of hydrogen storage in realistic conditions and hence design new hydrogen storage materials.

The search for new fuels to supersede fossil fuels has been intensified these recent decades. Among these fuels hydrogen has attracted much interest due to its advantages mainly cleanliness and availability. It can be produced from various raw materials (e.g. water biomass) using many resources mainly water electrolysis and natural gas reforming. However water electrolysis combined with renewable energy sources is the cleanest way to produce hydrogen while reducing greenhouse gases. Besides hydrogen can be used by fuel cells for producing both electrical and thermal energy. The aim of this work was towards efficient integration of this system into energy efficient buildings. The system is comprised of a photovoltaic system hydrogen electrolyzer and proton exchange membrane fuel cell operating as a cogeneration system to provide the building with both electricity and thermal energy. The system’s modeling simulations and experimentations were first conducted over a short-run period to assess the system’s performance. Reported results show the models’ accuracy in analyzing the system’s performance. We then used the developed models for long-run testing of the hybrid system. Accordingly the system’s electrical efficiency was almost 32%. Its overall efficiency reached 64.5% when taking into account both produced electricity and thermal energy.

By using a newly constructed bench-scale hydrogen energy system with renewable energy ‘Pure Hydrogen Energy System’ the present study demonstrates the operations of a metal hydride (MH) tank for hydrogen compression as implemented through the use solar thermal energy. Solar thermal energy is used to generate hot water as a heat source of the MH tank. Thus 70 kg of LaNi5 one of the most typical alloys used for hydrogen storage was placed in the MH tank. We present low and high hydrogen flow rate operations. Then the operations under winter conditions are discussed along with numerical simulations conducted from the thermal point of view. Results show that a large amount of heat (>100 MJ) is generated and the MH hydrogen compression is available.

Microgrids can be regarded as a promising solution by which to increase the resilience of power systems in an energy paradigm based on renewable generation. Their main advantage is their ability to work as islanded systems under power grid outage conditions. Microgrids are usually integrated into electrical markets whose schedules are carried out according to economic aspects while resilience criteria are ignored. This paper shows the development of a resilience-oriented optimization for microgrids with hybrid Energy Storage System (ESS) which is validated via numerical simulations. A hybrid ESS composed of hydrogen and batteries is therefore considered with the objective of improving the autonomy of the microgrid while achieving a rapid transition response. The control problem is formulated using Stochastic Model Predictive Control (SMPC) techniques in order to take into account possible transitions between grid-connected and islanded modes at all the sample instants of the schedule horizon (SH). The control problem is developed by considering a healthy operation of the hybrid ESS thus avoiding degradation issues. The plant is modeled using the Mixed Logic Dynamic (MLD) framework owing to the presence of logic and dynamic control variables.

Magnesium hydride (MgH₂) is a potential material for solid-state hydrogen storage. However the thermodynamic and kinetic properties are far from practical application in the current stage. In this work two-dimensional vanadium carbide (V₂C) MXene with layer thickness of 50−100 nm was fist synthesized by selectively HF-etching the Al layers from V₂AlC MAX phase and then introduced into MgH2 to improve the hydrogen sorption performances of MgH2. The onset hydrogen desorption temperature of MgH₂ with V2C addition is significantly reduced from 318 °C for pure MgH2 to 190 °C with a 128 °C reduction of the onset temperature. The MgH₂+ 10 wt% V₂C composite can release 6.4 wt% of H₂ within 10 min at 300 °C and does not loss any capacity for up to 10 cycles. The activation energy for the hydrogen desorption reaction of MgH₂ with V₂C addition was calculated to be 112 kJ mol−1 H₂ by Arrhenius's equation and 87.6 kJ mol−1 H₂ by Kissinger's equation. The hydrogen desorption reaction enthalpy of MgH₂ + 10 wt% V₂C was estimated by van't Hoff equation to be 73.6 kJ mol−1 H₂ which is slightly lower than that of the pure MgH₂ (77.9 kJ mol−1 H₂). Microstructure studies by XPS TEM and SEM showed that V₂C acts as an efficient catalyst for the hydrogen desorption reaction of MgH₂. The first-principles density functional theory (DFT) calculations demonstrated that the bond length of Mg−H can be reduced from 1.71 Å for pure MgH₂ to 2.14 Å for MgH₂ with V₂C addition which contributes to the destabilization of MgH₂. This work provides a method to significantly and simultaneously tailor the hydrogen sorption thermodynamics and kinetics of MgH₂ by two-dimensional MXene materials.