Since the majority of modern electronic devices rectify an AC input to operate via DC power, and since many distributed renewable energy sources (DRESs) inherently generate DC power, DC microgrids (MGs) are an increasingly attracting approach. DC MGs can provide a sustainable alternative for offshore facilities such as oil and gas rigs, marine shipboards, and aquaculture facilities, offering a sustainable and efficient substitute to conventional power systems. This is because these industries have access to different DRESs, especially ocean wave energy, and often utilise DC-powered modern electronic devices. When integrating different DRESs into a DC MG network for powering offshore industries, a robust control system is essential for maintaining system stability under all feasible operating conditions. This paper reviews the control system design challenges for offshore DC MGs, considering variations in generation output and in load characteristics. This review summarises the current state and technical challenges of control system design for offshore DC MGs and provides perspectives on how to address these challenges.

This study investigated the effect of subcritical heat treatment and cold work on the hydrogen embrittlement (HE) susceptibility of the X65 D pipeline steel, representative of the Dampier-Bunbury Natural Gas Pipeline (DBNGP). Specimens were subjected to sub-critical annealing at 200 degrees C, 400 degrees C, or 600 degrees C for 2 h or cold drawn to 5% reduction in area. Linearly increasing stress tests (LISTs) indicated subcritical annealing reduced strength and increased ductility, while cold working increased strength and decreased ductility. Hydrogen charging reduced the ductility of all specimens. Both subcritical annealing and cold working decreased somewhat the degree of HE. This was attributed to both treatments stabilising the dislocation distribution which possibly reduced the severity of hydrogen-enhanced localised plasticity (HELP). The novelty of this study lies in the evaluation of practical production changes and their influence on the HE of this steel.

Hydrogen embrittlement (HE) poses a significant challenge for high-strength steels. Although HE of wrought steels has been extensively studied, it remains limited in steels processed by additive manufacturing (AM). The present work (i) compares the HE susceptibility of AISI 4340 ultra-high-strength steel fabricated by selective laser melting (SLM) with its wrought counterpart; (ii) investigates the predominant factors and possible HE mechanisms in the AM-fabricated material; and (iii) correlates microstructures produced with different SLM processing parameters to HE susceptibility of the steel. Generally, conventionally processed AISI 4340 steel is used with a tempered martensitic structure to ensure the ultrahigh strength, and therefore is susceptible to HE. In contrast, SLM-fabricated 4340 exhibits a uniform, refined bainitic microstructure. How this change of microstructure influences the HE susceptibility of the steel is unknown and needs investigation. Our results demonstrate that, at the same level of strength, the SLM-fabricated 4340 steel exhibits significantly lower HE susceptibility than its wrought counterpart. The SLM-fabricated steel showed a higher hydrogen diffusion rate. Furthermore, the refined microstructure of the SLM-fabricated steel contributes to enhanced ductility, even with hydrogen. These findings indicate that AM of high-strength steels has strong potential to improve HE resistance, providing a pathway to solve this long-term problem. This study highlights the critical role of microstructure in influencing HE and offers valuable insights for developing steels for hydrogen applications.

The dissolution of gaseous hydrogen into pipeline steel has been previously shown to be influenced by the presence of oxygen in the hydrogen gas. This study reports on hydrogen permeation experiments using vintage X65 D pipeline steel extracted from the Dampier Bunbury Natural Gas Transmission Pipeline. The aim was to quantify the effect of oxygen on hydrogen permeation. A gas-phase permeation apparatus was designed and built. A permeation model incorporating the appropriate boundary conditions was derived. The hydrogen concentration dissolved in the X65 D using pure hydrogen in these experiments was considerably lower than previously reported. The first set of permeation experiments with hydrogen gas containing oxygen found no effect of oxygen on hydrogen permeation (for oxygen concentrations of 100, 300 and 1000 ppm) with a hydrogen pressure of 81 bar. The second set of permeation experiments found a slight effect of oxygen (for oxygen concentrations of 100, 5000 and 12000 ppm) with a hydrogen pressure of 94 bar. The steady-state hydrogen permeation flux slowly recovered to the value measured in pure hydrogen. This indicated that preadsorbed oxygen initially impeded hydrogen uptake and dissolution in the steel but was not an effective long-term measure to lower the hydrogen in solution in the X65 D under these conditions.

Hydrogen embrittlement testing using cathodic hydrogen charging is directly relatable to structures containing gaseous hydrogen if the hydrogen fugacity is known. The hydrogen fugacity, fHc, was evaluated by comparing the hydrogen concentration after cathodic charging with the hydrogen concentration in equilibrium with hydrogen gas: fHc 0.5 = 6.11 i0.5 + 10.9 for cathodic hydrogen charging X65 D in 0.10 M NaOH at a current density of i. The hydrogen concentration in equilibrium with gaseous hydrogen in X65 D, CHg, was evaluated from literature values and hydrogen gas-phase permeation results: CHg = 0.0062fHg0.5 + 0.0355, where fHg is the hydrogen gas fugacity.

Given the urgent need to accelerate all renewable energy capacities for hydrogen production, this study undertakes a techno-economic analysis of dynamic hydrogen production using offshore wind energy under “slow progress” and “fast progress” scenarios. To ensure a reliable wind power generation profile and to avoid overestimating output power, the study takes into account significant impacts of air density and wind plant-level losses, including wake effect and turbine performance losses. The economic modelling incorporates costs associated with wind turbines, foundations, submarine connections, offshore substations, and installations. For modelling the system of electrolysis, a dynamic power-dependent efficiency representing PEM technology is employed. To reflect the influences of a realistic project on the estimation of the levelised cost of hydrogen (LCOH), economies of scale and learning rate models are incorporated. Australian offshore wind locations are selected as a case study for implementing the model because of the enormous available wind resource. The findings indicate that the variable nature of input power has a meaningful impact on the yearly average energy consumption of the electrolysis system. Comparing the scenarios, it becomes evident that rapid scaling up is required to achieve a cost-competitive LCOH in the coming decades. Should interest rates and thus costs of capital return to the levels closer to pre-pandemic levels, the LCOH level of below AUD3/kg (USD2/kg) can be achieved under the “fast progress” scenario in two Australian offshore wind locations by around 2040.

This study investigates the sensitivity of solar-based hydrogen production cost to variations in rarely explored financial parameters including gearing, cost of equity, cost of debt along with technical factors of electrolyser stack lifetime and system degradation rate. The objective is not to calculate an authoritative value for the levelized cost of hydrogen (LCOH), but rather to ascertain the possible trade-offs between influential parameters to reach lower values for the LCOH. Along with a comparison between solar-based hydrogen production and the current industrial method, the impact on LCOH of a green subsidy based on CO2-eq emissions is examined. Finally, the study explores how major parameters should change to reach the target LCOH, set at AUD 3/USD 2. The study found that the LCOH was meaningfully impacted by the financial factors. The negative impacts of unfavourable financial factors were not offset effectively by improvements in the technical factors. However, the two technical parameters can offset each other's negative impact on the LCOH to an almost equal extent. Green subsidy would be a highly desirable hedge against the strongest influence of the parameters, with different extent of impact on the technical and financial variables. The results also indicate that to reach the target LCOH, significant reduction of electrolyser CAPEX is a key objective.

Degradation of performance over lifetime is a challenge for interstitial metal-hydride hydrogen storage systems, especially those employed in thermodynamic machines such as compressors and heat pumps, since these must execute many thousands of cycles of absorption and desorption with minimal loss of throughput. Degradation manifests typically as diminished reversible hydrogen capacity, sometimes accompanied by undesirable changes in the shape of the absorption/desorption isotherm or slower kinetics. Understanding the origin and evolution of degradation during absorption/desorption cycling is crucial to designing for long service life with minimal maintenance and replacement costs. This review examines the degradation mechanisms observed in interstitial metal hydrides, focussing on those relevant to thermodynamic machines. Based on the reviewed literature, identifying standard measures for evaluating the degradation of metal hydrides in thermodynamic machines proves challenging. This challenge stems from the variety of reported alloy compositions, and from the widely differing operational configurations employed in published research studies. Furthermore, the degradation mechanisms that manifest during extended absorption/desorption cycling (decrepitation, sintering, hydrogen trapping, loss of crystallinity, disproportionation) are intertwined, sometimes acting sequentially and sometimes concurrently. Time spent in the hydride phase at elevated temperature is a key controlling factor. This review offers insights to aid the selection of alloys for service in hydrogen storage generally and thermodynamic machines in particular. Additionally, an in-depth exploration of the degradation of LaNi5, by far the most studied hydrogen storage alloy, is presented, highlighting the intertwined nature of the acting degradation mechanisms.

This study evaluates the levelised cost of hydrogen (LCOH) dynamically produced using the two dominant electrolysis technologies, directly connected to wind turbines or photovoltaic (PV) panels in regions of Australia designated as hydrogen hubs. Hourly data are utilised to size the components required to meet the hydrogen demand. The dynamic efficiency of each electrolysis technology, as a function of input power, along with its operating characteristics and overload capacity are employed to estimate flexible hydrogen production. A sensitivity analysis is then conducted to capture the behaviour of the LCOH in response to inherent uncertainty in critical financial and technical factors. Additionally, the study investigates the trade-offs between carbon cost and lifecycle emissions of green hydrogen. This approach is applied to ascertain the impact of internalising environmental costs on the cost-competitiveness of green hydrogen compared to grey hydrogen. The economic modelling is developed based on the Association for the Advancement of Cost Engineering (AACE) guidelines. The findings indicate that scale-up is key to reducing the LCOH by a meaningful amount. However, scale-up alone is insufficient to reach the target value of AUD 3 (USD 2), except for PV-based plant in the Pilbara region. Lowered financial costs from scale-up can make the target value achievable for PV-based plants in Gladstone and Townsville, and for wind-based plants in the Eyre Peninsula and Pilbara regions. For other hubs, a lower electricity cost is required, as it accounts for the largest portion of the LCOH.

This study presents a technoeconomic analysis of renewables-based hydrogen production in Queensland, Australia under Optimistic, Reference and Pessimistic scenarios to address uncertainty in cost predictions. The goal of the work was to ascertain if the target fam-gate cost of AUD 3/kg (approx. USD 2/kg) could be reached. Economies of scale and the learning rate concept were factored into the economic model to account for the effect of scale-up and cost reductions as electrolyser manufacturing capacity grows. The model assumes that small-scale to large-scale wind turbine (WT)-based and photovoltaic (PV)-based power generation plants are directly coupled with an electrolyser array and utilises hourly generation data for the Gladstone hydrogen-hub region. Employing first a commonly used simplified approach, the electrolyser array was sized based on the maximum hourly power available for hydrogen production. The initial results indicated that scale-up is very beneficial: the levelised cost of green hydrogen (LCOH) could decrease by 49% from $6.1/kg to $3.1/kg when scaling PV-based plant from 10 MW to 1 GW, and for WT-based plant by 36% from $5.8/kg to $3.7/kg. Then, impacts on the LCOH of incorporating curtailment of ineffective peak power and electrolyser overload capacity were investigated and shown to be significant. Also significant was the beneficial effect of recognising that electrolyser efficiency depends on input power. The latter two factors have mostly been overlooked in the literature. Incorporating in the model the influence on the LCOH of real-world electrolyser operational characteristics overcomes a shortcoming of the simplified sizing method, namely that a large portion of electrolyser capacity is under-utilised, leading to unnecessarily high values of the LCOH. It was found that AUD 3/kg is achievable if the electrolyser array is properly sized, which should help to incentivise large-scale renewable hydrogen projects in Australia and elsewhere.

The shift from fossil fuels to clean energy carriers, such as renewable H2, 2 , is imminent. Consequently, a global H2 2 market is taking shape, involving countries with limited or insufficient energy resources importing from renewable-rich countries. This study evaluates the techno-economics of renewable hydrogen (H2) 2 ) export in a globally significant scenario in which Australia exports to Japan. To gain insight into the immediate, realisable future, the base year was selected as 2030, with a consequently small (in export terms) hydrogen production rate of 100 t/day landed capacity. Electricity was generated by photovoltaic arrays (PV) connected directly to proton exchange membrane (PEM) electrolyser plant, allowing for flexible gaseous hydrogen (GH2) 2 ) production. To enhance the fidelity of the technoeconomic model, we incorporated rarely applied but impactful parameters, including dynamic efficiency and the overload capacity of PEM electrolysers. The GH2 2 produced was assumed to be converted into condensed forms suitable for export by sea: liquid hydrogen (LH2), 2 ), and the chemical carriers liquid ammonia (LNH3), 3 ), methanol (MeOH), methylcyclohexane (MCH). These were assumed to be reconverted to GH2 2 at the destination. LNH3 3 and MCH emerged as promising carriers for export, yielding the lowest landed levelised cost of hydrogen (LCOH). LH2 2 yielded the highest LCOH unless boiloff gas could be managed effectively and cheaply. A sensitivity analysis showed that a lower weighted average cost of capital (WACC) and scale-up can significantly reduce the landed LCOH. Increasing the production rate to 1000 t/day landed capacity very significantly lowered the landed LCOH, providing a strong incentive to scale up and optimise the entire supply chain as fast as possible.

DC microgrids are becoming an attractive option for offshore applications owing to their capability to incorporate various distributed energy sources. However, connecting all generating units, storage systems, and loads to DC microgrids via multiple converters can lead to system instability. DC bus voltage may fluctuate based on load changes, converter operating conditions, and controller tuning. Therefore, maintaining voltage stability over a broad limit of operations poses a significant challenge for offshore DC MGs. To address this challenge, this paper presents mathematical models of various DC microgrid components and proposes a suitable controller design to ensure system stability. The designed cascaded controller is demonstrated to successfully control the voltage on the bus while maintaining overall system stability for a small DC microgrid simulated in MATLAB/Simulink. The system's performance has been validated by Electromagnetic Transient (EMT) simulations for small-signal stability analysis. The system's stability is analyzed, assessing transient responses, frequency responses, and the sensitivity of the small-signal model.

The emergence of smart grids has introduced new challenges to traditional power system control due to the increasing number of risk factors. This paper presents a parameter tuning strategy using an optimisation algorithm to optimise the weights of the objective function. This enhances the adaptive control capabilities of online supplementary control to address the complexities of power system control in smart grids and offers a promising solution for improving overall system performance. The proposed online control, based on approximate dynamic programming, operates in conjunction with an existing power system controller. The results demonstrate the effectiveness of the proposed approach in maintaining frequency within acceptable limits. Comparative studies are performed against conventional frequency control strategies to highlight the advantages of the proposed method. The findings of this study contribute to the development of efficient and adaptive frequency control strategies for power systems with high renewable energy penetration.

Metal-hydrides offer a potentially competitive method for compressing hydrogen, particularly where waste heat is available. Metal hydrides are metal alloys or intermetallic compounds that react reversibly with H2. They readily absorb low-pressure H2 at low temperature, and then release H2 at a higher pressure when the temperature is raised. The high pressure H2 is released at a pressure above that expected from standard presstemperature relations. The absorption and desorption pressures of the hydrides are determined by their thermodynamic properties (enthalpy and entropy). To achieve compression ratios above about 10, more than one stage of compression is typically required. The challenge is to find alloy pairs that can work together effectively to achieve the desired compression from the heating/cooling available. Previously, a thermodynamic model has been proposed for identifying suitable metal hydrides that can be paired together to achieve a desired compression. This paper describes methods used previously in the literature to select alloy pairs, and applies the current method to an example selection of 33 hydrides with potential for hydrogen compression. The example application aims to find pairs that can compress a H2 stream from 10 to 350 bar using a temperature range of 30-150 & DEG;C, however the theory could readily be adapted to different compression ratios and temperature ranges. For the specific example evaluated none of the potential pairs were able to meet the compression target, however, modification of the parameters (heating/cooling availability) or alloy properties could resolve this issue.& COPY; 2023 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications creativecommons.org/licenses/by-nc-nd/4.0/).

Compressors employing metal hydrides (MH) may operate on waste or solar heat and are mechanically simple in comparison to mechanical hydrogen compressors, requiring only standard cooling components.In principle, MH compressors operate by absorbing hydrogen at a low pressure (ρl) at the lower working temperature (Tl) by forming the concentrated hydride phase (β) and desorbing at the higher working temperature (Th) and higher pressure (ρh) by forming the solid- solution phase (α), in accordance with the van 't Hoff relation specific for the metal–H2 system in use. By pairing alloys, selected based on their thermodynamic parameters, higher compression ratios can be achieved. Microstructural changes in the host metal owing to hydrogen absorption (dislocations, vacancies, decrepitation, trapped hydrogen, amorphisation…), generally summed up as degradation, may lead to loss of accessible hydrogen capacity during repeated cycles of absorption and desorption. Because the b phase may be thermodynamically unstable, absorption-desorption cycling between Tl and Th in a compressor may exacerbate degradation compared to isothermal cycling.Here we present an apparatus designed to execute temperature cycles on multiple samples simultaneously, each isolated under an isochoral constraint by a valve, along with a mathematical model to describe approximately the locus of the metal–H2 system in pressure–composition space. This model allows estimation of the amount of metal sample needed to cycle isochorally between (ρl, Tl, xβ) and (ρh, Th, xα), where xα/β corresponds to hydrogen concentrations in the pure α/β phase, such that every sample will cycle between the β and α phases as the temperature cycles between Tl and Th, as depicted opposite. The pressure increase Δρ=ρh-ρl has contributions from hydrogen desorbed into the closed volume and the increase in the temperature of the free gas in that volume. The practical application of this model will be discussed.

This article proposes a novel framework to improve the prediction accuracy of very short-term (5-min) wind power generation. The framework consists of complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN), monarch butterfly optimization (MBO) and long short-term memory (LSTM), called CEMOLS. The CEEMDAN is employed to extract complex hidden features of time-series data into intrinsic mode functions that are predicted using LSTM models with dropout regularization to retain long-term relationships between input and output data, while the optimization algorithm tunes the hyperparameters of the forecasting model. Data from four real wind farms in New South Wales are collected and preprocessed to train and test the forecasting models. Recently developed rival models are compared to identify the best-performing prediction model. The analysis demonstrates that the proposed CEMOLS with low computation time can improve forecasting accuracy on average by 32.96% in mean absolute error, 47.10% in root mean square error and 32.33% in mean absolute percentage error as compared to the benchmark Persistence model. It also demonstrates that sensitive and statistical analysis needs to be carried out to determine robust prediction models among rival models for practical application.

International demand for green hydrogen is predicted to grow rapidly, particularly in Asia. A recent McKinsey study projects a 22 Mt/annum demand in Japan by 2050, corresponding to installed wind power capacity around 300 GW, some ten times the current peak power in the National Electricity Market. A recent study by the Blue Economy CRC assesses Australia’s readily accessible offshore wind resource as >2000 GW. The scale-up task is extreme, but technically feasible based on offshore wind. Accordingly, this study investigates the economics of wind-based green hydrogen export from eastern Australia to Asia, broken down as production, liquefaction, storage and transport. To supply the energy needed for unit hydrogen production (including reverse osmosis water desalination and electrolysis for splitting the purified water) and liquefaction, a wind-based battery-assisted power generation plant is sized. Then, an electrolyser array is sized to fulfil a daily hydrogen demand. Finally, an economic assessment based on lifecycle cost analysis (LCCA) is performed for each step to ascertain its cost contribution to the landed levelised cost of hydrogen (LCOH) in southern Japan. A learning-rate model is employed to predict the electrolyser replacement cost. A power-law scaling model is employed to explore economies of scale. The results are made more generally applicable by considering ranges for the learning rate and scaling exponent. This approach helps to gain a prospective range for LCOH within which the real LCOH is most likely to be. Monte Carlo simulation using triangular distributions under optimistic and pessimistic scenarios is employed for uncertainty analysis. Around two-thirds of the final cost of hydrogen is expected to come from production and around one-quarter from liquefaction, with a small contribution from transport, which suggests that the economic viability of hydrogen export from eastern Australia will not depend strongly on the geographic location of production.

Hydrogen carried by gas transmission pipelines will permeate into the pipeline walls, which can lead to hydrogen embrittlement. This paper details the design of an apparatus which will be used to study the permeation of gaseous hydrogen through pipeline steels at temperatures up to 200 °C and pressures up to 17 MPa. The results of the permeation tests will be used to (i) characterise the hydrogen solubility and diffusivity of pipeline steels, (ii) equate the conditions in hydrogen embrittlement studies which use electrochemical and gaseous hydrogen charging, and (iii) study the permeation of gaseous hydrogen blended with other gases, particularly trace amounts of oxygen. Permeation studies of hydrogen with oxygen will be used to evaluate the possible use of oxygen to inhibit hydrogen embrittlement.

Renewable hybrid hydrogen energy systems provide clean, sustainable energy sources that can be used for a wide range of applications, ranging from energy provision at remote locations to exporting energy on a large scale.