Transmission, Distribution & Storage

The location of hydrogen within Ti–Cr–V–Mo alloys has been investigated during hydrogen absorption and desorption using in situ neutron powder diffraction and inelastic neutron scattering. Neutron powder diffraction identifies a low hydrogen equilibration pressure body-centred tetragonal phase that undergoes a martensitic phase transition to a face-centred cubic phase at high hydrogen equilibration pressures. The average location of the hydrogen in each phase has been identified from the neutron powder diffraction data although inelastic neutron scattering combined with density functional theory calculations show that the local structure is more complex than it appears from the average structure. Furthermore the origin of the change in dissociation pressure and hydrogen trapping on cycling in Ti–Cr–V–Mo alloys is discussed.

Liquefaction of hydrogen is a promising technology for transporting large quantities of hydrogen across long distances. A key challenge is the high power consumption. In this work we discuss refrigeration strategies that give minimum entropy production/exergy destruction in a plate-fin heat exchanger that cools the hydrogen from 47.8 K to 29.3 K. Two reference cases are studied; one where the feed stream enters at 20 bar and one where it enters at 80 bar. Catalyst in the hot layers speeds up the conversion of ortho-to para-hydrogen. Optimal control theory is used to formulate a minimization problem where the objective function is the total entropy production the control variable is the temperature of the refrigerant and the constrains are the balance equations for energy mass and momentum in the hot layers. The optimal refrigeration strategies give a reduction of the total entropy production of 8.7% in the 20-bar case and 4.3% in the 80-bar case. The overall heat transfer coefficient and duty is higher in the 20 bar case which compensates for the increase in entropy production due to a thermal mismatch that is avoided in the 80 bar case. This leads the second law efficiency of the 20 bar case (91%) to be similar to the 80 bar case (89%). We demonstrate that equipartition of the entropy production and equipartition of the thermal driving force are both excellent design principles for the process unit considered with total entropy productions deviating only 0.2% and 0.5% from the state of minimum entropy production. Equipartition of the thermal driving force i.e. a constant difference between the inverse temperatures of the hot and cold layers represents a particularly simple guideline that works remarkably well. We find that both heat transfer and the spin-isomer reaction contribute significantly to the entropy production throughout the length of the process unit. Unlike previous examples in the literature the process unit considered in this work is not characterized by a “reaction mode” at the inlet followed by a “heat transfer mode”. Therefore it does not follow a highway in state space i.e. a band that is particularly dense with energy efficient solutions. By artificially increasing the spin-isomer conversion rate the highway appears when the conversion rate becomes sufficiently high.

Energy storage systems are required to address the fluctuating behaviour of variable renewable energy sources. The environmental sustainability of energy storage technologies should be carefully assessed together with their techno-economic feasibility. In this work an environmental analysis of a renewable hydrogen-based energy storage system has been performed making use of input parameters made available in the framework of the European REMOTE project. The analysis is applied to the case study of the Froan islands (Norway) which are representative of many other insular microgrid sites in northern Europe. The REMOTE solution is compared with other scenarios based on fossil fuels and submarine connections to the mainland grid. The highest climate impacts are found in the dieselbased configuration (1090.9 kgCO2eq/MWh) followed by the REMOTE system (148.2 kgCO2eq/MWh) and by the sea cable scenario (113.7 kgCO2eq/MWh). However the latter is biased by the very low carbon intensity of the Norwegian electricity. A sensitivity analysis is then performed on the length of the sea cable and on the CO2 emission intensity of electricity showing that local conditions have a strong impact on the results. The REMOTE system is also found to be the most cost-effective solution to provide electricity to the insular community. The in-depth and comparative (with reference to possible alternatives) assessment of the renewable hydrogen-based system aims to provide a comprehensive overview about the effectiveness and sustainability of these innovative solutions as a support for off-grid remote areas.

National Grid (NG) needs to understand the implications that a hydrogen rich gas mix may have on the existing pipeline network. The primary network consists extensively of X52 steel pipe sections welded together using girth welds. Different welding specifications that have been used in the past 40 years and girth welds with different specifications may behave differently when coming into contact with hydrogen gas.

The aim of the flow loop test programme is to begin to evaluate the durability of pipeline materials in the context of future proofing of gas grid service where the gas mix may include a significant proportion of hydrogen. One specific objective is to investigate the resistance to hydrogen embrittlement of a conventional steel (X52) with commonly used girth welds. The primary concern is that the phenomenon of hydrogen embrittlement may cause unexpected or early failure mechanisms especially in older pipe sections with less stringent girth weld specifications.

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Stand-alone systems in remote regions require the utilization of renewable resources; however their natural intermittence requires the implementation of energy-storage systems that allow a continuous power supply. More than one renewable source is usually available at the same site. Thus the choice of a hybrid system seems viable. It is relevant to study hybrid systems as they could reduce energy storage; however sizing the hybrid system might have several implications not only for the available daily energy but also for the required daily energy storage and surplus seasonal energy. In this work we present a case study of a stand-alone conventional household powered by photovoltaic and marine-current-energy systems in Cozumel Mexico. The analysis of different hybridization degrees serves as a guidance tool to decide whether hybrid systems are required for a specific situation; in contrast to previous approaches where ideal consumption and generation profiles have been utilized yearlong profiles were utilized here. The renewable potential data were obtained on site at an hourly resolution; requirements such as size of and cycles in the daily and seasonal energy storage were analyzed according to the degree of participation or hybridization of the proposed renewable systems through an algorithm that evaluates power generation and daily consumption throughout the year. A further analysis indicated that marine-current-energy implementation reduces the size of the daily energy-storage system by 79% in comparison to the use of only a photovoltaic system due to the similarity between the energy-demand profile and the marine-current-energy production profile. The results indicate that a greater participation of marine currents can help decrease daily storage while increasing seasonal storage by 16% compared to using only solar energy. On the other hand hybridization enabled a reduction in the number of daily charge and discharge cycles at 0.2 hybridization degrees. It also allowed us to reduce the seasonal energy storage by 38% at 0.6 hybridization degrees with respect to only using energy from marine currents. Afterwards energy-storage technologies were evaluated using the TOPSIS Multi-Criteria Decision Analysis to validate the best-suited technology for the energy-storage system. The evaluation considered the characteristics of the technology and the periods of energy storage. In this work hybrid storage systems were mandatory since for daily storage lithium-ion batteries are better suited while for seasonal storage hydrogen-producing systems are more suitable to manage the amount of energy and the storage duration due to the high seasonal renewable-energy variations.

Among the several typologies of storage technologies mainly on different physical principles (mechanical electrical and chemical) hydrogen produced by power to gas (P2G) from renewable energy sources complies with chemical storage principle and is based on the conversion of electrical energy into chemical energy by means of the electrolysis of water which does not produce any toxic or climate-relevant emission. This paper aims to pinpoint the potential uses of renewable hydrogen storage systems in Europe analysing current and potential locations regulatory framework governments’ outlooks economic issues and available renewable energy amounts. The expert opinion survey already used in many research articles on different topics including energy has been selected as an effective method to produce realistic results. The obtained results highlight strategies and actions to optimize the storage of hydrogen produced by renewables to face varying electricity demand and generation-driven fluctuations reducing the negative effects of the increasing share of renewables in the energy mix of European Countries.

The formation of elongated zirconium hydride platelets during corrosion of nuclear fuel clad is linked to its premature failure due to embrittlement and delayed hydride cracking. Despite their importance however most existing models of hydride nucleation and growth in Zr alloys are phenomenological and lack sufficient physical detail to become predictive under the variety of conditions found in nuclear reactors during operation. Moreover most models ignore the dynamic nature of clad oxidation which requires that hydrogen transport and precipitation be considered in a scenario where the oxide layer is continuously growing at the expense of the metal substrate. In this paper we perform simulations of hydride formation in Zr clads with a moving oxide/metal boundary using a stochastic kinetic diffusion/reaction model parameterized with state-of-the-art defect and solute energetics. Our model uses the solutions of the hydrogen diffusion problem across an increasingly-coarse oxide layer to define boundary conditions for the kinetic simulations of hydrogen penetration precipitation and dissolution in the metal clad. Our method captures the spatial dependence of the problem by discretizing all spatial derivatives using a stochastic finite difference scheme. Our results include hydride number densities and size distributions along the radial coordinate of the clad for the first 1.6 h of evolution providing a quantitative picture of hydride incipient nucleation and growth under clad service conditions.

For liquid hydrogen (LH₂) to become an energy carrier in energy commodity markets at scales comparable to for instance LNG liquefier capacities must be scaled up several orders of magnitude. While state-of-the-art liquefiers can provide specific power requirements down to 10 kWh/kg a long-term target for scaled-up liquefier trains is 6 kWh/kg. High capacity will shift the cost weighting more towards operational expenditures which motivates for measures to improve the efficiency. Detailed exergy analysis is the best means for gaining a clear understanding of all losses occurring in the liquefaction process. This work analyses in detail a hydrogen liquefier that is likely to be realisable without intermediate demonstration phases and all irreversibilities are decomposed to the component level. The overall aim is to identify the most promising routes for improving the process. The overall power requirement is found to be 7.09 kWh/kg with stand-alone exergy efficiencies of the mixed-refrigerant pre-cooling cycle and the cryogenic hydrogen Claude cycle of 42.5% and 38.4% respectively. About 90% of the irreversibilities are attributed to the Claude cycle while the remainder is caused by pre-cooling to 114 K. For a component group subdivision the main contributions to irreversibilities are hydrogen compression and intercooling (39%) cryogenic heat exchangers (21%) hydrogen turbine brakes (15%) and hydrogen turbines (13%). Efficiency improvement measures become increasingly attractive with scale in general and several options exist. An effective modification is to recover shaft power from the cryogenic turbines. 80% shaft-to-shaft power recovery will reduce the power requirement to 6.57 kWh/kg. Another potent modification is to replace the single mixed refrigerant pre-cooling cycle with a more advanced mixed-refrigerant cascade cycle. For substantial scaling-up in the long term promising solutions can be cryogenic refrigeration cycles with refrigerant mixtures of helium/neon/hydrogen enabling the use of efficient and well scalable centrifugal compressors.

Hydrogen is widely recognised as a promising option for storing large quantities of renewable electricity over longer periods. For that reason in an energy future where renewables are a dominant power source opportunities for Power to- Hydrogen in the long-term appear to be generally acknowledged. The key challenge today is to identify concrete short-term investment opportunities based on sound economics and robust business cases. The focus of this study is to identify these early business cases and to assess their potential replicability within the EU from now until 2025. An essential part and innovative approach of this study is the detailed analysis of the power sector including its transmission grid constraints.

A model has been derived for the magnesium hydrogenation reaction at conditions close to equilibrium. The reaction mechanism involves an adsorption element where the model is an extension of the Langmuir adsorption model. The concept of site availability (σs) is introduced whereby it has the capability to reduce the reaction rate. To improve representation of σs an adaptable semi-empirical equation has been developed. Supplement to the surface reaction a rate equation has been derived considering resistance effects. It was found that close to equilibrium surface resistance dominated the reaction.