Transmission, Distribution & Storage

A stable energy supply will require balancing the fluctuations of renewable energy generation due to the transition to renewable energy sources. Intraday and seasonal storage systems are often limited to local geographical or infrastructural circumstances. This study experimentally verifies the application of inexpensive and abundant natural iron ores for energy storage with combined hydrogen and heat release. The incorporated iron oxides are reduced with hydrogen from electrolysis to store energy in chemically bonded form. The on–demand reoxidation releases either pure hydrogen or high-temperature heat as valuable products. Natural iron ores as storage material are beneficial as the specific costs are lower by an order of magnitude compared to synthetic iron oxide-based materials. Suitable iron ores were tested in TG analysis and in a 1 kW fixed-bed reactor. Siderite a carbonate iron ore was verified as promising candidate as it shows significantly lower reaction temperatures and twice the storage capacity over other commercial iron ores such as ilmenite. The specific storage costs are as low as 80–150 $ per MWh hydrogen stored based on the experimental in-situ tests. The experimentally determined volumetric energy storage capacity for the bulk material was 1.7 and 1.8 MWh m− 3 for hydrogen and heat release respectively. The raw siderite ore was stable for over 50 consecutive cycles at operating temperatures of 500–600 ◦C in in-situ lifetime tests. The combination of high abundance low price and reasonable capacity can thus result in very low specific energy storage costs. The study proofs that suitable natural iron ores are an interesting economic solution for large-scale and seasonal energy storage systems.

This paper is a critical review of selected real-world energy storage systems based on hydrogen ranging from lab-scale systems to full-scale systems in continuous operation. 15 projects are presented with a critical overview of their concept and performance. A review of research related to power electronics control systems and energy management strategies has been added to integrate the findings with outlooks usually described in separate literature. Results show that while hydrogen energy storage systems are technically feasible they still require large cost reductions to become commercially attractive. A challenge that affects the cost per unit of energy is the low energy efficiency of some of the system components in real-world operating conditions. Due to losses in the conversion and storage processes hydrogen energy storage systems lose anywhere between 60 and 85% of the incoming electricity with current technology. However there are currently very few alternatives for long-term storage of electricity in power systems so the interest in hydrogen for this application remains high from both industry and academia. Additionally it is expected that the share of intermittent renewable energy in power systems will increase in the coming decades. This could lead to technology development and cost reductions within hydrogen technology if this technology is needed to store excess renewable energy. Results from the reviewed projects indicate that the best solution from a technical viewpoint consists in hybrid systems where hydrogen is combined with short-term energy storage technologies like batteries and supercapacitors. In these hybrid systems the advantages with each storage technology can be fully exploited to maximize efficiency if the system is specifically tailored to the given situation. The disadvantage is that this will obviously increase the complexity and total cost of the energy system.<br/>Therefore control systems and energy management strategies are important factors to achieve optimal results both in terms of efficiency and cost. By considering the reviewed projects and evaluating operation modes and control systems new hybrid energy systems could be tailored to fit each situation and to reduce energy losses.

Global energy sources are being transformed from hydrocarbon-based energy sources to renewable and carbon-free energy sources such as wind solar and hydrogen. The biggest challenge with hydrogen as a renewable energy carrier is the storage and delivery system’s complexity. Therefore other media such as ammonia for indirect storage are now being considered. Research has shown that at reasonable pressures ammonia is easily contained as a liquid. In this form energy density is approximately half of that of gasoline and ten times more than batteries. Ammonia can provide effective storage of renewable energy through its existing storage and distribution network. In this article we aimed to analyse the previous studies and the current research on the preparation of ammonia as a next-generation renewable energy carrier. The study focuses on technical advances emerging in ammonia synthesis technologies such as photocatalysis electrocatalysis and plasmacatalysis. Ammonia is now also strongly regarded as fuel in the transport industrial and power sectors and is relatively more versatile in reducing CO₂ emissions. Therefore the utilisation of ammonia as a renewable energy carrier plays a significant role in reducing GHG emissions. Finally the simplicity of ammonia processing transport and use makes it an appealing choice for the link between the development of renewable energy and demand.

An opportunity to decarbonise the offshore oil and gas sector lies in the integration of renewable energy sources with energy storage in a hybrid energy system (HES). Such concept enables maximising the exploitation of carbon-free renewable power while minimising the emissions associated with conventional power generation systems such as gas turbines. Offshore plants in addition to electrical and mechanical power also require process heat for their operation. Solutions that provide low-emission heat in parallel to power are necessary to reach a very high degree of decarbonisation. This paper investigates different options to supply process heat in offshore HES while the electric power is mostly covered by a wind turbine. All HES configurations include energy storage in the form of hydrogen tied to proton exchange membrane (PEM) electrolysers and fuel cells stacks. As a basis for comparison a standard configuration relying solely on a gas turbine and a waste heat recovery unit is considered. A HES combined with a waste heat recovery unit to supply heat proved efficient when low renewable power capacity is integrated but unable to deliver a total CO2 emission reduction higher than around 40%. Alternative configurations such as the utilization of gas-fired or electric heaters become more competitive at large installed renewable capacity approaching CO2 emission reductions of up to 80%.

Through the integration of multiple energy carriers with related technologies multi-energy systems (MES) can exploit the synergies coming from their interplay for several benefits towards decarbonization. In such a context inclusion of Power-to-X technologies in periods of excess renewable electricity supply removes the need for curtailment of renewable electricity generation. In order to achieve the environmental benefits of MES without neglecting their economic feasibility the optimal design problem is as crucial as challenging and requires the adoption of a multi-objective approach. This paper extends the results of a previous work by investigating hydrogen-based non-conventional storage for PV power in the eco-energetic optimization of an MES. The system under study consists of a reversible fuel cell (r-SOC) photovoltaic (PV) electric heat pump absorption chiller and thermal storage and allows satisfying the multi-energy needs of a residential end-user. A multi-objective linear problem is established to find the optimal MES configuration including the sizes of the involved technologies with the goal of reducing the total annual cost and the fossil primary energy input. Simulation results are compared with those obtained in previous work with a conventional nanogrid where a combined heat and power (CHP) system with gas-fired internal combustion engine and a battery were present instead of an r-SOC. The optimized configuration of the non-conventional nanogrid allows achieving a maximum primary energy reduction amounting to 66.3% compared to the conventional nanogrid. In the face of the environmental benefits the non-conventional nanogrid leads to an increase in total annual costs which compared to the conventional nanogrid is in the range of 41–65%.

Deep eutectic solvents (DES) are compounds of a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA) that contain a depressed melting point compared to their individual constituents. DES have been studied for their use as carbon capture media and biogas upgrading. However contaminants’ presence in biogas might affect the carbon capture by DES. In this study conductor-like screening model for real solvents (COSMO-RS) was used to determine the effect of temperature pressure and selective contaminants on five DES’ namely choline chloride-urea choline chloride-ethylene glycol tetra butyl ammonium chloride-ethylene glycol tetra butyl ammonium bromide-decanoic acid and tetra octyl ammonium chloride-decanoic acid. Impurities studied in this paper are hydrogen sulfide ammonia water nitrogen octamethyltrisiloxane and decamethylcyclopentasiloxane. At infinite dilution CO₂ solubility dependence upon temperature in each DES was examined by means of Henry’s Law constants. Next the systems were modeled from infinite dilution to equilibrium using the modified Raoults’ Law where CO₂ solubility dependence upon pressure was examined. Finally solubility of CO₂ and CH₄ in the various DES were explored with the presence of varying mole percent of selective contaminants. Among the parameters studied it was found that the HBD of the solvent is the most determinant factor for the effectiveness of CO₂ solubility. Other factors affecting the solubility are alkyl chain length of the HBA the associated halogen and the resulting polarity of the DES. It was also found that choline chloride-urea is the most selective to CO₂  but has the lowest CO₂ solubility and is the most polar among other solvents. On the other hand tetraoctylammonium chloride-decanoic acid is the least selective has the highest maximum CO₂ solubility is the least polar and is the least affected by its environment.

The presented work is dedicated to evaluation of strain and fatigue behaviour of the ferrite-pearlite low-alloyed pipeline steels under known hydrogen concentration in a bulk of metal. Tensile test results have shown on the existence of some characteristic value of the hydrogen concentration CH at which the mechanism of hydrogen influence changes namely: below this value the enhanced plasticity (decreasing of the yield stress value) takes place and above – the hydrogen embrittlement occurs. The ambiguous relationship between fatigue crack growth rate and hydrogen concentration CH in the bulk of steels under their cyclic loading in hydrogen-contained environments has been found. There is a certain CH value at which the crack growth resistance of steel increases and the diagram of fatigue crack growth rate shifts to higher values of stress intensity factor. The generalised diagram of hydrogen concentration effect on strength behaviour of low-alloyed ferrite-pearlite pipeline steels is presented and discussed with the aim of evaluation of different mechanisms of hydrogen effect conditions of their realization and possible co-existence.

The hydrogen permeation coefficient (ϕ) is generally used as a measure to show hydrogen permeation ability through dense metallic membranes which is the product of the Fick’s diffusion coefficient (D) and the Sieverts’ solubility constant (K). However the hydrogen permeability of metal membranes cannot be analyzed consistently with this conventional description. In this paper various methods for consistent analysis of hydrogen permeability are reviewed. The derivations of the descriptions are explained in detail and four applications of the consistent descriptions of hydrogen permeability are introduced: (1) prediction of hydrogen flux under given conditions (2) comparability of hydrogen permeability (3) understanding of the anomalous temperature dependence of hydrogen permeability of Pd-Ag alloy membrane and (4) design of alloy composition of non-Pd-based alloy membranes to satisfy both high hydrogen permeability together with strong resistance to hydrogen embrittlement.

Ductile cast iron (DCI) is one of prospective materials used for the hydrogen equipment because of low-cost good workability and formability. The wide range of mechanical properties of DCI is obtained by controlling microstructural factors such as graphite size volume fraction of graphite matrix structure and so on. Therefore it is important to find out an optimal microstructural condition that is less susceptible to hydrogen embrittlement. In this study the effects of graphite size on the hydrogen absorption capability and the hydrogen-induced ductility loss of ferritic DCI were investigated.<br/>Several kinds of ferritic DCIs with a different graphite diameter of about 10 µm - 30 µm were used for the tensile test and the hydrogen content measurement. Hydrogen charging was performed prior to the tensile test by exposing a specimen to high-pressure hydrogen gas. Then the tensile test was performed in air at room temperature. The hydrogen content of a specimen was measured by a thermal desorption analyzer.<br/>It was found that the amount of hydrogen stored in DCI was dependent on the graphite size. As the graphite diameter increased the hydrogen content sharply increased at a certain graphite diameter and then it became nearly constant irrespective of increase in graphite diameter. In other words there was the critical graphite diameter that significantly changed the hydrogen absorption capability. The ductility was decreased by hydrogen and the hydrogen-induced ductility loss was dependent on the hydrogen content. Therefore the hydrogen embrittlement of DCI became remarkable when the graphite size was larger than the critical value.

Precipitation hardenable (PH) nickel (Ni) alloys are often the most reliable engineering materials for demanding oilfield upstream and subsea applications especially in deep sour wells. Despite their superior corrosion resistance and mechanical properties over a broad range of temperatures the applicability of PH Ni alloys has been questioned due to their susceptibility to hydrogen embrittlement (HE) as confirmed in documented failures of components in upstream applications. While extensive work has been done in recent years to develop testing methodologies for benchmarking PH Ni alloys in terms of their HE susceptibility limited scientific research has been conducted to achieve improved foundational knowledge about the role of microstructural particularities in these alloys on their mechanical behaviour in environments promoting hydrogen uptake. Precipitates such as the γ′ γ′′ and δ-phase are well known for defining the mechanical and chemical properties of these alloys. To elucidate the effect of precipitates in the microstructure of the oil-patch PH Ni alloy 718 on its HE susceptibility slow strain rate tests under continuous hydrogen charging were conducted on material after several different age-hardening treatments. By correlating the obtained results with those from the microstructural and fractographic characterization it was concluded that HE susceptibility of oil-patch alloy 718 is strongly influenced by the amount and size of precipitates such as the γ′ and γ′′ as well as the δ-phase rather than by the strength level only. In addition several HE mechanisms including hydrogen-enhanced decohesion and hydrogen-enhanced local plasticity were observed taking place on oil-patch alloy 718 depending upon the characteristics of these phases when present in the microstructure.

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