Transmission, Distribution & Storage

This study proposes a multi-level model predictive control (MPC) for a grid-connected wind farm paired to a hydrogen-based storage system (HESS) to produce hydrogen as a fuel for commercial road vehicles while meeting electric and contractual loads at the same time. In particular the integrated system (wind farm + HESS) should comply with the “fuel production” use case as per the IEA-HIA report where the hydrogen production for fuel cell electric vehicles (FCEVs) has the highest unconditional priority among all the objectives. Based on models adopting mixed-integer constraints and dynamics the problem of external hydrogen consumer requests optimal load demand tracking and electricity market participation is solved at different timescales to achieve a long-term plan based on forecasts that then are adjusted at real-time. The developed controller will be deployed onto the management platform of the HESS which is paired to a wind farm established in North Norway within the EU funded project HAEOLUS. Numerical analysis shows that the proposed controller efficiently manages the integrated system and commits the equipment so as to comply with the requirements of the addressed scenario. The operating costs of the devices are reduced by 5% which corresponds to roughly 300 commutations saved per year for devices.

As a manufactured fuel hydrogen can be produced in a decentralized way in most countries around the world. This means even in a net zero economy the global trade of hydrogen could look quite different to the current international trade in fossil fuels including natural gas. With further declines in the costs of renewable electricity and electrolyzers regions which have lower cost renewable electricity may develop an economic advantage in the production of low-cost hydrogen but for hydrogen to become a globally traded commodity the cost of imports needs to be lower than the cost of domestic production. Unlike oil or natural gas transporting hydrogen over long distances is not an easy task. Hydrogen liquefaction is an extremely energy-intensive process while maintaining the low temperature required for long-distance transportation and storage purposes results in additional energy losses and accompanying costs. The upside is that hydrogen can be converted into multiple carriers that have a higher energy density and higher transport capacity and can potentially be cheaper to transport over long distances. Among the substances currently identified as potential hydrogen carriers suitable for marine shipping liquid ammonia the so-called ‘liquid organic hydrogen carriers’ in general (toluene-methylcyclohexane (MCH) in particular) and methanol have received the most attention in recent years. This paper compares the key techno-economic characteristics of these potential carriers with that of liquified hydrogen in order to develop a better understanding of the ways in which hydrogen could be transported overseas in an efficient manner. The paper also discusses other factors beyond techno-economic features that may affect the choice of optimum hydrogen carrier for long distance transport as well as the global trade of hydrogen.

Hydrogen storage is expected to play a crucial role in the comprehensive defossilization of energy systems. In this context the focus is typically on underground hydrogen storage (e.g. in salt caverns). However aboveground storage which is independent of geological conditions and might offer other technical advantages could provide systemic benefits and thereby gain shares in the hydrogen storage market. Against this background this paper examines the market relevance of aboveground compared to underground hydrogen storage. Using the opensource energy system model and optimization framework of Europe PyPSA-Eur the influence of geological independence storage cost relations and technical storage characteristics (i.e. efficiencies) on mentioned market relevance of aboveground hydrogen storage are investigated. Further the expectable market relevance based on current cost projections for the future is assessed. The studies show that in terms of hydrogen capacities aboveground hydrogen storage plays a considerably smaller role compared to underground hydrogen storage. Even when assuming comparatively low aboveground storage cost it will not exceed 1.7% (1.9 TWhH2LHV) of total hydrogen storage capacities in a cost-optimal European energy system. Regarding the amounts of annually stored hydrogen aboveground storage could play a larger role reaching a maximum share of 32.5% (168 TWhH2 LHV a-1) of total stored hydrogen throughout Europe. However these shares are only achievable for low cost storage in particularly suited energy system supply configurations. For higher aboveground storage costs or lower efficiencies shares drop below 10% sharply. The analysis identifies some especially influential factors for achieving higher market relevance. Besides storage costs the demand-orientation of a particular aboveground storage system (e.g. hydrogen storage at demand pressure levels) plays an essential role in market relevance. Further overall efficiency can be a beneficial factor. Still current projections of future techno-economic characteristics show that aboveground hydrogen storage is too expensive or too inefficient compared to underground storage. Therefore to achieve notable market relevance rather drastic cost reductions beyond current expectations would be needed for all assessed aboveground hydrogen storage technologies.

As the global market develops for green hydrogen and ammonia derived from renewable electricity the bulk transmission of hydrogen and ammonia from production areas to demand-intensive consumption areas will increase. Repurposing existing infrastructure may be economically and technically feasible but increases in supply and demand will necessitate new developments. Bulk transmission of hydrogen and ammonia may be effected by dedicated pipelines or liquefied fuel tankers. Transmission of electricity using HVDC lines to directly power electrolysers producing hydrogen near the demand markets is another option. This paper presents and validates detailed cost models for newly-built dedicated offshore transmission methods for green hydrogen and ammonia and carries out a techno-economic comparison over a range of transmission distances and production volumes. New pipelines are economical for short distances while new HVDC interconnectors are suited to medium-large transmission capacities over a wide range of distances and liquefied gas tankers are best for long distances.

An accurate estimation of the effective thermal conductivity of various insulation materials is essential in the evaluation of heat leak and boil-off rate from liquid hydrogen storage tanks. In this work we review the existing experimental data and various proposed correlations for predicting the effective conductivity of insulation systems consisting of powders foams fibrous materials and multilayer systems. We also propose a first principles-based correlation that may be used to estimate the dependence of the effective conductivity as a function of temperature interstitial gas composition pressure and structural properties of the material. We validate the proposed correlation using available experimental data for some common insulation materials. Further improvements and testing of the proposed correlation using laboratory scale data obtained using potential LH2 tank insulation materials are also discussed.

Hydrogen energy is an excellent carrier for connecting various renewable energy sources and has many advantages. However hydrogen is flammable and explosive and its density is low and easy to escape which brings inconvenience to the storage and transportation of hydrogen. Therefore hydrogen storage technology has become one of the key steps in the application of hydrogen energy. Solid-state hydrogen storage method has a very high volumetric hydrogen density compared to the traditional compressed hydrogen method. The main issue of solid-state hydrogen storage method is the development of advanced hydrogen storage materials. Metal borohydrides have very high hydrogen density and have received much attention over the past two decades. However high hydrogen sorption temperature slow kinetics and poor reversibility still severely restrict its practical applications. This paper mainly discusses the research progress and problems to be solved of metal borohydride hydrogen storage materials for solid-state hydrogen storage.

Hydrogen is expected to play a key role in the future as a clean energy source that can mitigate global warming. It can also contribute significantly to reducing the imbalance between energy supply and demand posed by deploying renewable energy. However the infrastructure is not ready for the direct use of hydrogen and largescale storage facilities are needed to store the excess hydrogen production. Geological formations particularly salt caverns seem to be a practical option for this large-scale storage as there is already good experience storing hydrocarbons in caverns worldwide. Salt is known to be ductile impermeable and inert to natural gas. Some cases of hydrogen storage in salt caverns in the United States the United Kingdom and Germany reinforce the idea that salt caverns could be a viable option for underground hydrogen storage especially when the challenges and uncertainties associated with hydrogen storage in porous media are considered. However cavern con struction and management can be challenging when salt deposits are not completely pure and mixed with nonsoluble strata. This review summarises the challenges associated with hydrogen storage in salt caverns and suggests some potential mitigation strategies linked to geomechanical and geochemical interactions. The Zechstein salt group in Northern Europe seems to be a feasible geological site for hydrogen storage but the effect of salt impurity particularly at deep offshore sites such as in the Norwegian North Sea should be carefully analysed. It appears that mechanical integrity geochemical reactions hydrogen loss by halophilic bacteria leaching issues and potential hydrogen diffusion are among the major issues when the internal structure of the salt is not pure.

The main goal stated at the Paris agreement is to limit the global temperature rise well below 2 °C above pre-industrial levels. Limiting the increase of global average temperature to 1.5 °C is striven since risks and impacts of the climate change would be reduced drastically. To face these challenges the European Green Deal was invented by the European Commission. The “Green Deal” is a growth strategy which aims to transform the economy of the EU into a resource-efficient modern and competitive one [1-1 1-2]. Figure 1: The key elements of the European Green Deal [1-2] In this context the European Commission proposed that the amount of renewable energy within the EU’s overall energy mix should reach 20 % by 2020 and therefore producing energy by solar and wind plants become even more important. For example the cumulative installed wind farm capacity increased from 117.3 GW in 2013 to a total capacity of 182.163 GW in 2018 within the EU [1-4-1-6]. Due to the fluctuations in energy produced by wind farms storage of electricity is crucial. One possibility for storage is the production of hydrogen via electrolysis using renewable energy sources like wind farms. The hydrogen is then either directly added to the gas distribution grid or is converted to methane with external CO or CO2 which is then added to the gas distribution grid as a substitute [1-4]. Increasing the knowledge about the impact of renewable gases on available gas meters in terms of accuracy and durability is the main object of the EMPIR NEWGASMET project. Therefore in activity A3.1.1 a literature study was performed to provide information on which technologies can be used to calibrate gas meters when using renewable gases.

Hydrogen is a clean fuel and an abundant renewable energy resource. In recent years huge scientific attention has been invested to invent suitable materials for its safe storage. Conducting polymers has been extensively investigated as a potential hydrogen storage and fuel cell membrane due to the low cost ease of synthesis and processability to achieve the desired morphological and microstructural architecture ease of doping and composite formation chemical stability and functional properties. The review presents the recent progress in the direction of material selection modification to achieve appropriate morphology and adsorbent properties chemical and thermal stabilities. Polyaniline is the most explored material for hydrogen storage. Polypyrrole and polythiophene has also been explored to some extent. Activated carbons derived from conducting polymers have shown the highest specific surface area and significant storage. This review also covers recent advances in the field of proton conducting solid polymer electrolyte membranes in fuel cells application. This review focuses on the basic structure synthesis and working mechanisms of the polymer materials and critically discusses their relative merits.

For the usage of domestic gas meters with combustible gases like hydrogen natural gas or mixtures of hydrogen and natural gas in public grids the metrological behaviour of the gas meters has to fulfil the requirements described in the Measuring Instrument Directive (MID). The MID requires also that a measuring instrument shall be suitable for the application. The tightness of a meter is required in order to obtain correct results in case of accuracy tests but also for an application in the grid or for durability tests to avoid risks such as explosive gas mixtures. Due to the different properties of renewable gases leak tightness to one gas mixtures does not necessarily imply leak tightness for other gases. Hydrogen molecules are smaller than those in conventional natural gas which can more easily result in a gas leakage. The EMPIR project NEWGASMET includes beside metrological investigations also a durability test with hydrogen. In order to carry out these activities but also for further hydrogen leakage investigations for instance the investigation of proper seal materials used in the gas meter installation a reliable gas tightness test was developed.