Publications

Technical economic and environmental assessments of projected power-to-gas (PtG) deployment scenarios at distributed- to national-scale are reviewed as well as their extensions to nuclear-assisted renewable hydrogen. Their collective research trends outcomes challenges and limitations are highlighted leading to suggested future work areas. These studies have focused on the conversion of excess wind and solar photovoltaic electricity in European-based energy systems using low-temperature electrolysis technologies. Synthetic natural gas either solely or with hydrogen has been the most frequent PtG product. However the spectrum of possible deployment scenarios has been incompletely explored to date in terms of geographical/sectorial application environment electricity generation technology and PtG processes products and their end-uses to meet a given energy system demand portfolio. Suggested areas of focus include PtG deployment scenarios: (i) incorporating concentrated solar- and/or hybrid renewable generation technologies; (ii) for energy systems facing high cooling and/or water desalination/treatment demands; (iii) employing high-temperature and/or hybrid hydrogen production processes; and (iv) involving PtG material/energy integrations with other installations/sectors. In terms of PtG deployment simulation suggested areas include the use of dynamic and load/utilization factor-dependent performance characteristics dynamic commodity prices more systematic comparisons between power-to-what potential deployment options and between product end-uses more holistic performance criteria and formal optimizations.

The exponentially growing contribution of renewable energy sources in the electricity mix requires large systems for energy storage to tackle resources intermittency. In this context the technologies for hydrogen production offer a clean and versatile alternative to boost renewables penetration and energy security. Hydrogen production as a strategy for the decarbonization of the energy sources mix has been investigated since the beginning of the 1990s. The stationary sector i.e. all parts of the economy excluding the transportation sector accounts for almost three-quarters of greenhouse gases (GHG) emissions (mass of CO2-eq) in the world associated with power generation. While several publications focus on the hybridization of renewables with traditional energy storage systems or in different pathways of hydrogen use (mainly power-to-gas) this study provides an insightful analysis of the state of art and evolution of renewable hydrogen-based systems (RHS) to power the stationary sector. The analysis started with a thorough review of RHS deployments for power-to-power stationary applications such as in power generation industry residence commercial building and critical infrastructure. Then a detailed evaluation of relevant techno-economic parameters such as levelized cost of energy (LCOE) hydrogen roundtrip efficiency (HRE) loss of power supply probability (LPSP) self-sufficiency ratio (SSR) or renewable fraction (fRES) is provided. Subsequently lab-scale plants and pilot projects together with current market trends and commercial uptake of RHS and fuel cell systems are examined. Finally the future techno-economic barriers and challenges for short and medium-term deployment of RHS are identified and discussed.

Governments and local authorities introduce new incentives and regulations for cleaner mobility as part of their environmental strategies to address energy challenges. Fuel cell electric vehicles (FCEVs) are becoming increasingly important and will extend beyond captive fleets reaching private users. Research on hydrogen safety issues is currently led in several projects in order to highlight and manage risks of FCEVs in confined spaces such as tunnels underground parkings repair garages etc. But what about private garages - that involve specific geometries volumes congestion ventilation? This study has been carried out in the framework of PRHyVATE JIP project which aims at better understanding hydrogen build-up and distribution in a private garage. The investigation went through different rates and modes of ventilation. As first step an HAZID (Hazard Identification) has been realized for a generic FCEV. This preliminary work allowed to select and prioritize accidental release scenarios to be explored experimentally with helium in a 40-m3 garage. Several configurations of release ventilation modes and congestion – in transient regime and at steady state – have been tested. Then analytical and numerical calculation approaches have been applied and adjusted to develop a simplified methodology. This methodology takes into account natural ventilation for assessment of hydrogen accumulation and mitigation means optimization. Finally a global risk evaluation – including ignition of a flammable hydrogen-air mixture – has been performed to account for the mostly feared events and to evaluate their consequences in a private garage. Thus preliminary recommendations good practices and safety features for safely parking FCEVs in private garages can be proposed.

The premixed propagation of lean isobaric H2-air flames (φ = 0.3) in Hele-Shaw cells (i.e. two parallel plates separated by a small distance h on the order of the thickness of the planar adiabatic flame δf ∼ 3 mm) is investigated numerically. Three-dimensional (3D) simulations with detailed chemistry and transport are used to examine the effect of h on the flame dynamics and its overall normalized propagation speed (S T /S L) for a semi-closed system of size 25δf × 25δf × h. To determine the validity of an existing quasi-two-dimensional (quasi-2D) formulation (derived in the limit of h → 0) to capture the 3D dynamics results for h = 0.1δf h = 0.5δf and h = δf are reported. For h = 0.1δf strong cell splitting/merging is observed with associated low frequency/high amplitude oscillations in the temporal evolution of S T /S L (10-17Hz; 6 ≤ S T /S L ≤ 10). Larger values of h exhibit a much smoother evolution. For h = 0.5δf the cell splitting/merging is milder relaxing to a steady propagating speed of S T /S L ∼ 6 after an initial transient; for h = 1δf the flame dynamics along the h direction starts to play an important role showing two distinct phases: (i) initial symmetric propagation with a linear increase in S T /S L (from 5.3 to 6.8) as early signs of asymmetry are visible (ii) followed by a fully non-symmetric propagation resulting in an abrupt increase in S T /S L that quickly relaxes to a constant value thereafter (S T /S L ∼ 10). Our preliminary results suggest that for the lean H2-air mixture considered the quasi-2D approximation breaks down for h > 0.1δf .

Hydrogen is widely considered a clean source of energy from the viewpoint of reduction in carbon dioxide emissions as a countermeasure against global warming and air pollution. Various efforts have been made to develop hydrogen as a viable energy carrier including the implementation of fuel cell vehicles (FCVs) and hydrogen refuelling stations (HRSs). A good network of hydrogen refuelling stations is essential for operating FCVs and several hydrogen refuelling stations have been constructed and are in operation worldwide [1]. However despite the potential benefits of hydrogen its flammability creates significant safety concerns. Furthermore even though the energy density of hydrogen is lower than that of gasoline and there is no carbon present which means the amount of radiant heat flux released during combustion is relatively small hydrogen must be handled at high pressure in order to make the cruising range of a fuel cell vehicle (FCV) equal to that of gasoline-powered vehicles. Therefore it is essential to properly evaluate these safety concerns and take reasonable and effective countermeasures. Approximately 50 accidents and incidents involving HRSs have been reported globally [2]. Sakamoto et al. [2] analysed accidents and incidents at HRSs in Japan and the USA to identify the safety issues. Most types of accidents and incidents are small leakages of hydrogen but some have led to serious consequences such as fire and explosion. Recently there was a serious incident in Norway at Kjørbo where a strong explosion was observed [3] – indeed this was within a short time of two other serious incidents in the USA and South Korea showing that the frequency of such incidents may be higher as deployments increase. Use of hydrogen forklifts (and the associated refuelling infrastructure) is another challenge to consider. Hydrogen refuelling stations are often installed in urban areas facing roads and are readily accessible to everyone. Therefore a key measure to approve the hydrogen refuelling stations is safety distances between the hydrogen infrastructure and the surrounding structures such as office buildings or residential dwellings. Whilst a lot of work has been carried out on safety distances (see e.g. [4-6) the accident scenario assumptions and safety distances varied widely in those studies. As a result no consensus has yet emerged on the safety distances to be used and efforts are still needed to bridge the gap between international standards and local regulations (see e.g. [7-8]). The paper analyses this issue and provides guidance on the way forward.

Import and export of fossil energy carriers are cornerstones of energy systems world-wide. If energy systems are to become climate neutral and sustainable fossil carriers need to be substituted with carbon neutral alternatives or electrified if possible. We investigate synthetic chemical energy carriers hydrogen methane methanol ammonia and Fischer-Tropsch fuels produced using electricity from Renewable Energy Source (RES) as fossil substitutes. RES potentials are obtained from GIS-analysis and hourly resolved time-series are derived using reanalysis weather data. We model the sourcing of feedstock chemicals synthesis and transport along nine different Energy Supply Chains to Germany and compare import options for seven locations around the world against each other and with domestically sourced alternatives on the basis of their respective cost per unit of hydrogen and energy delivered. We find that for each type of chemical energy carrier there is an import option with lower costs compared to domestic production in Germany. No single exporting country or energy carrier has a unique cost advantage since for each energy carrier and country there are cost-competitive alternatives. This allows exporter and infrastructure decisions to be made based on other criteria than energy and cost. The lowest cost means for importing of energy and hydrogen are by hydrogen pipeline from Denmark Spain and Western Asia and Northern Africa starting at 36 EUR/MWhLHV to 42 EUR/MWhLHV or 1.0 EUR/kgH2 to 1.3 EUR/kgH2 (in 2050 assuming 5% p.a. capital cost). For complex energy carriers derived from hydrogen like methane ammonia methanol or Fischer-Tropsch fuels imports from Argentina by ship to Germany are lower cost than closer exporters in the European Union or Western Asia and Northern Africa. For meeting hydrogen demand direct hydrogen imports are more attractive than indirect routes using methane methanol or ammonia imports and subsequent decomposition to hydrogen because of high capital investment costs and energetic losses of the indirect routes. We make our model and data available under open licenses for adaptation and reuse.

Green hydrogen could play a crucial role in the maritime industry’s journey towards decarbonization. Produced through electrolysis hydrogen is emission free and could be widely available across the globe in future – as a marine fuel or a key enabler for synthetic fuels. Many in shipping recognize hydrogen’s potential as a fuel but the barriers to realizing this potential are substantial.<br/>The 1st Edition of the ‘Handbook for Hydrogen-fuelled Vessels’ offers a road map towards safe hydrogen operations using fuel cells. It details how to navigate the complex requirements for design and construction and it covers the most important aspects of hydrogen operations such as safety and risk mitigation engineering details for hydrogen systems and implementation phases for maritime applications based on the current regulatory Alternative Design process framework.<br/>This publication is the result of the 1st phase of the DNV-led Joint Industry Project MarHySafe which has brought together a consortium of 26 leading company and associations. The project is ongoing and this publication will be continually updated to reflect the latest industry expertise on hydrogen as ship fuel.

This work reports on H2 fuel generation from sewage water using Cu/CuO nanoporous (NP) electrodes. This is a novel concept for converting contaminated water into H2 fuel. The preparation of Cu/CuO NP was achieved using a simple thermal combustion process of Cu metallic foil at 550 ◦C for 1 h. The Cu/CuO surface consists of island-like structures with an inter-distance of 100 nm. Each island has a highly porous surface with a pore diameter of about 250 nm. X-ray diffraction (XRD) confirmed the formation of monoclinic Cu/CuO NP material with a crystallite size of 89 nm. The prepared Cu/CuO photoelectrode was applied for H2 generation from sewage water achieving an incident to photon conversion efficiency (IPCE) of 14.6%. Further the effects of light intensity and wavelength on the photoelectrode performance were assessed. The current density (Jph) value increased from 2.17 to 4.7 mA·cm−2 upon raising the light power density from 50 to 100 mW·cm−2 . Moreover the enthalpy (∆H*) and entropy (∆S*) values of Cu/CuO electrode were determined as 9.519 KJ mol−1 and 180.4 JK−1 ·mol−1 respectively. The results obtained in the present study are very promising for solving the problem of energy in far regions by converting sewage water to H2 fuel.

Owing to their extremely high energy density single-bonded polymeric nitrogen and atomic metallic hydrogen are generally regarded as the ultimate energetic materials. Although their syntheses normally require ultrahigh pressures of several hundred gigapascals (GPa) which prohibit direct materials application research on their stability metastability and fundamental properties are valuable for seeking extreme energetic materials through alternative synthetic routes. Various crystalline and amorphous polymeric nitrogens have been discovered between 100 and 200 GPa. Metastability at ambient conditions has been demonstrated for some of these phases. Cubic-gauche and black-phosphorus polymorphs of single-bonded nitrogen are two particularly interesting phases. Their large hystereses warrant further application-inspired basic research of nitrogen. In contrast although metallic hydrogen contains the highest-estimated energy density its picosecond lifetime and picogram quantity make its practical material application impossible at present. “Metallic hydrogen” remains a curiosity-driven basic research pursuit focusing on the pressure-induced evolution of the molecular hydrogen crystal and its electronic band structure from a low-density insulator with a very wide electronic band gap to a semiconductor with a narrow gap to a dense molecular metal and atomic metal and eventually to a previously unknown exotic state of matter. This great experimental challenge is driving relentless advancement in ultrahigh-pressure science and technology.

Power to substitute natural gas (PtSNG) is a promising technology to store intermittent renewable electricity as synthetic fuel. Power surplus on the electric grid is converted to hydrogen via water electrolysis and then to SNG via CO2 methanation. The SNG produced can be directly injected into the natural gas infrastructure for long-term and large-scale energy storage. Because of the fluctuating behaviour of the input energy source the overall annual plant efficiency and SNG production are affected by the plant operation time and the standby strategy chosen. The re-use of internal (waste) heat for satisfying the energy requirements during critical moments can be crucial to achieving high annual efficiencies. In this study the heat recovery from a PtSNG plant coupled with wind energy based on proton exchange membrane electrolysis adiabatic fixed bed methanation and membrane technology for SNG upgrading is investigated. The proposed thermal recovery strategy involves the waste heat available from the methanation unit during the operation hours being accumulated by means of a two-tanks diathermic oil circuit. The stored heat is used to compensate for the heat losses of methanation reactors during the hot-standby state. Two options to maintain the reactors at operating temperature have been assessed. The first requires that the diathermic oil transfers heat to a hydrogen stream which is used to flush the reactors in order to guarantee the hot-standby conditions. The second option entails that the stored heat being recovered for electricity production through an Organic Rankine Cycle. The electricity produced is used to compensate the reactors heat losses by using electrical trace heating during the hot-standby hours as well as to supply energy to ancillary equipment. The aim of the paper is to evaluate the technical feasibility of the proposed heat recovery strategies and how they impact on the annual plant performances. The results showed that the annual efficiencies on an LHV basis were found to be 44.0% and 44.3% for the thermal storage and electrical storage configurations respectively.