Publications

Understanding the dynamic response of a solar fuel processing system utilizing concentrated solar radiation and made of a thermally-integrated photovoltaic (PV) and water electrolyzer (EC) is important for the design development and implementation of this technology. A detailed dynamic non-linear process model is introduced for the fundamental system components (i.e. PV EC pump etc.) in order to investigate the coupled system behavior and performance synergy notably arising from the thermal integration. The nominal hydrogen production power is ∼2 kW at a hydrogen system efficiency of 16–21% considering a high performance triple junction III-V PV module and a proton exchange membrane EC. The device operating point relative to the maximum power point of the PV was shown to have a differing influence on the system performance when subject to temperature changes. The non-linear coupled behavior was characterised in response to step changes in water flowrate and solar irradiance and hysteresis of the current-voltage operating point was demonstrated. Whilst the system responds thermally to changes in operating conditions in the range of 0.5–2 min which leads to advantageously short start-up times a number of control challenges are identified such as the impact of pump failure electrical PV-EC disconnection and the potentially damaging accentuated temperature rise at lower water flowrates. Finally the simulation of co-generation of heat and hydrogen for various operating conditions demonstrates the significant potential for system efficiency enhancements and the required development of control strategies for demand matching is discussed.

The transport sector remains at the centre of any debates around energy conservation exaggerated by the stubborn and overwhelming reliance on fossil fuels by its motorised forms whether passenger and freight road rail sea and air.<br/>The very slow transition to alternative fuel sources to date has resulted in this sector being increasingly and convincingly held responsible for the likely failure of individual countries including the UK to meet their obligations under consecutive international climate change agreements.<br/>Electrification of transport is largely expected to take us down the path to a ‘zero carbon future’ (CCC 2019; DfT 2018). But there are serious concerns about future technology performance availability costs and uptake by consumers and businesses. There are also concerns about the increasing gap between lab and ‘real world’ performance of energy use carbon and air pollution emissions. Recently the role of consumer ‘lifestyles’ has increased in prominence (e.g. IPCC 2018) but as yet has not been taken seriously by the DfT BEIS or even the CCC (2019).

The APPG on Hydrogen’s latest report urges the Government to move quickly on hydrogen and set ambitious policies to unlock investment create employment opportunities and support the UK’s net-zero targets.

The APPG on Hydrogen’s report developed as part of its inquiry into ‘How the UK’s hydrogen sector can help support the UK’s economic recovery’ sets out 15 recommendations to support and accelerate the growth of the UK’s hydrogen sector.

These include:

• Developing a cross-departmental hydrogen strategy between Government and industry
• Using regulatory levers to unlock private sector investment required including amending the GSMR and expanding the remit of the Bus Service Operator Grant
• Setting interim targets for low-carbon hydrogen production by 2030 alongside the introduction of a Low Carbon Obligation to enable investment in low carbon forms of heating such as hydrogen
• Mandating hydrogen-ready boilers by 2025
• Creating greater incentives in hydrogen alternatives to support organisations and customers who produce purchase or use hydrogen HGVs buses and trains
• Working with local and regional authorities exploring hydrogen’s potential to support the uptake and commercialisation of existing projects
• Setting more ambitious policies and financial targets on hydrogen to meet net-zero by 2050 ahead of other international competitors
• Ensuring the UK hydrogen industry plays a major role at COP26 allowing the UK to inspire other nations and sell its products and services
• Delivering funding models to create investment and economic jobs directly to the UK
• Implementing measures similar to Offshore Wind such as Contracts for Difference to incentivise industry and scale-up a hydrogen economy.

Because of the emergence of the U.E. “green deal” and because of the significant implication of national and regional authorities throughout Europe the “hydrogen” economy is emerging. And with it numerous questions and experimentations. One of them perhaps a key point is the storage and transport of hydrogen. Liquid hydrogen in cryogenic conditions is a possibility already used in the space industry but under a lot of constrains. What may be acceptable in a well-controlled and restrained domain may not be realistic in a wider application closer to the public. Safety should be ensured and there is a need for a better knowledge of the flammable and ignition properties of the “cold” hydrogen mixtures following a cryogenic spillage for instance to select adequate ATEX equipment. The purpose of PRESLHY project [4] is to investigate the ignition fire and explosion characteristics of cryogenic hydrogen spillages and to propose safety engineering methods. The present work is part of it and addresses the measurement of the laminar burning velocity (Sl) flammability limits (FL) minimum ignition energy (MIE)… of hydrogen air mixtures at atmospheric pressure but down to -150°C. To do this a special burner was designed with details given inside this paper together with the experimental results. It is found that the FL domain is reduced when the temperature drops that MIE increases slightly and Sl decreases.

A review of more than 60 studies (plus m4ore than 65 studies on P2G) on power and energy models based on simulation and optimization was done. Based on these for power systems with up to 95% renewables the electricity storage size is found to be below 1.5% of the annual demand (in energy terms). While for 100% renewables energy systems (power heat mobility) it can remain below 6% of the annual energy demand. Combination of sectors and diverting the electricity to another sector can play a large role in reducing the storage size. From the potential alternatives to satisfy this demand pumped hydro storage (PHS) global potential is not enough and new technologies with a higher energy density are needed. Hydrogen with more than 250 times the energy density of PHS is a potential option to satisfy the storage need. However changes needed in infrastructure to deal with high hydrogen content and the suitability of salt caverns for its storage can pose limitations for this technology. Power to Gas (P2G) arises as possible alternative overcoming both the facilities and the energy density issues. The global storage requirement would represent only 2% of the global annual natural gas production or 10% of the gas storage facilities (in energy equivalent). The more options considered to deal with intermittent sources the lower the storage requirement will be. Therefore future studies aiming to quantify storage needs should focus on the entire energy system including technology vectors (e.g. Power to Heat Liquid Gas Chemicals) to avoid overestimating the amount of storage needed.

Improving energy system modelling capabilities can directly affect the quality of applied studies. However some modelling trade-offs are necessary as the computational capacity and data availability are constrained. In this paper we demonstrate modelling trade-offs resulting from the modification in the resolution of four modelling capabilities namely transitional scope European electricity interconnection hourly demand-side flexibility description and infrastructure representation. We measure the cost of increasing resolution in each capability in terms of computational time and several energy system modelling indicators notably system costs emission prices and electricity import and export levels. The analyses are performed in a national-level integrated energy system model with a linear programming approach that includes the hourly electricity dispatch with European nodes. We determined that reducing the transitional scope from seven to two periods can reduce the computational time by 75% while underestimating the objective function by only 4.6%. Modelers can assume a single European Union node that dispatches electricity at an aggregated level which underestimates the objective function by 1% while halving the computational time. Furthermore the absence of shedding and storage flexibility options can increase the curtailed electricity by 25% and 8% respectively. Although neglecting flexibility options can drastically decrease the computational time it can increase the sub-optimality by 31%. We conclude that an increased resolution in modelling flexibility options can significantly improve the results. While reducing the computational time by half the lack of electricity and gas infrastructure representation can underestimate the objective function by 4% and 6% respectively.

The Fuel Cells and Hydrogen Joint Undertaking (FCH JU) has supported a range of initiatives in recent years designed to develop hydrogen fuel cell buses to a point where they can fulfil their promise as a mainstream zero emission vehicle for public transport.<br/>Within this study 90 different European cities and regions have been supported in understanding the business case of fuel cell bus deployment and across these locations. The study analyses the funding and financing for fuel cell bus deployment to make them become a mainstream zero emission choice for public transport providers in cities and regions across Europe. It also outlines possible solutions for further deployment of FC buses beyond the subsidised phase.<br/>In the light of the experience of the joint tender process in the UK and in Germany the study highlights best practices for ordering fuel cell buses. Other innovative instruments explored in other countries for the orders of large quantities of fuel cells buses are presented: Special Purpose Vehicles and centralised purchase office. Finally the study deeply analyses the funding and financing for fuel cell bus deployment to make them become a mainstream zero emission choice for public transport providers in cities and regions across Europe.

With the growth of aviation traffic and the demand for emission reduction alternative fuels like the so-called electrofuels could comprise a sustainable solution. Electrofuels are understood as those that use renewable energy for fuel synthesis and that are carbon-neutral with respect to greenhouse gas emission. In this study five potential electrofuels are discussed with respect to the potential application as aviation fuels being n-octane methanol methane hydrogen and ammonia and compared to conventional Jet A-1 fuel. Three important aspects are illuminated. Firstly the synthesis process of the electrofuel is described with its technological paths its energy efficiency and the maturity or research need of the production. Secondly the physico-chemical properties are compared with respect to specific energy energy density as well as those properties relevant to the combustion of the fuels i.e. autoignition delay time adiabatic flame temperature laminar flame speed and extinction strain rate. Results show that the physical and combustion properties significantly differ from jet fuel except for n-octane. The results describe how the different electrofuels perform with respect to important aspects such as fuel and air mass flow rates. In addition the results help determine mixture properties of the exhaust gas for each electrofuel. Thirdly a turbine configuration is investigated at a constant operating point to further analyze the drop-in potential of electrofuels in aircraft engines. It is found that electrofuels can generally substitute conventional kerosene-based fuels but have some downsides in the form of higher structural loads and potentially lower efficiencies. Finally a preliminary comparative evaluation matrix is developed. It contains specifically those fields for the different proposed electrofuels where special challenges and problematic points are seen that need more research for potential application. Synthetically-produced n-octane is seen as a potential candidate for a future electrofuel where even a drop-in capability is given. For the other fuels more issues need further research to allow the application as electrofuels in aviation. Specifically interesting could be the combination of hydrogen with ammonia in the far future; however the research is just at the beginning stage.

‟How crack growth is prevented” is key to improve both fatigue and monotonic fracture resistances under an influence of hydrogen. Specifically the key points for the crack growth resistance are hydrogen diffusivity and local ductility. For instance type 304 austenitic steels show high hydrogen embrittlement susceptibility because of the high hydrogen diffusivity of bcc (α´) martensite. In contrast metastability in specific austenitic steels enables fcc (γ) to hcp (ε) martensitic transformation which decreases hydrogen diffusivity and increases strength simultaneously. As a result even if hydrogen-assisted cracking occurs during monotonic tensile deformation the ε-martensite acts to arrest micro-damage evolution when the amount of ε-martensite is limited. Thus the formation of ε-martensite can decrease hydrogen embrittlement susceptibility in austenitic steels. However a considerable amount of ε-martensite is required when we attempt to have drastic improvements of work hardening capability and strength level with respect to transformation-induced plasticity effect. Since the hcp structure contains a less number of slip systems than fcc and bcc the less stress accommodation capacity often causes brittle-like failure when the ε-martensite fraction is large. Therefore ductility of ε-martensite is another key when we maximize the positive effect of ε-martensitic transformation. In fact ε-martensite in a high entropy alloy was recently found to be extraordinary ductile. Consequently the metastable high entropy alloys showed low fatigue crack growth rates in a hydrogen atmosphere compared with conventional metastable austenitic steels with α´-martensitic transformation. We here present effects of metastability to ε-phase and configurational entropy on hydrogen-induced mechanical degradation including monotonic tension properties and fatigue crack growth resistance.

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.