Publications

The present paper dwells on the role of green hydrogen in the transition towards climateneutral economies and reviews the central challenges for its emancipation as an economically viable source of energy. The study shows that countries with a substantial share of renewables in the energy mix advanced natural gas pipeline infrastructure and an advanced level of technological and economic development have a comparative advantage for the wider utilization of hydrogen in their national energy systems. The central conclusion this review paper is that a green hydrogen rollout in the developed and oil-exporting developing and emerging countries is not a risk for the rest of the world in terms of the increasing technological disparities and conservation of underdevelopment and concomitant socio-economic problems of the Global South. The targets anchored in Paris Agreement but even more in the EU Green Deal and the European Hydrogen Strategy will necessitate a substantial rollout of RESs in developing countries and especially in the countries of the African Union because of the prioritization of the African continent within the energy cooperation frameworks of the EU Green Deal and the EU Hydrogen Strategy. Hence the green hydrogen rollout will bridge the energy transition between Europe and Africa on the one hand and climate and development targets on the other.

The concerns over food security and protein scarcity driven by population increase and higher standards of living have pushed scientists toward finding new protein sources. A considerable proportion of resources and agricultural lands are currently dedicated to proteinaceous feed production to raise livestock and poultry for human consumption. The 1st generation of microbial protein (MP) came into the market as land-independent proteinaceous feed for livestock and aquaculture. However MP may be a less sustainable alternative to conventional feeds such as soybean meal and fishmeal because this technology currently requires natural gas and synthetic chemicals. These challenges have directed researchers toward the production of 2nd generation MP by integrating renewable energies anaerobic digestion nutrient recovery biogas cleaning and upgrading carbon-capture technologies and fermentation. The fermentation of methane-oxidizing bacteria (MOB) and hydrogen-oxidizing bacteria (HOB) i.e. two protein rich microorganisms has shown a great potential on the one hand to upcycle effluents from anaerobic digestion into protein rich biomass and on the other hand to be coupled to renewable energy systems under the concept of Power-to-X. This work compares various production routes for 2nd generation MP by reviewing the latest studies conducted in this context and introducing the state-of-the-art technologies hoping that the findings can accelerate and facilitate upscaling of MP production. The results show that 2nd generation MP depends on the expansion of renewable energies. In countries with high penetration of renewable electricity such as Nordic countries off-peak surplus electricity can be used within MP-industry by supplying electrolytic H2 which is the driving factor for both MOB and HOB-based MP production. However nutrient recovery technologies are the heart of the 2nd generation MP industry as they determine the process costs and quality of the final product. Although huge attempts have been made to date in this context some bottlenecks such as immature nutrient recovery technologies less efficient fermenters with insufficient gas-to-liquid transfer and costly electrolytic hydrogen production and storage have hindered the scale up of MP production. Furthermore further research into techno-economic feasibility and life cycle assessment (LCA) of coupled technologies is still needed to identify key points for improvement and thereby secure a sustainable production system.

Wind and solar energy are often expected to fall victim to their own success: the higher their share in electricity generation the more their revenue in electricity markets (their “market value”) declines. While market values may converge to zero in conventional power systems this study argues that “green” hydrogen production can effectively and permanently halt the decline by adding flexible electricity demand in low-price hours. To support this argument this article further develops the merit order model and uses price duration curves to include flexible hydrogen electrolysis and to derive an analytical formula for the minimum market value of renewables in the long-term market equilibrium. This hydrogen-induced minimum market value is quantified for a wide range of parameters using Monte Carlo simulations and complemented with results from a more detailed numerical electricity market model. It is shown that—due to flexible hydrogen production alone—market values across Europe will likely stabilize above €19 ± 9 MWh− 1 for solar energy and above €27 ± 8 MWh− 1 for wind energy in 2050 (annual mean estimate ± standard deviation). This is in the range of the projected levelized cost of renewables and other types of flexible electricity demand may further increase renewable market values. Market-based renewables may hence be within reach.

The classical approach to use hydrogen as a fuel for Internal Combustion Engines (ICEs) is premixed combustion. In order to avoid knocking and to limit NOx emissions very lean mixtures are employed thus resulting in a high boost pressure demand or low specific engine power. To overcome these limitations the possibility of a diesellike jet-guided combustion of hydrogen is explored. The approach is to ignite a directly injected hydrogen jet at its periphery by means of a conventional spark discharge followed by a diffusion-controlled combustion while injection remains active. An optically accessible Rapid Compression Expansion Machine (RCEM) is used to investigate ignition and combustion of underexpanded hydrogen jets in air by means of simultaneous Schlieren visualization and OH chemiluminescence. Different injection and ignition timing are investigated resulting in premixed partially premixed and diffusion-controlled (jet-guided) combustion conditions. The possibility of ignition and combustion of the hydrogen jets in diffusion-controlled conditions is investigated for different orientations of the incoming fuel jet with respect to spark location. The combustion tests are analyzed in terms of ignition success rate ignition delay reacting surface and heat release rate and an optimal orientation of the jet is assessed. The present study provides insights for optimizing hydrogen direct injection ignition and combustion for later application in ICEs.

The construction of hydrogen refueling stations is an important part of the promotion of fuel cell vehicles. In this paper a multi-period hydrogen refueling station location model is presented that can be applied to the planning and construction of hydrogen infrastructures. Based on the hydrogen demand of fuel cell passenger cars and commercial vehicles the model calculates the hydrogen demand of each zone by a weighting method according to population economic level and education level. Then the hydrogen demand of each period is calculated using the generalized Bass diffusion model. Finally the set covering model is improved to determine the locations of the stations. The new model is applied to the scientific planning of hydrogen refueling stations in Jiading District Shanghai; the construction location and sequence of hydrogen refueling stations in each period are given and the growth trend of hydrogen demand and the promoting effect of hydrogen refueling stations are analyzed. The model adopted in this model is then compared with the other two kinds of node-based hydrogen refueling station location models that have previously been proposed.

This report presents the results of research into consumer perceptions and the subsequent degree of acceptance of blended hydrogen in domestic properties. Evidence from two trial sites of the HyDeploy programme: i) a private site trial at Keele University North Staffordshire; ii) and a public site trial at Winlaton Gateshead are discussed.

Hydrogen derived from biomass feedstock (biohydrogen) can play a significant role in Germany’s hydrogen economy. However the bioenergy potential and environmental benefits of biohydrogen production are still largely unknown. Additionally there are no uniform evaluation methods present for these emerging technologies. Therefore this paper presents a methodological approach for the evaluation of bioenergy potentials and the attainable environmental impacts of these processes in terms of their carbon footprints. A procedure for determining bioenergy potentials is presented which provides information on the amount of usable energy after conversion when applied. Therefore it elaborates a four-step methodical conduct dealing with available waste materials uncertainties of early-stage processes and calculation aspects. The bioenergy to be generated can result in carbon emission savings by substituting fossil energy carriers as well as in negative emissions by applying biohydrogen production with carbon capture and storage (HyBECCS). Hence a procedure for determining the negative emissions potential is also presented. Moreover the developed approach can also serve as a guideline for decision makers in research industry and politics and might also serve as a basis for further investigations such as implementation strategies or quantification of the benefits of biohydrogen production from organic waste material in Germany

The  understanding  of  physical  phenomena  occurring  during  the  refueling  of  H2  tanks  used for hydrogen mobility applications is the key point towards the most optimal refueling protocol. A lot of experimental investigations on tank refueling were performed in the previous years for different types and sizes of tank. Several operating conditions were tested through these experiments. For instance the HyTransfer project gave one of the major outputs on the understanding of the physical phenomena occurring during a tank refueling. From a numerical perspective the availability of accurate numerical tools is another key point. Such tools could be used instead of the experimental set-ups to test various operating conditions or new designs of tanks and injectors. The use of these tools can reduce the cost of the refueling protocol development in the future. However they first need to be validated versus experimental data. This work is dedicated to CFD (Computational Fluid Dynamics) modeling of the hydrogen refueling of a long horizontal 530L type IV tank. As of now the number of available CFD simulations for  such  a large  tank  is  low  as  the  computational  cost  is  significant  which  is  often considered as a bottleneck for this approach. The simulated operating conditions correspond to one of the  experimental  campaigns  performed  in  the  framework  of  the  HyTransfer  project. The  3D  CFD model is presented. In a first validation step the CFD results are compared with experimental data. Then  a  deeper  insight  into  the  physics  predicted  by  the  CFD  is  provided.   Finally  two  other methodologies  with  the  aim  to  reduce  the  computational  cost  have   been  tested.

To address the negative influence caused by power randomness of distributed PV output on energy system’s economic operation in this work an economic operation strategy considering the uncertainty features of PV output has been designed and applied on an integrated hydrogen energy system. First the thermal system operation model and the thermoelectric output control model are precisely built for the integrated hydrogen energy system and the hydrogen-based fuel cell respectively. Then referring to the PV output prediction data the uncertainty of light intensity variation is analyzed to correct the PV output prediction curve. Finally a cost–benefit model for the optimal economic operation of the integrated hydrogen energy system including PV hydrogen fuel cell and cogeneration unit is designed with an objective function of achieving an optimal economic operation of the multi-energy coupling devices. The simulation tests validate that considering the influence of PV output uncertainty on hydrogen fuel cell output can make the system operation more reasonable which ensures the economic and reliable operation of hydrogen energy systems.

Hot water and space heating account for about 80% of total energy consumption in the residential sector in the UK. It is thus crucial to decarbonise residential heating to achieve UK's 2050 greenhouse gas reduction targets. However the decarbonisation transitions determined by most techno-economic energy system models might be too optimistic or misleading for relying on cost minimisation alone and not considering households' preferences for different heating technologies. This study thus proposes a novel framework to incorporate heterogeneous households' (HHs) preferences into the modelling process of the UK TIMES model. The incorporated preferences for HHs are based on a nationwide survey on homeowners' choices of heating technologies. Preference constraints are then applied to regulate the HHs' choices of heating technologies to reflect the survey results. Consequently compared to the least cost transition pathway the preference-driven pathway adopts heating technologies gradually without abrupt increases of market shares. Heat pumps and electric heaters are deployed much less than in the cost optimal result. Extensive district heating using low-carbon fuels and conservation measures should thus be deployed to provide flexibility for decarbonisation. The proposed framework can also incorporate preferences for other energy consumption technologies and be applied to other linear programming based energy system models.