Publications

With the long-standing efforts of green transition in our society underground hydrogen storage (UHS) has emerged as a viable solution to buffering seasonal fluctuations of renewable energy supplies and demands. Like operations in hydrocarbon production and geological CO2 storage a successful UHS project requires a good understanding of subsurface formations while having different operational objectives and practical challenges. Similar to the situations in hydrocarbon production and geological CO2 storage in UHS problems the information of subsurface formations at the field level cannot be obtained through direct measurements due to the resulting high costs. As such there is a need for subsurface characterization and monitoring at the field scale which uses a certain history matching algorithm to calibrate a numerical subsurface model based on available field data. Whereas subsurface characterization and monitoring have been widely used in hydrocarbon production activities for a better understanding of hydrocarbon reservoirs to the best of our knowledge at present it appears to be a relatively less touched area in UHS problems. This work aims to narrow this noticed gap and investigates the use of an ensemble-based workflow for subsurface characterization and monitoring in a 3D UHS case study. Numerical results in this case study indicate that the ensemble-based workflow works reasonably well while also identifying some particular challenges that would be relevant to real-world problems.

Hydrogen is considered one of the key pillars of an effective decarbonization strategy of the energy sector; however the potential of hydrogen as an electricity storage medium is debated. This paper investigates the role of hydrogen as an electricity storage medium in an electricity system with large hydropower resources focusing on the Swiss electricity sector. Several techno-economic and climate scenarios are considered. Findings suggest that hydrogen storage plays no major role under most conditions because of the large hydropower resources. More specifically no hydrogen storage is installed in Switzerland if today’s values of net-transfer capacities and low load-shedding costs are assumed. This applies even to hydrogen-favorable climate scenarios (dry years with low precipitation and dam inflows) and economic assumptions (high learning rates for hydrogen technologies). In contrast hydrogen storage is installed when net-transfer capacities between countries are reduced below 30% of current values and load-shedding costs are above 1000 EUR/MWh. When installed hydrogen is deployed in a few large-scale installations near the national borders.

Climate change is obvious in many ways. The weather changes rapidly from day to day reaching high temperatures such as 28 ◦C one day and heavy rain the next with temperatures below 18 ◦C. There are also very strong storms caused by this phenomenon. The way the environment acts is different than the current epoch would predict indicating a long-term shift in weather and temperature patterns. The mean temperature of earth is rising due to the greenhouse effect that is caused by human activity and mostly by the burning of fossil fuel emitting CO2 and other pollutant gasses. Nowadays every country is trying to lower CO2 emissions from everyday human activities a movement called “decarbonization”. Since the 18th century there has been a great deal of research carried out on possible alternatives to fossil fuels. Some of the work was just to discover ways to power heaters or automotive vehicle but there is a great deal of work remaining to complete regarding this issue after discovering the greenhouse effect and its impact on the planet’s climate in order to eliminate it by using fuel whose combustion emissions are more environmentally friendly. In the present work many discoveries will be presented that use hydrogen (H2 ) or hydroxy (H-OH) as fuel. The main reason for this is the emission of pure water after combustion but the most interesting part is the approach every scientist uses to create the fuel gas from water.

This perspective article delves into the critical role of hydrogen as a sustainable energy carrier in the context of the ongoing global energy transition. Hydrogen with its potential to decarbonize various sectors has emerged as a key player in achieving decarbonization and energy sustainability goals. This article provides an overview of the current state of hydrogen technology its production methods and its applications across diverse industries. By exploring the challenges and opportunities associated with hydrogen integration we aim to shed light on the pathways toward achieving a sustainable hydrogen economy. Additionally the article underscores the need for collaborative efforts among policymakers industries and researchers to overcome existing hurdles and unlock the full potential of hydrogen in the transition to a low-carbon future. Through a balanced analysis of the present landscape and future prospects this perspective article aims to contribute valuable insights to the discourse surrounding hydrogen’s role in the global energy transition.

Due to its low NOx emission index the micromix burner technology is a promising alternative for using hydrogen in combustion. Various universities and research centers in Germany England and Spain have documented and studied this technology. However the number of studies on micromix burners is limited which hinders their implementation on an industrial scale. The present study aims to review developed works focused on micromix combustion technologies to identify the main gaps and research needs. A sample of 76 articles from 2008 was selected using the PRISMA methodology which was categorized based on the study methodology simulation software and fuels used. An experimental gap has been identified in the combustion of hydrogen and methane in the selected article sample. This gap is a critical research need due to the opportunity to implement this tech nology in existing natural gas networks facilitating the transition from fossil fuels to cleaner combustion processes.

In order to achieve the ambitious goal of “carbon neutrality” countries around the world are striving to develop clean energy. Against this background this paper takes China and Italy as representatives of developing and developed countries to summarize the energy structure composition and development overview of the two countries. The paper analyzes the serious challenges facing the future energy development of both countries and investigates the possibilities of energy cooperation between the two countries taking into account their respective advantages in energy development. By comparing the policies issued by the two governments to encourage clean energy development this paper analyzes the severe challenges faced by the two countries’ energy development in the future and combines their respective energy development advantages to look forward to the possibility of energy cooperation between the two countries in the future. This lays the foundation for China and Italy to build an “Energy Road” after the “Silk Road”.

The present paper offers a thorough examination of the safety measures enforced at hydrogen filling stations emphasizing their crucial significance in the wider endeavor to advocate for hydrogen as a sustainable and reliable substitute for conventional fuels. The analysis reveals a wide range of crucial safety aspects in hydrogen refueling stations including regulated hydrogen dispensing leak detection accurate hydrogen flow measurement emergency shutdown systems fire-suppression mechanisms hydrogen distribution and pressure management and appropriate hydrogen storage and cooling for secure refueling operations. The paper therefore explores several aspects including the sophisticated architecture of hydrogen dispensers reliable leak-detection systems emergency shut-off mechanisms and the implementation of fire-suppression tactics. Furthermore it emphasizes that the safety and effectiveness of hydrogen filling stations are closely connected to the accuracy in the creation and upkeep of hydrogen dispensers. It highlights the need for materials and systems that can endure severe circumstances of elevated pressure and temperature while maintaining safety. The use of sophisticated leak-detection technology is crucial for rapidly detecting and reducing possible threats therefore improving the overall safety of these facilities. Moreover the research elucidates the complexities of emergency shut-off systems and fire-suppression tactics. These components are crucial not just for promptly managing hazards but also for maintaining the station’s structural soundness in unanticipated circumstances. In addition the study provides observations about recent technical progress in the industry. These advances effectively tackle current safety obstacles and provide the foundation for future breakthroughs in hydrogen fueling infrastructure. The integration of cutting-edge technology and materials together with the development of upgraded safety measures suggests a positive trajectory towards improved efficiency dependability and safety in hydrogen refueling stations.

This paper presents the development of a thermodynamic model for the hydrogen refuelling station (HRS) to simulate the process of refuelling which involves the transfer of hydrogen gas from a high-pressure storage tank to the onboard tank of a fuel cell electric vehicle (FCEV). This model encompasses the fundamental elements of an HRS which consists of a storage tank compressor piping system heat exchanger and an on-board vehicle tank. The model is implemented and validated using experimental data from SAE J2601. Various simulations are conducted to assess the impact of the Joule-Thomson effect and compression on the temperature of hydrogen flow specifically focusing on an average pressure rate of 18 MPa/min. Furthermore a comprehensive analysis is conducted to examine the impact of pressure variations in the storage tank (10–90 MPa) and the initial pressure within the vehicle tank (5–35 MPa) as well as variations in ambient temperature (0–40 °C). The study revealed that the energy consumption in the cooling system surpasses the average power consumption in the more advantageous scenario of 60 MPa by a range of 36% to over 220% when the pressure in the storage system drops below 30 MPa. Furthermore it was noted that the impact of ambient temperature is comparatively less significant when compared to the initial pressure of the vehicle's tank. The impact of an ambient temperature change of 10 °C on the final temperature of a hydrogen vehicle is found to be approximately 2 °C. Similarly a variation in the initial vehicle pressure of 10 MPa results in a modification of the final hydrogen vehicle temperature by approximately 8.5 °C.

Hydrogen is an environmentally friendly fuel that can facilitate the upcoming energy transition. The development of an extensive infrastructure for hydrogen transport and storage is crucial. However the mechanical properties of structural materials are significantly degraded in H2 environments leading to early component failures. Pipelines are designed following defect-tolerant principles and are subjected to periodic pressure fluctuations. Hence these systems are potentially prone to fatigue degradation often accelerated in pressurized hydrogen gas. Inspection and maintenance activities are crucial to guarantee the integrity and fitness for service of this infrastructure. This study predicts the severity of hydrogen-enhanced fatigue in low-alloy steels commonly employed for H2 transport and storage equipment. Three machine-learning algorithms i.e. Linear Model Deep Neural Network and Random Forest are used to categorize the severity of the fatigue degradation. The models are critically compared and the best-performing algorithm are trained to predict the Fatigue Acceleration Factor. This approach shows good prediction capability and can estimate the fatigue crack propagation in lowalloy steels. These results allow for estimating the probability of failure of hydrogen pipelines thus facilitating the inspection and maintenance planning.

The chemical industry serves as a global economic backbone and it is an intensive consumer of conventional energy. Due to the depletion of fossil fuels and the emission of greenhouse gases it is necessary to analyze energy supply solutions based on renewable energy sources in this industrial sector. Unlike other sectors such as residential or service industries which have been thoroughly analyzed by the scientific community the use of renewable energies in the chemical industry remains comparatively less examined by the scientific community. This article studies the use of an energy supply system based on photovoltaic technology or a PEM fuel cell for a styrene production industry analyzing the integration of energy storage systems such as batteries as well as different uses for the surplus hydrogen produced by the facility. The most interesting conclusions of the article are: (1) the renewable microgrid considered is viable both technically and economically with a discounted payback period between 5.4 and 6.5 years using batteries as an energy storage system; and (2) the use of hydrogen as energy storage system for a styrene industry is not yet a viable option from an economic point of view.

Reducing the cost of hydrogen fuel cell technology is crucial in propelling the hydrogen economy and achieving decarbonized energy systems. This study identifies the hydrogen fuel cell cost trajectory through a multi-stage learning curve model highlighting technology learning mechanisms across different stages. Findings show that innovation and production contribute to cost reduction and the learning by researching holds a more significant role presently while the learning by doing takes precedence in the long term achieving a 14% learning rate. The cost predictions imply that the system cost of hydrogen fuel cell is expected to fall below 1000 yuan/kW after 2031. Moreover the scenario analyses highlight the conducive role of various hydrogen production technologies and the evolution of cost influencing factors on cost reduction. Our research provides critical insights into the evolving dynamics of technological learning and cost trajectory in the hydrogen fuel cell industry with significant implications for policy-making.

Hydrogen is a promising fuel because it has good capabilities to operate gas turbines. Due to its ignition speed which exceeds the ignition of traditional fuel it achieves a higher thermal efficiency while the resulting emissions are low. So it was used as a clean and sustainable energy source. This paper reviews the most important research that was concerned with studying the characteristics of hydrogen combustion within incinerators and power generation equipment where hydrogen was used as a fuel mixed with traditional fuel in the combustion chambers of gas turbines. It also includes an evaluation of the combustion processes and flame formation resulting from the enrichment of gaseous fuels with hydrogen and partial oxidation. A large amount of theoretical and experimental work in this field has been reviewed. This review summarizes the predictive and experimental results of various research interests in the field of hydrogen combustion and also production.

The war in Ukraine caused Europe to more than double its imports of liquefied natural gas (LNG) in only one year. In addition imported LNG remains a crucial source of energy for resource-poor countries such as Japan where LNG imports satisfy about a quarter of the country’s primary energy demand. However an increasing number of countries are formulating stringent decarbonization plans. Liquefied hydrogen and liquefied ammonia coupled with carbon capture and storage (LH2-CCS LNH3-CCS) are emerging as the front runners in the search for low-carbon alternatives to LNG. Yet little is currently known about the full environmental profile of LH2-CCS and LNH3-CCS because several characteristics of the two alternatives have only been analyzed in isolation in previous work. Here we show that the potential of these fuels to reduce greenhouse gas (GHG) emissions throughout the supply chain is highly uncertain. Our best estimate is that LH2-CCS and LNH3-CCS can reduce GHG emissions by 25%–61% relative to LNG assuming a 100 year global warming potential. However directly coupling LNG with CCS would lead to substantial GHG reductions on the order of 74%. Further under certain conditions emissions from LH2-CCS and LNH3-CCS could exceed those of LNG by up to 44%. These results question the suitability of LH2-CCS and LNH3-CCS for stringent decarbonization purposes.

Hydrogen production and storage in hybrid systems is a promising solution for sustainable energy transition decoupling the energy generation from its end use and boosting the deployment of renewable energy. Nonetheless the optimal and cost-effective design of hybrid hydrogen-based systems is crucial to tackle existing limitations in diffusion of these systems. The present study explores net-zero energy management via a multi-objective optimization algorithm for an outdoor test facility equipped with a hydrogen-based hybrid energy production system. Aimed at enabling efficient integration of hydrogen fuel cell system the proposed solution attempts to maximize the renewable factor (RF) and carbon mitigation in the hybrid system as well as to minimize the grid dependency and the life cycle cost (LCC) of the system. In this context the techno-enviroeconomic optimization of the hybrid system is conducted by employing a statistical approach to identify optimal design variables and conflictive objective functions. To examine interactions in components of the hybrid system a series of dynamic simulations are carried out by developing a TRNSYS code coupled with the OpenStudio/EnergyPlus plugin. The obtained results indicate a striking disparity in the monthly RF values as well as the hydrogen production rate and therefore in the level of grid dependency. It is shown that the difference in LCC between optimization scenarios suggested by design of experiments could reach $15780 corresponding to 57% of the mean initial cost. The LCOE value yielded for optimum scenarios varies between 0.389 and 0.537 $/kWh. The scenario with net-zero target demonstrates the lowest LCOE value and the highest carbon mitigation i.e. 828 kg CO2/yr with respect to the grid supply case. However the LCC in this scenario exceeds $57370 which is the highest among all optimum scenarios. Furthermore it was revealed that the lowest RF in optimal scenarios is equal to 66.2% and belongs to the most economical solution.

This study explores the potentiality of low/zero carbon fuels such as methanol methane and hydrogen for motor applications to pursue the goal of energy security and environmental sustainability. An experimental investigation was performed on a spark ignition engine equipped with both a port fuel and a direct injection system. Liquid fuels were injected into the intake manifold to benefit from a homogeneous charge formation. Gaseous fuels were injected in direct mode to enhance the efficiency and prevent abnormal combustion. Tests were realized at a fixed indicated mean effective pressure and at three different engine speeds. The experimental results highlighted the reduction of CO and CO2 emissions for the alternative fuels to an extent depending on their properties. Methanol exhibited high THC and low NOx emissions compared to gasoline. Methane and even more so hydrogen allowed for a reduction in THC emissions. With regard to the impact of gaseous fuels on the NOx emissions this was strongly related to the operating conditions. A surprising result concerns the particle emissions that were affected not only by the fuel characteristics and the engine test point but also by the lubricating oil. The oil contribution was particularly evident for hydrogen fuel which showed high particle emissions although they did not contain carbon atoms.

This study performs a cradle-to-grave life cycle assessment of a 5 MW protonexchange membrane water electrolysis plant. The analysis follows a thoroughengineering-based bottom-up design based on the electrochemical model of thesystem. Three scenarios are analyzed comprising a state-of-the-art (SoA) plantoperated with the German electricity grid-mix a SoA plant operated with acompletely decarbonized energy system and a future development plantelectrolyzer with reduced energy and material demand operated in a completelydecarbonized energy system. The results display a global warming potential of34 kg CO2-eq. kg-H 21 and indicate a reduction potential of 89% when the plantis operated in a decarbonized energy system. A further reduction of 9% can beachieved by the technological development of the plant. Due to the reducedimpacts of operation in a completely decarbonized energy system the operationat locations with large offshore wind electricity capacity is recommended. In theconstruction phase the stacks especially the anode catalyst iridium bipolarplates and porous transport layers are identified as dominant sources of theenvironmental impact. A sensitivity analysis shows that the environmentalimpact of the construction phase increases with a decreasing amount ofoperational full load hours of the plant.RESEARCH ARTICLEwww.advenergysustres.comAdv. Energy Sustainability Res. 2024 5 2300135 2300135 (1 of 19) © 2023 The Authors. Advanced Energy and Sustainability Researchpublished by Wiley-VCH GmbH

Hydrogen is considered as an attractive alternative to fossil fuels in the transportation sector. However the penetration of Fuel Cell Electric Vehicles (FCEV) is hindered by the lack of hydrogen refueling station infrastructures. In this study the feasibility of a hybrid PV/wind system for hydrogen refueling station is investigated. Refueling events data is collected in different locations including industrial residential highway and tourist areas. Station Occupancy Fractions (SOF) and Social-to-Solar Fraction (STSF) indicators are developed to assess the level of synchronization between the hydrogen demand and solar potential. Then a validated computer code is used to optimize the renewable system components for off/on-grid cases based on minimizing the Net Present Cost (NPC) and the Loss of Hydrogen Supply Probability (LHSP). For off grid cases the results show that STSF attains maximum value in the industrial area where 0.62 fraction of refueling events occur during the sunshine hours and minimum NPC is achieved. It is observed that when STSF attains lower values of 0.52 0.41 and 0.38 for residential highway and tourist areas NPC increases by 8 16 and 31% respectively. This is associated with lower level of coordination between the hydrogen demand and solar potential. The same conclusion can be stated for the on-grid cases. Therefore for green hydrogen production via solar energy utilization it is recommended that a tariff should be applied to encourage refueling hydrogen vehicles during the availability of solar radiation while reducing the environmental impact storage requirements and eventually the cost of hydrogen production.

If hydrogen fuel is available to support the transportation sector decarbonization its usage can be placed either directly onboard in a fuel cell vehicle or indirectly off-board by using a fuel cell power station to produce electricity to charge a battery electric vehicle. Therefore in this work the direct and indirect conversion scenarios of hydrogen to vehicle propulsion were investigated regarding energy efficiency. Thus in the first scenario hydrogen is the fuel for the onboard electricity production to propel a fuel cell vehicle while in the second hydrogen is the electricity source to charge the battery electric vehicle. When simulated for a drive cycle results have shown that the scenario with the onboard fuel cell consumed about 20% less hydrogen demonstrating higher energy efficiency in terms of driving range. However energy efficiency depends on the outside temperature when heat loss utilization is considered. For outside temperatures of − 5 ◦C or higher the system composed of the battery electric vehicle fueled with electricity from the off-board fuel cell was shown to be more energyefficient. For lower temperatures the system composed of the onboard fuel cell again presented higher total (heat + electricity) efficiency. Therefore the results provide valuable insights into how hydrogen fuel can be used for vehicle propulsion supporting the hydrogen economy development.

This paper presents an analysis of a treatment system selection for municipal wastewater stream based on the DuPont Water Solutions WAVE software. The results obtained based on an analysis of 7 different processing cases studies (ultrafiltration and reverse osmosis) confirmed that the application of 2-pass membrane systems enables the reclamation of water from municipal wastewater that fulfills the requirements concerning the quality of water intended as electrolyzer feedstock as the obtained water exhibited a conductivity of < 5 µS/cm. Depending on the analyzed case study the attainable level of water reclamation ranged from 68.8 to 84.1 % at an energy consumption of 606.1 – 2 694 kWh/d. The results of this work not only confirm that the selected pro cessing solutions make it possible to reclaim water from municipal wastewater but also confirm the necessity of using software to simulate the membrane system operation to select the most economic and cost-effective solution.

The transition to a sustainable future with hydrogen as a key energy carrier necessitates a comprehensive understanding of the safety aspects of hydrogen including liquid hydrogen (LH₂). Hence this study presents a detailed computational fluid mechanics analysis to explore accidental LH₂ leakage and dispersion in a hydrogen refuelling station under varied conditions which is essential to prevent fire and explosion. The correlated impact of influential parameters including wind direction wind velocity leak direction and leak rate were analysed. The study shows that hydrogen dispersion is significantly impacted by the combined effect of wind direction and surrounding structures. Additionally the leak rate and leak direction have a significant effect on the development of the flammable cloud volume (FCV) which is critical for estimating the explosion hazards. Increasing wind velocity from 2 to 4 m/s at a constant leak rate of 0.06 kg/s results in an 82% reduction in FCV. The minimum FCV occurs when leak and wind directions oppose at 4 m/s. The most critical situation concerning FCV arises when the leak and wind directions are perpendicular with a leak rate of 0.06 kg/s and a wind velocity of 2 m/s. These findings can aid in the development of optimised sensing and monitoring systems and operational strategies to reduce the risk of catastrophic fire and explosion consequences.

The cost of green hydrogen production is very dependent on the price of electricity. A control system that can schedule hydrogen production based on forecast wind speed and electricity price should therefore be advantageous for large-scale wind-hydrogen systems. This work presents a novel price-based control system integrated in a techno-economic analysis of hydrogen production from offshore wind. A polynomial regression model that predicts wind power production from wind speed input was developed and tested with real-world datasets from a 2.3 MW floating offshore wind turbine. This was combined with a mathematical model of a PEM electrolyzer and used to simulate hydrogen production. A novel price-based control system was developed to decide when the system should produce hydrogen and when it should sell electricity to the grid. The model and control system can be used in real-world wind-hydrogen systems and require only the forecast wind speed electricity price and selling price of hydrogen as inputs. 11 test scenarios based on 10 years of real-world wind speed and electricity price data are proposed and used to evaluate the effect the price-based control system has on the levelized cost of hydrogen (LCOH). Both current and future (2050) costs and technologies are used and the results show that the novel control system lowered the LCOH in all scenarios by 10–46%. The lowest LCOH achieved with current technology and costs was 6.04 $/kg H2. Using the most optimistic forecasts for technology improvements and cost reductions in 2050 the model estimated a LCOH of 0.96 $/kg H2 for a grid-connected offshore wind farm and onshore hydrogen production 0.82 $/kg H2 using grid electricity (onshore) and 4.96 $/kg H2 with an offgrid offshore wind-hydrogen system. When the electricity price from the period 2013–2022 was used on the 2050 scenarios the resulting LCOH was approximately twice as high.

Hydrogen has a key role to play in decarbonising industry and other sectors of society. It is important to develop low-carbon hydrogen production technologies that are cost-effective and energy-efficient. Sorption-enhanced steam methane reforming (SE-SMR) is a developing low-carbon (blue) hydrogen production process which enables combined hydrogen production and carbon capture. Despite a number of key benefits the process is yet to be fully realised in terms of efficiency. In this work a sorption-enhanced steam methane reforming process has been intensified via exergy analysis. Assessing the exergy efficiency of these processes is key to ensuring the effective deployment of low-carbon hydrogen production technologies. An exergy analysis was performed on an SE-SMR process and was then subsequently used to incorporate process improvements developing a process that has theoretically an extremely high CO2 capture rate of nearly 100 % whilst simultaneously demonstrating a high exergy efficiency (77.58 %) showcasing the potential of blue hydrogen as an effective tool to ensure decarbonisation in an energy-efficient manner.

Porous carbons have been extensively investigated for hydrogen storage but to date appear to have an upper limit to their storage capacity. Here in an effort to circumvent this upper limit we explore the potential of oxygen-rich activated carbons. We describe cellulose acetate-derived carbons that combine high surface area (3800 m2 g−1 ) and pore volume (1.8 cm3 g−1 ) that arise almost entirely (>90%) from micropores with an oxygen-rich nature. The carbons exhibit enhanced gravimetric hydrogen uptake (8.1 wt% total and 7.0 wt% excess) at −196 °C and 20 bar rising to a total uptake of 8.9 wt% at 30 bar and exceptional volumetric uptake of 44 g l −1 at 20 bar and 48 g l −1 at 30 bar. At room temperature they store up to 0.8 wt% (excess) and 1.2 wt% (total) hydrogen at only 30 bar and their isosteric heat of hydrogen adsorption is above 10 kJ mol−1 .

This study presents and analyses three plant configurations of the Ocean Thermal Energy Conversion (OTEC) technology. All the solutions are based on using the OTEC system to obtain hydrogen through an electrolyzer. The hydrogen is then compressed and stored. In the first and second layouts a Rankine cycle with ammonia and a mixture of water and ethanol is utilised respectively; in the third layout a Kalina cycle is considered. In each configuration the OTEC cycle is coupled with a polymer electrolyte membrane (PEM) electrolyzer and the compression and storage system. The water entering the electrolyzer is pre-heated to 80 ◦C by a solar collector. Energy exergy and exergo-economic studies were conducted to evaluate the cost of producing compressing and storing hydrogen. A parametric analysis examining the main design constraints was performed based on the temperature range of the condenser the mass flow ratio of hot and cold resource flows and the mass fraction. The maximum value of the overall exergy efficiency calculated is equal to 93.5% for the Kalina cycle and 0.524 €/kWh is the minimum cost of hydrogen production achieved. The results were compared with typical data from other hydrogen production systems.

Knowledge production activity is central within a technological innovation system. The number of patent ap plications is commonly used to evaluate this activity. However it is subject to bias and inaccurate evaluations can occur. This article proposes a multi-criteria framework based on seven complementary patent indicators taking into account the persistence commitment and coherence of knowledge production activities for a more comprehensive evaluation. We demonstrate the value of our proposal through a case study on hydrogen storage comparing patent data since 2000 about three technological solutions: physical chemical and adsorption technologies. Our framework clearly shows that physical hydrogen storage is the most advanced in terms of knowledge production despite not having the highest number of patent applications.