Hydrogen Technologies vs. Battery Ones in the Green Energy Transition

This study evaluates the performance and feasibility of hybrid photovoltaic–hydrogen systems integrated with 4.2 MW PV installations, focusing on the interplay between electrolyzer capacity, energy storage, and hydrogen production. Key findings reveal that downsizing electrolyzers, such as using a 1 MW unit instead of a 2 MW model, increases operational efficiency by extending nominal power usage, though it reduces total hydrogen output by approximately 50%. Meanwhile, expanding energy storage systems show diminishing returns, with added capacity offering minimal gains in hydrogen production and raising economic concerns. The system’s performance is highly weather-dependent, with daily hydrogen production ranging from 26 kg on cloudy winter days to 375 kg during sunny summer conditions. Surplus energy export to the grid peaks at 3300 kWh during periods of high solar generation but is minimal otherwise. For economic and operational viability, the system design must prioritize directing a majority of PV energy to hydrogen production while minimizing grid export, requiring a minimum of 50% PV energy allocation to the hydrogen value chain. Cost analysis estimates a Levelized Cost of Hydrogen (LCOH) as low as €6/kg with an optimized configuration of a 2 MW electrolyzer and 2 MWh battery. Although high production costs challenge economic sustainability, careful component optimization and supportive policies can enable competitive hydrogen pricing and a positive net present value (NPV) over the system’s lifetime. Full article

Hydrogen (H2) offers a green medium for storing the excess from renewables production instead of dumping it, thus being crucial to decarbonisation efforts. Hydrogen also offers a storage medium for the grid’s cheap electricity to be used during grid peak demand or grid power cutoffs. Funded by the Scottish Government’s Emerging Energy Technologies, this paper presents the design and performance analysis of a hydrogen uninterruptible power supply (H2GEN) for Cygnas Solutions Ltd., which is intended to enable continuity of supply in the residential sector while eradicating the need for environmentally and health risky lead–acid batteries and diesel generator backup. This paper presents the design, optimal sizing and analysis of two H2Gen architectures, one powered by the grid alone and the other powered by both the grid and a renewable (PV) source. By developing a model of each architecture in the HOMER space and using residential location weather data, the home yearly load–demand profile, and the grid yearly power outages profile in the developed models, the optimal sizing of each H2Gen design was realised by minimising the costs while ensuring the H2Gen meets the home power demand during grid outages To enable HOMER to optimise its selection, the sizes, technical specifications and costs of all the market-available H2GEN components were added in the HOMER search space. Moreover, the developed models were also used in assessing the sensitivity of the simulation outputs to several changes in the modelled system design and settings. Using a residential home with frequent power outages in New Delhi, India as a case study, it was found that the optimal sizing of H2Gen Architecture 1 is comprised of a 2 kW electrolyser, a 0.2 kg type-I tank, and a 2 kW water-cooled fuel cell directly connected to the AC bus, offering an operational lifetime of 14.3 years. It was also found that the optimal sizing of Architecture 2 is comprised of a 1 kV PV utilised with the same 2 kW electrolyser, 0.2 kg type-I tank and 2 kW water-cooled fuel cell connected to the AC bus. While the second design was found to have a higher capital cost due to the added PV, it offered a more cost-effective and environmentally friendly architecture, which contributes to the ongoing energy transition. This paper further investigated the capacity expansion of each H2GEN architecture to meet higher load demands or increased grid power outages. From the analysis of the simulation results, it has been concluded that the most feasible and cost-effective H2GEN system expansion for meeting increased power demands or increased grid outages can be realised by using the developed models for optimally sizing the expanded H2Gen on a case-by-case basis because the increase in these profiles is highly time-dependent (for example, an increased load demand or increased grid outage in the morning can be met by the PV, while in the evening, it must be met by the H2GEN). Finally, this paper investigated the impact of other environmental variables, such as the temperature and relative humidity, on the H2GEN’s performance and provided further insights into increasing the overall system efficiency and cost benefit through utilising the H2GEN’s exhaust heat in the home space for heating/cooling and selling the electrolyser exhaust’s O₂ as a commodity. Full article

Internal combustion engines (ICEs) are one of the significant sources of wasted energy, with approximately 65% of their input energy being wasted and dissipated into the environment. Given their wide usage globally, it is necessary to find ways to recover their waste energies, addressing this inefficiency and reducing environmental pollution. While previous studies have explored various aspects of waste energy recovery, a comparative analysis of different bottoming configurations has been lacking. In this research, an extensive review of the existing literature was conducted by an exploration of four key bottoming cycles: the steam Rankine cycle (SRC), CO₂ supercritical Brayton cycle, inverse Brayton cycle (IBC), and air bottoming cycle. In addition, these four main bottoming systems are utilized for the waste energy recovery of natural gas-fired ICE with a capacity of 584 kW and an exhausted gas temperature of 493 °C. For the efficient waste heat recovery of residual exhausted gas and heat rejection stage of the main bottoming system, two thermoelectric generators are utilized. Then, the produced power in bottoming systems is sent to a proton exchange membrane electrolyzer for hydrogen production. A comprehensive 4E (energy, exergy, exergy-economic, and environmental) optimization is conducted to find the best main bottoming system for hydrogen production. Results showed that the SRC-based system has the highest exergy efficiency (21.93%), while the IBC-based system results in the lowest efficiency (13.72%), total cost rate (25.58 $/h), and unit cost of hydrogen production (59.91 $/GJ). This combined literature review and research article underscore the importance of finding an economically efficient bottoming cycle in the context of waste energy recovery and hydrogen production. Full article

Currently, large-volume type IV composite vessel tube trailers garner significant attention and development within the hydrogen energy storage and transportation industry due to their cost-effectiveness and practicality. This study aims to assess the static strength and sealing performance of the boss structure in order to optimize its design. Firstly, a model of the mouth structure of type IV vessels was constructed to analyze the stress distributions in the boss and liner. Subsequently, innovative boss and liner structures were developed based on the primary mouth structure to investigate the impact of geometric dimensions through finite element analysis. This study revealed that changes in geometrical dimensions led to significant alterations in the stresses of the plastic liner in comparison to metallic bosses. Building upon these findings, the structural safety and sealing performance of the boss and liner structure were further validated through finite element analysis. The outcomes of this research can serve as a reference for guiding the structural design of bosses and aiding in the development of hydrogen storage vessels. Full article