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This paper reports on an energy/exergy analysis of a standalone solar-hydrogen system with a metal hydride (MH) system thermally managed using a phase change material (PCM). This is a self-contained thermal management arrangement that stores the heat released from the MH unit, when it is being charged and transfers it back to the MH while discharging hydrogen. The first and second laws of thermodynamics were used to develop a mathematical model in MATLAB to simulate this system and quality its performance from the energy and exergy viewpoints. The model was then applied on a passive standalone house, with ∼3.8 MWh/year electricity demand, located in southeast Australia. The exergy efficiencies of the solar PV, electrolyser, fuel cell and the whole solar hydrogen system were found to be 6.5%, 88%, 50.6%, and 3.74%, respectively. The paper also provides the detailed entropy generation and exergy analysis on the MH hydrogen storage unit together with its PCM-based thermal management arrangement. The results show that the annual entropy generation, exergy destruction and exergy efficiency of the MH hydrogen storage unit were 173 Wh/K, 51.5 kWh, and 98.8%, respectively. • Exergy analysis of phase change material used for metal hydride thermal management in solar hydrogen system. • The energy and exergy efficiencies of the solar PV are around 6.1% and 6.5%, respectively. • Energy and exergy of solar-hydrogen system were 3.48% and 3.74%, respectively. • Exergy efficiency of the MH thermal management using PCM was 98.8%. [ABSTRACT FROM AUTHOR]

• Metal hydride (MH) thermal management in a solar-hydrogen system was modelled. • A phase change material (PCM) was used for thermal management of MHs. • Low conductivity of PCMs was a major challenge for thermal management of MHs. • Using PCM offers an energy saving equivalent to about 15% of the total yearly hydrogen production. In this paper, a model of a metal hydride thermal management using phase change material in the context of a standalone solar-hydrogen system is proposed and investigated. The HOMER software is used to simulate the optimal system architecture and yearly power profiles of the electrolyser and fuel cell stacks used in a case study of a remote household in southeast Australia. A dynamic theoretical model of a phase change material arrangement for thermal management of the metal hydride hydrogen storage unit is then built in MATLAB environment to study the performance behaviour of the hydrogen storage system in this context. Based on the case used for this study, it was found that approximately equivalent to ~12% of total energy content of the hydrogen generated by the electrolyser can be saved annually by replacing an external energy thermal management system with the proposed phase change material thermal management solution. It was also found that the conductivity of phase change materials must be improved to a minimum of 1.5 W/mK, in order to make this thermal management arrangement more practical. [ABSTRACT FROM AUTHOR]

Trees play a vital role in urban cooling. The present study tested if key canopy characteristics related to tree shade could be used to predict the cooling potential across a range of urban surface materials. During the austral summer of 2018–2019, tree and canopy characteristics of 471 free-standing trees from 13 species were recorded across Greater Sydney, Australia. Stem girth and tree height, as well as leaf area index and ground-projected crown area was measured for every tree. Surface temperatures were recorded between noon (daylight saving time) and 3:00 p.m. under the canopy of each tree in the shade and in full sun to calculate the temperature differential between adjacent sunlit and shaded surfaces (∆Ts). The limited control over environmental parameters was addressed by using a large number of randomly selected trees and measurement points of surface temperatures. Analyses revealed that no systematic relationship existed among canopy characteristics and ∆Ts for any surface material. However, highly significant differences (p < 0.001) in ∆Ts existed among surface materials. The largest cooling potential of tree shade was found by shading bark mulch (∆Ts = −24.8 °C ± 7.1), followed by bare soil (∆Ts = −22.1 °C ± 5.5), bitumen (∆Ts = −20.9 °C ± 5.8), grass (∆Ts = −18.5 °C ± 4.8) and concrete pavers (∆Ts = −17.5 °C ± 6.0). The results indicate that surface material, but not the tree species, matters for shade cooling of common urban surfaces. Shading bark mulch, bare soil or bitumen will provide the largest reductions in surface temperature, which in turn results in effective mitigation of radiant heat. This refined understanding of the capacity of trees to reduce thermal loads in urban space can increase the effectiveness of urban cooling strategies. [ABSTRACT FROM AUTHOR]