/library/oar/handle/123456789/1182 2025-11-06T08:19:27Z /library/oar/handle/123456789/139293 Title: Using carbon dioxide for subsea long-duration energy storage Authors: Cutajar, Charise; Sant, Tonio; Briffa, Luke Jurgen Abstract: This paper investigates the operating benefits and limitations of utilizing carbon dioxide in hydro-pneumatic energy storage systems, a form of compressed gas energy storage technology, when the systems are deployed offshore. Allowing the carbon dioxide to transition into a two-phase fluid will improve the storage density for long-duration energy storage. A preliminary comparative study between an air-based and a carbon dioxide-based subsea hydro-pneumatic energy storage system is first presented. The analysis is based on thermodynamic calculations assuming ideal isothermal conditions to quantify the potential augmentation in energy storage capacity for a given volume of pressure containment when operating with carbon dioxide in lieu of air. This is followed by a transient thermal analysis of the carbon dioxide-based hydro-pneumatic energy storage system, taking into account the real scenario of a finite thermal resistance for heat exchange between the gas and the surrounding seawater. Results from numerical modelling revealed that the energy storage capacity of a carbon dioxide-based subsea hydro-pneumatic energy storage system operating under ideal isothermal conditions can be theoretically increased by a factor of 2.17 compared to an identical air-based solution. The numerical modelling revealed that, under real conditions under which transient effects resulting from a finite thermal resistance are accounted for, the achievable factor is lower, depending on the charging and discharging time, the initial temperature, and whether a polyethene liner for corrosion prevention is considered or not. 2024-01-01T00:00:00Z /library/oar/handle/123456789/136561 Title: Overcoming uncertainties associated with local thermal response functions in vertical ground heat exchangers Authors: Extremera-Jiménez, Alejandro J.; Casanova-Peláez, Pedro J.; Yousif, Charles; Cruz-Peragón, Fernando Abstract: The short-term performance of ground heat exchangers (GHEs) is crucial for the optimal design of ground-source heat pumps (GSHPs), enhancing their contribution to sustainable energy solutions. Local short-time thermal response functions, or shorttime g-functions (STGFs) derived from thermal response tests (TRTs), are of great interest for predicting the heat exchange due to their fast and simple applicability. The aim of this work is to perform a sensitivity analysis to assess the impact of thermal parameter variability and TRT operating conditions on the accuracy of the average fluid temperature (Tf ) predictions obtained through a local STGF. First, the uncertainties associated with the borehole thermal resistance (Rb), transmitted from the soil volumetric heat capacity (CS) or some models dependent on GHE characteristics, such as the Zeng model, were found to have a low impact in Tf resulting in long-term deviations of ±0.2 K. Second, several TRTs were carried out on the same borehole, changing input parameters such as the volumetric flow rate and heat injection rate, in order to obtain their corresponding STGF. Validation results showed that each Tf profile consistently aligned well with experimental data when applying intermittent heat rate pulses (being the most unfavorable scenario), implying deviations of ±0.2 K, despite the variabilities in soil conductivity (λS), soil volumetric heat capacity (CS), and borehole thermal resistance (Rb). 2025-01-01T00:00:00Z /library/oar/handle/123456789/133924 Title: Field measurement on the wind and thermal microenvironment of distributed PV array Authors: Wang, Jiawei; Jiang, Fujian; Lin, Xiaowen; Yousif, Charles; Ji, Wenhui; Yuan, Yanping; Zhou, Jinzhi Abstract: The wind and thermal microenvironment around PV arrays play an important role on their structural safety and power output. Most existing research predominantly focuses on numerical simulation methods, which usually involve various idealized assumptions that may lead to distortions in the simulation results. This study employs field tests to investigate the wind and thermal microenvironment of distributed PV array in a high-altitude cold region, which has higher wind speeds, lower atmospheric pressure and colder temperatures. The experiment compared the roof microenvironment with and without the PV arrays, and analyzed the wind speed, roof and PV panel temperatures and wind loads. The experimental results indicated that the installation of PV array significantly alters the wind environment and convective heat transfer on the roof, reducing the surface temperature of the roof, decreasing radiation and convective heat transfer and improving energy efficiency and sustainability. The convective heat transfer intensity at the front of the PV array reached 36.19 W/(m2·°C) at 15:00, which is twice the convective heat transfer coefficient of the unoccupied roof. The surface temperature of the PV panels reached its peak of 49.47 °C around 13:30. The wind load fluctuations on the front side of the PV panels were found to be significant, especially in the first row of panels, which calls for careful design and installation methods to ensure the structural integrity and safe operation of distributed PV array. 2025-01-01T00:00:00Z /library/oar/handle/123456789/130753 Title: Islanded offshore hydrogen production plant with integrated energy storage for Maltese waters - hydrogeneration Authors: Pirotti, Oleksii; Scicluna, Diane; Farrugia, Robert N.; Sant, Tonio; Buhagiar, Daniel Abstract: Project HydroGenEration investigates co location of offshore wind power, Hydro Pneumatic Energy Storage (HPES) with a Hydrogen (H 2 ) production unit (HPU) and its storage system for use as a fuel by seagoing vessels, thus helping decarbonise the maritime transport sector. Wind power plants generate green, yet intermittent electricity and can supply an offshore H2 production unit; but the latter would benefit from electrical power stabilisation. Energy storage decouples the electrical demand from the supply, thus smoothening variability. This R&I project investigates the synergies and performance of an offshore green hydrogen production concept system operating under Central Mediterranean wind conditions. 2024-01-01T00:00:00Z