Search Results (8)

The high intermittency of offshore renewable energy presents a major challenge to the power grid’s secondary frequency control capability. Underwater Compressed Air Energy Storage (UWCAES), which uses flexible airbags for constant-pressure energy storage and release, is a key technology for smoothing grid fluctuations. Because the storage pressure in a UWCAES system is directly proportional to the water depth, deploying airbags at different depths allows for the flexible dispatch of compressed air at multiple pressure levels. Multi-level UWCAES (M-UWCAES) deploys airbags at different depths to provide compressed air at multiple pressure levels, significantly enhancing system flexibility. This paper proposes a turbine-side power tracking strategy for M-UWCAES based on adaptive fuzzy PID. A dynamic model of the turbine side is first established to elucidate the multi-stage energy storage and release mechanism. An adaptive fuzzy PID controller is then designed to adapt to the system’s multi-mode operational characteristics. Simulation results show that compared with conventional UWCAES, M-UWCAES exhibits smaller off-design deviations under low regulation demands, with partial-load exergy efficiency improved by 4.69–13.75%. The M-UWCAES system, utilizing adaptive fuzzy PID control, exhibits a faster power tracking response speed and effectively mitigates the overshoot caused by mode switching. Full article

Renewable energy is a prominent area of research within the energy sector, and the storage of renewable energy represents an efficient method for its utilization. There are various energy storage methods available, among which compressed air energy storage stands out due to its large capacity and cost-effective working medium. While land-based compressed air energy storage power stations have been constructed worldwide, their efficiency remains low. Underwater compressed air energy storage has the potential to significantly enhance efficiency, although no such device currently exists. This paper presents the design of an UWCA-FABESD utilizing five flexible air bags for underwater gas storage and discharge. Additionally, it introduces the working principle of the adiabatic underwater compressed air energy storage system and device. Furthermore, a small-scale physical model with similar functionality was designed and manufactured to simulate the charging process of the air bag in onshore charging and discharging tests as well as posture adjustment and lifting arrangement tests, along with underwater charging and discharging tests. These experiments validated the related functions of the designed underwater compressed air flexible bag energy storage device while proposing methods for its improvement. This research provides a new approach to underwater compressed air energy storage. Full article

An unmanned underwater vehicle (UUV) powered by a compressed air power system is proposed to address challenges for battery/motor-powered vehicles under high-speed navigation, long endurance, and high mobility. These vehicles actively utilize supercavitation drag reduction by the exhausted gas from the compressed air power system. MATLAB/Simulink and FLUENT are used to establish theoretical models of the compressed air power system and ventilation supercavitation. The relationship between system power and navigation resistance is examined with different air flows, along with a comparison of endurance of different power vehicles at various speeds. The issue of the endurance-enhancing effect of supercavitation at high speed is investigated. The results demonstrate that increasing the air flow leads to higher power and reduced navigation resistance, and there is a balance between them. Furthermore, compared to the battery-powered vehicles with equal energy storage capacity, the compressed air power system shows 210.08% to 458.20% longer endurance times at speeds of 30 kn to 60 kn. Similarly, considering equal energy storage mass, it achieves 42.02% to 148.96% longer endurance times at high speeds (30 kn to 60 kn). The integration of supercavitation and air-powered systems can greatly enhance the endurance and maneuverability of the vehicle at high speeds while ensuring a compact system structure. The investigations could offer valuable ideas for the development and application of compressed air power systems for UUV at 30 kn to 60 kn or higher maneuvering. Full article

Underwater compressed gas energy storage (UW-CGES) holds significant promise as a nascent and viable energy storage solution for a diverse range of coastal and offshore facilities. However, liquid accumulation in underwater gas pipelines poses a significant challenge, as it can lead to pipeline blockages and energy transmission interruptions and adversely impact pipeline operation. In this paper, experimental and Oil and Gas Assays (OLGA) simulation studies have been conducted on the formation process of slug flow in pipelines. Firstly, experiments are conducted to capture high-speed camera images of slug flow under various liquid accumulation volumes and inclination angles. Subsequently, an OLGA model is developed to verify the experimentally observed flow regime, pressure, and slugging speed. Therefore, the flow regime verification results exhibit substantial consistency, and pressure variations display uniform trends, with an average slugging velocity error of 6.42%. The results indicate that the formation of slug flow involves three distinct stages: slug flow growth, ejection, and backflow. By analyzing slug flow, it can gain insights into the relationship between pressure and slug flow formation, exposing the sensitivity of this phenomenon to pressure fluctuations. These results further enhance recognition of the operational status of UW-CGES pipelines and provide support for safe operation. Full article

Underwater compressed air energy storage (UCAES) is an advanced technology used in marine energy systems. Most components, such as turbines, compressors, and thermal energy storage (TES), can be deployed on offshore platforms or on land. However, underwater gas-storage devices, which are deployed in deep water, have specific characteristics. Flexible inflatables have become a viable alternative for underwater compressed air energy storage (UCAES) as air storage devices. Few studies have been conducted on the characteristics of partially inflated structures during the inflating and deflating processes. A tank experiment of a 1 m model of an underwater spherical airbag was performed to investigate the characteristics of the deformed shape, pressure, and volume of the stored compressed air. A finite element (FE) simulation of an airbag model with the same dimensions was established in Abaqus/Explicit. The simulation under shallow testing conditions was in good agreement with the experimental results. Furthermore, studies on the performance of a 4 m airbag prototype with different water depths are presented. The results indicated that the shape variation was only related to the volume (inflation ratio). The pressure varied approximately linearly with the inflation ratio during the quasi-static process from an empty shape to a zero-pressure shape. The operating depth had a slight effect on the deformation. Because the scaling factor influences the pressure difference of the surface at the same height proportion, the larger the dimensions of the airbag, the higher the pressure difference will be. Full article

As an emerging flexible-scale energy storage technology, underwater compressed gas energy storage (UW-CGES) is regarded as a promising energy storage option for offshore platforms, offshore renewable energy farms, islands, coastal cities, etc. Liquid accumulation often occurs in underwater gas transmission pipelines, which is a challenge to overcome. In this study, an experimental investigation is carried out on the pressure distribution characteristics of liquid accumulation flow in hilly terrain under the condition of Zero Net Liquid Flow. A slug flow pressure model with different inclination angles at four times is established and verified, and its error range is within ±20%. Analysis revealed that reduction and growth in pressure difference are related to the outflow of slug in an inclined pipe. A high-speed camera is used to capture the movement of liquid accumulation under Zero Net Liquid Flow (ZNLF) and record the associated dynamic parameters. By imaging the motion of liquid accumulation and detecting the pressure changes in the pipeline at various times, the pressure fluctuation in the pipeline at the slug flow cause is studied. Outcomes from this work can be leveraged to help further the development of underwater compressed gas energy storage technology. Full article

Underwater compressed air energy storage was developed from its terrestrial counterpart. It has also evolved to underwater compressed natural gas and hydrogen energy storage in recent years. UWCGES is a promising energy storage technology for the marine environment and subsequently of recent significant interest attention. However, it is still immature. In this study, the latest progress in both academic and industrial fields is summarized. Additionally, challenges facing this emerging technology are analyzed. The pros and cons of UWCGES are provided and are differentiated from the terrestrial variant. Technical, economic, environmental, and policy challenges are examined. In particular, the critical issues for developing artificial large and ultra-large underwater gas storage accumulators and effective underwater gas transportation are comprehensively analyzed. Finally, the demand for marine energy storage technology is briefly summarized, and the potential application scenarios and application modes of underwater compressed gas energy storage technology are prospected. This study aims to highlight the current state of the UWCGES sector and provide some guidance and reference for theoretical research and industrial development. Full article

The need for electrical energy storage technologies (EEST) in a future energy system, based on volatile renewable energy sources is widely accepted. The still open question is which technology should be used, in particular in such applications where the implementation of different storage technologies would be possible. In this study, eight different EEST were analysed. The comparative life cycle assessment focused on the storage of electrical excess energy from a renewable energy power plant. The considered EEST were lead-acid, lithium-ion, sodium-sulphur, vanadium redox flow and stationary second-life batteries. In addition, two power-to-gas plants storing synthetic natural gas and hydrogen in the gas grid and a new underwater compressed air energy storage were analysed. The material footprint was determined by calculating the raw material input RMI and the total material requirement TMR and the carbon footprint by calculating the global warming impact GWI. All indicators were normalised per energy fed-out based on a unified energy fed-in. The results show that the second-life battery has the lowest greenhouse gas (GHG) emissions and material use, followed by the lithium-ion battery and the underwater compressed air energy storage. Therefore, these three technologies are preferred options compared to the remaining five technologies with respect to the underlying assumptions of the study. The production phase accounts for the highest share of GHG emissions and material use for nearly all EEST. The results of a sensitivity analysis show that lifetime and storage capacity have a comparable high influence on the footprints. The GHG emissions and the material use of the power-to-gas technologies, the vanadium redox flow battery as well as the underwater compressed air energy storage decline strongly with increased storage capacity. Full article