Pub Date : 2019-07-01DOI: 10.1109/OSES.2019.8867241
Weiqing Xu, S. Garvey, T. Ren, Y. Hu
Underwater Compressed Air Energy Storage takes advantage of the hydrostatic pressure in deep water to provide a means of storing large amounts of pressurized air without expending very large sums of money on pressure containments. A key attractive feature of all underwater storage of pressurised air is that the containment may be largely isobaric (i.e. the pressure of the stored air remains relatively constant irrespective of the level of fill). One of the common issues for isobaric containments is air dissolution into water. The dissolution is controlled by the concentration of the air in the water and Henry's law can be applied to determine the steady-state concentration of dissolved air in seawater. The charge/discharge process is clearly dynamic. In dynamic processes, steady state is never reached. This paper examines whether the dynamic effects may be useful. Experiments are performed to investigate air dissolution in a water tank. The results reveal that the mass of the air dissolved in water in first 0.1s accounts for 97.5% of total mass determined by Henry's law. This means time of air dissolution is in the order of 0.1s. UWCAES systems are often used for long duration energy storage in the order of hours. The time of air dissolution is short enough to cause air loss in UWCAES systems.
{"title":"Dynamics of dissolution for underwater compressed air energy storage","authors":"Weiqing Xu, S. Garvey, T. Ren, Y. Hu","doi":"10.1109/OSES.2019.8867241","DOIUrl":"https://doi.org/10.1109/OSES.2019.8867241","url":null,"abstract":"Underwater Compressed Air Energy Storage takes advantage of the hydrostatic pressure in deep water to provide a means of storing large amounts of pressurized air without expending very large sums of money on pressure containments. A key attractive feature of all underwater storage of pressurised air is that the containment may be largely isobaric (i.e. the pressure of the stored air remains relatively constant irrespective of the level of fill). One of the common issues for isobaric containments is air dissolution into water. The dissolution is controlled by the concentration of the air in the water and Henry's law can be applied to determine the steady-state concentration of dissolved air in seawater. The charge/discharge process is clearly dynamic. In dynamic processes, steady state is never reached. This paper examines whether the dynamic effects may be useful. Experiments are performed to investigate air dissolution in a water tank. The results reveal that the mass of the air dissolved in water in first 0.1s accounts for 97.5% of total mass determined by Henry's law. This means time of air dissolution is in the order of 0.1s. UWCAES systems are often used for long duration energy storage in the order of hours. The time of air dissolution is short enough to cause air loss in UWCAES systems.","PeriodicalId":416860,"journal":{"name":"2019 Offshore Energy and Storage Summit (OSES)","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116825477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-01DOI: 10.1109/OSES.2019.8867352
Robert Mecrow, S. Garvey
Heave plates are commonly employed as an effective and sustainable method to dampen unwanted oscillations of floating offshore structures caused by wave action. Such motion in the case of offshore floating wind turbines (OFWT) can reduce aerodynamic performance and increase fatigue loading. While the performance of flat heave plates is well documented, there is a lack of research assessing plates of conical shape. Thus, in the present study, the performance of conically shaped heave plates is assessed with reference to OFWT. Experiments consisting of forced oscillations of scale models were conducted in a large water tank at a range of frequencies and amplitudes relevant to OFWT. Plate added mass and damping properties were calculated using a frequency independent extension of the Morison equation. Conical plates were found to have improved performance over their flat counterparts. A conical plate of incline angle 56.8° exhibited an improvement on flat plate damping and added mass of approximately 45% and 94% respectively. Increasing conical incline angle was observed to increase plate added mass while having little effect on damping. The extended model's performance was a significant improvement on the standard Morison equation for all amplitudes investigated.
{"title":"Hydrodynamic Performance of Conical Shaped Heave Plates","authors":"Robert Mecrow, S. Garvey","doi":"10.1109/OSES.2019.8867352","DOIUrl":"https://doi.org/10.1109/OSES.2019.8867352","url":null,"abstract":"Heave plates are commonly employed as an effective and sustainable method to dampen unwanted oscillations of floating offshore structures caused by wave action. Such motion in the case of offshore floating wind turbines (OFWT) can reduce aerodynamic performance and increase fatigue loading. While the performance of flat heave plates is well documented, there is a lack of research assessing plates of conical shape. Thus, in the present study, the performance of conically shaped heave plates is assessed with reference to OFWT. Experiments consisting of forced oscillations of scale models were conducted in a large water tank at a range of frequencies and amplitudes relevant to OFWT. Plate added mass and damping properties were calculated using a frequency independent extension of the Morison equation. Conical plates were found to have improved performance over their flat counterparts. A conical plate of incline angle 56.8° exhibited an improvement on flat plate damping and added mass of approximately 45% and 94% respectively. Increasing conical incline angle was observed to increase plate added mass while having little effect on damping. The extended model's performance was a significant improvement on the standard Morison equation for all amplitudes investigated.","PeriodicalId":416860,"journal":{"name":"2019 Offshore Energy and Storage Summit (OSES)","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115847376","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-01DOI: 10.1109/OSES.2019.8867345
A. Slocum, J. Kluger, Sébastien Mannai
This paper investigates the potential for combining energy harvesting and damping systems as a means for stabilizing floating offshore wind turbines while increasing the total amount of power generated. Ever taller wind turbine towers are needed to accommodate ever larger rotor diameters, which for floating offshore turbines would normally necessitate ever deeper draft marine structures, such as spar buoys, to provide required stability. Damping structures, some of which have energy harvesting mechanisms, have been proposed and shown to be effective for floating turbines, but face the problem of transforming low frequency variable amplitude motion into steady power output. Here the idea of a piston pump in the form of a moving float mechanism is introduced to pump water out of a temporary storage chamber located at the bottom of a floating platform structure. Water flowing down the floating structure through a power turbine empties into the chamber. The entire structure might ideally now only depend on a single anchor line projecting from its center bottom to the seafloor, thereby also reducing the cost of moorings.
{"title":"Energy Harvesting and Storage System Stabilized Offshore Wind Turbines","authors":"A. Slocum, J. Kluger, Sébastien Mannai","doi":"10.1109/OSES.2019.8867345","DOIUrl":"https://doi.org/10.1109/OSES.2019.8867345","url":null,"abstract":"This paper investigates the potential for combining energy harvesting and damping systems as a means for stabilizing floating offshore wind turbines while increasing the total amount of power generated. Ever taller wind turbine towers are needed to accommodate ever larger rotor diameters, which for floating offshore turbines would normally necessitate ever deeper draft marine structures, such as spar buoys, to provide required stability. Damping structures, some of which have energy harvesting mechanisms, have been proposed and shown to be effective for floating turbines, but face the problem of transforming low frequency variable amplitude motion into steady power output. Here the idea of a piston pump in the form of a moving float mechanism is introduced to pump water out of a temporary storage chamber located at the bottom of a floating platform structure. Water flowing down the floating structure through a power turbine empties into the chamber. The entire structure might ideally now only depend on a single anchor line projecting from its center bottom to the seafloor, thereby also reducing the cost of moorings.","PeriodicalId":416860,"journal":{"name":"2019 Offshore Energy and Storage Summit (OSES)","volume":"105 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123288930","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-01DOI: 10.1109/OSES.2019.8867353
Daniel Chidiebere Onwuchekwa
This project is primarily focused on numerical analysis of an innovative technique that significantly improves the harvesting of energy from underwater compressed air energy storage (CAES) systems. The underwater CAES system stores compressed air at constant pressure in Energy Bags anchored at the bottom of the water body (1). This project presents the Buoyancy Engine, a renewable energy concept which generates short term electrical power sufficient to produce additional heat energy required for the expansion of the compressed air. The short term electrical energy is harvested and utilised to generate an electrical arc which is used to heat up charged molten salt to over 500°C (2), for a more efficient, controlled and extended electricity generation period. Molten salt energy storage systems have been known to produce electricity for 15 hours from only stored energy (3). This work shows the results of numerical investigations of the net buoyancy acting on ascending energy bags and the techniques for converting it to useful energy for the air expansion stage.
{"title":"Offshore Renewable Energy Storage: CAES with a Buoyancy Engine","authors":"Daniel Chidiebere Onwuchekwa","doi":"10.1109/OSES.2019.8867353","DOIUrl":"https://doi.org/10.1109/OSES.2019.8867353","url":null,"abstract":"This project is primarily focused on numerical analysis of an innovative technique that significantly improves the harvesting of energy from underwater compressed air energy storage (CAES) systems. The underwater CAES system stores compressed air at constant pressure in Energy Bags anchored at the bottom of the water body (1). This project presents the Buoyancy Engine, a renewable energy concept which generates short term electrical power sufficient to produce additional heat energy required for the expansion of the compressed air. The short term electrical energy is harvested and utilised to generate an electrical arc which is used to heat up charged molten salt to over 500°C (2), for a more efficient, controlled and extended electricity generation period. Molten salt energy storage systems have been known to produce electricity for 15 hours from only stored energy (3). This work shows the results of numerical investigations of the net buoyancy acting on ascending energy bags and the techniques for converting it to useful energy for the air expansion stage.","PeriodicalId":416860,"journal":{"name":"2019 Offshore Energy and Storage Summit (OSES)","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129384646","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-01DOI: 10.1109/OSES.2019.8867343
A. Jarquin-Laguna, F. Greco
The integration of renewable energy sources to power seawater desalination is crucial to mitigate CO2 emissions and to face the increasing challenges that are stressing fresh water resources depletion. In particular wind energy is one of the most cost-effective forms of renewable energy with a high potential to reduce the seawater desalination”s environmental impact. While most applications are aimed at using conventional wind technologies to produce the electricity required by the desalination processes, wind turbines with hydraulic transmission can bring new opportunities to avoid the multiple energy conversion steps and make fresh water production from wind energy more simple and cost-effective. This paper elaborates on two potential configurations, numerical modelling and possible control strategies which are able to directly combine a horizontal axis wind turbine rotor, a hydraulic transmission and a seawater reverse osmosis (SWRO) desalination unit. The integration of an ideal pressure exchanger as energy recovery devices (ERD) to increase the operating efficiency of the SWRO unit is analysed. Results are shown for the most relevant operating conditions of the integrated system in terms of wind speeds, pressures, brine salinity and fresh water productions. Intermediate results are also shown for the dynamic analysis and simulation of the wind powered direct-driven SWRO system subject to turbulent wind speed conditions.
{"title":"Integration of Hydraulic Wind Turbines for Seawater Reverse Osmosis Desalination","authors":"A. Jarquin-Laguna, F. Greco","doi":"10.1109/OSES.2019.8867343","DOIUrl":"https://doi.org/10.1109/OSES.2019.8867343","url":null,"abstract":"The integration of renewable energy sources to power seawater desalination is crucial to mitigate CO2 emissions and to face the increasing challenges that are stressing fresh water resources depletion. In particular wind energy is one of the most cost-effective forms of renewable energy with a high potential to reduce the seawater desalination”s environmental impact. While most applications are aimed at using conventional wind technologies to produce the electricity required by the desalination processes, wind turbines with hydraulic transmission can bring new opportunities to avoid the multiple energy conversion steps and make fresh water production from wind energy more simple and cost-effective. This paper elaborates on two potential configurations, numerical modelling and possible control strategies which are able to directly combine a horizontal axis wind turbine rotor, a hydraulic transmission and a seawater reverse osmosis (SWRO) desalination unit. The integration of an ideal pressure exchanger as energy recovery devices (ERD) to increase the operating efficiency of the SWRO unit is analysed. Results are shown for the most relevant operating conditions of the integrated system in terms of wind speeds, pressures, brine salinity and fresh water productions. Intermediate results are also shown for the dynamic analysis and simulation of the wind powered direct-driven SWRO system subject to turbulent wind speed conditions.","PeriodicalId":416860,"journal":{"name":"2019 Offshore Energy and Storage Summit (OSES)","volume":"79 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126326983","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-01DOI: 10.1109/OSES.2019.8867347
A. Hillis, A. Plummer, X. Zeng, J. Chapman
A simulation study is conducted to assess the feasibility of a Wave Energy Converter Power Electronic Converter architecture to achieve a four quadrant torque demand resulting from an active control strategy. The system consists of four induction generators controlled by three phase inverters, a DC bus with short term energy storage provided by supercapacitors and batteries, and an active rectifier to control the DC bus voltage and provide AC power to the grid. The components are realistically modelled and it is shown that the torque and speed requirements of the active control strategy can be achieved and that the electrical energy storage can provide required reactive power on a wave-by-wave time scale and longer term energy supply during a lull in wave excitation. The WaveSub WEC is used as a target device in order to make a meaningful study with realistic inputs. However the architecture of the PEC system is applicable to any device with a bi-directional rotary PTO requiring four-quadrant active control at the generators. Furthermore the PEC architecture and simulation model are readily expandable to arrays of wave energy converters.
{"title":"Simulation of a power electronic conversion system with short-term energy storage for actively controlled wave energy converters","authors":"A. Hillis, A. Plummer, X. Zeng, J. Chapman","doi":"10.1109/OSES.2019.8867347","DOIUrl":"https://doi.org/10.1109/OSES.2019.8867347","url":null,"abstract":"A simulation study is conducted to assess the feasibility of a Wave Energy Converter Power Electronic Converter architecture to achieve a four quadrant torque demand resulting from an active control strategy. The system consists of four induction generators controlled by three phase inverters, a DC bus with short term energy storage provided by supercapacitors and batteries, and an active rectifier to control the DC bus voltage and provide AC power to the grid. The components are realistically modelled and it is shown that the torque and speed requirements of the active control strategy can be achieved and that the electrical energy storage can provide required reactive power on a wave-by-wave time scale and longer term energy supply during a lull in wave excitation. The WaveSub WEC is used as a target device in order to make a meaningful study with realistic inputs. However the architecture of the PEC system is applicable to any device with a bi-directional rotary PTO requiring four-quadrant active control at the generators. Furthermore the PEC architecture and simulation model are readily expandable to arrays of wave energy converters.","PeriodicalId":416860,"journal":{"name":"2019 Offshore Energy and Storage Summit (OSES)","volume":"779 ","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133848410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-01DOI: 10.1109/OSES.2019.8867115
T. Sant, R. Farrugia, D. Buhagiar
Coupling energy storage to floating wind turbines will facilitate the integration of large floating wind farms into electricity grids. This paper deals with a hydro-pneumatic energy storage concept integrated in a floating offshore wind turbine in order to stabilize the intermittent power output from the turbine. The energy storage concept includes two pressure vessel bundles, one installed on the seabed and the other integrated in the floating spar supporting the turbine itself. The present study investigates the potential reductions in steel requirements for the storage system by introducing high strength wire winding around the cylindrical pressure vessels. The study is based on a storage system integrated in a spar supporting a 6 MW FOWT. A new mathematical approach for sizing the pressure vessels, determining the concrete requirements for ballasting the spar-type floater and anchoring the pressure vessels on the seabed is presented. A parametric analysis is then presented to examine the impact of the yield strength and diameter of the wound wire on the steel and concrete requirements for the energy storage system. It is shown that while circumferential wire winding brings about considerable reduction in the overall steel mass, the concrete requirements increase. Yet the increase in concrete required is not significant and, given that concrete cost is much lower than that of steel, it is expected that the net impact of wire winding would still result in reduced cost for the storage system.
{"title":"On the Use of Wire-wound Pressure Vessels for a Hydro-Pneumatic Energy Storage Concept Integrated in Floating Wind Turbines","authors":"T. Sant, R. Farrugia, D. Buhagiar","doi":"10.1109/OSES.2019.8867115","DOIUrl":"https://doi.org/10.1109/OSES.2019.8867115","url":null,"abstract":"Coupling energy storage to floating wind turbines will facilitate the integration of large floating wind farms into electricity grids. This paper deals with a hydro-pneumatic energy storage concept integrated in a floating offshore wind turbine in order to stabilize the intermittent power output from the turbine. The energy storage concept includes two pressure vessel bundles, one installed on the seabed and the other integrated in the floating spar supporting the turbine itself. The present study investigates the potential reductions in steel requirements for the storage system by introducing high strength wire winding around the cylindrical pressure vessels. The study is based on a storage system integrated in a spar supporting a 6 MW FOWT. A new mathematical approach for sizing the pressure vessels, determining the concrete requirements for ballasting the spar-type floater and anchoring the pressure vessels on the seabed is presented. A parametric analysis is then presented to examine the impact of the yield strength and diameter of the wound wire on the steel and concrete requirements for the energy storage system. It is shown that while circumferential wire winding brings about considerable reduction in the overall steel mass, the concrete requirements increase. Yet the increase in concrete required is not significant and, given that concrete cost is much lower than that of steel, it is expected that the net impact of wire winding would still result in reduced cost for the storage system.","PeriodicalId":416860,"journal":{"name":"2019 Offshore Energy and Storage Summit (OSES)","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127675452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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