Introduction of the hybrid tidal system

Deng, Sheng 2017. Introduction of the hybrid tidal system. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

One of the major accepted operating challenges with marine turbines is the harsh operating conditions and the resulting difficulties incurred with maintenance and repair. This thesis initially investigates the conceptual conversion of the conventional tidal stream turbine system, with built-in generator, into a hydraulically driven system. This design allows the generator and gearbox to be relocated on-shore, for a better accessibility for maintenance and repair. This study shows that the proposed hydraulic system would have an overall efficient of 83%. However, the estimated high construction and installation costs, together with the potential for a catastrophic oil leak causing an environmental hazard, led to the conclusion that the proposal is currently infeasible. Tidal range energy is not a new concept and has been used over the centuries to generate energy. It has the potential to generate power on both ebb and flood tides, with the advantage of temporal predictability. This research investigates the potential of converting architected commercial docks into small-scale tidal energy, electrical generation systems. The electricity generated would be used locally, thereby limiting transmission losses. This research proposes a solution to convert a conceptual dock, into a tidal lagoon electrical generation site. The proposed “hybrid” system, incorporates a pumping facility, powered by a tidal stream turbine, which enables the head difference between the dock and the local tide, to be increased. A Matlab program simulates the pumping/storage system, and the results are compared with a storage-only system. Results show that there is an increase in power production and generation time, when using the hybrid system. Another advantage of the hybrid system is that it can be used as a power storage facility for peak demands. It is proposed that this methodology could be applied to other tidal energy sites, including docks, to supply energy to the national grids, not just locally. vi The results of the hybrid system show that the total power output generated can be increased by 2% compared with a similar tidal lagoon. However, this increase would vary at different sites, under different parameters such as the size of the reservoir, the number and the size of the tidal turbines installed, and the stream velocity. The simulation model was developed with the use of comprehensive real data from the Jiangxia Tidal Power Station, recorded over one year. A portion of this his data was initially used to further develop and refine the model. The rest of the data was used to validate the model. To facilitate this work, a Matlab programme was developed to help analyse the recorded data, to identify the key stages during the power generation, and to summarise the operating parameters and the power produced for any chosen period. The hybrid pumped/storage system was applied to two active commercial docks (Avonmouth, and Cardiff Docks), located in the Bristol Channel. These locations provide a significant potential to generate tidal renewable energy due to the large tidal range. Unfortunately, simulations revealed that 39% of the time, the tidal stream speed was below 1m/s during the randomly selected 16 consecutive days used for testing. This stream velocity is too low to effectively drive the large-scale tidal stream turbines which are used in the numerical model for the pumping operation. As a result of these findings, the simulations modelled on Avonmouth, and Cardiff Docks, were not based on the hybrid system, but merely operated as tidal lagoons – the pumping system was removed. Results are presented which demonstrate the power generating potential for these docks. However, in the real world, a commercial dock must allow for the arrival and departure of ships, a feature that will impact on the water storage capacity in the docks, and the potential for power generation. To explore the consequences of shipping, the model was re applied to Avonmouth, and Cardiff Docks, to incorporate the scheduled shipping for the same 16 day period, where the shipping information was downloaded from www.marinetraffic.com. Two scenarios are investigated. The vii first scenario is where the docks are operated to comply with the shipping schedule, with no regard to the effect on power generation. This requires the water level in the dock must be maintained to a depth required for the ship with the largest draught. The second scenario is where the ships are located, where possible, in the smallest dock, which is maintained at the required depth. This removes the requirement to maintain the water level in the largest dock, thereby allowing the head to be used to generate power. The results of these simulations are compared, and it is shown that both scenarios can be used to generate power, although, as expected, the second scenario generates more power. It is suggested that the simulation could be developed as a facility to influence the scheduling of ships, in order to minimise the effect on power generation.

Item Type:	Thesis (PhD)
Date Type:	Submission
Status:	Unpublished
Schools:	Engineering
Uncontrolled Keywords:	Tidal Energy; Tidal Lagoon; Pumped Storage; Dock.
Date of First Compliant Deposit:	3 May 2019
Last Modified:	04 Aug 2022 01:58
URI:	https://orca.cardiff.ac.uk/id/eprint/122135

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