Demand Led Tidal Lagoon Power and Hydrogen Energy Storage - Supervisory Control and Optimisation

Student thesis: Doctoral Thesis


Electrical energy generated from a tidal lagoon turbine system is intermittent leading to long periods of no power generation. A system consisting of electrolysers and compression produce hydrogen to storage, while fuel cells supplying power from that storage can bridge the intermittency to meet a continuous unpredictable power demand. This requires start-stop signals for the equipment as well a references to run at the required load.

Mixed Logical Dynamical Model Predictive Control (MLD MPC) uses a mathematical model of a system to predict actions required by the system using logical and continuous control. In this thesis MLD MPC is used at a supervisory level, in a novel manner, to optimise the start-stop of equipment in the hydrogen storage system, and provide continuous output references. It uses a novel implementation of the logical and continuous interaction within the MLD-MPC to set logical inputs to start and stop the hydrogen storage equipment first, while feedback into the controller from the equipment confirms that start or stop instruction has been carried and releases the continuous references to be tracked.

This thesis is the first demonstration of supervisory control of a tidal lagoon generation system to meet power demand using only hydrogen energy storage. In addition,a novel aspect of the physical system modelled allows the fuel cells to provide power to start the electrolysers making the tidal lagoon system independent of import from the power grid, and would facilitate private wire arrangements or be available for islanded systems.

This research demonstrates that MLD-MPC supervisory control of a hydrogen storage system optimises the tidal lagoon generated power to meet a continuous or dispatchable demand pattern. Alternatively, it shows the maximum power to the grid can be limited. It demonstrates the control can start and stop the equipment and track a required power demand closely. For the proposed Swansea Bay 320 MW tidal lagoon system the thesis shows an electrolyser system of 285 MW or 225 MW would suffice to produce enough hydrogen to meet an average continuous annual demand pattern of12.3 MW and for an ebb and flow tidal lagoon generation pattern. Using a 285 MW electrolyser system ebb only tidal lagoon generation supplied an average continuous demand pattern of 9.3 MW for 303 days before the hydrogen storage emptied, and for an ebb and flow pumped generation pattern 15.9 MW average was supplied continuous for a year. The thesis provides evidence that would be achieved with the fuel cells using1 % to 3 % of the hydrogen produced to support the electrolysers making the tidal lagoon independent of imported power or other energy storage. It is applicable to any tidal lagoon system, and could be applied to tidal stream systems. Despite the novel approach of hydrogen storage system use and control design it can be implemented in commercially available control software.
Date of Award2022
Original languageEnglish
SupervisorFan Zhang (Supervisor), Alan Guwy (Supervisor) & Jon Maddy (Supervisor)

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