OPTIMISATION OF TIDAL RANGE ELECTRICITY GENERATION AND ECONOMICS

Vandercruyssen, David and Aggidis, George (2026) OPTIMISATION OF TIDAL RANGE ELECTRICITY GENERATION AND ECONOMICS. PhD thesis, Lancaster University.

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Abstract

The purpose of this study is to improve knowledge and understanding of tidal range power by investigating the potential for generation and its economics. The approach used an existing model of electricity generation (Lancaster 0-D tidal model) to investigate optimal generation and financial return. The thesis examines the question of the feasibility of tidal range power and the issues that are commonly presented as barriers preventing deployment. Those barriers include economics (finance, scale, rate of construction and power generation), environment (climate change, habitat loss, pollution) and engineering (mechanical, civil and electrical).Two case study sites were selected for investigation using scenarios with multiple configurations of: - numbers and size of turbines - sluice ratios - generator ratings. The economic issues were partly addressed by developing a simple financial model for the capital cost of schemes (CAPEX). It was used to indicate how specific components within a scheme best contribute to the financial return of investment. It can also be used to compare schemes in different locations and rank them in order of profitability. A major environmental consideration is climate change; it is especially important as tidal range schemes are designed to have a functional life of at least 120-years. The climate change driven challenge of sea level rise (SLR) over the proposed operation life must be considered in both planning and operation. This study models tidal range power schemes so that they protect coastal habitats and communities by maintaining the existing tidal range. For the two sites studied, as sea level begins to rise, the annual electricity production (AEP) increases due to the greater water head in flood tides. As SLR continues, the AEP falls due to increased pumping required to achieve low tide levels. Initially, pumping can be performed by the turbines used as pumps (TaP). The TaPs are not sufficient for higher levels of SLR, so after about 40-years it may be necessary to install submersible pumps to effectively match the desired low tide limits. The disciplines within engineering run as a constant thread through this thesis, essential in design, deployment, operation, maintenance and decommissioning. The time taken to deploy a barrage is constrained by the civil engineering options. A preliminary analysis of precast concrete barrage designs was made, with both existing vertical units and my proposed horizontal units. The latter can be cast on shore and floated out in shallower water, the sloping sides reduce both ground bearing pressures and the volume of concrete needed. The times of high and low tide are predictable for any site even though the tidal range varies for each cycle. A simplified 0-D program has been proposed based on varying the start of generation relative to the time of the previous high or low tide. The aim is to analyse a whole year of individual tides and include an efficiency reduction for reverse flow generation. During the development a simple spreadsheet was produced for a period of 22-days from the start of 2024 to be used to check the program. This identified that the simple time base program was effective but that it was not sufficient for operational use; there were several periods of generating at negative price which need not happen during operation. Consequently, a modified model was proposed that weighted the flow according to price and so better reflect demand. The adjustment created a significant increase in financial return whilst the total generation reduced. The algorithm will be complex and there was not sufficient time to write a program during this study. It is hoped to continue this work in future. Finally, the methods of comparing costs of different energy generating technologies have been examined and a new metric developed. It overcomes some of the problems with the commonly used levelised cost of energy by comparing continuous generation over the longest lifespan of the technologies considered (120-years). For example, a tidal barrage is equivalent to two nuclear sites of 60-years operational life or four gas turbine stations with 30-year operational lives. The analysis shows how tidal range power is economically viable and would fit into the national power generation system. If the annual benefits of flood protection are included in the analysis, tidal range power becomes the cheapest of all grid scale renewable technologies.