A Feasibility Study of a Hybrid Power Generation System Using Offshore-wind Turbine and Tidal Turbine
In New Zealand, the government aims for 100% of electricity production to be from renewable sources and reduce greenhouse gas emissions by 30% from 2005 levels by 2030. Despite increasing energy demands, depleting fossil fuel resources, and pressure to reduce Greenhouse Gas emissions, reducing the cost electricity is still not fully utilized.
This thesis presents methods to target, optimise and design more practical hybrid systems of wind and tidal energies in large scale for connecting to national grid and in small scale for offgrid design, and overcome technical limitations of current methods.
Original contributions of this thesis to literature include novel developments and applications in six areas: i) a new off-grid design: define a method for using tidal energy for off-grid design and how to apply wind and tidal data into a microgrid system in an optimized offshore site;
ii) a new on-grid design: define a method for using tidal energy for on-grid design and how to apply wind and tidal data into a microgrid system in an optimized offshore site;
iii) Define a method that could be used to optimize wind generation using climate models for precise forecast of wind generation in different directions;
iv) Define a method that could be used to optimize tidal generation using climate models for precise forecast of tidal generation in different directions;
v) Define a method of foundation design of integrated wind and tidal structures in shallow water depths using monopile and spar buoy floating respectively in order to investigate acceptability of microgrid design in terms of structural modelling; and
vi) Compare how off-grid and on-grid designs can reduce the amount of emissions as an alternative of using fossil fuels.
The developed methods have been applied to two optimized sites after ensuring getting same coordinates from both python codes of moana project of MetOcean company and Goring model of NIWA.
Offgrid results confirms that using two wind and four tidal turbines (2W+4T) is the optimized design to produce higher electricity with lower cost. The model reduced the COE from 23 cent to 21 cent for Oban and is a clean replacement to current diesel station has pollution. In comparison to other scenarios, the proposed system can generate higher power, higher renewable fraction, lower pollutants and more economic. To ensure about results, a sensitivity analysis about efficiency of inverter and economical viability performed validated 2W+4T is the optimized scenario. For Ongrid design, Cook Strait is selected for providing electricity demand of node CPK0331 (Central Park) using EMI data and then proved using 36 wind turbines (36W) is the optimized design to produce higher electricity with lower cost. In comparison to other scenarios, the proposed system results higher renewable fraction in lower COE. To ensure about results, a sensitivity analysis about efficiency of inverter and economic viability was performed and validated that 36W is the optimized scenario. Depending on water height less and over 30m, two types of foundation in Cook Strait (monopile and spar buoy floating) evaluated after contacting NIWA and getting long/lat. Different load scenarios of wind and wave according to imposed to structures to find ULS (ultimate limit state) and calculating the required sizes for each foundation to tolerate against loads. Based on monopile design, diameter, thickness, and length of monopile can be 6, 0.083, and 60 meter respectively. In spar buoy floating foundation, the minimum diameter of the caisson and the embedment depth can be 6.9 and 22.07 meter respectively. The maximum load for both type of foundations occurs in extreme wind load scenario when wind and wave act in same direction.