Abstract:
New Zealand is well known for its clean and green image, investment in alternative energy is required to retain this image. Locations such as Cook Strait and Kaipara Harbour contain many sites with sufficiently high currents to support tidal stream farms. So the suitability of the various possible locations around the country must be studied. For example, Kaipara Harbour may not be an ideal location for tidal farms due to the amount of sand in the region, causing problems for mountings and damaging turbines. Another Problem is the number of turbines that are able the be placed in the region, for example placing 200 turbine system in Kaipara Harbour leads to a significantly high drag force that may cause the current to be redirected around the tidal farm. Other strong current areas such as Karori Rip and Tory Channel may be better options. Computer simulations are used to model the effects that turbines have in a uniform flow, this provides an idea of the disruption of the flow in the channel if turbines are installed, therefore optimal spacing between turbines can be investigated. High currents are more prominent in shallow channels, and due to the limits on the strength of the blade material, turbines are limited to 15-20m in rotor blade diameter. Traditional single turbine configurations are expensive and limited to extracting energy near the bottom of the channel, therefore research is carried out in this thesis to determine the technical viability of systems of turbines placed in close proximity, leading to lower installation and interconnecting cost of tidal farms. Simple economic considerations will give an indication of the validity of tidal farms near Cook Strait, and the extent to which their installation will need to be subsidized.