Instream generation using tethered kites in the carousel configuration

Abstract

In recent years, kites are beginning to be considered as viable alternatives to oshore wind turbines, due to the potential reduction in levelised cost of energy and the increase in exploitable resource due to versatility of kite based generators. This thesis focuses on the kite carousel design, which consists of a ground based vertical axis generator with a number of kites attached. The kites are flown in a pattern that induces motion in the generator and thus produces power. This method of energy harvesting allows substantial scaling of devices. Device output depends not only on the available ow and kite size, but is further influenced by the length of the kite tether, the radius of the carousel structure, and the number of kites attached.

Although kites have been studied extensively in recent years, there is no consensus on the optimum design and configuration of the carousel. The thesis presents a minimum order model of a kite carousel. This numerical model is used to indicate the driving principles of the carousel and the importance of flightpath design on output. The presented model can be applied to various ow conditions. However, due to the definition of dimensionless power used, there is a scaling dependency of the model outputs regarding the kite tether length. An alternative method of describing the swept area of the carousel, based on the swept area of the kite flightpath, is used to mitigate this and indicate device efficiency in power extraction.

The flightpath optimisation and parameter study illustrate this scaling dependency and highlight the effect of the carousel radius and tether length on the optimized flightpath. These results then inform a case study for a carousel placed in a representative tidal flow. The case study describes a device with 8 kites attached to a 5 m diameter carousel that produces 64 kW over a representative tidal cycle with a peak flow of 2.2 m/s.