M. Grabbe – PhD Dissertation, Uppsala University, April, 2013
The kinetic energy present in tidal currents and other water courses has long been appreciated as a vast resource of renewable energy. The work presented in this doctoral thesis is devoted to both the characteristics of the hydro-kinetic resource and the technology for energy conversion. An assessment of the tidal energy resource in Norwegian waters has been carried out based on available data in pilot books. More than 100 sites have been identified as interesting with a total estimated theoretical resource—i.e. the kinetic energy in the undisturbed flow—in the range of 17 TWh. A second study was performed to analyse the velocity distributions presented by tidal currents, regulated rivers and unregulated rivers. The focus is on the possible degree of utilization (or capacity factor), the fraction of converted energy and the ratio of maximum to rated velocity, all of which are believed to be important characteristics of the resource affecting the economic viability of a hydro-kinetic energy converter.
The concept for hydro-kinetic energy conversion studied in this thesis comprises a vertical axis turbine coupled to a directly driven permanent magnet generator. One such cable wound laboratory generator has been constructed and an experimental setup for deployment in the river Dalälven has been finalized as part of this thesis work. It has been shown, through simulations and experiments, that the generator design at hand can meet the system requirements in the expected range of operation. Experience from winding the prototype generators suggests that improvements of the stator slot geometry can be implemented and, according to simulations, decrease the stator weight by 11% and decrease the load angle by 17%. The decrease in load angle opens the possibility to reduce the amount of permanent magnetic material in the design.