Adaptation of wave power plants to regions with high tides

University dissertation from Uppsala : Acta Universitatis Upsaliensis

Abstract: The wave energy converter (WEC) developed at Uppsala University is based on the concept of a heaving point absorber with a linear generator placed on the seafloor. The translator inside the generator oscillates in a linear fashion and is connected via a steel wire to a point absorbing buoy. The power production from this device is optimal when the translator’s oscillations are centered with respect to the stator. However, due to the tides, the mean translator position may shift towards the upper or lower limits of the generator’s stroke length, thereby affecting the power production. This effect will be severe if the WEC operates in an area characterized by a high tidal range. The translator may be stuck at the top or rest at the bottom of the generator for a considerable amount of time daily.One of the solutions to this problem is to develop a compensator that is able to adjust the length of the connecting line. With an estimated weight of 10 tonnes of the connecting line and the translator, the use of a pocket wheel wound with steel chain was deemed suitable. Not being connected to an external power supply, the device needs a alternative local power supply to charge batteries that run the system. A hybrid system of solar photovoltaics (PV) and a small WEC was proposed to power the device and, based on the simulations for two different sea states, the hybrid system was found suitable for powering the device all year round. The experimental work carried out in the lab environment has shown that the compensator was able to lift the estimated load of the translator and to position the chain so that it follows the variations in the sea level from meteorological websites.The second part of the thesis is a study on the wave energy potential in the Nordic synchronous grid. A model for the allocation of wave farms for four energy scenarios was developed, linearly weighted to the intensity of the wave energy flux. As an extension to this study, a net load variability study for a highly or a fully renewable Nordic power system was conducted. It involved four different intermittent renewable energy (IRE) sources: solar PV, wind, tidal power, and wave. The study shows that an optimal combination of IRE sources to replace fossil fuels and nuclear energy is possible from the perspective of net load variability.