Hybrid wave-wind offshore power for an islandresource, energy output and nearshore impact PhD

Abstract

The island of Tenerife, a UNESCO Biosphere Reserve in the Atlantic Ocean, aims to be energy self-sufficient in order to reduce its carbon footprint. To accomplish this goal it should develop the renewable sources, in particular wave and offshore wind energy. The first objectives of this Thesis are twofold; (i) to characterize the wave and offshore wind power distribution around the island and (ii) to determine which offshore area is best suited for their exploitation, taking into account the resource and other conditioning factors such as the bathymetry, distance to the coastline and ports, and offshore zoning. To carry out this research, hindcast wave and wind data obtained with numerical models are used alongside observations from meteorological stations. One area, in the vicinity of Puerto de la Cruz, is identified as having great potential for installing a hybrid floating wave-wind farm. Both resources are characterized for the area selected: the wave resource in terms of wave directions, significant wave heights and energy periods; the offshore wind resource in terms of directions and speeds in addition to the seasonality for the both resources. It is found that most of the wave resource is provided by N and NNW waves with significant wave heights between 1.5 m and 3.0 m and energy periods between 10 s and 14 s. It follows that the Wave Energy Converters deployed in the area should have maximum efficiency in those ranges. As for the offshore wind resource, most of the energy corresponds to NNE and NE winds with speeds between 9 and 14 ms¿1, which should be taken into account when selecting the offshore wind turbines. The second step is to analyse the energy that could be obtained from a hybrid wave-wind farm located in the aforementioned optimum area. Such a farm, consisting of offshore wind turbines and co-located Wave Energy Converters (WECs), would realise the synergies between wave and offshore wind energy. The cited hindcast database spanning 44 years are used, and the seasonal variability of the hybrid farm's output is investigated. It is found that the hybrid farm does constitute an excellent approach to satisfying the energy requirements of Tenerife, and that most of the wave and offshore wind energy will be produced in summer mainly because of the high occurrence of winds and waves in the ranges for which offshore wind turbines and WECs are most efficient. The third step is to analyse the impacts of wave exploitation on the nearshore wave climate of the island. For such assessment, two wave conditions, typical of winter and summer, and three values of the wave transmission coefficient of the Wave Energy Converters (WECs) are used. For each of these six cases, the neashore wave conditions in the lee of the farm are compared with the baseline scenario. The impact is characterized in terms of: wave height, power, energy period, directional spreading and energy dissipation due to bottom friction. We find that the impact is relevant, in particular in some of these cases, with the value of the wave transmission coefficient playing a significant role.