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AUTHOR(S): Wilsnon Monteiro, António Sarmento, António Fernandes, Joaquim Fernandes
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KEYWORDS Wave Energy; Resources Characterization; Natural Caves; Statistical Analysis; Cape-Verde |
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ABSTRACT Using the time-series of significant wave height and the peak period between 1979 and 2009, generated by SOWFIA - Streamlining of Ocean Wave Farm Impact Assessment, some relevant statistical information about energy content available in ocean waves in Cape-Verde is obtained. The monthly and annual-average time-series of the average power are analysed and the confidence intervals for their values are defined. Considering all of the 31 years of data, the results show that the most energetic month, from the average power point of view is January (23.49 kW/m) and the least energetic month is July (15.04 kW/m). In fact, the monthly average power decays from January to July and increases from July to December (21.21 kW/m). The annual-average power for the 31 years of data exhibits a weak attenuation caused by data aggregation. However, using the moving average smoothing curve it is possible to note that, between 1999 and 2009, the values of annual-average power seem to stabilize around 18 kW/m. Using the appropriate Autoregressive Integrated Moving Average (ARIMA) model we verified that the future values of the annualaverage power tend to oscillate around the same level of average power (18 kW/m).The outliers present in time-series of annual average power were identified and their influence in the value of annual-average power was quantified. Removing outliers from the annual time-series of power caused a maximum relative attenuation in the values of the annual-average power between 1.85 and 13%. Through the Coefficient of Variation of Power (COVP), obtained by dividing the standard deviation of the power time-series by the average power, it is possible to conclude that the wave resource is stable, with COVP between 0.46 and 0.66. The values of the Monthly Variation Index (MVI), the maximum range of the monthly mean wave power relative to the yearly mean level, show that the resource is relatively stable, with MVI < 1.2. The present work calculates the deep water power available for the Natural Caves (NC) in Cape Verde Islands, through a rigorous analysis of the wave climate that excites them. The minimum sampling size and the corresponding numbers of days of measurements per month in order to quantifying the output power from NC are also estimated. The results show that the required number of days of measurements is lower in spring (March to May) and summer (June to August). This is due to the lower level dispersion of wave data for these seasons, in comparison with the rest of the months. |
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Cite this paper Wilsnon Monteiro, António Sarmento, António Fernandes, Joaquim Fernandes. (2017) Statistical Analysis of Wave Energy Resources Available for Conversion at Natural Caves of Cape-Verde Islands. International Journal of Renewable Energy Sources, 2, 1-18
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