Assessment of Offshore Wave Energy Resources in Taiwan Using Long-Term Dynamically Downscaled Winds from a Third-Generation Reanalysis Product

Shih-Chun Hsiao,Jiun-Huei Jang,Tzu-Yin Chang,Wei-Bo Chen,Lee-Yaw Lin,Han-Lun Wu,Chao-Tzuen Cheng

doi:10.3390/en14030653

Abstract

In this study, long-term wind fields during 1991–2010 from the Climate Forecast System Reanalysis (CFSR) were dynamically downscaled over Taiwan and its offshore islands at a 5 km horizontal resolution using the Weather Research and Forecasting (WRF) model. Simulations of the 10 m (above sea level) dynamically downscaled winds served as the atmospheric forcing for driving a fully coupled wave-circulation model. The sea states of the waters surrounding Taiwan during 1991–2010 were hindcasted to evaluate the offshore wave energy resources and optimal wave energy hotspots. This study reveals that the southeastern offshore waters of Taiwan and the Central Taiwan Strait exhibited the highest mean wave power density (WPD), exceeding 20 kW/m. The annual mean WPD, incidence of the hourly WPD greater than or equal to 4 kW/m, monthly variability index and coefficient of variation of the WPD indicated that the sea areas located between Green Island and Orchid Island (OH_1), southeast of Orchid Island (OH_2), south of the Hengchun Peninsula (OH_3), and north of the Penghu Islands (OH_4) were the optimal hotspots for deploying wave energy converters. The most energetic months were October for OH_1 and OH_2 and November for OH_3 and OH_4, while the wave power was weak from March to June for OH_1, OH_2 and OH_3 and in May for OH_4. The wave direction is prevailingly east-northeast for OH_1, OH_2 and OH_3 and nearly northeast for OH_4. These phenomena reveal that wave power in the waters offshore Taiwan is induced primarily by the northeast (winter) monsoon. The exploitable annual WPD was estimated to be 158.06, 182.89, 196.39 and 101.33 MWh/m for OH_1, OH_2, OH_3 and OH_4, respectively.

Highlights

Offshore winds and waves have the greatest energy potential among all types of renewable energy, as the oceans cover a majority of the Earth’s surface [1]
To confirm that the regional dynamically downscaled wind fields are superior to the global reanalysis fields in hindcasting wave parameters, hourly winds from the original Climate Forecast System Reanalysis (CFSR) and from CFSR_5km were employed as atmospheric boundary conditions for Scale Hydroscience Integrated System Model (SCHISM)-WWM-III to reproduce the significant wave height (SWH), peak wave periods and wave directions in the waters surrounding Taiwan in 2010
The validation results revealed that the hindcasting performance of SCHISM-WWM-III for the wave parameters, such as significant wave height (SWH), peak wave period and wave direction, by employing the winds from CFSR_5km was superior to those adopting the CFSR wind field

Summary

Introduction

Offshore winds and waves have the greatest energy potential among all types of renewable energy, as the oceans cover a majority of the Earth’s surface [1]. Wave energy is unique because it is the most concentrated form of renewable energy on Earth, with its power density being much higher than that of either wind or solar energy [2]; wave energy converters have been installed and operated in many countries for decades [3]. Even small ripples on the ocean surface allow the wind to transfer some of its energy to the waves, causing the waves to grow from wind interactions over long distances. Even when the wave power is relatively invariable and more predictable than wind or solar power [5], compared to other established renewable energy sources, e.g., wind power, hydropower and solar power, wave power generation is not a widely employed commercial technology

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Conclusion