Preliminary plan of underwater environmental monitoring in the offshore wind farm in the western sea of Taiwan

Abstract

The offshore wind energy is more economic than the otherwise renewable energy. Therefore, many countries have already owned the offshore wind farms or planned to develop in recent years. Taiwan is going to build the demonstration project including offshore wind turbines and meteorological masts in the western sea of Taiwan. Before installation of wind turbines, site selection and condition survey are request. However, monitoring of wind turbines and ambient environments are also needed to collect data for the operation and the maintenance in the offshore wind farms. We know that Taiwan is a high-risk area with frequent natural disasters, such as typhoons, earthquakes, and monsoon. While the foundation and infrastructure of wind farms are designed and manufactured by higher safety factors to reduce the damage, the environmental impact might increase as well. Generally, the meteorological masts are the main part of environmental monitoring in the offshore wind farms. According to the demonstration project of offshore wind farms in Taiwan, the meteorological masts need some instruments for ocean environmental observations, which are tidal levels, sea surface waves, sea currents, seawater temperatures, salinities, and densities. Most of specifications in those instruments are followed by the IEC International Standard 61400-12-1. Moreover, the demonstration project requests the developers, who are in charge of the meteorological masts have to provide a long term data of 5 years at least. Because those instruments need retrieved and calibrated every 6-12 months. For lower capital expense, we design a seabed-mounted junction box to connect all underwater instruments and reserved an extensive capability for a monitoring network in the future. Moreover, we also integrate more underwater instruments, such as hydrophone for underwater noise measurement and seismometer. Although most of the planned wind farms in Taiwan have avoided away the habitats of the Chinese White Dolphins (Sousa chinensis), the noise impacts are still concerned. Thus, the underwater noises include the piling noise, the shipping noises, the cable laying noises, and the wind turbine operation noises, all of which are highly emphasized in the strategy for environmental impact assessments and monitoring plans. The power supply for those instruments is designed to depend on the rechargeable batteries at the meteorological masts, so those subsystems are designed using low power consumptions. A fiber-optic cable is used for the power and data transmission between the junction box and the meteorological mast. All collected data would be preliminarily processed in the meteorological mast and then transmit via the wireless transmission system to the land station for the owners and end-users. In addition, an offsite back of archive data is planned as well.