Fiber to the deep ocean

Abstract

This research project is set up together with Bluerise B.V. and the Technical University of Delft. The project is initiated as a pre-research for a future Ecopark, located next to the international airport of Curacao. The Ecopark is an innovative design thought of by Curacao Airport Holding (CAH). The Ecopark will consist of an ocean thermal energy conversion plant (OTEC) and a sea water air-conditioning plant (SWAC). Because of the high costs of air-conditioning and energy on the island, cheap green energy solutions are very welcome. To make sure that the OTEC and SWAC plant perform as expected, a detailed temperature profile over the whole water depth is essential. If the water is too cold at the top layers of the ocean and/or too warm at the seabed, the plant will not reach its full potential. The purpose of the research project is to deliver a design and installation method of an appropriate Distributed Temperature Sensing (DTS) system. This measurement system provides near-real time and high resolution temperature data. The data is obtained by installing a fiber optic cable 7 km offshore at the north coast of Curacao at a depth of 1 km. A focus has been put on the technical, economic and political aspects of installing a DTS system in deep water and on land. With the help of a geographical-, cultural-, stakeholder- and system analysis important background data and information will be considered and processed. The optimal configuration is the configuration with a subsurface buoy, where the computer is located on shore. This configuration has some technical challenges, which are analysed. Several alternatives of the different components are developed. A preliminary design is chosen through a multi criteria analysis. There is chosen for a mooring line in which the fiber optic cable is integrated, this combination of two cables will be called the DTS cable. The DTS cable is suspended in a vertical line spanning over 950m water, with the use of a submerged buoy and dead weight anchor combination. An Ultima-L DTS computer will send a signal from the shore through 7km of the cable to the anchor location and then upward for 950m to the submerged buoy. Along the whole length of the cable the signal will be reflected, which will be analysed by the DTS computer. The data will be saved in an online shared file, enabling the data to be read in the Netherlands. The wind- and wave loads can be considered as rough at the north side of the island. These two components and the current profile are of major importance for the design of the DTS system. The technical challenges of the project depend on the choice of equipment used in the design, the installation procedures and the type of shore landing of the DTS cable. The DTS cable has a limited tensile strength and in combination with the extreme water depth narrow margins have to be implemented to realize the design. This limitation determines the size of the anchor and of the buoy, which will have a profound impact on the quality of the data generated by the DTS system. For the installation procedures a research vessel named the Chapman, a smaller RIB and divers are necessary. The Chapman will install the buoy, the anchor and the DTS cable. With this procedure, the biggest risk in the project arises. The risk during the installation method described in this report is the entanglement of the different cables, which still needs further research. The success of the project depends on the cooperation with the stakeholders. The permit approval of Maritime Authority Curacao (MAC) and the approval of CAH to build on their ground are the most important aspects of the stakeholder analysis. Economic aspects of the design are closely linked to the technical solutions, to the technical challenges, and to the measurement accuracy required by the client Bluerise B.V.. A comparison has been made between the accuracy of the DTS system measurements and the costs. These trade-off result in the definitive design that consists of a subsurface buoy, a dead weight anchor and a computer on land. The result is presented to the client Bluerise B.V.