This paper provides a summarized status update ofthe Lysekil wave power project. The Lysekil project is coordinatedby the Div. of Electricity, Uppsala University since 2002, with theobjective to develop full-scale wave power converters (WEC). Theconcept is based on a linear synchronous generator (anchored tothe seabed) driven by a heaving point absorber. This WEC has nogearbox or other mechanical or hydraulic conversion systems,resulting in a simpler and robust power plant. Since 2006, 12 suchWECs have been build and tested at the research site located atthe west coast of Sweden. The last update includes a new andextended project permit, deployment of a new marine substation,tests of several concepts of heaving buoys, grid connection,improved measuring station, improved modelling of wave powerfarms, implementation of remote operated vehicles forunderwater cable connection, and comprehensive environmentalmonitoring studies.

To make wave power a viable energy source, large clusters of wave energy converters should be deployed. For most of the farms the output power of the WECs should be aggregated in a marine substation and then transmitted to the grid. The need for cost effective underwater cable connection operations is one of the main issues in offshore operations. Underwater connections can be conducted with wet- or dry-mateable connectors, performed by divers or ROVs. Although there are existing solutions used by the oil and gas industry that could be employed, the capital expenditure needed is not compatible with the offshore renewable energy industry.

The objective of this research is to decrease costs and minimize working hazards associated with sub-sea work when performing these underwater electrical connections. This article presents a solution using small ROV’s instead of divers to execute the task. The main idea is to perform the connection underwater, but using dry-mateable connectors. A solution to make this possible is to install air pockets at the substation enclosing the connectors. These boxes are meant to be filled with air and hence create a dry environment in which to perform the connections. This is achieved with help of two tools. First a docking system allows the operator to fix the ROV at the substation before doing the connection. Then a gripper tool added to the ROV grasps the cable and connects it to the substation in the air pocket. The procedure and design of this low-cost solution are described, and the different prototypes that have been tested for offshore operation are also shown.

The history of underwater electrical connectors is relativelynew: In 1858, the first transatlantic communication cable was created. Sincethen, the need for subsea electrical connectors has been growing very fastin the offshore industry. Today numerous companies offer a large choiceof underwater connectors and assemblies, and it can be intricate to distinguish the different technologies employed for each of them. However theuse, deployment, maintenance, and lifetime of any subsea equipment, froma simple sonar to a wave energy converter, relies on its connectors. Hencethe design of an underwater electrical connector is to be carefully lookedat, and especially for tailor-made applications that have more specific requirements. To produce a good connector, it is necessary to account for thermal, electrical, and mechanical properties, as well as to determine thebest materials that should be used for the application. Finally, connector issues go hand in hand with the deployment and operation of any electrical equipment, and it is of interest to review the different techniques for cable connection, as well as the challenges related to cable layout. Those challenges can be of different nature, but they should all be taken into account for any subsea connection.

Ocean renewable technologies have been rapidly developing over the past years. However, current high installation, operation, maintenance, and decommissioning costs are hindering these offshore technologies to reach a commercialization stage. In this paper we focus on the use of divers and remotely-operated vehicles during the installation and monitoring phase of wave energy converters. Methods and results are based on the wave energy converter system developed by Uppsala University, and our experience in offshore deployments obtained during the past eleven years. The complexity of underwater operations, carried out by either divers or remotely-operated vehicles, is emphasized. Three methods for the deployment of wave energy converters are economically and technically analyzed and compared: one using divers alone, a fully-automated approach using remotely-operated vehicles, and an intermediate approach, involving both divers and underwater vehicles. The monitoring of wave energy converters by robots is also studied, both in terms of costs and technical challenges. The results show that choosing an autonomous deployment method is more advantageous than a diver-assisted method in terms of operational time, but that numerous factors prevent the wide application of robotized operations. Technical solutions are presented to enable the use of remotely-operated vehicles instead of divers in ocean renewable technology operations. Economically, it is more efficient to use divers than autonomous vehicles for the deployment of six or fewer wave energy converters. From seven devices, remotely-operated vehicles become advantageous.

To make wave power a viable energy source, large clusters of wave energy converters (WECs) will be deployed into large farms. For most of these farms, the output power of the WECs will be aggregated in a marine substation and then transmitted to the grid. The need for cost effective underwater connection operations is one of the main challenges with this kind of offshore installation. Our research is related to underwater connection with help of Observation Class Remotely Operated Vehicles (OC ROVs). The main idea is to use a docking system in order for the small and light ROV to perform the connection, using the reaction force from its docking point instead of the motors propulsion, the latter being too little. This docking operation has to be very accurate and needs both an autopilot and a good positioning tool. In this paper we present an optical positioning system made of green lasers that together with the ROV’s camera measure the distances to the docking point. This is obtained by tracking the laser beams on the images captured from the camera and using triangulation of the points extracted. The tool has been implemented into an OCROV and tested in a tank.

This paper addresses the development, testing and verification of a relative positioning system for underwater vehicles. The position and orientation of the vehicle relative to a plane based target is estimated through a laser-based optical system. The sensor package consists of two green line-lasers and a camera. The image processing algorithm is built on the probabilistic Hough transform and a light but robust filtering method. This decreases the computational time to 13.6 ms per image. Experimental results from laboratory testing show that the mean absolute error in distance measurement is as low as 6 mm at 0.7 m from the target, whereas in heading is 2°.

Underwater docking is of high interest as it could be used to chargeunderwater robots while on a mission, thus extending their range of ac-tion, or to upload data without retrieving the vehicle, thus increasing itsmemory capacity. In this paper, the purpose of the docking system is toperform cable connections using remotely operated vehicles. The modelof an autopilot for autonomous docking is presented and the performancesof its components are analysed. This autopilot is based on measurementsfrom an optical positioning system which localizes the vehicle based onfeature detection from image processing. It shows that this positioning system could be integrated to the modelled autopilot and used in closed-loop for autonomous docking.