Deployment and Maintenance of Wave Energy Converters at the Lysekil Research Site: A Comparative Study on the Use of Divers and Remotely-Operated Vehicles

Abstract

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.

Assessment of Extreme and Metocean Conditions in the Swedish Exclusive Economic Zone for Wave Energy

“…A choice of threshold of 3 m or higher for the significant wave height should be recognized as a fairly high threshold, and crews and divers would likely avoid operating above 1.5 m to 2 m, even if the marine vessel used was capable of operating in those conditions. However, it may be possible that more of the required O&M for near-shore and offshore energy devices would be performed using Remotely Operated Vehicle (ROV) robotics and Autonomous Underwater Vehicles (AUVs) in the future [45,63,64], so that higher threshold values could be useful to consider. Based on experiences from the Lysekil research site on the west coast of Sweden, a comparative study on the use of divers and ROVs found economic advantages for ROVs starting from seven deployed devices or more [45].…”

“…The seasonal ice-cover of the Baltic Sea [39,40] is, however, known to influence the wave climate, and Tuomi et al [41] suggested ways to calculate different types of statistics taking the ice-time into account. In practice, experience from both the WESA (Wave Energy for a Sustainable Archipelago) project [42][43][44] and several field tested deployment strategies [45,46] of wave energy equipment have increased the awareness of wave energy as an available potential renewable energy source in the region. Wave energy converters are, however, not very likely to be deployed if the presence of sea-ice is consistent for long periods of time every year.…”

Managing Biofouling on Submerged Static Artificial Structures in the Marine Environment – Assessment of Current and Emerging Approaches

“…Simulations by Yang et al (2017) showed that biofouling on mooring lines and power cables associated with wave energy converters reduced energy performance (up to 17%) and caused significant reductions (up to 76%) in the fatigue life of moorings. Wave energy converters have been designed for 20-25 years of maintenance-free service, however, supporting infrastructure such as safety lines, underwater cables, and subtidal equipment may be prone to biofouling (Rémouit et al, 2018). As an emerging technology, there is little information on biofouling management approaches for wave energy converters, although manual or mechanical cleaning via diving and ROVs may be required (Rémouit et al, 2018) and should be considered in economic forecasting.…”

Effects of a Wave Power Park with No-Take Zone on Decapod Abundance and Size

“…2 km off the Swedish west coast near the Islandsberg lighthouse. The site is marked at the northern and southern boundaries with a sea marking (northern marking 58 • 11 850 N; 11 • 22 460 E and southern marking 58 • 11 630 N; 11 • 22 460 E) (Figure 1A) and covers an area of around 0.5 km 2 [49]. The seafloor at the research site is at a depth of 25 m, consists of sand, and shows little relief [50].…”