IFAC PapersOnLine 52-13 (2019) 1337–1342 ScienceDirect ScienceDirect Available online at www.sciencedirect.com 2405-8963 © 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Peer review under responsibility of International Federation of Automatic Control. 10.1016/j.ifacol.2019.11.384 1. INTRODUCTION Wind energy provides one of the most promising tech- nologies to produce renewable and sustainable energy. Currently, a large amount of renewable energy is generated using on- and offshore wind farms, as the technology has achieved a high level of maturity (Dolores et al., 2010). In 2017, new wind farms producing approximately 52 Gi- gawatts were constructed worldwide, increasing the total amount of energy produced by wind turbines by approxi- mately 11% to a total of 539 Gigawatts (REN21, 2018). In particular, offshore wind farms (OWF) are capable to generate large amounts of energy, due to high wind speeds and -availability at sea (Breton and Moe, 2009), (Sun et al., 2012). Over the last decade, an exponential increase in energy generated by OWFs can be observed, resulting in an increase of 4.4 Gigawatts to a total of 18.8 Gigawatts of wind energy worldwide generated in 2017 (REN21, 2018). Despite the advantages of offshore wind farms, the construction and operation of these farms poses particular challenges compared to onshore wind farms, due to their increased dimensions and weight. Higher costs for founding structures, network connection and for resources, like vessels and storage spaces, require a detailed planning, to ensure an efficient construction of OWFs (Junginger et al., 2004). In contrast, dynamic weather conditions at sea interfere with long-term plans, which sometimes cover horizons of several years. Consequently mechanisms for short-term control and dynamic adjustments are required, which can react in matters of days and even hours, e.g. if weather forecasts change. In general, about 15% to 20% of the costs for OWFs can be attributed to logistics during the construction process, demonstrating high potentials for optimization (Lange et al., 2012), (Dewan et al., 2015), (Muhabie et al., 2018). Over the next years, more high- powered wind turbines with capacities over 10 Megawatts will be built, e.g. see (European Council, 2018). These turbines are usually constructed in deeper water with a depth starting at 30m. Such locations are commonly located at distances further than 50km off the shoreline (Muhabie et al., 2018), complicating the pexecution of operations. This article aims to identify requirements towards a de- cision support tool for the installation process of OWFs. It presents a review of existing literature to summarize the problem (section 2) and shows current approaches in this field (section 3). Section 4 provides a decomposition of the planning problem into smaller tasks and closes with a discussion of suitable methods for these tasks. 2. CONSTRUCTION OF OFFSHORE WIND FARMS This section describes the overall process for the construc- tion of OWFs and presents a review of existing literature focusing on the installation process. 2.1 Installation Process According to Quandt et al. (2017), there is no standardized process for the installation of OWFs. Each project differs Keywords: Hierarchical decision making, Simulation, Optimization, Wind energy, Installation of offshore wind farms Abstract: Offshore wind farms provide a promising technology to produce renewable and sustainable energy. Nevertheless, the installation and operation of offshore wind farms pose a particular challenge to the planning and execution of operations. This article aims to identify requirements towards a decision support tool for the installation planning. Therefore, it provides a review of existing research in planning approaches and summarizes the overall planning problem. Afterwards this problem is decomposed into single tasks, according to their planning horizons. This decomposition shows a high level of interconnection between tasks across all levels. Higher levels provide constraints for the tasks on lower levels, while the results of these tasks are incorporated at higher levels. Finally, the article discusses the advantages and disadvantages of different approaches to solve these tasks. Copyright ǚ 2019 IFAC * BIBA - Bremer Institut f¨ ur Produktion und Logistik GmbH at the University of Bremen, Bremen, Germany (e-mail: [rip, jat, ltj]@biba.uni-bremen.de). ** Leibnitz University Hannover, Hannover, Germany (e-mail: [xmb, hsz]@sim.uni-hannover.de) *** University of Bremen, Bremen, Germany, (e-mail: fre@biba.uni-bremen.de) Daniel Rippel * Nicolas Jathe * Matthias Becker ** Michael L¨ utjen * Helena Szczerbicka ** Michael Freitag *,*** A Review on the Planning Problem for the Installation of Offshore Wind Farms © 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.