Comparative analysis of winch-based wave energy converters Aleksandar Nachev Bachelor Thesis MMK 2017:04 MKNB 090 KTH Industrial engineering and management Machine Design SE-100 44 STOCKHOLM 1 2 Acknowledgments I would like to thank my supervisors, Dr Richard Neilson and Dr. Ulf Sellgren, for their advice and support. I would like to thank the Dr. Panagiotis Kechagiopoulos and the Erasmus teams in the University of Aberdeen, UK, and the Royal Institute of Technology, Sweden, for their technical support during my time abroad and the preparations beforehand. 3 BachelorThesis MMK 2017:504 MKNB 090 Comparative analysis of winch-based wave energy converters Alexandar Nachev Approved Examiner Supervisor 2016-04-20 Ulf Sellgren Ulf Sellgren Commissioner Contact person KTH Machine Design Ulf Sellgren Abstract Renewable energy sources are probably the future of the mankind. The main points advocating wave energy in particular include its huge potential, low environmental impact and availability around the globe. In order to harvest that energy, however, engineers have to overcome, among others, the corrosive sea environment and the unpredictable storms as well as secure funding for research and development. A lot of effort has been put into building and testing WECs after the oil crisis in the 1970s and is now being used as a starting point to create the modern alternatives to fossil fuels. The purpose of this thesis is to analyze the available winch-based wave energy converters (WECs) in comparison with other devices of similar scale, such as linear and hydraulic point absorber WECs. First, an introduction to the physics and geography of waves is presented, covering wave formation and particle motion. Then a number of designs, their working principles and history are described – oscillating water columns, floating or bottom-fixed devices using translational or rotational motion. Environmental and economic effects in the long term have to be taken into account. Narrowing down to point absorbers, different power take-off systems are available – linear, hydraulic or winch-based, each of them with specific advantages and disadvantages. Focusing on winch-based systems, three different concepts are described – the counter weight, the counter buoy and the Lifesaver devices. A set of comparison criteria, covering technical, economic and environmental aspects of the device performance, is prepared. Using this set, the three concepts are compared and results are analyzed. Keywords: winch, PTO, wave, energy 4 Examensarbete MMK 2017:04 MKNB 090 Jämförande analys av vinschbaserade vågenergikonverterare Aleksandar Nachev Godkänt Examinator Handledare 2017-04-20 Ulf Sellgren Ulf Sellgren Uppdragsgivare Kontaktperson KTH Maskinkonstruktion Ulf Sellgren Sammanfattning (in Swedish) Förnybara energikällor är förmodligen människans framtid. De viktigaste argumenten för just vågenergi är att vågenergi har en särskilt stor potential, en liten miljöpåverkan och att den finns tillgänglig i hela världen. För att kunna skörda denna eneri måste ingenjörerna emellertid övervinna den korrosiva havsmiljön och de oförutsägbara stormarna, samt säkerställa finansiering för forskning och utveckling. Efter oljekrisen på 1970-talet, har stora ansträngningar har gjorts för att bygga och prova WEC och det pionjärarbetet används nu som utgångspunkt för att skapa moderna alternativ till fossila bränslen. Syftet med denna avhandling är att analysera de tillgängliga vinschbaserade vågenergiomvandlarna (WEC) och att jämföra dessa med andra liknande enheter, såsom WEC-linjer med linjära och hydrauliska system (WEC). Först ges en introduktion till vågornas fysik och geografi, en beskrivning som innefattar vågbildning och partikelrörelse. Därefter beskrivs ett antal konstruktionslösningar, deras arbetsprinciper och historia - oscillerande vattenkolumner, flytande eller bottenfasta enheter, som baseras på translaterande- eller roterande rörelser. Miljömässiga och ekonomiska långtidseffekter måste beaktas för denna typ av system. Om vi begränsar oss till punktabsorberare (PTO), så finns olika typer av kraftuttagssystem tillgängliga - linjära, hydrauliska eller vinschbaserade, var och en med specifika fördelar och nackdelar. Med fokus på vinschbaserade system beskrivs tre olika koncept - motvikt, motverkande boj och ”Lifesaver”-enheter. En uppsättning jämförelsekriterier, som täcker tekniska, ekonomiska och miljömässiga aspekter av enhetens prestanda definieras. Med hjälp av dessa kriterier jämförs de tre koncepten och resultaten analyseras. Keywords: energi, vinsch, PTO, vågenergi 5 List of figures Figure 1: Wave formation diagram. Figure 2: Simplified wave model Figure 3: Deep and shallow water waves; water particles motion. Figure 4: Six degrees of freedom. Figure 5: Classification of the spectrum of ocean waves according to wave period. Figure 6: World wave energy resource. Figure 7: Seasonal variation in wave energy intensity. Figure 8: Wells turbine schematic. Figure 9: Shoreline oscillating water column (OWC) plant. Figure 10: Backward Bent Duct Buoy. Figure 11: WEC classification according to orientation to incoming waves. Figure 12: Singe body WEC. Figure 13: Two body WEC. Figure 14: Wave Star WEC – an example of a multi body system. Figure 15: Salter’s duck. Figure 16: Bottom hinged WEC. Figure 17: Bristol cylinder. Figure 18: Tapered channel, Norway. Figure 19: Wave dragon over-topping device. Figure 20: Hose-pump WEC. Figure 21: Pelamis WEC. Figure 22: Bottom-fixed heaving WEC – the Archimedes wave swing (AWS). Figure 23: Pendulor WEC. Figure 24: Counter weight WEC. Figure 25: Pulley-gear system. Figure 26: Counter buoy device configuration. Figure 27: Capstan equation. Figure 28: BOLT Lifesaver. Figure 29: Winch-based PTO. 6 List of tables Table 1: WEC classification according to location. Table 2: Sea state and device parameters. Table 3: Environmental impact of WECs. Table 4: Cost comparison between Lifesaver and the next-generation device by FO. Table 5: Winch-based WECs comparison. 7 Abbreviations CB – counter buoy CCL – creative commons license CW – counter weight ECMWF – European Centre for Medium Range Weather Forecasts EPRI TAG – Electric Power Research Institute Technical Assessment Guide FO – Fred.Olsen LIMPET – Land Installed Marine Power Energy Transmitter OWC – oscillating water column PGS – pulley gear system PTO – power take-off SWL – still water level WEC – wave energy conversion (converter) List of symbols A – wave amplitude d – distance to seabed D – buoy diameter H – wave height Hs – wave height L – wavelength T – wave period Te – energy period P – designed power Pw – wave power 8 Contents Acknowledgments 3 Abstract 4 Sammanfattning (in Swedish) 5 List of figures 6 List tables 7 Abbreviations 8 List of symbols 8 1. Introduction 11 1.1 Background 11 1.2 Motivation 12 1.3 Challenges 13 1.4 Thesis outline 15 1.5 Methodology and delimitations 15 2. Frame of reference 16 2.1 Wave physics 16 2.1.1 Wave formation 16 2.1.2. Wave structure 17 2.1.3. Water particle motion and relation to WEC motion 19 2.1.4. Types of waves 20 2.2. World wave energy resource 21 2.3. WECs classification 25 2.3.1. Classification according to location-based 25 2.3.2. Classification according to energy extraction method 26 2.3.2.1. Oscillating water column – OWC 26 2.3.2.1.1. Fixed OWC 27 2.3.2.1.2. Floating OWC 28 2.3.2.2. Oscillating bodies 29 2.3.2.2.1 Translational 30 2.3.2.2.2. Rotational 33 2.3.2.2.3. Mixed 35 2.3.2.3. Other 36 2.4. Existing WECs around the world 37 9 2.4.1. Europe 38 2.4.2. North America 42 2.4.3. Asia 43 2.4.4. Australia 44 2.4.5. Alternative uses of WECs 44 2.5. PTO systems in point absorbers 44 2.5.1. PTO systems 44 2.5.2. Alternative to electric generators 46 2.6. Control mechanisms 47 2.7. Existing winch-based PTO systems 48 2.7.1. Counter weight 48 2.7.2. Counter buoy 52 2.7.3. Lifesaver 54 2.7.4. Aquaharmonics 57 2.8. Environmental impact 58 2.9. Economy of WEC 61 3. Comparative analysis of winch-based PTO systems 63 3.1. Comparison criteria 63 3.2. Comparison and analysis of existing WECs 64 4. Conclusion and future work 67 5. Bibliography 68 Appendix 1 – Coefficients of importance 71 Appendix 2 – Fred. Olsen design guidelines 73 10 1. Introduction 1.1. Background The main renewable source of energy on Earth is the Sun. All forms of electrical, mechanical or chemical energy are converted from solar radiation. In recent years, mankind has become more aware of the harmful effects of fossil fuels on the planet (air, water and soil pollution); hence, a global tendency has emerged to replace fossil fuels with cleaner renewable energy sources. Even though wave energy converters (WECs) are not as common as wind turbines yet, there is huge potential for energy extraction. The global theoretical energy wave power resource corresponds to is approximately 8*106 Twh/year (Rodrigues, 2008; Brooke, 2003). Producing the same amount of energy using fossil fuels would result in releasing 2 million tones of CO2 into the air (Rodrigues, 2008). Even though only 10 – 15 % of this energy is practically available due to various reasons such as location or extraction efficiency (Rodrigues, 2008) this could still be a major contributer to global energy supply. A French man named Girard and his son were the first people to attempt capturing wave energy. They obtained a patent in 1799 and since then more than 1000 different devices were patented (McCormick, 1981; Ross, 1995). The first of the modern technologies were developed by Yoshio Masuda (1925- 2009). A former Japanese navy officer, Masuda started his research around 1940s and developed a navigation powerbuoy that used air turbine and could be classified as floating oscillating water column (OWC). It was commercialized in Japan, 1965 (and later in the USA) and a similar but much larger device, Kaimei, was built and tested in the 1970s (Falcão, 2014). After the oil crisis in 1973, a lot of effort was made in research and development of large scale renewable energy systems.