Energy Sail Ships
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Energy Sail Ships Tagiadin Assenai Oscar Bröte Bachelor of Science Thesis KTH School of Industrial Engineering and Management Energy Technology EGI-2020 TRITA-ITM-EX 2020:225 SE-100 44 STOCKHOLM Bachelor of Science Thesis EGI-2020 TRITA-ITM-EX 2020:225 Energy Sail Ships Tagiadin Assenai Oscar Bröte Approved Examiner Supervisor Peter Hagström Jens Fridh Commissioner Contact person Abstract Oceans offer a vast supply of energy through ever-present winds and currents. Offshore wind energy alone could provide many times the current global energy demand. One concept approach that aims to tap into these reserves are energy sail ship, wind powered vessel that take advantage of oceanic energy to produce and store harvested energy. This report studies the different systems involved in designing an energy sail ship; finding suitable waters to operate, shell vessel design, wind propulsion method, electricity generation, and hydrogen production and storage. Suitable operating waters are identified as having strong prevailing winds and currents, as well as proximity to land. One particularly suitable example of this is the southern coast of New Zealand, which is studied in this report. Catamarans are identified for use as energy sail ship design, as they offer low water resistance as well as large surface areas needed to place systems. Three methods of ship propulsion are considered; Flettner rotors, Parawings and Wing sails. A method of effective and reliable saltwater electrolysis is identified, with cells that last thousands of hours without maintenance. Finally, hydrogen storage methods are evaluated, including chemical conversion into methanol or ammonium, as well as compressed hydrogen storage. A simplified energy analysis is preformed to determine an approximate energy efficiency of a theorized ESS that utilizes proposed technologies. The energy sail ship was found to produce roughly 2.5 GWh. Sammanfattning Havet innehåller stora mängder energi från både vindar och strömmar. Endast energi från kustnära vindar uppskattas vara tillräckligt för att täcka världens årliga energibehov. Ett koncept som avser att ta till vara på havets energi är vinddrivna och vätgasproducerande skepp (engelska: energy sail ships). I denna rapport studeras de olika system och teknologier som bygger upp en energy sail ship, så som lämpliga vattenområden, skeppsdesign, vinddrivningsmetod, elgenereringsmetod, vätgasproduktion och energilagring. Områden med konstanta och starka vindar, i kombination med starka havsströmmar, identifieras. Nya Zeelands södra kust är ett särskilt lämpligt område som studeras närmare i denna rapport. Katamarandesign föreslås som skeppsdesign för dess låga vattenmotstånd samt att de erbjuder det stora ytområde som behövs för vätgasproduktion och lagring. Tre metoder för vinddrivning identifieras; Flettnerrotorer, fasta segel samt skärmsegel. Energieffektiva och underhållsfria elektrolysceller föreslås för saltvattenselektrolys. Dessa celler har en livslängd på tusentals timmar istället för endast några få timmar för celler som inte är anpassade för saltvatten. Till slut utvärderas vätgaslagring i form av metanol, ammonium eller komprimerad vätgas. En enklare energianalys utförs för att bestämma energieffektiviteten av en energy sail ship som använder de föreslagna teknologierna. Detta skepp får en approximativ årlig energiproduktion på 2,5 GWh. Table of Contents 1 Introduction 1 2 Purpose and Objectives 2 3 Methodology 2 3.1 Limit of Scope 2 4 Background 3 4.1 Sailing Routes 3 4.1.1 Wind Conditions 3 4.1.2 Ocean Currents 4 4.2 Ship Design 5 4.2.1 Catamaran 5 4.2.1 CNG and LNG carriers 6 4.3 Ship Propulsion 6 4.3.1 Parafoil 6 4.3.2 Flettner Rotors 7 4.3.3 Wing Sails 9 4.4 Power Generation 9 4.5 Electrolysis 10 4.5.1 Cell Lifespan 10 4.5.2 Energy Efficiency 11 4.6 Energy Storage 11 4.6.1 Physical Hydrogen Storage 12 4.6.2 Chemical Hydrogen Storage 12 5 Results 13 5.1 Sailing Routes 13 5.2 Ship Design 14 5.3 Ship Propulsion 14 5.4 Power Generation 14 5.5 Electrolysis 15 5.6 Energy Storage 15 5.7 Energy Analysis 16 6. Discussion 19 6.1 Future Work 19 7. Conclusion 19 References 21 Appendix 23 List of Figures 25 List of Tables 26 Nomenclature AF – Flettner rotor surface area AT – Turbine blade area Aw – Parafoil area Awet – The wetted area of the ship CB – Drag coefficient of a ship CDF – Drag coefficient of a Flettner rotor CLF – Lift coefficient of a Flettner rotor CDw – Drag coefficient of a deployed parafoil. CPt – Power coefficient of turbines DF – Drag from Flettner rotor DW – Drag from parafoil ESS – Energy sail ship 퐸푛푒푟푔푦 표푢푡 푓푟표푚 푠푦푠푡푒푚 ER = η – Efficiency ratio, given as: 퐸푛푒푟푔푦 푖푛푡표 푠푦푠푡푒푚 FDS – Drag force from ship’s hull FDT – Drag force from turbines FG – Power generated from turbines LF – Lift for Flettner rotor LW – Lift from parafoil VS – Velocity of the ship Vr – Wind velocity relative to ship Vwt – Water velocity relative to turbines CAES – Compressed Air Energy Storage CH3OH – Methanol NiCd – Nickel-Cadmium batteries TEU – Twenty-foot-equivalent unit WPD – Mean Wind Power Density WS – Mean Wind Speed 흆풂 – Air density 흆풘 – Water density ηblade – Efficiency of the blade ηgen – Efficiency of the generator ηbox – Efficiency of the gearbox αr – Spin ratio between Flettner rotor and wind speed 1 Introduction In the Paris Climate Accord, many of the world’s nations have promised to wean themselves off coal and fossil fuels, yet figures show that global emissions from these sources continue to grow. Global energy demand is posed to continue to rise as more people achieve middle-class living standards. It is estimated that by 2030 the global energy demand will rise 50% from the 2018 level of 23,000 TWh per year, according to the U.S. Energy Information Administration (Kahan, A., 2019). One large reserve of untapped clean, renewable energy is in and on our oceans. The moons gravitational force coerces currents, waves and winds in a constant flow of energy. (Cho, 2017) writes that, not including wind, ocean currents could generate 1,100 TWh yearly. Add to that the enormous offshore wind energy potential, estimated at 44,000 TWh per year in the United States alone, many times the global demand for energy (L. Hartman, 2016). To meet the energy demands of tomorrow, new technologies are needed to tap into the vast reserves of green energy. One technological concept that aims to take advantage of both ocean currents and offshore winds are Energy Sail Ships (ESS) (Platzer et al., 2014). The concept involves wind-powered ships sailing in ocean regions selected for near constant wind and current flow, providing a reliable source of renewable energy. These ships harvest the wind power for propulsion, which together with underwater currents drive turbines, generating electricity used to produce hydrogen gas from seawater through electrolysis. The resulting gaseous hydrogen can be compressed and stored onboard, to later be offloaded at port. Figure 1 shows the general concept of ESSs. The interest and subsequent research into this concept, as well into sub-system technologies, has grown in the last decade to where the first ESS proof-of-concept was built, see Section 4.0. Hydrogen has long been a proposed replacement for oil and gas for off grid use, such as in vehicles and ships. Large scale electrolysis could pose challenges (Lee, U. et. al., 2019), as hydrogen is most commonly produced from freshwater. If hydrogen gas is to become more generally used, the electrolysis production in many areas must almost certainly be from seawater, a near endless water source. The ESS concept aims to bridge oceanic energy potential and seawater hydrogen production. Wind propulsion Wind Turbines Electrolysis cells and energy storage system Figure 1: Energy Sail Ship (ESS) general concept. 1 2 Purpose and Objectives This report aims to identify, analyze and present technologies that might contribute to the viability of wind powered ships, that produce hydrogen gas from sea water. A simplified energy balance is presented, and sources of significant energy loss identified. 3 Methodology In this report, information from different scientific papers covering Energy Sail Ships aims to be consolidated. Major technology systems involved in implementing this concept, including sailing routes, wind propulsion, and hydrogen production and storage will be studied. Different system alternatives will be presented. In some cases, technologies that may be suitable for use in the ESS have not yet been linked to or considered for use in ESS. Some of these suitable technologies will be identified and studied for us in ESS. A number of scientific papers on the ESS concept examine how to best connect existing technologies into an operable ship. However, many of these papers take different approaches to ESS implementation and therefore the envisioned ESSs may differ between authors. By focusing on the systems involved in each ESS proposal instead considering these proposed concepts as a whole, this report aims to bridge these different ideas together. A simplified energy analysis will be performed to determine the energy efficiency of a hypothetical ESS, which uses technology proposed in the report. This aims to give an overview on how systems in ESSs interact, the flow of power between these different systems, and identify sources of energy losses. Finally, this report gives several proposals of what is needed to further the ESS concept. 3.1 Limit of Scope As to keep this report an overview on ESSs, and to keep it at a reasonable length for reader, the scope of the report will be limited in several respects. • The economic feasibility of ESSs will not be considered. An important aspect when designing an ESS the cost of implementing your design, and the ability to return a profit when operating the ship. In some cases, a superior technology may be passed over for cost-saving measures. While the economic feasibility of ESSs is certainly important, production costs are not yet relevant until the ESS concept has come further along.