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.

• Technologies presented in this report will not be studied for cross-compatibility.

• An energy analysis will be performed for a theoretical ESS. This report does not propose this as an ESS which can or may be built.

2

• Only the primary systems that build up an ESS will be studied in this report. These are the technologies that build the foundation of the ESS concept. An example of a primary system would be a wing sail for wind propulsion, and a secondary system would be the rudder design for steering the ship.

4 Background

In 2017, the world’s first self-sufficient hydrogen producing ship was launched. Named Energy Observer, the vessel is a research and proof-of-concept catamaran that set out on a seven-year long cruise around the world to raise awareness of the Energy Sail Ship-concept and to test performance in harsh environments.

The Energy Observer is 30 m in length and has a height of 13 m with a total weight of 28 tons. One tenth of Energy Observers’ power is produced by two vertical wind turbines. It is 2 also equipped with a 50 m parasail (The National, 2016).

The ship is also called Solar Impulse of the Seas because of the 120 m2 solar panels the ship uses, solar electricity together with wind power is used to power the vessel. The panels are bifacial, meaning both direct and reflected sunlight generates electricity. The ship produces hydrogen, which can be used in a shortage of wind power. (RFI, 2017).

Thus far the Energy Observer has proven successful, however ESS for commercial use are more complex and face greater developmental challenges. Although there has not generally been, as of yet, considerable research into commercializing the ESS concept, many of the technologies are not exclusive to ESS. These technologies have long been studied in relation to other ideas, such as coastal wind farms, shipping efficiency, hydrogen energy production and compression storage. Therefore, by collecting the most recent information within each “puzzle piece”, the viability of ESS can analyzed. 4.1 Sailing Routes An important factor in the viability of the ESS concept is finding suitable waters in which to operate these ships. These areas must be able to provide a constant and dependable energy source from currents and winds that do not significantly vary seasonally. The distance sailing region is from shore and how prone it is to serious storms are also important. Ocean weather patterns have long been an area of interest for scientists, as wind and currents conditions greatly impact trade routes. More recently, the necessity for ocean data in the deployment of wind and wave energy farms has led to more detailed information of conditions on both the micro and macro level.

4.1.1 Wind Conditions To provide wind data for global coastlines and land regions, the World Bank together with the Technical University of Denmark created the Global Wind Atlas tool (World Bank Group, 2019). The application was developed to assist in determining placement and planning of wind turbines and provides both metrics data and a mapped visual representation of the data, see Figure 2. Using this tool, a potential ESS operating region can be evaluated for, among other things, mean wind speed (WS) and mean wind power density (WPD) at different heights above sea level, and for obtaining the regions wind rose.

3

Figure 2: A screen captureg of the Global Wind Atlas tool. Depicted is the WPD at 50 meters above sea level, for the Northern Hemisphere.

4.1.2 Ocean Currents Ocean currents are the naturally occurring, continuous flow of seawater throughout the world’s oceans, as shown in Figure 3. Seawater can circulate great distances, altering the nature of the waters through which it flows. Ocean currents influence weather patterns such as temperatures, stormfronts and precipitation levels (National Ocean Service, 2008). For example, the North Atlantic Current transports warmer waters from the Gulf Stream, giving Europe a more temperate climate than other regions at similar latitudes. Ocean salinity is also affected by these currents as fresh and brackish water from the poles mixes with saltier water near the equator.

Figure 3: Global ocean current map which indicated major currents (SAGE,2020). However, currents are an important area of research for more than just their effects on weather; they also are a potential source of a vast amounts of energy. For thousands of years currents have been utilized in sailing and trading routes, giving ships a reliable source of assisted propulsion on their fares. Energy Sail Ships could benefit from tapping into this reserve as an additional source of energy, besides wind, when powering underwater turbines, see Section 4.4.

4

In the order of hundreds of meters of depth, currents with varying strengths. The flow intensity in a current is measured in sverdrup (sv), where 1 sv is equivalent to a million cubic meters of waterflow per second. Typical flow intensity ranges from 0 sv up to ±80 sv (Kessler, 2006). While strong currents may indicate high surface current speed, that is not necessarily the case. The Climate Data Guide provides ocean analyses of surface current speeds (Shea, D. et al., 2017), shown in Figure 4.

Figure 4: Surface Current Speeds (Shea, D. et al., 2017).

4.2 Ship Design

An ESS must be designed so it can operate satisfactory in all kinds of weather conditions, without substantially affecting the performance of the vessel.

4.2.1 Catamaran A Catamarans is a ship with two equal sized stabilizing hulls on either side of the ship. The hull and ship are designed to minimize contact with water, thus lessening the friction between ship and water. There are other variations of this ship construction design, such as monohulls (one hull) and multihulls. Multihulls include two hulls (catamaran) and three hulls (trimarans), and in some cases more than three hulls (Liang, 2019). These designs can be seen in Figure 5, and Figure 6 shows a catamaran ship outfitted with a sail. Catamarans and trimarans have been proposed for use as ESSs by (Platzer et al., 2017) and (Gilloteaux J. C., et al., 2017).

5

Figure 5: Catamaran, trimaran and a ship with one hull (Wikimedia, 2009). Figure 6: A catamaran (Britannica, 2015)

4.2.1 CNG and LNG carriers A bulkier and significantly less flexible ship type that could be suitable for use together with ESSs is a Compressed Natural Gas carrier (CNG) or Liquified Natural Gas carrier (LNG). Currently, these ships designs are commonly for transportation of natural gas because of their sizes (Karanassos H. 2015). For ESSs, hydrogen storage through hydrogen compression or chemical conversion is can be used, see Section 4.6. These ship types may meet many of the technical demand’s hydrogen storage entails.

LNGs or CNGs have been proposed for use strictly for hydrogen energy storage. ESSs ccould offload produced hydrogen energy at sea to such ships, eliminating the need for ESSs to offload in a harbor, see Section 4.6.

Regardless of the design of the ship, the drag from the water on the ship is given by equation (1).

1 (1) 퐹 = 0.004( 휌 푉2)퐴 퐷푆 2 푤 푠 푊

4.3 Ship Propulsion The method through which the winds’ energy is harnessed differs in various ESS research proposals. The most suitable propulsion method may depend on ship size and type, i.e. smaller catamaran or larger merchant vessel (Barbarit, 2018). Moreover, drag must also be taken into consideration as larger drag will lead to additional energy losses. Generally, three options have been identified as the most efficient potential methods; parafoils, Flettner rotors and wing sails (Barbarit, 2018).

4.3.1 Parafoil Larger ocean-crossing ships, such as shipping vessels, military vessels and cruise ships, are increasingly faced with stricter environmental regulations. To lower diesel fuel usage,

6 parafoils are considered a cost efficient, environmentally sound and easily retrofitted alternative to assist in propulsion. Parafoils are essentially large kites that fly high up ahead of a vessel, catching wind and pulling it forward. These are typically deployed in favorable conditions reduce fuel consumption. Advanced computers alter the parafoils yaw and pitch to change course or alter speed. As wind speeds increase at higher altitudes, and as parafoils can fly at ~1000m altitude, windspeeds and energy potentials are considerably higher than that at ship height.

A 2010 paper by Jong Chul Kim and Chul Park outlines the full concept of a hydrogen producing vessel utilizing a parafoil (Kim et al., 2010). The vessel selected was a catamaran, with hydraulic turbines producing electricity. These aspects of ESS are further covered in Section 4.2 and 4.4 respectively. Kim and Park explain that modern parafoils are able to 2 achieve a lift-to-drag ratio of 5, and parafoil areas 퐴푤 of up to 696.8 m have been successfully utilized. The parafoil deploys with a small pilot chute and stores neatly in between the hulls of a catamaran vessel. Outlined are the drag (Dw) and lift (Lw) produced from a deployed parafoil. 2 퐷푤 = 0.5퐶퐷푤휌푎푉푟 퐴푤 (2)

2 퐿푤 = 0.5퐶퐿퐹휌푎푉푟 퐴푤 (3)

Jong and Chul (Kim et al., 2010) describe a 300m long catamaran, using a 600,000 m2 parafoil. If sailed in areas of strong yearly winds (see section 4.1), the power output of such a vessel was calculated to 0.8 GW.

Parafoils have already seen a certain degree of commercial success on freight ships to reduce fuel usage. A leading company in this field, SkySails, has supplied parafoils to numerus such ships, including an Airbus shipping vessel, shown in Figure 7. SkySails claim up that vessel can achieve 20% fuel savings using their retrofitted technology. Unlike the parafoils described by Kim and Park, these have a surface area of ~80 m2 and fly 100-200 m in altitude. In favorable wind conditions, these parafoils propel a ship with an additional 5,000 kW of power. Figure 7: SkySails' parafoil (Rotkop, 2020).

4.3.2 Flettner Rotors In 1923, German engineer and inventor Anton Flettner invented a ship mounted rotor that generates thrust simply from wind flow. These so called Flettner rotors are large, upright cylinders connected to discs, which spin on their own axis, shown in Figure 8. Wind passes around the cylinder resulting in a perpendicular thrust caused by the Magnus effect.

7

The Magnus effect is a phenomenon where an object spinning in a liquid or gaseous stream result in a force on the object perpendicular to that of the stream. As the object rotates in a fluid stream, the stream is disrupted by the rotation. Fluid passing in the rotational direction accelerates and fluid passing against the rotation retards, creating a pressure difference between either side of the rotating object. Figure 8: The ship Fehn Pollux The retarded flow has a positive pressure, whereas the equipped with a Flettner rotor (van accelerated flow has a negative pressure, creating a force on Otterdyk, 2018). the object perpendicular to the flow of the fluid, see Figure 9.

An example of the Magnus effect is in the throwing of a tennis ball. If the ball is thrown through the air without any rotation, its horizontal flight path will be identical to the direction of the throw. If, however, the ball flicked when thrown so that it spins in the air, the flight path of the ball will curve laterally.

The large upright cylinders of the Flettner rotor is regarded as the object, so for the Magnus effect to be applied these cylinders must first be spun by electric motors. These motors can vary the rotational speed of the rotating cylinders and thus the resulting thrust can be varied. As with traditional cloth sails, wind flow direction is important; to achieve forward thrust, wind must pass ±20o perpendicular to the bow of the ship. Peak thrust Figure 9: A birds-eye view of a Flettner rotor o propelling a vessel (Dan-yell, 2013). would be achieved at 0 when wind is completely Figure A birds-eye view of a Flettner rotor perpendicular to the bow. In order for a Flettner rotor propelling a vessel (Dan-yell, 2013). to produce more thrust than is required input energy to rotate the cylinders, wind speeds of at least 5 m/s are necessary. Net efficiently rises quickly with faster winds speeds to around five times more efficient at 10 m/s winds compared to 5 m/s winds (Gilloteaux J. C., et al., 2017).

Flettner rotors have been conceptualized for ESS propulsion by, among others Aurélien Babarit and Jean-Christophe Gilloteaux (Gilloteaux J. C., et al., 2017). They outline two catamaran vessel designs, one single-rotor and another quad-rotor. The average wind speed assumed when determining the Flettner rotor design was 8 m/s, which gave peak efficiency when the rotor length was 27m and the diameter was 4m. The drag factor (DF) and lift (LF) for a Flettner rotor are also given.

2 퐷퐹 = 0.5퐶퐷퐹휌푎푆푣훼푟푉푟 (4)

2 퐿퐹 = 0.5퐶퐿퐹휌푎푆푣훼푟푉푟 (5)

For both conceptual vessels designs, considerable amounts of energy can be produced. The former was able to produce in the order of hundreds of kW, and the latter in the order of several MW. In both cases these vessels are quite efficient, and both were able to exceed Betz’ limit. Bentz’ which states that a maximum of 59.3% of the kinetic energy of wind can be converted into electricity.

8

4.3.3 Wing Sails Wingsails are rigid or partially rigid sails, shaped similarly to airplane wings, mounted upright on a vessels hull. These rigid sails are controlled by adjusting the camber to respond to changes of wind direction, wind speed and tack changes. Wingsails are most commonly used on smaller vessels, such as on the Energy Observer.

(Platzer et al., 2017) describe a hydrogen producing sail ship with a power output of 1.5 MW. Using a David Taylor Model Basin Wave Cancellation Multihull trimaran, wingsails are coupled with an oscillating-wing power generator submerged in seawater. To achieve the desired power output in different windspeed conditions, 7.5 m/s, 10 m/s and 12.5 m/s, the wingsail area needed is determined and shown in Figure 10. Figure 10: Wingsail area for 1.5 MW of power output (Platzer et al., 2014). 4.4 Power Generation ESSs must produce electricity to power various ship functions, as well as for seawater electrolysis. To convert the energy produced by wind, and thus the ships propulsion, an underwater generator can be outfitted to harness waterflow. Solar panels can be placed on available surface areas of the vessel to provide additional electricity.

Hydro generators are an effective way to generate power from waterflow. A turbine is designed to have propellers that are connected to a generator. Using the kinetic energy of the waterflow to spin the propellers and convert the kinetic energy into electric energy. The electricity is then used in the production of hydrogen (Smith, 1994).

Figure 11: A general idea on the design of the hydro turbines (OceanVolt).

Figure 12: An example of how the hydro turbine can be placed under the hull (Watt and Sea).

A turbine on the hull of a ship will add to the total drag force on the ship. They will be placed under the vessel so the characteristics of the water will have a major impact on the drag force

9 from the turbines. According to (Babarit et al. 2017) the drag force can be calculated with equation (6) where a is the induction factor of the rotor.

1 (6) 퐹 = 휌 퐴 푉3 4푎(1 − 푎)2 퐷푇 2 푤 푇 푊푇

4.5 Electrolysis Electrolysis is a process where water is split into oxygen and hydrogen gas, as shown in Figure 13. A source of current is connected to two electrodes at each pole. These electrodes are placed in a medium, in the case of Energy Sail Ship’s seawater. An electric current is passes through the medium due to the voltage potential difference between the electrodes. At the anode an oxidation occurs, and at the cathode a reduction, producing hydrogen and oxygen, an endothermic reaction shown in equation (7). Hydrogen is energy-dense, FigureFigure 13 An: An electrolyser electrolyser (Esposito, (Esposito, D., D., 2017). 2017). volatile and easily combustible. Therefore, large amounts of hydrogen are dangerous and must be handled in a controlled manner.

퐻2푂 + 286 푘퐽/푚표푙 ⟶ 퐻2 + 1/2 푂2 (7)

Traditionally, purified fresh water is most commonly used to produce hydrogen gas. Fresh water can be a precious commodity in many places, conversely the supply of sea water is virtually infinite. A large-scale energy dependency shift to hydrogen gas would most likely require further development in seawater electrolysis.

A series of challenges are posed by seawater electrolysis, primarily regarding cell lifespan and energy-efficiency. These challenges are not as prevalent in traditional freshwater electrolysis methods (Platzer et al., 2014). Improving and developing seawater electrolysis techniques has been a subject of research, where substantial progress has been made in the last decade.

4.5.1 Cell Lifespan Having longer lifespan electrolysis cells is fundamental for the ESS concept. Constantly replacing cells at sea would be inhibitive from both a cost and an efficiency perspective. One of the most serious challenges associated with seawater hydrogen production is the high levels of corrosion incurred in the process. The chloride in seawater can quickly corrode the positive anode end of an electrolysis system.

In a recent publication (Kuang et al., 2019), a group of Stanford researchers developed a promising cell design that has been shown to greatly improve cell lifespan, energy efficiency and at a lower cost. In this paper, they lay out a method for elongating the life span of electrolysis cells operated with seawater from around 12 hours, to potentially thousands of hours, while operating at a higher efficiency rate than traditional seawater electrolysis. The researchers found that an anode consisting of a nickel foam core and layered with nickel sulfide can be beneficially coated in nickel-iron hydroxide. During the electrolysis process the nickel sulfide becomes rich in negative charges. As chloride is also negatively charged, it will be repelled by the anode, reducing corrosion.

10

4.5.2 Energy Efficiency Electrolysis of seawater is vastly more energy-demanding than traditional distilled water electrolysis. The commercial energy usage, when using fresh water, to produce 1kg of hydrogen gas is 48 kWh. When seawater is used it has typically been desalinated and PH- neutralized, substantially raising the energy usage to split seawater 2-3 times higher than that of fresh water (Giudici, 2008). The difference in efficiency is an important factor in making ESSs cost-effective, and recent progress has been made to the splitting process to improve the energy efficiency.

One of these improved methods has been demonstrated by Zenta Kato. In the paper Energy- saving seawater electrolysis for hydrogen production, Kato describes an electrolysis cell built much the same way as a traditional cell. These cells do not require desalination and offer pH damage protection. Kato’s method, although less efficient than freshwater electrolysis, is a considerable improvement at 93.8 kWh per kg (Kato et al., 2009).

4.6 Energy Storage Off-shore ESSs do not have the option of sending produced energy directly into the grid, or to separate energy storage facilities. Storing large amount of energy on a wind-propelled vessel is not without challenges. Excessive energy storage capacity adds weight and is volumous, lowering production efficiency. In some cases, large scale storage techniques entail a number of technical difficulties. By reducing the energy storage capacity of an ESS, these issues can be partially curbed. However, reducing energy capacity may not be practical, as these reservoirs may be quickly filled. Purpose built, energy storage ships that sail with ESSs in energy producing water can act in place of large storage systems onboard ESSs; when a ship is reaching energy capacity, the energy is off-loaded, at sea, into the storage ship. According to (Barbarit et al., 2018), an ESS can expected to produce at least 2 MWh per week. In (Gilloteaux, J.C., et al., 2017), two proposed methods produce 33.6 MWh per week and 168 MWh per week respectively. As energy production levels differ for ESS concepts, so do the storage requirements. For this report it is assumed that an ESS could generate 100 MWh per week, and that such a ship offloads energy at least once per week, requiring an energy storage capacity of 100 MWh.

There is no definitive best option for storing energy; power rating, storage duration, capital cost, energy density, lifetime and cycle life, as well as environmental impact all must be considered when designing an ESS. One of the objectives of the ESS concept is to produce a fuel, liquid or gaseous, that can be later utilized off-grid in fuel cells. This eliminates a number of otherwise suitable energy storage systems, such as compressed air energy storage (CAES) or Nickel-cadmium batteries (NiCd), leaving hydrogen storage as the conditional option.

Uncompressed hydrogen gas, at standard temperature and pressure (STP), has a volumetric density of 11 m3/kg (Andersson et al., 2019). Storing 100 MWh of uncompressed hydrogen gas would require tanks ~35,000 m3 in volume, which is not feasible. Therefore, hydrogen must be stored in another manner. Typically, one of three methods are used; it can be physically stored, stored through absorption or chemically converted. Chemical storage consists of, among other methods, methanol conversion or ammonium conversion. Physical storage encompasses compression storage and liquid storage. As liquid storage requires

11 temperatures of less than -200 oC, at-sea hydrogen storage is limited to compression storage as well as chemical storage.

4.6.1 Physical Hydrogen Storage The energy density of hydrogen gas is 33.33 kWh/kg, meaning that in total, a 100 MWh ESS would have to store at least 3,000 kg of pure hydrogen. The most significant issue with storing large amounts of hydrogen, however, is not the weight but rather the large volumes needed, and so to store these quantities at a lower volumetric density, compression is needed.

Two main components are needed in compression storage; compressors and storage tanks. According to (Andersson et al., 2019), pressures of a maximum of 10MPa are attainable in above-ground vessels, and while pressures of 70 MPa have been achieved in fuel cell vehicles, this is not considered possible for large scale hydrogen storage needed in ESSs. Pipe-shaped storage vessels offer the greatest maximum storage pressures and are commonly used in other applications such as natural gas storage.

4.6.2 Chemical Hydrogen Storage

Methanol (CH3OH) conversion of hydrogen in ESSs has been proposed by (Kim et al., 2010) through hydrogenation of carbon dioxide (CO2), see equation (9).

퐶푂2 + 3퐻2 + 50 푘퐽/푚표푙 → 퐶퐻3푂퐻 + 퐻2푂 (9)

Methanol has a volumetric density of 99 kg/m3 and a gravimetric density of 12% (wt) (Andersson et al., 2019).

Production of ammonium (NH3) from hydrogen is a well-known process used in the production of fertilizer, and as such the technology is more mature than methanol production. The dehydrogenation process of ammonia, equation (10), is more energy demanding than for methanol.

푁2 + 3퐻2 + 92 푘퐽/푚표푙 → 2푁퐻3 (10)

Ammonium has a volumetric density of 123 kg/m3 and a gravimetric density of 17.7% (wt) (Andersson et al., 2019).

12

5 Results

5.1 Sailing Routes

Figure 14: Areas with suitable wind conditions for ESSs (Babarit et al., 2018).

Finding an appropriate region in which to operate ESSs is essentially finding the center of a Venn diagram, with suitable wind and current conditions, hydrogen infrastructure capacity, and distance winds are deemed suitable. The map in Figure 14 can further be refined by only accepting sailing regions within 1,000 km from large areas of population and strong ocean currents.

Figure 15: Wind data for the southern coast of New Zealand. Figure 16: Wind intensity surrounding New Zealand.

Figure Wind data for the southern coast of New Zealand.

Figure Wind intensity surrounding New Zealand. A region that fulfills all the necessary metrics is the southern coast of New Zealand. New Zealand is an advanced economy with the ability invest and operate ESSs. Currents are relatively strong, around 20 sv, with surface speeds of ~5 m/s as shown in Figure 4. Wind conditions are particularly suitable, with a constant, intense north-eastern wind sweeping the

13 region. Figures 15 and 16 this region in the Global Wind Atlas tool, including the Wind Rose, WPD and WS. Expected WPD in this region is ~1650 W/m2, with windspeeds ~11.5 m/s. This information is important when dimensioning a ship propulsion system, energy storage capacity and power generation system.

5.2 Ship Design (Babarit, 2017) argue that the optimal design for an Energy Sail Ship is a catamaran. The conclusion is made because of how much the reduction of from the ship resistance can be made, this can maximize the produced energy. This can be seen in the Energy Observer where the design of the ship is a catamaran. An LNG/CNG-carrier might have been a good candidate in the long run when the tanks are filled up but in the start the ship would probably be too big and heavy.

5.3 Ship Propulsion All three wind propulsion methods outlined in 4.3, parafoils, Flettner rotors and wing sails, have been proposed for use in ESSs (Barbarit, 2018). The Energy Observer, for example, utilizes rigid wing sails. Flettner rotors, however, are the only wind-harnessing propulsion method that have been used as a sole source of propulsion on large ships (Gallant, 2017). Given the scale of ESSs generally proposed by (Kim J, et al., 2010) and (Gilloteaux J. C. et al., 2017), which must be capable of transporting hundreds of tons, parafoil and wing sail technology may not currently be well developed enough to be implemented in ESSs. Thus, Flettner rotors are the only viable wind propulsion method for ESSs in the near future. Flettner rotors also offer excellent efficiency ratios (ER), in some cases greater than Betz’ limit, e.g. the 27 m long and 4 m in diameter Flettner rotor proposed in (Gilloteaux J. C., et al., 2017) reaches an ER of 77%.

5.4 Power Generation For a turbine to generate electricity, the ship must be propelled through the water faster than the surface waterflow speed. By sailing against surface currents, the speed of waterflow into the turbine would be greater, spinning the propellers faster. Table 1 shows differences in power generation from a turbine proposed in (Yutuc W., 2013), in different sailing conditions. The velocity of the ship is constant on all cases while the velocity of the current differs.

Table 1: Going against the current gives a higher electricity production (Yutuc W., 2013).

14

In Table 1 the velocity of the ship is constant in all cases and assumed to be 15.5 knots ( ~8 m/s). Table 1 also shows the difference on the generated power with and without a current. It is beneficial to sail into to a current, for example, if the current has a velocity of 0.5 m/s power generation increases by 20% compared to if the current did not have a velocity (Yutuc W. 2013).

According to (Babarit et al. 2017) 70% of the total possible output from the kinetic energy from the water can be converted into electric power.

5.5 Electrolysis The two technologies proposed in Section 4.5 for cell lifespan elongation and energy efficiency have been developed separately, thus it is not currently known how these two technologies, or technologies similar to them, can be combined.

Before ESSs can be considered for commercial use, cells must be reliable and require little to no maintenance. The annual energy output of an ESS that must have electrolysis cells replaced each week is a fraction of an otherwise maintenance-free ESS. Also, of great importance is energy efficiency of the electrolysis process. In Section 4.5.2, it is shown that the seawater hydrogen production, even using newly developed techniques, results in significant energy losses. As 65% of the energy supplied for electrolysis is lost to heat and the chemical reaction process in equation (8), only 35% of the energy supplied for electrolysis will be converted into storable hydrogen.

5.6 Energy Storage As mentioned in 4.6.1, an energy storage capacity of 100 MWh is a realistic assumption for an ESS. The uncompressed volumetric density of 100 MWh pure hydrogen gas, 11 m3/kg, is considerably lowered when compressed to 10 MPa, to roughly 0.128 m3/kg (Andersson et al., 2019). Therefore, the compressed volume needed to be stored in the ESS is 385 m3, compared to 35,000 m3 if left uncompressed. Using storage pipes with a diameter of 1.4 m, the total length of pipe needed is 250 m.

Energy losses occur both in compression and in storage of hydrogen, outlined in Table 3 in (Andersson et al., 2019). The isothermal efficiency, or work ratio lost in compression, for 100 bar storage is 0.7. The energy required for storing is 1 kWh/kg(H2) or a factor of 0.03. In total energy losses for the system amount to 0.67.

Generally, compressed hydrogen storage offers good performance at lower storage capacity. When handling large amounts of hydrogen, however, the required storage volume may make it infeasible. In such cases, chemical storage may be a more suitable option.

Methanol is produced and stored at 250oC and subsequently compressed to 5 MPa. In order to store 100 MWh hydrogen gas equivalent methanol, 250 m3 storage vessels are needed. Assuming isothermal efficiency factor of 0.64 and 1.5 kWh/kg(H2) electric storage consumption, the total energy losses for the system amount to 0.59.

Ammonium is produced and stored at 400oC and subsequently compressed to 25 MPa. Only 137 m3 storage vessels space is needed to store 100 MWh hydrogen gas equivalent

15 ammonium, considerably less than both compressed hydrogen and methanol. Assuming isothermal efficiency factor of 0.6 and 3 kWh/kg(H2) electric storage consumption, the total energy losses for the system amount to 0.51. As ammonium has large agricultural demand, if ammonia is selected to store hydrogen it could be more practical to use the ammonia directly for agricultural purposes rather than reconverting to hydrogen.

The most advantageous method for energy storage is, as long as the ESS has the capacity for the storage vessels, compressed hydrogen. This is reflected in the highest efficiency rate, as well as being a less complicated process.

5.7 Energy Analysis There are considerable energy losses between harnessing wind power and the resulting stored hydrogen energy. For economic and environmental reasons, losses must be minimized to the greatest extent possible. Identifying areas and systems within an ESSs where considerable losses occur and improving that technology as to reduce those losses is an important piece of ESS development. A method in which to identify where losses occur within the ESS concept is by creating an energy flow chart. Each section of the chart represents a subsystem within the ESS concept, with the losses displayed through the approximated ER of the subsystem. Using the different ER values, the theoretical energy production levels can be calculated.

Figure 16 shows an energy flow chart has been modeled for a theoretical ESS, using technologies outlined in 4.1-4.6. This is meant to demonstrate how a potential ESS may be evaluated through an energy analysis and is not being proposed as an ESS design alternative.

EXAMPLE OF ESS SYSTEM OVERVIEW

SOLAR: 0.2 MW

WIND: WIND SHIP TURBINE ELECTROL- ENERGY PROPULSI- DESIGN: YSIS: STORAGE: 2.24 MW 1.72 MW ON: 1.38 MW 0.98 MW 0.41 MW 0.28 MW η = 0.35 η = 0.67 η = 0.77 η = 0.8 η = 0.71

WPD of 1650 Four Catamaran, with drag from Ship turbine as Marine solar panels Seawater 100 MWh compressed and total Flettner Flettner rotors, turbine and ship. described by that produce 200 electrolysis hydrogen storage. Energy Flettner surface rotors, 27m (Yutu W., 2013). W/m2. Total area 2375 described by reserves are offloaded at area of 1350 tall and 4m m2. Operate at 50 % (Kato et al. 2009). sea, at least once a week. m2. in diameter. efficiency.

Figure 17: A simplified ESS energy system overview, of an ESS outlined in 5.7.

The ESS modeled in Figure 16 is a catamaran vessel, with four Flettner rotors, an electricity generating turbine, solar panels, and compressed hydrogen storage. This ESS is assumed to sail off the southern coast of New Zealand, where WPD measures around 1650 W/m2, as described in Section 5.1. The ocean currents in this area are assumed to give a surface flow of 0.5 m/s and it is further assumed that the ESS sails directly into these currents.

The Flettner rotors each measure 27 m in vertical height and 4 m in diameter. These dimensions where found to be most effective in Section 4.3.2, with an assumed ER of 0.77. The resulting power output to propel the ESS may then be calculated as the total Flettner rotor surface area, multiplied by WPD and the ER, equation (13). The calculation can be found in Attachment [1]. 16

퐴퐹푙푒푡푡푛푒푟 ∙ 푊푃퐷 ∙ 퐸푅퐹푙푒푡푡푛푒푟 = 푃푟표푝푢푙푠𝑖표푛 푃표푤푒푟 (8)

Because of drag, not all the potential wind energy can be directly applied for propulsion. According to equation (4) and (5) the difference between the propulsion and the drag divided by the total propulsion will give the proportion between the used potential energy and the actual energy that is used for propulsion.

퐿 − 퐷 (9) 푇ℎ푒 푝푟표푝표푟푡𝑖표푛 표푓 푒푛푒푟푔푦 푡ℎ푎푡 𝑖푠 푢푠푒푑 = 퐹 퐹 퐿퐹

The proportion in equation (9) will only consider the Flettner rotors Since the energy analysis only used them for propulsion. Most of the components in the equation for lift (4) and equation for drag (5) are same the only factors that will have an effects are the lift and drag coefficients. According to the paper (J.Kim, 2009) the values Lf = 1.5 and DF = 0.3 can be used, this gives the efficiency a value of 0.8, a loss by 20% (see Attachment [2] for calculation).

To calculate the drag force with the equation (4) some assumptions must be made. From (J.Kim 2009) a good estimation for the spin ration is 훼푟 = 1.40. As stated in Figure 16, the Flettner Rotors surface are that will be used is 1350m2. The velocity of the ship will be assumed to be 5 m/s, the same velocity the EES. The velocity of the ship will be assumed to 5 m/s, the same velocity the ESS. The drag coefficient CDF for a sphere can be set to 0.47 since the ship’s velocity is low which gives a Reynolds number under 104 (laminar flow). This will now give DF a value of 9.6MN (see Attachment [3] for calculation).

Drag from the turbines is according to equation (6) The induction factor of the rotor can be set to 0.25 (Babarit et al. 2017), the velocity of the ship, VWT will be assumed to be 5m/s which 2 will and the turbine’s blade area AT can be set to 4m , this is an assumption made by the authors. The size of the turbines from commercial use such as from the company Ocean Volt and the turbines used in the Energy Observer has been taken into consideration and came to the conclusion of 4m2. The total drag from the five turbines is now given by multiplying equation (5) with equation (6), this gives the 703 125 N (see Attachment [4] for calculation).

The wetted surface area AW can be assumed from the sailing (Platzer et al., 2014), a trimaran with a wetted surface area of 3891m2 is used. In section 5.2 it was established that a catamaran will be used. The hulls are identical in size so by dividing the wetted area by three and multiplying it with two will give the wetted surface area of a catamaran with the same 2 dimensions, 2594m . The drag FDS can now be calculated by using equation (1) when the velocity is 5m/s which will be 129 700 N (see Attachment [5] for calculation).

Assuming that marine solar panels produce 200 W/m2 (Hammarlund T., et al., 2017), and that the total solar surface includes 2x70 m2 pontoons as well as a 45x45 m2 deck surface, additional electricity can be fed directly to the electrolysis process. Assuming furthermore that these panels will, on average, contribute 50% of their peak power output, the total additional power contribution can be determined, equation (21).

푆표푙푎푟 푝표푤푒푟 푝푒푟 푠푞푚 ∙ 푃푟표푑푢푐푡𝑖표푛 푅푎푡𝑖표 ∙ 퐴푆표푙푎푟 (10) = 푆표푙푎푟 푃표푤푒푟 푂푢푡푝푢푡

17

The ship will need to draw a certain amount of power for miscellaneous vessel equipment, such as the motors that spin up the Flettner rotors. This draw is assumed to be, on average, 16 kW, thus the total net power contribution from the solar panels is 0.02 MW.

The seawater electrolysis processes involves substantial energy losses, as the ER for electrolysis was determined as 35% in Section 4.5.2. The amount of hydrogen power produced by the ESS shown in equation (22) and calculated in Attachment [6].

(푃표푤푒푟 푓푟표푚 푇푢푟푏𝑖푛푒 + 푃표푤푒푟 푓푟표푚 푆표푙푎푟 푃푎푛푒푙푠) ∙ 퐸푅푒푙푒푐푡푟표푙푦푠푖푠 (11) = 푃표푤푒푟 𝑖푛 푃푟표푑푢푐푒푑 퐻푦푑푟표푔푒푛

If the ESS here is assumed to offload produces hydrogen energy once per week, the total storage capacity of the ship will be low enough for compressed hydrogen storage. As described in Section 4.6.1, this process has an ER of 67%. This gives the total power generation for the ESS, as the produced hydrogen multiplied by the losses from hydrogen compression, equation (23).

푃표푤푒푟 𝑖푛 푃푟표푑푢푐푒푑 퐻푦푑푟표푔푒푛 ∙ 퐸푅퐶표푚푝푟푒푠푠푖표푛 푆푡표푟푎푔푒 (12) = 퐶표푛푡𝑖푛표푢푠 푃표푤푒푟 푂푢푡푝푢푡

The yearly energy output for the described ESS can be calculated as the total continuous power output from equation (23), multiplied by the number of hours in a year, equation (24).

퐶표푛푡𝑖푛표푢푠 푃표푤푒푟 푂푢푡푝푢푡 ∙ 24 ℎ ∙ 365 푑푎푦푠 (13) = 푌푒푎푟푙푦 퐸푛푒푟푔푦 푃푟표푑푢푐푡𝑖표푛

In Attachment [7], the continuous power output and yearly energy production are calculated for the example ESS outlined in Figure 16. Total continuous power output is 0.28 MW and the total yearly energy production 2.5 GWh. To put this into perspective, the average Swedish household consumes 2500 kWh per year (E on, 2020), meaning that the modeled ESS produces enough energy to power close to 1000 homes for a full year.

18

6. Discussion Hydrogen producing vessels are still a long way from being commonplace on global seas. This report hopes to outline the general ESS concept and the kinds of technologies involved in developing ESSs. Also, this report aims to identify areas where further development is needed.

We believe the main technological challenges lie in the hydrogen production and storage systems. For example, seawater electrolysis is still in its infancy, currently efficiency levels are low, and cells require constant maintenance. Storing produced hydrogen is also not without its difficulties, partially because it is hazardous, but also for the advanced technologies and systems required. Meanwhile, both battery and biofuel technology has seen rapid development in the global attempt to wean off dependency on fossil fuels. This has left hydrogen a niche fuel type that lacks access to the types of global infrastructure needed to secure its position on the global energy map. If hydrogen-based fuels become more prevalent in aircraft and large commercial vessels, ESSs may be important meeting that demand.

6.1 Future Work This is a promising future concept that can establish hydrogen as one of the main forces as the new fuel in the future. An economic analysis should be done for this to blossom and entering in the market, such as if it is better to produce ESS or to remake todays ships. A development for the hydrogen production should be studied and the general concept of the electrolysis in seawater.

This does not seem too far into the future, a developed concept of a yacht that used liquid hydrogen was presented in September 2019 (Cormack ,2019). This is a huge step towards making this concept more attractive in for future investors.

Currently, most papers on ESSs take different approaches to implementation, and therefore the resulting ideas on how ESSs should be designed vary significantly. We believe that the next step in ESS development is for the scientific community to reach a certain degree of consensus on some basic aspects of ESS design, such as how hydrogen should be stored, a feasible wind propulsion method or if seawater electrolysis is even feasible for ESSs. This would give a base for which further research can be built upon previous work, focusing more on the subsystems involved in developing an ESS, including some of the primary system described in Sections 4.1-4.6, but also some of the secondary system such as autonomous operation and hydrogen off-loading vessels.

7. Conclusion In conclusion, this report consolidated information from different scientific concept papers on ESSs. The major technology systems involved in implementing this concept, including sailing routes, wind propulsion and hydrogen production/storage where studied and technology alternatives presented. Several technologies, that have not yet been linked to the ESS concept, were studied for potential implementation.

19

Using some of the technologies studied in Sections 4.1 - 4.6, a theoretical ESS was comprised and a simplified energy analysis was performed, see Section 5.7. The yearly energy output was that might be expected from the theoretical ESS was determined to be roughly 2.4 GWh.

20

References

Andersson, J., Grönkvist S., (2019) Large-scale storage of hydrogen, International Journal of Hydrogen Energy (issue 44), (taken 14/05/2020) https://www-sciencedirect-com.focus.lib.kth.se/science/article/pii/S0360319919310195 Babarit, A., Gilloteaux, J. C., Clodic, G., Duchet, M., Platzer, M. et al., (2018), Techno-economic feasibility of fleets of far offshore hydrogen- producing wind energy converters. International Journal of Hydrogen Energy, Elsevier, 2018. hal-01766205 Chen, H., T. Ngoc Cong, W. Yang, C. Tan, Y. Li, Y. Ding (2009) Progress in electrical energy storage system: a critical review., Progress in Natural Science, Vol. 19, pp. 291-312. Cho, R., (2017) Tapping into Ocean Power, Earth Institute Columbia University, (taken 20/03/2020) https://blogs.ei.columbia.edu/2017/02/14/tapping-into-ocean-power/ Cormack, (2019), “ ‘Aqua’ pushes the envelope in every possible way, Robb Report, (taken 9/06/2020) https://robbreport.com/motors/marine/inside-the-radical-new-hydrogen-powered-yacht-concept-that-could-change-the-marine- industry-as-we-know-it-2870615/

Dan-yell, (2013), Magnus Effect at Flettner Rotor Boat, wikimedia.org, https://commons.wikimedia.org/wiki/File:Flettnerrotor.png E on, (2020) Normal elförbrukning i hemmet – vad är en genomsnittlig årsförbrukning på el i ett hushåll? (taken 17/05/2020) https://www.eon.se/el/elforbrukning Esposito, D., (2017) Engineers develop floating solar fuels rig for seawater electrolysis, Columbia Engineering (taken 01/04/2020), https://scx1.b-cdn.net/csz/news/800/2017/3-columbiaengi.jpg

Gallant, J. (2017) First rotor ship Diving records and aquatic superlatives (taken 01/06/2020) https://divingalmanac.com/first- rotor-ship/ Garcia de Jesus, E., Stanford researchers create hydrogen fuel from seawater (2019), Stanford Digest, https://news.stanford.edu/2019/03/18/new-way-generate-hydrogen-fuel-seawater/ Gilloteaux, J.C., Babarit A., (2017) Preliminary design of a wind driven vessel dedicated to hydrogen production. In Proc. of the ASME 36th International Conference on Ocean, Offshore and Artic Engineering (OMAE2017), Trondheim, Norway. https://asmedigitalcollection-asme-org.focus.lib.kth.se/OMAE/proceedings/OMAE2017/57786/V010T09A065/282052 Giudici, F. A., (2008) Feasibility study of hydrogen production using electrolysis and wind power in Patagonia, Argentina. University of Florida, https://ufdcimages.uflib.ufl.edu/UF/E0/02/23/29/00001/giudici_f.pdf Hammarlund T., et al., (2017) Solar Cell Powered Boat, (Taken 18/05/2020) http://www.diva- portal.se/smash/get/diva2:1118793/FULLTEXT01.pdf

Hartman, L., (2016), Computing America’s Offshore Wind Energy Potential, Office of Energy Efficiency & Renewable Energy, (taken 20/03/2020) https://www.energy.gov/eere/articles/computing-america-s-offshore-wind-energy-potential Kahan, Ari (2019) EIA projects nearly 50% increase in world energy usage by 2050, led by growth in Asia, U.S. Energy Information Administration (taken 20/04/2020) https://www.eia.gov/todayinenergy/detail.php?id=41433 Karanassos H., (2015). Commercial Ship Surveying: On/Off Hire Condition Surveys and Bunker Surveys, Elsevier Science & Technology. 2015 Kato, Z., Izumiya, K., Kumagai, N. et al., (2009) Energy-saving seawater electrolysis for hydrogen production. J Solid State Electrochem 13, 219–224 . https://doi-org.focus.lib.kth.se/10.1007/s10008-008-0548-9 Kessler, W., (2006) Re: Sverdrup Streamfunction- indefinite integral withirregular (!) boarders, e-mail sent 03/04/2006, https://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2006/gif00014.gif

Kim, J., Park C., (2010) Wind power generation with a parawing on ships, a proposal. Energy, Vol. 35, pp. 1425-1432 https://www- sciencedirect-com.focus.lib.kth.se/science/article/pii/S0360544209005167 Kuang, Y., Kenny, M. J., Meng, Y. et al. (2019)“Solar-driven, highly sustained splitting of seawater into hydrogen and oxygen fuels” PNAS 116 (14) 6624-6629 https://doi.org/10.1073/pnas.1900556116 Lee, U., et al. (2019), Quantifying water stress impacts of energy systems in the United States, AWARE-US (taken 20/04/2020),https://www.sciencedirect.com/science/article/pii/S0048969718332145 Liang, Y (2019), High Speed Catamarans and Multihulls technology, Performance, and Applications, Imprint Springer NYC, New York, https://link-springer-com.focus.lib.kth.se/book/10.1007%2F978-1-4939-7891-5 National Ocean Service (2008). Currents. National Oceanic and Atmospheric Administration, (taken 24/04/2020) https://oceanservice.noaa.gov/education/tutorial_currents/welcome.html

OceanVolt, https://oceanvolt.com/solutions/hydro-generator/

21

Platzer, M. F., Sarigul-Klijn, N., Young, J., Ashraf, M. A., and Lai, J. C. S. (2014). Renewable Hydrogen Production Using Sailing Ships. ASME. J. Energy Resources Technology, Vol. 136 June 2014; 136(2): 021203. https://doi-org.focus.lib.kth.se/10.1115/1.4026200

RFI, (2017) Hydrogen-powered catamaran Energy Observer launched in sea at Saint Malo 2017,(taken 09/05/2020) http://www.rfi.fr/en/france/20170415-hydrogen-powered-catamaran-energy-observer-launched-sea-saint-malo Rotkop, N., (2020) SkySails – Towing Kites For Ships, The Future of Things (taken 01/04/2020) https://thefutureofthings.com/5795-skysails-towing-kites-for-ships/ SAGE (Satellite Applications for Geoscience Education), Ocean Currents, Cooperative Institute for Meteorological Studies, (taken 24/02/2020) https://cimss.ssec.wisc.edu/sage/oceanography/lesson3/concepts.html

Saksia, (2018) LNG: what is boil-off gas and what does it do? Fluenta (taken 07/05/2020) https://www.fluenta.com/lng-boil-off-gas/ Shea, D., et al. (2017) The Climate Data Guide: GODAS: NCEP Global Ocean Data Assimilation System. (taken 03/06/2020) https://climatedataguide.ucar.edu/climate-data/godas-ncep-global-ocean-data-assimilation-system Smith, N, (1994) Motors as generators for Micro-hydro power, Intermediate Technology, London https://fulldisplay.datasource.46KTH_ALMA_DS

Sogurd W, (2009), Multihull, wikimedia.org, https://commons.wikimedia.org/wiki/File:Multihull.svg

The National, (2016) Solar Impulse of the Seas’ readies for round-the-world voyage (taken 09/05/2020) https://www.thenational.ae/world/solar-impulse-of-the-seas-readies-for-round-the-world-voyage-1.228456

Tikkanen A, (2015), Catamaran, britannica, https://cdn.britannica.com/35/175635-050-3CB7D7D9/Catamaran.jpg

Van Otterdyk, F., (2018) Fehn Pollux underway sailing with Eco Flettner Rotor, Marigreen.eu, (taken 01/04/2020), http://en.marigreen.eu/wordpress_marigreen/wp-content/uploads/sites/2/2018/06/Fehn-Pollux-unterwegs.jpg

Watt And Sea, https://www.wattandsea.com/en/products/cruising-hydrogenerators World Bank Group, Technical University of Denmark et al., (2019) Global Wind Atlas, (taken 27/04/2020) https://globalwindatlas.info/ Yutuc W., (2013) Use of Hydro Generator on a Tanker Ship: A Computer-Generated Simulation Study, International Conference Ho Chi Minh City 2013.

22

Appendix

[1] Calculation of propulsion power output.

푃푟표푝푢푙푠𝑖표푛 푃표푤푒푟 = 4 ∙ 108 ∙ 휋 ∙ 1650 ∙ 0.77 = 1.72 푀푊

[2] Calculation for the proportion of the energy that is harnessed.

퐿 − 퐷 푇ℎ푒 푝푟표푝표푟푡𝑖표푛 표푓 푒푛푒푟푔푦 푡ℎ푎푡 𝑖푠 푢푠푒푑 = 퐹 퐹 퐿퐹

and with numbers inserted

1.5 − 0.3 푇ℎ푒 푝푟표푝표푟푡𝑖표푛 표푓 푒푛푒푟푔푦 푡ℎ푎푡 𝑖푠 푢푠푒푑 = = 0.8 1.5

[3] Calculation for the drag force from the Flettner rotors.

2 퐷퐹 = 0.5퐶퐷퐹휌푎퐴푟훼푟푉푟 and with numbers inserted

2 퐷퐹 = 0.5 ∙ 0.47 ∙ 1000 ∙ 1.40 ∙ 5.5 ∙ 1350 = 9 596 813 푁

[4] Calculation for the drag force from the turbines.

1 퐹 = 휌 퐴 푉3 4푎(1 − 푎)2 퐷푇 2 푤 푇 푊푇 and with numbers inserted

1 퐹 = ∙ 1000 ∙ 4 ∙ 53 ∙ 4 ∙ 0.25 ∙ (1 − 0.25)2 ∙ 6 = 843 750푁 퐷푇 2

[5] Calculation for the drag force from the catamaran.

The wetted area from one hull

3891 Area of two hulls = ∙ 2 = 25794푚2 3

This will give the drag force from the hulls

23

1 퐹 = 0.004( 1000 ∙ 25794 ∙ 52) = 129 700푁 퐷푆 2

[6] Calculation of solar power output and power in produced hydrogen.

푆표푙푎푟 푃표푤푒푟 푂푢푡푝푢푡 = 200 ∙ 0.5 ∙ (2 ∙ 70+45 ∙ 45) = 0.216 MW

푃표푤푒푟 𝑖푛 푃푟표푑푢푐푒푑 퐻푦푑푟표푔푒푛 = (0.98+0.2) ∙ 0.35=0.41 MW

[7] Calculation of continuous power output and yearly energy production.

퐶표푛푡𝑖푛표푢푠 푃표푤푒푟 푂푢푡푝푢푡 = 0.41 ∙ 0.67 = 0.28 푀푊

푌푒푎푟푙푦 퐸푛푒푟푔푦 푃푟표푑푢푐푡𝑖표푛 = 0.28 ∙ 24∙ 365=2.5 GWh

24

List of Figures

Figure 1 Sketch of an example energy sail ship, and the primary systems involved in the concept.

Figure 2 A screen clipping of the Global Wind Atlas tool. Depicted is the WPD at 50 meters above ground level, for the Northern Hemisphere.

Figure 3 Global ocean current map including major currents.

Figure 4 Ocean surface current flow speeds in m/s at 5m of depth.

Figure 5 Different kind hull designs for a ship.

Figure 6 A Catamaran with sail.

Figure 7 A ship outfitted with SkySails' parafoil.

Figure 8 The ship Fehn Pollux equipped with a Flettner rotor.

Figure 9 A birds-eye view of a Flettner rotor propelling a vessel.

Figure 10 Wingsail area for 1.5 MW of power output.

Figure 11 General idea of different types of hydro turbines.

Figure 12 A turbine placed under the hull

Figure 13 Sketch of an electrolyser.

Figure 14 Areas with suitable wind conditions for ESSs.

Figure 15 Wind data for the southern coast of New Zealand.

Figure 16 Wind intensity surrounding New Zealand.

Figure 17 A simpilied ESS energy system overview, of an ESS outlined in 5.7.

25

List of Tables

Table 1 Table of electricity production from a generator when going against a current.

26