Paper ID #29290

Hybrid Green Vessel Design

Joseph C Rodriguez, United States Coast Guard AcademyScott C. Pierce, U.S. Coast Guard AcademyBrennen McCullochMr. George McBurney, United States Coast Guard Academy

Mechanical engineer at the United States Coast Guard Academy

Dr. Tooran Emami, U.S. Coast Guard Academy

Tooran Emami is an associate professor of Electrical Engineering at the U. S. Coast Guard Academy.She received M.S. and Ph.D. degrees in Electrical Engineering from Wichita State University in 2006and 2009, respectively. Dr. Emami was an adjunct faculty member of the Department of ElectricalEngineering and Computer Science at Wichita State University for three semesters. Her research interestsare Proportional Integral Derivative (PID) controllers, robust control, time delay, compensator design, andfilter design applications, for continuous-time and discrete-time systems.

c©American Society for Engineering Education, 2020

Hybrid Green Vessel Design

Abstract

This paper presents the milestones of a Hybrid Green Vessel Design capstone project. The

motivation of this project is to develop knowledge and skills in green energy applications, hybrid

vessels, and power management systems. To accomplish this, undergraduate students are

researching and designing a hybrid power plant for a green vessel that utilizes a variable electric

trolling motor.

The team of four undergraduates working on this project include three Electrical

Engineering students and one Mechanical Engineering student. The project objective is to learn

about hybrid green vessel design and operation. The design process includes: 1) Literature review

of hydrogen fuel cells and its applications in the maritime domain. 2) Designing a hybrid hydrogen

fuel cell and battery power system. 3) Modeling the power system in computer simulation to test

and verify the design. 4) Implementing the design to physically build a 100W fuel cell system to

validate the simulation.

Introduction

As a sea-going service that seeks to protect and preserve the environment, it is the Coast

Guard’s responsibility to look for practical alternative fuel sources beyond traditional fossil fuels.

One alternative that is growing in scientific and commercial communities is the hydrogen fuel cell.

Hydrogen fuel cells use the abundant element hydrogen to produce electricity with the only

byproducts being water and heat. Hydrogen fuel cell applications currently range from cars and

buses, to large scale power plants. Most fuel cell projects are still focused on land transportation;

however, fuel cell prototypes are beginning to enter the maritime domain. It is very important to

be prepared to take on a regulatory role and learn about the potential applications within the

service.

The goal of this capstone project is to explore hydrogen fuel cell applications in the

maritime industry by constructing a hybrid hydrogen fuel cell and battery system to power a small

motor, which will simulate a variable electronic load similar to a direct current (DC) electric

trolling motor with varying speed levels. This project has the goal of combining the fast system

response of a battery with the renewable aspect of a hydrogen fuel cell, while developing and

applying electrical and mechanical engineering knowledge to develop a functional and efficient

system. The current paper presents the results of one semester working on this project.

Research into the current state of hydrogen and hybrid technologies provide a fundamental

background context for this project and is required to ensure that all safety concerns are understood

and addressed. The Dr. Fuel Cell Model Car Kit ™, which includes a small-scale hydrogen fuel

cell and DC motor was used as a part of this project to learn about hydrogen fuel cell technology.

Testing fuel cell behavior on a small scale provides a reference point for how a larger scale fuel

cell will behave. This fuel cell can also be compared to an equivalently sized battery to contrast

performance. A system model for the hybrid fuel cell battery system is necessary to develop a

working design and to simulate how the system will function. This model must include a controller

to decide how the battery and fuel cell will interact to meet the systems power requirements of a

variable load. The final phase of the project includes the physical construction of the system, as

well as verification and validation of the system using the digital model.

While some testing has been done in the maritime domain using fuel cells, this project

hopes to contribute a unique perspective on small boat applications that has yet to be explored.

While fuel cell technology currently serves a niche market, as research continues and technology

advances, hydrogen fuel cell applications will likely continue to expand.

Literature Review

A fuel cell consists of three parts; the anode, the cathode, and the electrolytic membrane.

Hydrogen is inserted into the fuel cell on the anode side where a thin catalyst layer helps accelerate

the reaction to split the hydrogen molecule into two hydrogen ions and two electrons. The

electrolytic membrane prevents electrons from passing through it, forcing the electrons to travel

through a circuit, producing electricity, while the hydrogen ions lass through the membrane. Once

through the circuit, the electrons recombine with the hydrogen and oxygen ions in the cathode to

produce H2O in the form of water vapor and heat. The chemical reaction that happens throughout

the fuel cell process is found in the following equations [1], [8].

2: 2 2Anode side H H e+ − + (1)

2 2

1: 2 2

2Cathode side O H e H O+ −+ + (2)

2 2 2

1:

2Total cell reaction H O H O+ (3)

A study of fuels used in the shipping industry conducted by Ballard industries found that

hydrogen has on average three times more energy per unit mass than diesel fuel [4]. Clean

emissions and high energy density are two of the primary advantages of hydrogen fuel cell

technology, however, hydrogen is far from the perfect fuel.

Hydrogen is currently produced in numerous ways including: steam reforming, pyrolysis,

plasma reforming, gasification, and partial oxidation. However, all of these methods use fossil

fuels resulting in 96% of current hydrogen production being from fossil fuels [6], rendering it

unsustainable. Green options for producing hydrogen include: photolytic splitting, thermal

splitting, and electrolysis. Photolytic splitting, and thermal splitting use solar, while electrolysis

can use solar, wind, or hydro power. Electrolysis is the primary source of hydrogen produced via

renewable energy [6], however, the current infrastructure for electrolysis is underdeveloped and

inefficient.

Hydrogen storage is another hurdle impeding the implementation of fuel cell systems.

Hydrogen has a low energy per unit volume compared to other fuels. Ballard industries’ study of

fuels used in the shipping industry found hydrogen’s energy per unit volume to be around eight

times lower than diesel fuel [4]. At average atmospheric temperatures, hydrogen is a low density

gas, and thus to store or transport large quantities, hydrogen must be cooled and pressurized [5].

The energy required for renewable hydrogen production and storage affect the overall

efficiency of hydrogen fuel cell systems. Electrolysis requires energy to separate hydrogen from

water. After electrolysis, the cooling of hydrogen for storage purposes requires energy. Before it

can be used in a fuel cell, the pressure of the stored hydrogen may be regulated based on the desired

voltage or current output, requiring further energy. All of these processes add up, bringing the

practicality and cost of implementing hydrogen fuels cells into question.

The safety of hydrogen is another important consideration. One of the foremost goals

driving Coast Guard regulation is to ensure the safety of all mariners upon the high seas. With

potential applications in the maritime domain as a power plant or integrated system, fuel cells must

be studied and understood in order to ensure their practical and safe assimilation aboard ships and

other vessels on the seas. One of the most notable safety hazards of the hydrogen fuel cell lies

within the combustible nature of the fuel. Hydrogen is highly combustible but necessary for a fuel

cell to work. The most general and practical approach to this issue assumes the fuel cell is used as

a power plant on land, where the hydrogen can be stored underground, however, this is not feasible

for shipboard applications [2]. Although certain technologies such as electrolyzers allow for

onboard hydrogen production, eliminating the need for large scale storage of fuel, the risk of fire

and explosion will always remain a premiere concern, not that this risk doesn’t already exist when

working with traditional fossil fuels [2]. The safety of hydrogen storage presents a central issue

that is mainly being explored on land. With the project’s focus being the maritime domain, it has

the opportunity to explore hydrogen storage in the maritime domain and compare the levels of

safety between a hybrid and pure battery system.

While these issues have limited the number of hydrogen fuel cell applications, the industry

is growing faster than ever, with increasing rates of research and development. More hydrogen

fuel cell power plants are opening, and car manufacturers are investing in hydrogen fuel cell

technology. Hyundai released their first hydrogen powered car for sale in January of 2019. Aircraft

manufacturers such as Airbus and Boeing are looking into hydrogen fuel cell powered aircraft [7].

With increasing pressure on commercial vessels to limit their carbon footprint, maritime

companies have been researching hydrogen fuel cell propulsion applications in river tenders,

ferries, and yachts, along with applications in auxiliary systems on larger vessels, including

powering navigational equipment and heating, ventilation, and cooling systems [4].

In 1997, the United States Coast Guard researched and developed a plan to implement a

fuel cell power plant on its own vessels. For this study the Coast Guard selected the USCGC

Vindicator, an old spy ship acquired from the U.S Navy. The USCGC Vindicator served from

1994 to 2001 and with the fuel cell implemented; the ship would have been faster, quieter, more

efficient, more cost effective, and produce potable water. With the fuel cell implemented the vessel

would have an increase in range of over 250%. The Feasibility study from USCGC Vindicator

found that the benefits and fuel savings would vastly outweigh the up-front cost of implementing

a fuel cell on board a ship. Regardless of savings in fuel and increase in efficiency, fuel cells are

smaller and completely silent. Fuel cells would allow for more space on ships for auxiliary

systems. Producing a silent military vessel would create an unprecedented operational advantage

for ships during reconnaissance missions [10].

Commercial maritime research and development into hydrogen technologies include the

development of a ferry running solely on a PEM fuel cell. This ferry was built in 2006 in Germany.

It transported passengers quickly and quietly while emitting only heat and water as exhaust and

could refuel in under thirty minutes. However, an efficiency analysis determined the PEM fuel cell

system to be around 30% efficient, leading to the termination of the project in 2013 [3].

Hydrogen energy is a growing technical field that has global implications. The demand for

renewable energy continues to increase as the environmental impact of fossil fuels becomes more

and more apparent. In addition to disrupting the earth’s climate, there is a finite supply of

conventional fossil fuels, and as it decreases and the climate changes, societies will be forced to

turn to alternative energy sources. Globally, fossil fuel emissions are degrading air quality and

playing a major role in climate change. The health and climate impacts are worsening the longer

societies rely on fossil fuels. In addition, the fact that fossil fuels are finite and limited to certain

regions has generated conflict as nations attempt to control regions that supply the fuels.

A hydrogen and renewable energy fueled planet can decrease and theoretically eliminate

harmful emissions because hydrogen and renewable energy can be produced virtually anywhere,

slowing and preventing the negative global impacts of fossil fuels. The social benefits of hydrogen

energy are well worth the challenges the technology poses. Hydrogen energy along with other

renewable energy technologies can have a massive global influence through the reduction of

greenhouse gas emissions and air pollution. The long-term health and climate benefits of clean

energy can help prevent new climate and health challenges from continued fossil fuel use.

Hydrogen technologies offer largely positive societal impacts domestically and internationally.

The main dilemma facing hydrogen technologies regarding societal impacts is the competition it

presents to the already established fossil fuel industry, which maintains 56% of total energy

industry jobs [9]. While hydrogen technologies are a threat to the established fossil fuel industry,

they reinforce the positive trend of the growth in renewable energy technologies and boast

proportionally positive societal impacts.

Hybrid power management systems revolve around the concept of incorporating multiple

power sources, and alternating or combining these sources based on the power demands of the

load. An experimental study on a passive fuel cell and battery hybrid power system provides a

foundation for the incorporation of fuel cell stacks with batteries. This experiment utilized the fuel

cell as the primary power source for the load, while the secondary battery pack provided support

for sudden power consumption during start up and acceleration [11]. The battery system also

allows the system to provide a faster response when compared to a system utilizing a fuel cell as

a primary power source, and effectively meet all demands from the load.

System Design

The main objective of this project is to explore hybrid green energy power systems that

can be implemented in the maritime domain. The project hopes to provide a working model for a

fossil fuel free small boat propulsion system design. To do so, this project focuses on a hybrid

hydrogen fuel cell and battery system, designed to power a variable load such as an electric motor.

Simulink is used to design and model the system and a physical small-scale system will be

constructed with the capacity to power a 3-speed motor (a variable electric motor) to validate the

design. The initial goal of the project was to build a hybrid system that could power the 400-watt

trolling motor of a small boat. The decision to downscale the project and use a fan was due to

safety and cost concerns. Creating a simulation of a hybrid hydrogen fuel cell and battery system

will make it easier to design a similar system to meet different scale and performance requirements

as needed. The specific design of the hybrid and control system model will be discussed in the

next sub-sections.

I. Hybrid System Model

The fuel cell uses a constant input of hydrogen fuel to output constant power. When the

power supplied by the fuel cell exceeds the power needed for the load, the excess power is used to

charge the battery. When the power from the fuel cell cannot meet the demand of the load, the

battery is activated to pick up the slack. When a large change in the power demanded by the load

is detected, the battery is activated. The block diagram of the Simulink model of the hybrid system

design is pictured in Figure 1.

Figure 1. Hybrid system Simulink model

II. Controller Model

The controller block of the Simulink model determines how the hydrogen fuel cell and

battery interact with each other. To design the controller, Simulink’s stateflow library is used. This

library allows for states to be defined and the transitions between the states to be controlled via

complex conditions. Currently, the fuel cell is activated when the system is turned on and the

controller monitors the current demanded from the variable load. When the current draw of the

load exceeds a threshold value, the battery is activated to supplement the fuel cell and meet the

load’s power demand. This system allows the fuel cell to act as the primary power source, while

using a feedback loop to monitor power requirements from the variable load and supplements the

fuel cell with the battery when needed. An example of the stateflow logic used in the controller to

turn the battery on when the load exceeds the power supplied by the fuel cell is depicted in Figure

2.

The controller will include states to use excess power generated by the fuel cell to charge

the battery as well as activate the battery when a drastic increase in power is demanded by the load

to improve the response time of the overall system. The controller will also monitor the output

voltage of the fuel cell and will activate the battery in the event this voltage drops below a threshold

value, signifying a fuel casualty or the expenditure of all hydrogen fuel.

Figure 2. Simulink stateflow diagram of controller

III. Variable Load Model

A variable load describes a load that can require a range of different resistance values, and

transitions between these values. Each of the load levels require a different amount of voltage and

current to operate. To simulate a varying load in MATLAB Simulink, the staircase block outputs

different values for different periods of time. The controller for this system analyzes the current

demands from the load, so the outputs of the staircase block represent varying current demands

from the load. Running the current Simulink simulation of the hybrid system produces the plot

depicted in Figure 3, which includes simulated current supplied to the variable load from the fuel

cell in blue and the battery in green. This figure also displays the current demands from the load

in orange.

Figure 3. Simulink simulation results

In this simulation, the load demands 1 A from 1.5 - 3 s, 2 A from 3 - 4.5 s, 12 A from 4.5

- 6 s, and 4 A from 6 - 8.5 s. The output current from the fuel cell of 8.2 A is sufficient to power

the variable load until 4.5 s when the required current spikes to 12 A. At this point, the controller

recognizes that the demand exceeds the nominal output of the fuel cell and activates the battery.

The current supplied to the variable load from the fuel cell and battery combined slightly exceeds

the demand of the load from time 4.5 - 6.0 s. When the demand from the variable load drops to 4

A at 6 s, the controller turns off the battery and the system is again powered solely by the fuel cell.

This simulation demonstrates the capability of the controller to react to the variable nature of the

load and respond by utilizing the appropriate component of the hybrid design. In the future, the

controller will no oversupply the load, as can be seen from time 0 - 4.5 s, instead this power will

be used to charge the battery. The load of the simulation will also be updated to accurately reflect

the transition in demand of the variable load, opposed to the current, instantaneous changes in

demand. This poses a future challenge of programming a controller to recognize the changing

demands from the load and activate the battery to improve system response.

Results

I. Load Testing

Testing the power draw of the trolling motor while testing it at various rpm settings was

required to find the maximum power required to power the Minn Kota trolling DC motor. Utilizing

water front and a dinghy provided, it was found that the maximum power draw to be 400 watts

with a maximum amperage draw of 40 amps which can be seen in Figure 4 and Table 1 for testing

at the beach.

Figure 4. Power draw at the various speed settings of the trolling motor

Table 1. Values obtained from trolling motor measurements at each speed setting

Setting 1 Setting 2 Setting 3 Setting 4 Setting 5

Voltage (V) 12.45 12.24 12.20 12.05 11.42

Current (A) 7.71 9.89 13.6 17.25 34.7

Power (W) 96.98 121.10 165.30 208.00 396.49

Implementing the load into the Simulink model requires the transfer function of the load

to be known. Therefore, it was necessary to figure out a way to properly find the time constant and

steady-state value of the trolling motor under no load condition. For these characteristics to be

discovered, the voltage step response of the motor had to be tested. It was found that the time

constant of the motor was 8.2 milliseconds, which is extremely fast. Also, the normalize steady-

state gain was 1.05. After these two values were obtained, the transfer function was implemented

into Simulink as seen in Figure 5.

Figure 5. Verification model in Simulink of the trolling motor

Comparing the simulation to what was physically obtained, the transfer function of the

trolling motor was verified as shown in Figure 6.

Figure 6. Step response comparison of the model and physical system

II. Small Scale Fuel Cell and Battery

To begin understanding the concepts behind fuel cell analysis and operation The Dr. Fuel

Cell model car kit was assembled and analyzed. The primary component of this kit was a reversible

Proton Exchange Membrane fuel cell, capable of creating a small amount of hydrogen from an

electrolysis reaction which splits water into hydrogen and oxygen molecules. Once connected to a

load, the fuel cell will recombine the separated hydrogen and oxygen molecules back into the

water. One of the main focuses of this project is the integration of a battery into the hybrid design

to improve the response of the system. This response characterizes how quickly a power source

can meet the demands from a load. To understand how fuel cells respond to the addition of a load,

the voltage response of the fuel cell, which characterizes how quickly the fuel cell can provide

voltage to the load, was measured and compared to that of a comparable battery. The set up for

this test is shown in Figure 7 where the PEM fuel cell is integrated as the power source.

This test utilized varying load levels inside of a load measurement box provided in the Dr.

Fuel Cell model kit. The load measurement box contains load levels of 1, 3, 5, 10, 50, 100, and

200 ohms. To analyze the differences between the responses of a fuel cell compared to a battery,

each of these sources were utilized as the primary power source and separately connected to the

load measurement box. The load was then incremented every 3 seconds, which allowed the source

to fully respond to the load before continuing to the next load setting. The test began with a load

of 1 ohm and finished on the 200-ohm setting. Using an Arduino MEGA the voltage across the

load was measured as an analog value and converted using MATLAB code into a voltage value.

These voltage values were measured every millisecond over a time period of 21 seconds and

graphed to show the response of the power source over time. First, the PEM fuel cell was used as

the power source as shown in Figure 7, and the voltage was recorded. The response of the system

is shown in Figure 8. This Figure shows the gradual response of the fuel cell as the load is

increased.

Figure 7. Dr. FuelCell measurement setup

Figure 8. Voltage response of PEM fuel cell across varying loads

Next, a AA battery providing 1.5 V was used as the power source for the DC motor. The response

of the system is shown in Figure 9.

Figure 9. Voltage response of AA battery across varying loads

Figure 9 shows the almost instantaneous response of the AA battery as the load is increased.

To compare the responses of the fuel cell and battery the response from the 1-ohm to 3-ohm

transition were normalized and plotted on the same graph. Figure 10 demonstrates the difference

in response time for the fuel cell when compared to the battery. The battery, shown in orange, has

an almost immediate response to the demand from the load, while the fuel cell, shown in blue,

takes more time to respond to the demand. This experiment demonstrates the reason a battery is

incorporated in the hybrid design, especially considering the varying nature of the load.

Figure 10. Normalized response of fuel cell and battery for 1 Ohm to 3 Ohm transition

Future plan of this project is to build a physical 100W fuel cell system as it is shown in

Figure 11, to clarify and validate this design for a motor that required less that 100W power.

Figure 11. 100W fuel cell system

Conclusions

The team has tested a trolling motor by finding the step response and the rpm to power

output correlation and obtaining the transfer function. Utilizing the smaller fuel cell in the provided

Dr. Fuel Cell kit, the team tested the response time and behavior of the PEM fuel cell and an AA

battery to estimate how a larger fuel cell and battery will act. Using the data collected, the team

has begun implementing the variable load, fuel cell, and battery into Simulink models. In

Simulink, the group has developed a basic controller for the hybrid system that determines when

to disconnect the fuel cell to conserve hydrogen. By using Simulink, the team can experiment

with different controllers to optimize the power system without consequence.

Hydrogen technology is advancing into the maritime domain and the Coast Guard needs to

be prepared to take on a regulatory role. Hydrogen is a volatile gas and its storage, transportation,

and use can be dangerous if proper safety measures are not followed. Hydrogen technologies have

the potential to greatly reduce environmental impacts in the transportation domain and bolster the

increasing movement towards green energy and the reduction of greenhouse gas emissions.

Research conducted in this project further elaborates on hybrid system designs specifically

focusing on the maritime domain, laying the foundation for further research into the integration of

hydrogen technologies aboard maritime vessels.

At this stage of the project, the fundamentals of hydrogen fuel cell technology have been

explored, a hybrid power system design has been created, and a basic computer simulation of the

design has been completed in Simulink. The next milestones for the project are to improve the

Simulink model to account for more variables and scenarios and build the physical system to

validate the simulation. The team plans to further develop the Simulink models to accurately

predict the responses of the hybrid system in real time by testing and measuring the operating

characteristics of physical components. The majority of the work will be building a physical model

and comparing those results to the simulations. PEM fuel cells have incredible potential to be the

future of power generation, yet there are still many improvements to be made.

ABET Student Outcomes

Some of the performance indicator for ABET student outcomes [12] can be addressed in this

project. Students learned to solve complex engineering problem by applying the principles of

engineering, science and mathematics. They recognized the professional responsivities in

engineering education and considered the impact of engineering solutions in global, cultural,

social, environmental, and economic problems today. A team for four undergraduate students in

two different major demonstrated the ability to establish realistic goals, plan for weekly tasks, and

met majority of their millstone in one semester. They improved their knowledge by independently

seeking to find different sources and solving the new problems. They learned different new

engineering tools, skills, programming language, computer tools while working on this project

[12].

Disclaimer

“The views expressed in this article are the personal views of the authors and do not necessarily

represent the views of the United States, the Department of Homeland Security, or the United

States Coast Guard.”

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