Hydrogen Fuel-Cell Vehicles

Hydrogen Fuel-Cell Vehicles The Future of Transportation Sam Glidden Jared Delahanty

Project Advisor: Mike Mangini

June 2004

Table of Contents Introduction......................................................................................................................... 3 A Hydrogen Future ............................................................................................................. 4 System Overview ................................................................................................................ 8 The Fuel Cell..................................................................................................................... 12 The Hydrogen Storage Tanks ........................................................................................... 23 The Motor ......................................................................................................................... 30 AC Motor Controller......................................................................................................... 34 Regenerative Braking........................................................................................................ 36 Intermediate Energy Storage............................................................................................. 38 Platform Vehicle and Modifications................................................................................. 46 Cooling.............................................................................................................................. 50 Performance Analysis ....................................................................................................... 51 Costs.................................................................................................................................. 60 Appendix 1: Sources of Hydrogen.................................................................................... 62 Appendix 2: How Safe is Hydrogen? ............................................................................... 64 Appendix 3: References.................................................................................................... 66

Special Thanks to: The project received a generous donation from New York State Electric and Gas Co. (NYSEG) to help with research and design. We would like to thank Mike Mangini for donating countless hours answering our questions, managing the administrative details of our project, and editing the final work.

We would also like to thank: Charles Hanley, Mr. Engel, Mr. During, Mrs. Michaels, Mrs. Bustamante, Dryden High School, Steve Glidden, Nancy Tomlinson, Scott Warren, Cathryn Ourtel.

2

Introduction We began this project as two seniors at our local high school looking for something extra to do. Jared was interested in cars in general and was currently rebuilding an old Jaguar. I have always been fascinated by the latest technology, and I was really interested in the future of vehicular technology, especially because gas-electric hybrid cars were making their debut. We both wanted to do something in that area and we had heard of cars powered by hydrogen. This sounded perfect, because it was futuristic enough to be exciting but practical enough to be possible. In fact, a little research showed us that current automotive companies were building hydrogen car prototypes and that hydrogen cars had a lot of potential. They could improve both the performance and environmentalfriendliness of vehicles. We were sold, and decided to turn our interest into something real. After a little thought we went to Mike Mangini, our physics instructor, to propose an independent study project through our school to design a hydrogen vehicle. We knew it would be challenging but that it would also be possible; after all, hydrogen cars already existed. The independent study project would give us motivation to see the project through to the end and would give us a little extra credit. When the administrative details were out of the way, we began to research and design. Our project has two main goals. First we wish to learn more about fuel cells and hydrogen technology with respect to automobiles. Secondly we want to educate to community about the benefits and feasibility of hydrogen cars. We hope to dispel any myths about the possibility that they would be underpowered, dangerous, or too expensive. We want to encourage to adoption of hydrogen vehicle technology because it can benefit all. By completing our project, we can show that it is possible to create an efficient and practical vehicle. This booklet is the attempt to complete those objectives. The further we delved into the project, the more we realized how complex the situation really is. Every section of this book could be many times as long as it is. The motor section alone could encompass hundreds of pages discussing types, functions, efficiencies, powers, manufacturers, etc.,

3

but we had neither the time nor the inclination to go that deeply into a specific topic. Will our design create the best, most efficient vehicle? No – but it is a working vehicle, and we did take into account everything we could. This car could be built, driven and used to prove the technology.

A Hydrogen Future As everyone knows, current vehicles are powered by an internal combustion engine that runs off gasoline or diesel (fossil fuels). Current vehicles are also capable of nearly everything we ask of them, whether it is reaching high speeds, pulling heavy loads or undergoing rapid acceleration. However, the internal combustion engine is also a century-old invention. Internal combustion engines are beginning to show signs of age. Running off fossil fuels, they require a giant supply of oil. Without going into the politics of it, securing this supply of oil has cost the United States and many other countries billions of dollars, required compromising our values, and weakened the US economically as we become increasingly dependant on foreign importation. The dependence has, at the time of this writing, become particularly obvious as gas prices soar past the $2 dollar a gallon mark. And because many people believe that we have either reached or will soon reach the peak in the world’s supply of oil, prices will only rise. The increasing scarcity of oil points to the imminent doom of the internal combustion engine. There is a second price to gasoline vehicles: pollution. Ignore it as some might, clouds of smog hang over many of the country’s cities. This problem can be even worse in other nations around the world. It is not fully known at this point what this smog does to our health and how responsible it is for causing various cancers, leading to the national increase in allergies and asthma, and creating other health problems. Burning oil in our cars dumps an estimated 302 million metric tons of carbon dioxide into the atmosphere each year. Many other greenhouse gases are also released. It is gradually becoming clear 4

that global warming is a real problem, and at this point the only people who deny this are people who don’t want to bother fixing it. The gasoline engine is not something the planet can sustain for much longer, both in terms of providing fuel and in terms of keeping the environment hospitable. The development and adoption of alternative options now would enable the use of gasoline engines for the next several hundred years at least. However, keeping and continuing to expand the number of internal combustion engine vehicles will only hasten their cataclysmic end when fuel supplies run out. We do not advocate abandoning oil power, but we do feel that in order to preserve the technology for uses where it is required, critical, or essential, we must stop wasting fuel in applications where other alternatives exist. A gradual shift to alternative energy sources, beginning now, could reduce or possibly even eliminate any economic plight that would be caused by the sudden expiration

of

internal

combustion engines as a usable technology. The

most

obvious

alternatives to gasoline engines

are

electric

motors. Electric motors are, actually, far more suited to a transportation application than internal combustion Figure 1: Under the hood of an electric car. The large metal box is the motor controller. Image from http://auto.howstuffworks.com/electric-car1.htm.

engines.

Electric motors sport far higher efficiencies, lower

weights, and higher torques than their gasoline equivalents. Motors can also provide adequate power over a large range of engine speeds, potentially eliminating the need for a transmission in a vehicle. However, an electric motor system has one fatal downfall: energy storage. A well-made internal combustion engine can propel a car for 30 or more

5

miles per gallon of gasoline. Vehicular ranges average around 300 miles on a tank, with a lot of variation depending on the vehicle. Hybrid vehicles, which feature the marriage of internal combustion engines and electric motors, get even better mileage, still consuming only oil. The best electric cars, however, can barely travel 100 miles on a full battery charge. Unfortunately, the current generation of batteries is unable to hold enough energy to power an electric car any further. The batteries are heavy, consume a lot of space and take several hours to recharge. Consequently, electric vehicles have never become practical alternatives to conventional cars. Also unfortunate is that in effort to squeeze the highest possible mileage out of an electric vehicle, the electric motors have been minimized to a size unable to match today’s standards of performance and power in gasoline engines. This has fostered the myth that electric vehicles are not and cannot be as powerful as conventional cars. Dispelling this myth brings us to the topic of this booklet: hydrogen power. Hydrogenpowered vehicles come in two types: hydrogen combustion engines and hydrogen fuel cells. Through combustion, a hydrogen engine acts like an ordinary engine, except hydrogen is burned in the cylinders instead of gasoline. However, this requires the use of a modified

combustion

engine that still results in Figure 2: Honda’s FCX Fuel cell vehicle. Image from http://hondacorporate.com/?onload=fcx.

the

inherent exothermic

inefficiency of

any

reaction.

The other option, using hydrogen fuel cells, is far better. Hydrogen fuel cells take hydrogen and combine it with oxygen. This generates electricity. The electricity is then used to power an electric motor, using the same technology as today’s electric vehicles. Because the energy is stored in the form of hydrogen, and not in a battery, this enables electric vehicles to carry significantly more energy. This allows for vehicles with larger motors and longer ranges. In fact, with development, the average hydrogen vehicle

6

should be able to go further and be more powerful than the average gasoline vehicle. The use of hydrogen fuel cells will allow us to advance automotive technology to levels unreachable in past times. Hydrogen fuel cells overcome the two major flaws of internal combustion engines. First, hydrogen is the universe’s most common element. There is no risk of ever running out. As hydrogen can be produced from the electrolysis of water, it can be made in any county anywhere. The issue of importing hydrogen will not exist. And because fuel cells output water, there is no need to worry about consuming

the

world’s

water

supply.

Essentially, the hydrogen can be manufactured anywhere in large quantities by breaking down water into oxygen and hydrogen. The hydrogen is then distributed to the “gas” stations of the

Figure 3: A hydrogen fueling station that recently opened in Iceland. Image from Renewable Energy World at http://www.jxj.com/magsandj/rew/news /2003_04_04.html.

future to fill your car. The car will be powered by the fuel cells, which recombine the hydrogen with oxygen in the ambient air to form all the water originally used. For more information on the manufacturing process of creating hydrogen, see Appendix 1: Sources of Hydrogen. Secondly, hydrogen vehicle will not pollute. The fuel cell potentially enables a hydrogen car to be completely environmentally friendly. Because a fuel cell needs only hydrogen and oxygen, no carbon, greenhouse, or other harmful gases are produced. Oxygen is already found freely in the air. The hydrogen involved is also not environmentally damaging for two reasons. First, the pure hydrogen will be completely contained at all times during the process, and will not come in contact with the outside world. Second, even if any hydrogen does leak into the atmosphere, it will immediately combine with atmospheric oxygen to form H2O (water). Water does not damage the environment. Appendix 1: Sources of Hydrogen deals with the possible methods of obtaining the necessary pure hydrogen and their various environmental impacts.

7

Hydrogen vehicles have the potential to revolutionize the transportation industry. However, the massive size of the automotive business makes it slow to change and hesitant to adopt new technology. Only through public and political pressure will hydrogen vehicles be developed within a reasonable time frame. Hydrogen could very likely be the future. The sooner we reach that future, the sooner we decrease pollution of the planet and cure the economic and political woes caused by a dependency on foreign oil. This booklet is an effort to explain just how easy that future is to construct.

System Overview Before we go into the details of a hydrogen vehicle, it is important to get a sense of how the components work together. This overview shows each component and what it does to power the car. The specific details concerning each component, such as manufacturing and user specs, how we chose it, and what it does, can be found in the following sections of this booklet. The simple diagram on the following page shows the flow of energy through the vehicle.

8

Hydrogen from the tanks and oxygen from the air combine in the fuel cells to generate electricity. The fuel cell is the primary source of power in the vehicle. Running at a maximum of 80 kW, it sends power to the motor controller. The more the driver pushes down on the accelerator pedal (calling it a “gas” pedal is no longer accurate), the more energy the controller asks for and the more energy the fuel cell puts out. Because the preferred car motor is AC, not DC like the fuel cells and the rest of the system, the

9

controller will convert the DC power from the fuel cells to AC of the correct frequency and power to drive the motor. The motor outputs a maximum of 100 kW, powering a fixed gearbox and the drivetrain. The car does not require a multi-gear transmission because unlike internal combustion engines, electric motors can be made to yield high torque over a wide RPM range. Gasoline engines operate best over a very small RPM band and so a complex transmission is necessary to keep the engine running efficiently. An electric motor is not so limited. A hydrogen fuel-cell car should also have integrated regenerative braking. This complicates the system somewhat. When the driver brakes, instead of conventional brakes slowing the car through friction, the motor begins to act as a generator. Regulated by the controller, which receives information the brake petal, the motor slows the car at the desired rate. At the same time this generates electricity, which goes through the controller, is converted from the AC of the motor to DC, and charges the ultracapacitors. Hence, when the car brakes the ultracapacitors gather electricity. This increases vehicular efficiency. The amount of heat generated when a conventional 2500 lb car brakes from 60 mph to rest is enough to light a 100 W bulb for an hour. This energy is normally vented off to the atmosphere providing no useful function. When the driver accelerates again, the ultracapacitors are drained to power the car. During times of high acceleration, both the ultracapacitors and the fuel cell will be powering the motor. Running the fuel cell at 80 kW and the ultracapacitors at 20 kW, the motor can run at maximum output for 11.25 seconds before the ultracapacitors are drained. The car should be able to reach 60 mph in that time. Additionally, if the car is completely stopped, and the ultracapacitors are not fully charged, the fuel cell will turn on and charge them. This assures the driver will have maximum acceleration when he or she wants it. To actually build the car, a more detailed electric schematic is needed. Voltages need to match and current needs to fall within limits of the components. The result is a slightly more complicated system.

10

As you can see, a DC-to-DC converter is needed to up the voltage of the ultracapacitors to match that of the fuel cell. Heavy gauge wiring will also be needed for most of the circuit where the current reaches several hundred amps. The power output of the motor during regenerative braking will vary on the rate at which the vehicle brakes. Therefore, the power rate between the controller and the ultracapacitors will also vary. However, it is important that it does not exceed 100 volts and 450 amps (45 kW) or it may overload the ultracapacitors, destroying them. The controller can be set to prevent this problem. 11

The diode and switch system between the ultracapacitors and fuel cell tie the ultracapacitors into the system. The diode allows the ultracapacitors to power the controller without current flowing from the fuel cells towards the ultracapacitors. As such, the switch is open during normal driving. However, when the car comes to a complete stop, the switch will close. The ultracapacitors can then be refilled by the fuel cell is they are not already full from regenerative braking. The driver will thereby have fully charged ultracaps to assure he or she has maximum power for the next acceleration. Most of the remainder of this book is intended to describe each individual component and how we arrived at the various specifications for them. Details on the physical locations of various components can be found in the Platform Vehicle and Modifications section.

The Fuel Cell The fuel cell is the heart of a hydrogen-powered vehicle. A fuel cell uses the combination of hydrogen and oxygen to generate electricity. The side effect of this process is the generation of water and heat. The electricity can then be used to power the car. The fuel cell is the primary device that turns ordinary electrical vehicles into a practical, competitive alternative.

An Extremely Brief History Fuel cells were first invented back in 1839. However, it was not until the 1960s that NASA demonstrated the first practical use of fuel cells in space flight. From there the technology has grown. In the 1990s fuel cells began to become a viable option for powering a car. The late 1990s and the 2000s saw the first prototype hydrogen vehicles.

12

Types of Fuel Cells There are multiple types of fuel cells. Each has different operating conditions and some use a fuel other than pure hydrogen. For example, methanol fuel cells are commonly used. They break down methanol into hydrogen and carbon, and then combine the hydrogen with oxygen to produce water and energy. However, they release the carbon into the atmosphere, thereby polluting. The only practical type of fuel cell for a clean, efficient vehicle is a Proton Exchange Membrane cell (PEM). PEMs are the most suitable type of fuel cell for vehicular applications because of their lower operating temperature. (They operate at the lowest temperature, around 80 degrees Celsius. Other cells require higher temperatures, which makes them unsuitable for a vehicular application.) PEM fuel cells rely on the simple combination of hydrogen and oxygen to produce electricity. At all points in this book, whenever “fuel cell” is mentioned, we are talking about PEM fuel cells.

How Fuel Cells Work The basic concept behind how a fuel cell works is very simple. The following illustration from Ballard Power Systems provides an excellent view into the workings of a fuel cell.

13

Figure 4: Fuel Cell Illustration from Ballard Power System – http://www.ballard.com

On the left side of this illustration, hydrogen enters the fuel cell. On the right, oxygen is provided. Hydrogen is a reactive element, and will combine with oxygen given the opportunity. Each hydrogen molecule, H2, has two hydrogen atoms each with one electron. The oxygen has 6 valence electrons. The rules of chemistry tell us that each atom is in its most stable state when it has a full outer shell of electrons, which for hydrogen is 2 electrons and for oxygen is 8. Each atom tries to move towards this optimal quantity and arrangement of electrons by binding with other atoms. In this case, each oxygen atom needs two more electrons. Each hydrogen atom needs one. The oxygen will therefore pull in two hydrogen atoms to fill its valence electron shell to a total of eight electrons. Each hydrogen atom, in return, shares one of the oxygen’s electrons, resulting in a full shell of 2 electrons to stabilize the hydrogen. This process requires the hydrogen and oxygen to bind together, and in the above illustration, they are on opposite sides of the fuel cell. The hydrogen, being the smaller atom, is more mobile and is pulled to the right. To reach the oxygen atom the hydrogen 14

must pass though the Proton Exchange Membrane. The PEM membrane, as its name suggests, allows only the passage of a proton, which happens to be the nucleus of a hydrogen atom. As the hydrogen atom passes through the membrane the hydrogen’s electron is left behind. Upon reaching the oxygen, the hydrogen nucleus is joined by another which also crossed the membrane, and both bond to the oxygen. However, the oxygen-hydrogen complex (which is H20 – water) is missing the two electrons that the two hydrogen atoms left behind when they crossed the PEM membrane. The oxygen is not yet satisfied because it still only has 6 valance electrons as the hydrogen arrived without any. The hydrogen-oxygen complex is therefore positively charged, because electrons carry a negative charge and the hydrogen-oxygen complex is missing two. Meanwhile, the left side of the fuel cell, where the hydrogen originally was, now has two extra electrons. An electric circuit connects the two sides of the cell. The electrons (negatively charged) are drawn around the circuit, attracted to the hydrogen-oxygen complex because it is positively charge. The only path to the oxygen is along the electric circuit. The potential difference in charges (positive and negative) between each side of the cell creates voltage, generally in the range of 1 to 2 volts for a PEM cell. If the electric circuit is closed, the electrons are allowed to cross over to the hydrogen-oxygen complex, generating current. There is now electricity that can be used to turn a motor and power a car. To produce enough electricity to do this, many of the single cells illustrated above are connected together in series to generate higher voltage. The output of the fuel cell is obviously electricity, and also water (the hydrogen-oxygen complex with the two electrons) and heat. The fuel cell therefore needs to dissipate this heat into either the ambient air or a water system; more details on this can be found in the Cooling section.

15

Development Current hydrogen fuel cells need further development before they will be able to replace internal combustion engines. The present generation of fuel cells requires expensive metals such as platinum, which is required as a catalyst to speed the reaction between the hydrogen and oxygen. Additionally, fuel cells today require very pure hydrogen gas. Hydrogen gas with small amounts (even fractions of a percent) of sulfur or carbon in it will cause degradation of the fuel cell by binding to the platinum catalyst. This decreases both efficiency and lifetime. Obtaining hydrogen without any impurities is difficult and expensive. Therefore, current fuel cells are not cost-effective. However, research is underway at Cornell University, other universities, and the private sector to solve these problems. While today’s fuel cells cost tens of thousands of dollars, tomorrow’s could be far cheaper. Hydrogen fuel cells also face several other issues that are rapidly being solved. The first concerns temperature. To operate, a PEM fuel cell must run at 80 degrees Celsius to perform the hydrogen-oxygen combination. Fuel cells consequently have trouble in lower temperatures. However, this issue can simply be solved by proper thermal management and providing the cell with a heater when necessary. The other major issue concerns start-up times; many fuel cells take several minutes to warm up before a car can begin driving. However, this has recently improved – a fuel cell system by the manufacturer Ballard Power Systems can start in less than 40 seconds. Most people give their cars a few seconds to warm up when they first start them, and so this amount of time is not unreasonable. It should also improve even further in the future. The final issue is weight; a current 80 kW fuel cells weighs nearly 500 lbs (220 kg). This is a significant fraction of the total weight of a vehicle and consequently degrades the vehicle’s performance. However, this issue can be solved hand in hand with the cost issue – a cheaper fuel cell would by necessity use lesser amounts of platinum and would therefore weigh less. Additionally, clever designing of the car can decrease the weight of other systems so the fuel cell’s weight becomes less onerous.

16

Fuel Cell Size The size (i.e. power output) of the fuel cell depends on the desired performance of the vehicle. Because the fuel cell is the most costly component of a hydrogen car, it is important to keep its size to a minimum. What this booklet refers to as the “fuel cell” actually consists of numerous small fuel cells stacked together to generate the necessary voltage and current. Therefore, minimizing the required kW output of the overall cell will decrease its size more or less proportionally. As noted in both the sections on Intermediate Power Storage and Regenerative Braking the main way to decrease the output requirements of the fuel cell in a car is by augmenting it with ultracapacitors. The ultracapacitors provide extra power during cases of high acceleration. This power comes from either of two sources: first, regenerative braking will charge the car whenever it decelerates; and second, in the event that regenerative braking doesn’t provide the necessary power, the fuel cell will charge the ultracapacitors when the vehicle is at a complete stop. Therefore, when the driver wants the maximum amount of power the motor can provide (which is 100 kW – see the Motor section), the fuel cells need not provide all that power because a portion of it can come from the charged ultracapacitors. The key to this strategy is finding the balance between fuel cells and ultracapacitors. Draining the ultracapacitors at their maximum rate will empty them quickly, leaving the fuels cell to provide the remaining power to finish the acceleration. However, the alternative is to increase the size of the fuel cell, thereby increasing the weight and cost of the vehicle. There are several things to consider when determining the size of the fuel cell. 1. A higher number of ultracapacitors will decrease the required size of the fuel cell. 2. The combination of fuel cell and ultracapacitors should not exceed 100 kW. 3. Running the ultracaps at maximum power will allow for the smallest fuel cell, but the ultracaps will most likely be drained before the driver finishes accelerating.

17

The driver will then have to finish the acceleration using only a smaller fuel cell. This will greatly decrease the vehicle’s performance on a 0 to 60 speed test. 4. As vehicle weight can vary several hundreds pounds depending on the car model, equipment, etc., the estimated performance relies on the optimism or pessimism of the designer. This makes choosing the optimal balance between fuel cells and ultracapacitors difficult. In light of all this, we have chosen to present several fuel cell solutions. Given an unlimited budget, we would obviously choose the most powerful combination. However, the car can be made more economical by sacrificing some performance. We propose three possible solutions: Maximizing the fuel cell so the ultracapacitors will be guaranteed to last for more than the duration of any given acceleration; minimizing the fuel cell to reduce the cost of the powerplant, but causing the car’s 0 to 60 mph time to increase; or finding an intermediate solution preserving some performance and some economy between the two. This data comes from other sections of this booklet: Ultracapacitor Max Output

45 kW

Ultracapacitor Total Storage

225,000 Joules

Estimated Vehicle Weight

1350 – 1590 (3000 – 3500 lbs)

Max Motor/Controller Power

100 kW

Solution 1: Large Fuel Cell Either of the two motors we selected in the Motor section should enable the vehicle to reach 60 mph in around 10 seconds. This will be considered the basis for a conservative fuel cell estimate; the sum of the ultracapacitors’ and the fuel cell’s power output should equal 100 kW for a duration exceeding 10 seconds.

18

The ultracapacitors store 225,000 joules, 225,000 J / 10 sec = 22.5 kW Because this is the high performance option and to assure the ultracaps will last more than the necessary 10 seconds, we will rely on the ultracapacitors to store about 90% of their rated capacity, or 20 kW instead of 22.5 kW. This will allow the ultracaps to run for 11.25 seconds before being drained. 100 kW – 20 kW = 80 kW fuel cell Therefore, a high performance car would need an 80 kW fuel cell.

Solution 2: Minimal Fuel Cell It is slightly harder to determine the minimum size the fuel cell can be. Theoretically a car could get by with a fuel cell only large enough to overcome wind resistance and friction at the max cruising speed. Depending on the car body, this will be less than 20 kW. In this situation, however, acceleration would be terrible. Because the ultracaps maximum output is 45 kW, the motor would never have enough power to reach its full potential. Therefore, without redesigning the entire vehicle, the smallest the fuel cell should be is 55 kW. 225,000 J / 45 kW = 5 seconds Because the ultracapacitors will be emptied after 5 seconds, it will only be possible to run the motor at full power for 5 seconds. However, these five seconds would enable the vehicle to reach a speed of around 40 mph. After that, the motor will run off only the 55 kW fuel cell. Any remaining acceleration after the initial 5 seconds will be poor.

19

On the other hand, the decrease in weight resulting from the drop in fuel cell size would help compensate for the lower power which the motor would run at. In fact, going with a smaller fuel cell would make sense if the motor power was also decreased by 20 or 30 kW. However, the goal of this project has always been to create a high performance hydrogen vehicle that could compete directly with most consumer gasoline cars. While minimizing the fuel cell size would result in an economical, slightly more efficient vehicle, it would also have poor acceleration. A poor performing vehicle would lead to the public perception that hydrogen electric vehicles are sluggish performers as compared to combustion vehicles. This is a myth we are trying to dispel. Minimizing the fuel cell size is not the option we would choose for our vehicle.

Solution 3: A Compromise The final option involves meeting a compromise between performance and economy. Having an 80 kW fuel cell could be considered by some to be overkill. In standard driving, most drivers do not push their vehicle to the limit. A 15 to 20 second acceleration from 0 to 60 mph is perfectly acceptable most of the time. Decreasing the fuel cell somewhat would still provide decent performance by allowing the ultracapacitors to last a reasonable duration. If the fuel cell was decreased from 80 kW to 70 kW, that would require running the ultracaps at 30 kW to achieve maximum acceleration. 225,000 / 30 kW = 7.5 seconds The driver would therefore have 7.5 seconds of full acceleration before the ultracaps gave out. This would enable the driver to make a rapid acceleration into heavy traffic on a freeway, for instance. While it is unlikely the driver could go from 0 to 60 in that time, it would provide the opportunity to get up to 45 or 50 before acceleration slowed. Finally, because the performance estimates are based around a heavier car with an 80 kW cell,

20

acceleration would improve simply because the vehicle weighs less. Those 7.5 seconds of full acceleration would get a 70 kW vehicle going faster than it would an 80 kW one.

Specs

Solution 1

Solution 2

Solution 3

Fuel Cell Size

80 kW

55 kW

70 kW

Ultracap Power Rate

20 kW

45 kW

30 kW

Duration of 100 kW power

11.25 seconds

5 seconds

7.5 seconds

0 to 60 mph time

~10 seconds

(see the Performance section) For our vehicle, Solution 1 would be the best. Because our goals are to maximize performance, the largest fuel cell is the most appropriate. However, Solution 3 would make a good compromise; acceleration would still be reasonable, and weight would be decreased. If a 70 kW fuel cell were much cheaper or easier to produce, Solution 3 would make sense. For Solution 2 to be practical, a redesign of the vehicle, with an emphasis on economy and efficiency, is needed. Various elements, such as the motor size, should be changed.

Fuel Cell Control There are several aspects to the support systems for hydrogen fuel cells. This system obviously varies by manufacturer. The primary need is to regulate the flow of hydrogen from the fuel tank and oxygen from the air to the fuel cell. The delivery rate of these gases will need to vary with the instantaneous power output of the fuel cell. The control system will therefore need to communicate with the motor controller to provide the correct amount of power at the required times. There will also need to be some sort of control to regulate the cooling system.

21

Ballard Fuel Cell System As mentioned, Ballard Power Systems is the leading manufacturer of fuel cells for vehicles. The majority of prototype hydrogen vehicles made by the major car manufacturers (Ford, GM, Honda, Toyota, etc) use a Ballard Fuel Cell. Ballard provides a fuel cell and control system,

which

is

likely what we would use in our car. The fuel cells can be built to output a wide range

of

different

Figure 5: Ballard Mark 902 Fuel Cell from http://www. ballard.com

power levels. An 80 kW fuel cell is near the norm for light transportation vehicle applications. Along with the basic cell, called a Mark 902, Ballard provides the Xcellsis HY-80 system. It includes all the necessary support systems. The control unit communicates with the motor controller via a CAN bus, the standard for vehicle systems and found on our chosen controllers. No doubt a little programming will be necessary to get the controller and control unit to communicate properly, but it shouldn’t be too difficult. The fuel cell control unit tells the system module to send hydrogen and oxygen to the fuel cell. The system module also humidifies, heats, and compresses ambient air containing the oxygen to the correct levels necessary for the fuel cells. A power distribution module measures and regulates the output power of the cell. The Xcellsis also includes a cooling pump. Another useful feature is a built-in 12 volt output so that 12 V car systems can easily be integrated. Finally, the entire system can be configured in different packages to fit into various chassis types. The Xcellsis is designed to output only 68 kW, but a slight variation of the system to include a larger fuel cell should not be difficult.

22

Ballard Fuel Cell Mark 902 (no control system) Rated net power

85 kW continuous

Current (maximum)

300 Amps

DC voltage (minimum)

284 Volts

Weight

96 kg (212 lbs)

Volume

75 liters (2.7 cubic ft)

Xcellsis HY-80 system (customizable; includes fuel cell such as Mark 902) Max efficiency

48%

Start-up time

< 40 seconds

Operating temperature

< 85 degrees C

Weight

220 kg (485 lbs)

Volume

220 liters

Hydrogen Interface Pressure

10–13 bara (130–175 psig)

Max Power output

68 kW

The Hydrogen Storage Tanks A hydrogen car needs hydrogen, obviously. The car is powered by the energy given off by the combination of hydrogen and oxygen into water. Oxygen is readily available from the air, but hydrogen must be supplied by a separate source. The traditional method for storing hydrogen (or any other gas) is in a pressurized tank. This is the storage method we have opted for here, but it does, however, have several disadvantages. Hydrogen is a very low-density gas, and so to store the necessary quantity to provide adequate driving range to a car, very large or high-pressure tanks are required. This is obviously not all that desirable because high pressures can be dangerous and difficult to use and larger tanks consume a lot of vehicle space and weight. However, as

23

hydrogen storage tanks increase in pressure – the latest are available at pressures up to 10,000 psi – vehicle range rivals that of conventional gasoline vehicles. There are several other methods of storing hydrogen that look promising for the future. None have reached a point where they can be integrated into our car, but ten years from now they may well have replaced compressed hydrogen tanks. The first option involves storing hydrogen by binding it in a metal. The metal compound is heated, and it absorbs hydrogen. Done correctly, this allows for the storage of more hydrogen molecules per volume than with pressurized tanks. However, the total weight per mole of hydrogen is more than with conventional pressurized tanks. The process is also more Figure 6: A seemly ordinary hydrogen tank, the BL-400 can actually store up to 400 liters of H2 by compressing it into a metal. Image from fuelcellstore.com.

complicated; the metal has to be heated when hydrogen is being pumped in, and heated again to get the hydrogen out. This would create an additional drain on a fuel cell in a car, decreasing the overall efficiency slightly. This

system also has another advantage: even if the tank is broken open, the hydrogen cannot leak out because it is bound to the metal. The car becomes even safer in an accident because a hydrogen fire would be extremely unlikely. Another option is storing hydrogen as a liquid instead of a gas. However, to liquefy, hydrogen must decrease to a temperature only 20 K above absolute zero. This requires quite a lot of energy, and it is difficult to maintain such a low temperature in a car. While a few prototype vehicles exist that store hydrogen as a liquid, it is unlikely this technique will become a practical option given our current technology. Other schemes are also in development. One of the more promising options involves storing hydrogen in carbon nanotubes. Like metal storage, this increases the number of

24

hydrogen molecules per volume, thus creating smaller fuel tanks and longer vehicle range. This option is still too new to be considered at this point. Consequently, the most viable plan at this time is to use hydrogen storage tanks with 5000 psi compression capabilities, which is the current industry standard for such applications.

Vehicular Hydrogen Requirements The size of the tanks used will depend on the amount of hydrogen the vehicle needs. The car requires a range of around 250 miles per tank to be competitive. 250 miles = about 400 kilometers It would be extremely difficult to calculate the average number of joules a car expends going 250 miles. However, a rough estimate can be done by calculating air resistance of a vehicle going 60 mph for 250 miles. Rolling resistance is less significant than air resistance, and can vary widely depending on a number of factors concerning the vehicle, tires, and road surface. It will be left out of this estimate. Because we have regenerative braking, much of the excess energy used in acceleration during this hypothetical trip will be regained during braking. For the sake of simplicity, acceleration will be ignored; it will be assumed that the car begins and ends the 250 mile trip going 60 mph. These assumptions will doubtlessly cause the fuel estimation to be optimistically low. The proposed vehicle (see Performance Calculations) loses approximates 6.3 kW of power to air resistance during a 250 mile trip at 60 mph. 250 miles / 60 mph = 4.17 hours 6.3 kW * 4.17 hours = 26.271 kWh (9.5 x 107 joules)

25

Therefore, it takes 9.5 x 107 joules to move a car 250 miles at 60 mph. Hydrogen holds 118,800 kJ (33 kWh) of energy per kilogram. This turns out to be remarkably similar to the amount of energy per gallon of gas. Like a combustion engine, however, a fuel cell is not 100 % efficient. Some of the energy is converted into heat. Then, of course, there are further inefficiencies within the vehicle which need to be taken into account. 50% Fuel Cell * 90% Controller * 90% Motor * 90% Drivetrain = 36% total efficiency These estimates are slightly conservative; a well designed AC motor can reach efficiencies of over 95%, and the drivetrain, if a fixed gearbox is used instead of a transmission, should also be better. PEM fuel cells theoretically max out at an efficiency of 83%, a number yielded from calculating the resulting energy from the combustion of oxygen and hydrogen. In the future, there is no reason to suspect fuel cells will not move closer towards their maximum theoretical efficiency. For the record, gasoline engines are about 15% efficient, with those in larger SUVs and trucks obviously even less. 118,800 J * 36% = 42,768 J of usable energy / kg of H2 9.5 x 107 J / 4.28 x 104 J/kg = 2.2 kg of hydrogen A way to check this estimation is by looking at current prototype vehicles.

Prototype Vehicle

Year

Range

Hydrogen (kg)

Honda FCX

2002

220 miles

3.75 kg

Toyota FCHV-4

2001

155 miles

~ 3 kg

GM Hy-Wire

?

80 miles

2 kg

Ford Focus FCV-Hybrid

2004

160-200 miles

4 kg ?

26

As you can see, there is quite a lot of variation in vehicle range. The range depends just as much on other factors as it does on the amount of hydrogen fuel the vehicle has at its disposal. However, it can be seen that the estimation reached earlier is optimistic. This makes sense, considering that rolling resistance and acceleration were both ignored. Nevertheless, by looking at our estimation and the real-world prototypes, the H2 quantity necessary can be realistically estimated. The car should be able to hold at least 3 kg of hydrogen and closer to 3.5 kg if possible. This will hopefully enable around 250 miles per tank at highway driving speeds. City driving will probably cut down on the range; however, regenerative braking will make up a portion of the potential losses. While 3 kg of hydrogen may not sound like a lot, it is considerable when you calculate the volume it would occupy at standard pressure. H2 has a molar mass of 2, and so 3000 grams (3 kg = 3000 g) equals 1500 moles. At STP (standard temperature – 25 degrees C, and pressure – sea level) an ideal gas such as hydrogen occupies 22.4 liters of space per mole. 22.4 * 1,500 = 33,600 liters As 3 kg of hydrogen could fill 33,600 liters of space, you can see why extreme pressures are needed to compress it to a practical volume.

The Tanks One manufacturer of hydrogen tanks is Dynetek Industries Ltd. They build 5000 psi hydrogen tanks specifically for vehicular applications that are lightweight and have fastfilling capabilities. This is important, because filling a tank to 5000 psi suddenly creates a lot of friction and heat. Dynetek’s tanks are designed to handle this, enabling refueling times on the order of minutes. The tanks are still rather large and heavy compared to the amount of hydrogen they store. Dynetek’s largest tanks are nearly 7 feet long, and unless the chassis has been specifically designed to accommodate this, the tank is impractical due to its weight and size.

27

However, smaller tanks do not hold more than 2 kg. In a smaller car, therefore, the only reasonable option is to use two or more smaller tanks. This will complicate the fuel system, but may be necessary to provide the vehicle with a range comparable to combustion vehicles.

Model

Size

Weight

Capacity per tank

V 74 (x2)

399 x 900 mm (15.7 x 35.4”)

35.4 kg (78 lbs)

1.79 kg

W 150

413 x 1534 mm (16.3x60.4”)

65.6 kg (144.5 lbs)

3.63 kg

Either option above would work. One model W 150 would be sufficient; however, it is over 5 feet long. If it could fit in the vehicle, it would allow for the simplest refueling and hydrogen gas line plumbing. The other option, two V 74s, would provide a total storage of 3.58 kg of hydrogen. However, additional fuel lines would be necessary to connect the two tanks. Unfortunately, while the simplest method would be to connect the two tanks together with a gas line and treat them as a single tank, it is not a good idea to have a thin fuel line pumped at 5000 psi. The line should be able to handle it, but it is dangerous to have a fuel line at such a high pressure when driving. The tanks are specifically designed to resist breaking in a collision to minimize the amount of hydrogen that could leak into the atmosphere. Having a 5000 psi line connecting the two tanks would cancel out some of this built-in safety. Consequently, the pressure will need to be stepped down by valves at the exit of each tank to the lower pressure used by the fuel cell. Only then can the two tanks be merged into one fuel line, going to the fuel cell. It may also be necessary to fill each tank independently when refueling the car, although clever designing could get around this.

28

Hydrogen Fuel Lines The two schemes for fuel lines depend on the tanks chosen above. A W 150 would need only a connection to the outside of the car and to the fuel cell. Two V74s would also need to be connected together. The two diagrams on the next page illustrate the two schemes.

Figure 7: A single tank (W150) system. As you can see, it is extremely simple.

Figure 8: A double tank (two V 74s) system. It is only slightly more complicated.

The hydrogen gas lines themselves would be fairly simple. They could be made out of thin flexible metal pipe as the hydrogen flow rate is small. Ideally, the hydrogen tanks would be located next to the fuel cell, so the length of the fuel lines and the consequent

29

risk they would pose in an accident would be minimized. The tanks also need to be located so they can be conveniently refilled.

The Motor In place of the combustion engine powering modern automobiles, a fuel cell vehicle receives its mechanical power from an electric motor. As mentioned in the Hydrogen Future section of this booklet, electric motors are particularly well suited to powering vehicles as they have relatively high torque outputs and wide rpm operating ranges when compared to standard combustion engines.

Both DC and AC motors can be used in conjunction with fuel cell systems; however, there are several fundamental and significant differences to consider when selecting a motor. DC motors are much simpler to install and control and for this reason they are historically found in earlier or homemade electric vehicles. A DC motor system is also less expensive, particularly because the DC motor controllers are much less complex than AC controllers.

Also of

note, most DC motors can be driven far above their rated limits for short amounts of time. This allows for added power in acceleration, which is ideal for automotive applications. Despite being inexpensive

Figure 9: A NetGain WarP 9" DC motor. We were seriously considering this motor before we decided to go AC. Image from http://www.go-ev.com/misc/Motor.pdf.

and simple to control there are many drawbacks to DC motors. DC motors of

the size needed to power a vehicle are not commonly mass manufactured and can be hard to find. They also require more maintenance and the motor itself is more complicated

30

than a comparable AC motor. Finally, one of the most grievous downfalls of DC motors is that they are inefficient when used as a generator and are seldom used in conjunction with regenerative braking systems. AC motors have numerous disadvantages as well. AC motors require an AC power source, and since the rest of the electrical systems run on DC power, this requires at least one and possibly several DC to AC power converters.

However, many AC motor

controllers include built in power converters, which could reduce or eliminate the use of separate power converters. Unfortunately AC motor controllers are very expensive due to the complex nature of controlling an AC motor, another downfall of an AC motor system. In our design we decided an AC motor would best fit our needs due to the great efficiency of the motor when used in regenerative braking, the simplicity and reliability of AC motors, the low cost of the motor, and because AC motors are widely manufactured in the size, weight, and power, requirements we anticipate for use in powering an automobile. The following table outlines the motor specifications we find necessary. These were determined both by calculating the power required to accelerate a vehicle at the pace we want, and by looking at currently available motors on the market for electric vehicles. The following specs match what most electric-vehicle manufacturers consider “performance” components. Average Power

20

kW

Maximum Power

100

kW

Maximum Torque

100+ ft/lbs

Maximum Weight

200

lbs

The average desired power is the energy needed to overcome rolling friction and wind resistance. Most of the time a vehicle is not accelerating, and so the only thing the motor is overcoming is friction. Consequently, the average power requirement is low. Both the 31

maximum power and torque need to be high, however, because we want the vehicle to have competitive performance. Torque is the primary determinate for acceleration whereas maximum power determines top speed. We wanted a maximum torque of at least 100 lb-ft, and more if we can get it. Acceleration is critical to the success of a vehicle. However, few motors currently designed for electric vehicles have torques much higher than 100 lb-ft without having excessive weight and maximum power. Weight needs to be kept down for obvious reasons; the lighter the car, the better the performance. Such motors are not exceedingly hard to come by, and we have found two motors that meet our requirements and that we are considering for our design. Both the MES 200250 and the Siemens 1PV5133-4WS18 are feasible.. The following is a chart of the specifications of both the MES 200-250 and the Siemens 1PV5133-4WS18.

Specification

MES 200-250

Siemens 1PV5133-4WS18

Average Power

30 kW (40.8 hp)

30 kW (40.8 hp)

Maximum Power

94.8 kW (123 hp)

78.4 kW (106.6 hp)

Weight

61 kg (134 lb)

68 kg (150 lb)

Rated Torque

100 Nm (73.8 ft-lb)

85 Nm (62 ft-lb)

Maximum Torque

n/a (estimated 250 Nm)

175 Nm (129 ft-lb)

Rated RPM

2,850 RPM

3,500 RPM

Maximum RPM

9,000 RPM

9,700 RPM

The MES 200-250 is our preferred motor as it has specifications that are slightly more favorable to our project. The MES unit weighs 134 lb, which is a reasonably low weight. The power, RPM and torque are all reasonable, and the engine can be bought with an attached gearbox, which is extremely useful for our design. The Siemens 1PV51334WS18 is similar; however, its rpm range is slightly higher, max at 9,700. It is slightly less powerful, max power of 78.4 kW and 106.6 hp. And it weighs 150 lb. Additionally the Siemens motor does not have a gearbox available; because of this we would need a

32

custom designed and manufactured gearbox

that

might

be

fairly

expensive. Ideally we would like to have a higher torque, lower weight motor that has a very wide rpm band and a straighter torque curve. While the motors we selected aren’t prefect in these aspects they are a much closer

fit

than

the

combustion

engines currently being used in the Figure 10: The MES 200-250 AC motor. Image from metricmind.com.

automotive industry.

For information on specific performance of these two motors, see the section on Vehicular Performance.

The Transmission A transmission is not necessary in a hydrogen car because of the superior nature of electric motors. Electric motor’s wide RPM range allows them to power the car through a direct gear ratio and stay efficient over the full spectrum of speeds. Electric motors create the highest torque at lower RPMs,

which

is

when

the

majority of vehicles need it the most. At higher speeds the torque decreases (as it does in a gasoline engine with a transmission) and consequently acceleration at high speeds will not be as effective as at low speeds. This, however, is similar

to

performance

of

vehicles today. In the future,

Figure 11: MES-DEA Carraro gear box. Image from metricmind.com.

33

motors may be mass-produced and perfected to deliver higher torque over even wider ranges, thus making acceleration at all speeds excellent. Skipping a transmission is yet one more way in which hydrogen cars can be more efficient and simpler than internal combustion vehicles. An electric motor will still need a fixed gear box to provide the most efficient use of the motor’s torque. The MES 200-250 comes with a fixed gear transmission designed to fit the motor.

AC Motor Controller An AC motor will need an AC controller. The car will need some way for signals from the driver’s foot pressing on the accelerator petal to reach the motor and tell it to accelerate. Compared to the simpler DC motor, an AC motor is trickier to control – with DC, these signals could directly control the current running the motor. An AC motor, however, requires a controller that can read the amount that the driver has pushed down on the petal and then transform the DC power coming from the fuel cells to the correct amount and frequency of AC power. This is primarily why AC controllers are more expensive. Additionally, there may be slightly more power losses in an AC controller, but this is balanced by the fact that the average AC motor is more efficient. The AC controller behaves in response to the petal, which in this case is connected to a potentiometer. A waterproof Figure 12: A Bosch potentiometer designed to be attached to the accelerator petal. Image from metricmind.com.

potentiometer designed to work with these controllers via a RS232 interface is made by Bosch. It can easily be attached to a foot petal.

34

The AC controller also makes regenerative braking possible. Most commercial AC controllers (designed for conventional electric vehicles) have regenerative braking built in, as it is not very difficult to integrate. Most DC controllers, on the other hand, lack this important feature. This was considered in the Motor section. The choice of AC controller depends largely on the AC motor used. Each manufacturer (Siemens and MES-DEA) produces a motor controller designed specifically for their motor. Matching the manufacture’s controller with the manufacture’s motor will result in the greatest efficiency and the easiest setup. Therefore, the final decision on the controller will go hand in hand with the motor.

The Siemens Simotion or the MES-DEA TIM-600 The two controllers are rather similar. Both are water-cooled and feature regenerative

Figure 13: MES-DEA TIM-600 (photo from metricmind.com)

braking capabilities. Both handle the conversion from DC to AC because this is an integral part of controlling the vehicle’s acceleration. Both max out at 100 kW, perfect for our application.

Siemens Simotion Input voltage max

380 V

Input current max

282 A

Weight

17 kg (30.8 lbs)

Dimensions

47 cm x 20 cm x 18 cm (18.5” x 7.9” x 7.1”)

Total Volume

9,900 cubic cm (650 cubic inches)

35

MES-DEA TIM-600 Input voltage max

400 V

Input current max

325 A

Weight

10 kg (22 lbs)

Dimensions

33 cm x 25 cm x 12 cm (13” x 10” x 5”)

Total Volume

9,900 cubic cm (650 cubic inches)

The MES-DEA appears to be slightly better than the Siemens in terms of higher power input, size, and weight. However, the difference is slight enough that the controller should not be the determining factor in the decision between manufacturers.

Regenerative Braking Regenerative braking has greatly benefited hybrid cars, increasing both their range and efficiency. Regenerative braking requires an electrical power system, and so is impossible to incorporate into a conventional internal combustion vehicle. With electric and hydrogen cars, it is easy to implement. Regenerative braking recaptures the kinetic energy of a vehicle when it brakes. A car traveling at 30 mph has significant kinetic energy; it used a lot of fuel to get its mass going that fast. When a normal car brakes, all that energy is transformed to heat in the brakes and is essentially wasted. With regenerative braking, that energy is used to turn a generator and charge up a battery, or in our case, a bank of ultracapacitors. The generator is often the very same motor that powers the car – one advantage of electric motors is that while putting electricity in turns the motor, turning the motor also sends electricity out. Regenerative braking can therefore be incorporated into the system with little addition to the vehicle’s weight.

36

In practical terms, regenerative braking is handled by the motor controller. The brake petal will be attached to the controller. When the driver wants to brake, he or she will push down on the petal in the normal fashion. This will send a signal to the controller to open up the connection to the ultracapacitors, which will effectively put a load on the generator (the motor). Because the motor is connected to the wheels, it will be spinning with the wheels. Adding a load (the ultracaps) will force the motor to generate electricity. Because the energy comes form the kinetic energy of the vehicle, the motor will slow down as it charges the ultracaps, slowing the wheels and thereby the car. The rate at which the motor slows the vehicle will be determined by the controller and in turn by the amount the driver pushes down on the brake petal. All this happens in real time, and many drivers would not notice the difference between regenerative and conventional braking. For normal braking situations, regenerative braking is all that is necessary. However, it would be wise to include regular friction brakes in case of an emergency. Also, long downward hills would generate more electricity than the ultracapacitors could hold. After the capacitors filled up, regenerative braking would no longer slow the car. Friction brakes would be necessary to allow the driver to maintain control of his or her vehicle. For that reason, in a hydrogen vehicle conventional brakes would also be connected to the brake petal, albeit at a level where they would not engage until the petal was pressed most of the way down. If a driver slammed on the brakes, both the regenerative and conventional brakes would go on, giving the car maximum braking power. Otherwise only regenerative braking would come into play, as long as the ultracapacitors are not fully charged. For more information the specific energy involved in regenerative braking, see the section on Ultracapacitors. In summary, our car will contain enough ultracapacitors to store 225,000 Joules of energy, which is the approximate amount that a car, given some internal inefficiency, can gain from a 44 mph deceleration to zero. Ideally, for regenerative braking to be most effective, the ultracaps should be able to store all the power generated from any deceleration. However, having that quantity of ultracapacitors

37

is not feasible at this point in time. Regenerative braking can still be very effective, especially in city driving, even if it can capture the energy from only a 44 mph speed decrease. Because regenerative braking reclaims energy, it can provide the car with an extra boost of power during acceleration. Not only will the energy allow for the fuel cell to spend less time running, and therefore consume hydrogen at a slower rate, but it can also be used to augment the fuel cell and provide the motor with more power. If the driver “puts the petal to the metal,” both the fuel cell and the ultracaps power the motor. Because the motor tops out at 100 kW, this means that the total power provided by the fuel cell and ultracaps should not exceed 100 kW. Therefore, instead of needing a 100 kW fuel cell to completely take advantage of the motor, the car can now have only an 80 kW fuel cell and 20 kW of ultracaps. Other combinations for further decreasing the fuel cell size are possible – see the section on the Fuel Cells for more details. Finally, regenerative braking will reduce pollution caused by ordinary brakes. Surprisingly, brake pad dust is the second largest cause of pollution among some urban highways. Regenerative braking will greatly decrease the rate at which standard brakes are used, thereby decrease pollution from brake pad dust.

Intermediate Energy Storage It is possible to run a hydrogen car directly off the fuel cell. The fuel cell would burn hydrogen as needed to directly power the controller and motor. This solution has merit because it is simpler and cheaper. However, for this application it is not the best solution. Adding an intermediate energy storage system will have multiple benefits: 1. Allow for the addition of regenerative braking to the system, thereby increasing efficiency 38

2. Provide additional power to augment the fuel cells during acceleration Regenerative braking has been of great benefit to hybrid gas-electric vehicles by storing energy normally lost during braking to be reused during acceleration. This further increases the efficiency and range of the vehicle. Regenerative braking can easily be integrated into a hydrogen vehicle because the system is completely electrical. However, regenerative braking requires intermediate energy storage to store the energy captured during braking. Having temporarily stored power will be useful during acceleration. The energy storage devices can be charged by either regenerative braking or by the fuel cell when it is not already running at peak power, such as when the vehicle is maintaining a constant speed. This stored energy can then be added to the max output of the fuel cells to increase acceleration. Because acceleration uses the most power, it determines the size of the fuel cell. Adding intermediate energy storage devices allow the fuel cell to decrease in size while maintaining the same potential rate of acceleration, thereby decreasing the weight of the fuel cell. This will in turn decrease the weight of the vehicle, because the power density of an intermediate storage device (if ultracapacitors are used, anyway) is higher than that of a fuel cell. Therefore, any fully developed hydrogen vehicle will have a form of temporary energy storage.

Batteries or Ultracapacitors? There are currently two forms of energy storage solutions that exist in the market today. The first is the tried-and-true battery, which currently serves to capture energy from regenerative braking in most hybrid vehicles. The second is a newer technology, ultracapacitors, which have several benefits and drawbacks compared to batteries. Ultracapacitors are a type of capacitor and so do not store energy in a chemical reaction as batteries do. The major relevant difference between ultracapacitors and batteries has to

39

do with their energy storage capabilities. Batteries can hold ten times or more watt-hours per kilograms than ultracapacitors, and can therefore store more energy. However, ultracapacitors have a much higher power density, at around 10 times more watts per kilograms than batteries. Also, ultracapacitors can charge and discharge much faster than batteries, in the order of seconds, not hours. The have a much longer life, in excess of 500,000 cycles. For a hydrogen car, the energy must be stored and surrendered quickly. Braking from 60 mph down to zero happens in seconds. Similarly, the car will accelerate to cruising speed in less than a minute, depending on the tendencies of the driver. Ultracapacitors, with a higher power density, are better suited to this. In an electric vehicle, which is similar to a hydrogen car, large amounts of power needs to be stored to maximize the vehicle’s range, so batteries are used. In a hydrogen car, however, range will depend only on amount of H2 stored. The temporary energy storage devices need to hold little Figure 14: Two batteries suitable for electric vehicles. Image from Electro Automotive at http://electroauto.com/catalog/batte ry.shtml.

relative energy but be able to move that energy quickly. Ultracapacitors are better suited to this application.

The application also involves completely cycling the energy storage device from empty to full to empty. This would decrease the lifetime of batteries further, but have little detrimental effect of ultracapacitors. Batteries in a hydrogen car would probably have to be replaced at least once, while ultracapacitors would last the lifetime of the car. Finally, the fact that ultracapacitors are lighter is no small benefit. Therefore, we have decided to incorporate ultracapacitors instead of batteries into our vehicle design.

40

Ultracapacitor Details The decision regarding the amount of ultracapacitors is based primarily on regenerative braking. We originally wanted to be able to capture all the energy theatrically generated by a vehicle decelerating from 60 mph to 0 mph. This is dependant on the weight, and because that is not finalized we used an estimate of 3500 lbs. It will hopefully be less. The energy gathered from a deceleration to zero is as follows: Kinetic Energy = ½ (mass) (velocity)2 3,500 lbs = 1,589 kg

60 mph = 26.817 m/s

½ (1589) (26.817)2 = 571,365 joules A decent car can decelerate from 60 to 0 in around 7 seconds. 571,365 / 7 = 81,623 watts or 82 kW These numbers represent the absolute maximum energy you could extract from a moving car. This, as you can see, is quite a lot of energy. Ultracapacitors are not designed to store this volume of energy. Batteries would fail to deliver the 82 kW rate of power in a reasonable weight. Therefore, storing this amount of energy is not feasible. Even after the consideration of inefficiencies due to friction and the electrical components, this number is simply too large. An alternative solution is needed. All things considered, a car does not go directly from 60 to 0 all that regularly. Often the vehicle goes only from 30 to 0 when, say, the driver pulls off a town road and into his or her driveway. Or perhaps the vehicle brakes from 45 on a country road to 0. In either situation, far fewer ultracapacitors are needed. It should be reasonable to incorporate enough ultracapacitors to be able to capture all the energy in many braking situations where the speed change is not so great. For a 60 to 0 deceleration, the majority of the energy will be still be regained. If that 60 to 0 deceleration does not occur all at once, it

41

may still be possible to capture all the energy. If, for instance, the vehicle brakes from 60 to 45 when it enters a developed area, the ultracapacitors can store all that power. The car may than drive for a little while, draining the ultracaps, and thereby enabling them to store the energy from any subsequent deceleration. Analyzing the kinetic energy of a moving car at various velocities shows that a decrease in speed corresponds with a decrease in energy as an inverse square (as you would expect from the KE equation). The nature of the physics will enable the vehicle to be able to handle all the energy from a deceleration of nearly 60 to 0 while having significantly fewer ultracapacitors. ∆v to 0 (mph)

∆v (m/s) Mass (kg)

Resultant max kinetic energy

30

13.4

1589

142,660 J

40

17.9

1589

254,566 J

45

20.1

1589

320,986 J

50

22.4

1589

398,648 J

60

26.8

1589

571,365 J

We would like to keep the total weight of the ultracaps below 50 lbs and the total volume inside a cubic foot. Cost is also an issue, but the price of ultracapacitors has decreased in recent years and would continue to do so if they were implemented in a mass-produced vehicle. Cost, therefore, will only be considered in extreme cases (such as when buying enough ultracaps to handle the 60-0 mph speed change). Before the number of ultracapacitors is decided, inefficiency of the system must be taken into account. The efficiency of charging the ultracapacitors via regenerative braking will not exceed the net controller, motor, and drivetrain efficiency. This is: Motor Efficiency * Drivetrain Efficiency * Controller Efficiency = Net Efficiency 90% * 90% * 90% = 73%

42

Finally, it is important to take into account the other function of ultracapacitors besides that of regenerative braking. The ultracapacitors are also used to increase vehicular acceleration by augmenting the fuel cells. In this case, the more ultracaps, the better. The motor and controller max out at 100 kW (see the sections on Motors and Controllers), so the net power provided by both the fuel cells and the ultracaps should not exceed this value. The motor will probably not be run at 100 kW for more than 10 seconds, the approximate time it will take to go from 0 to 60 mph. While the fuel cells will have to do most of the work during these 10 seconds, the ultracaps should be able to contribute. If the ultracapacitors are going to have any reasonable impact, they should run at 20 kW or more. Running the ultracaps at 20 kW for ten seconds will require them to have at least 200,000 joules of stored power.

Desired Ultracapacitor Characteristics: Maximum Weight:

50 lbs (22.7 kg)

Maximum Volume:

1 cubic foot (28.3 liters)

Minimum Stored Power:

200,000 J

Power Rate:

20 kW

Example Solution: Maxwell Ultracapacitors There are several manufacturers of ultracapacitors, and ideally one would go with the cheapest solution. Any type of ultracapacitors that meet the specs will do. For the purposes of this booklet, we have chosen to go with Maxwell’s BCAP0008 ultracapacitors. The analysis, using specific ultracapacitors, will give us good estimates in terms of weight, cost and viability. If we were to actually build the car, we would go with

43

Figure 15: Maxwell BCAP0008 ultracapacitor (from http://www.maxwell.com)

whatever was available. The BCAP0008 Ultracapacitors last several hundred thousand cycles and are shock and vibration proof. A single BCAP0008 ultracapacitor has the following specs: Capacitance:

1,800 Farads

Voltage:

2.5 V

Max Current:

450 A

Stored Energy:

5625 Joules

Weight:

400 g

Volume:

.3 liters

Using the BCAP0008 specs, around 55 ultracaps would total 50 lbs. A volume of 1 cubic foot would hold up to 90 capacitors. The minimum number required to hold 200,000 joules is 200,000 J / 5625 J = 36 ultracaps The capacitors can handle up to 450 A, so running at 20 kW requires 20 kW / 450 A = 44 V 44 V / 2.5 V per cap = 18 ultracaps Therefore, we want a number of ultracaps somewhere between 36 and 55. To keep cost, weight and volume down, the number of caps should be closer to 36. We have decided to go with 40. Having determined this, a few quick calculations will yield exact data:

44

40 * 5256 J = 225,000 J total storage 225,000 J / 73% efficiency = 308,220 J √ [308,220 / (½ * 1589 kg)] = 19.7 m/s = 44 mph Therefore, the ultracapacitors can handle all the power generated from a 44 mph deceleration. Energy from a single deceleration of any more than that will be wasted as heat. To keep the amperage down, the capacitors would be connected in series. 40 * 2.5 V = 100 V total 100 V * 450 A = 45 kW max 225,000 J / 45 kW = 5 seconds Therefore, if the car brakes from 44 mph down to 0 in less than 5 seconds, the ultracapacitors will not be able to absorb all the energy. This is perfectly reasonably as it is unlikely that a driver will slow the car that rapidly during normal driving. Additionally, in the case where a driver needs to stop extremely quickly and stomps on the brake petal, both conventional and regenerative brakes will come into play (see the section on Regenerative Braking). During acceleration, it is likely that the caps would be run at only 20 kW, thus reducing the amperage and the time to drain them. 225,000 / 20 kW = 11.25 seconds until empty A DC-DC converter will most likely be required at some point to step the 100V capacitors up to the higher voltage that the motor controller requires. And for physical characteristics: 40 * 400 g = 16 kg

45

40 * .3 L = 12 L It should be noted that while the volume of each ultracapacitor is .3 L, they are cylindrical, so it would be impossible to fit them in only a 12 liter space. However, because each ultracap is a separate device, it should be feasible to pack them around other components, thereby maximizing space usage.

Final Results:

BCAP0008 Quantity: 40

Total Storage:

225,000 Joules

Net Voltage:

100 V

Total Power Rate:

45 kW

Total Weight:

16 kg (35 lbs)

Minimum Volume:

12 L (.4 cubic feet)

Platform Vehicle and Modifications As the primary goal of our project and of fuel cell vehicles is to limit the use of fuel and to increase the efficiency of automobiles it would be ideal to build the vehicle on an extremely lightweight and aerodynamic chassis. This in mind the most effective chassis for our project would be a chassis and body constructed of aluminum or carbon fiber and having an aerodynamic drag coefficient of less than .30. As weight is a very important factor in the construction of an efficient high-performance vehicle, a smaller chassis and body is more desirable. A two-door sport car type body is the most attractive solution to the design. However, it may be difficult to fit the necessary components into a small car. For this reason a rear-wheel type drive train may be beneficial as it allows the drive train components to be spread down the length of the car, providing more room under the hood and in the trunk of the car. While a custom-designed and built body and chassis would be most desirable, it is at this point out of reach of our project. A custom-built body and

46

chassis would be very expensive and require an extremely high amount of work and time. Using a custom frame and body, we would also be forced to incorporate all other components of standard automobiles into our design (steering, braking, suspension, and electronic systems). Additionally, it would be exceedingly difficult to obtain the proper authorization to make the car street-legal. For these reasons we will simply redesign an existing vehicle to meet the requirements of the fuel cell systems. The following is a list of traits desired for the platform vehicle: •

Low Weight

•

Low Drag Design

•

Large Area Under Hood

•

Large Storage Area

•

Even Weight Distribution

•

Well Designed Factory Steering, Suspension, and Braking Systems

•

Two Wheel Drive Type – Rear

•

Easily Redesigned / Removed Drive Train.

There are several cars that meet with our requirements and are not difficult to obtain. Of these, a second generation Mazda RX-7 meets almost every desired trait while offering outstanding performance with respect to steering, suspension, and braking. These cars also offer low weight, low drag, plenty of room under the hood and in the back of the car, and a nearly perfect front to back weight distribution. The low weight and drag as well as the higher performance factory components are especially important to our project as we wish to promote the value of fuel cell vehicles not only as a clean and efficient alternative to combustion engine vehicles, but also as vehicles that can rival combustion powered cars in performance on the street. As mentioned above weight is one of the most critical aspects of building an efficient high performing vehicle. The RX-7 weighs only 2,800 lbs from the factory and many of the heavier components of the car, such as the engine, transmission, and gas tank, can be removed as they will be replaced by the fuel cell system. (See the Performance Analysis section for a chart detailing the weights of components for the fuel cell system.) Despite the fact that many heavy components can 47

be removed the final weight of the fuel cell vehicle will likely be larger than the weight of the platform vehicle as the fuel cell stack and fuel tanks can be quite heavy.

Figure 16: A Mazda RX-7. Image from http://www.mazda.co.jp/history/rx7/Java/Catarog/img/85 2.jpg.

In addition to removing many gasoline components several other modifications must be made to the platform vehicle. As a general rule we have found that it is best to use existing systems to the largest extent possible and to modify the factory systems only when required. Many of the components being added as parts of the fuel cell system will require redesigned mounts. The engine in particular will need to have quite stable mounts and these must be fitted exactly to the motor. Such strong mounts are required as a large amount of torque will be exerted on the engine during acceleration. As these mounts must be extremely stable it seems the best solution is to simply design a sub frame that would attach to the existing engine mounts and to the electric motor. This approach is much simpler than welding a completely separate mounting system to the frame and should be much less expensive. The mounting and powering of the vehicle’s subsystem compressors and pumps must also be modified. In modern vehicles the pumps and compressors for systems such as the cooling, power steering, air conditioning, power braking, and vacuum systems are all powered by a belt-pulley system connected to the crank pulley located at the front of the

48

engine. As the electric motors that we are considering in our design do not have both front and rear drive shafts this technique is not possible. To power the pumps and compressors of the accessory systems the crank pulley of a combustion engine must be replaced with a small electric motor that can power the subsystems through the original technique of belts and pulleys. This requires a very small amount of modification to these systems thus providing for a cost and time-effective solution. However, several other considerations must be made. As these components mount to the engine block in the original design, new mounts must be made. If the accessories requiring new mounts are light enough it would be possible, and most logical, to construct a mounting system that would secure the pumps and compressors to the side of the engine compartment. If, however, the components are heavier and the engine compartment walls do not provide adequate strength a system for mounting the accessories to either the frame, engine mounts or suspension crossbeam should be implemented. In addition to considering new engine mounts the matter of engine vacuum must also be taken into account. In most modern cars numerous systems are powered or controlled by engine vacuum. As electric motors do not create this vacuum, a small electric air pump must be installed as a replacement. This pump may need a basic controller in order to properly mimic the pressure created by a combustion engine. A final modification that should be made to the vehicle is the replacement of the tires. While this may seem rather insignificant, a set of harder, high-pressure tires can increase the efficiency and performance of the vehicle quite appreciably by reducing the amount of deformation of the tires during driving. As this deformation creates heat and requires mechanical energy itself it is clearly inefficiency and a waste of energy. This problem can be minimized with addition of the aforementioned tires. Also of importance when discussing the platform vehicle is the location of the fuel cell components. Ideally all components would be located in close proximity to each other. Extremely high amounts of electric power, as well as pressurized hydrogen gas, must be transported between fuel cell components, which can be rather difficult. Unfortunately, there is not enough room either under the hood or in the back of the car to accommodate

49

all of the components. For this reason the fuel cell stack as well as the hydrogen tanks will be located in the back of the car, while the motor, controllers, ultracapacitors, and gearbox will be located under the hood. This design minimizes the distance the highpower electric cables and hydrogen lines will have to travel. The hydrogen lines will be limited to the distance from the tanks to the fuel cells; the tanks and fuel cells will be in close proximity to each other, both units being located in the back of the car. This location is also desirable for the hydrogen containing components, as it does not require the hydrogen lines to run under the passenger compartment, thus avoiding serious safety issues due to a hydrogen leak. Unfortunately, high power electric lines must be run the length of the car to supply power from the fuel cells to the motor and ultracapacitors. However, the majority of the lines will be running between components in the engine compartment such as the motor, controller, and ultracapacitors. These lines, while numerous, will be quite short, thusly reducing the amount of energy lost to the resistance of the wires. The wires that will be installed to carry the electricity from the fuel cells to the motor must be quite heavy in gauge and very low in resistance. It would be best to have braided cables, and an effort must be made to run the wires along the shortest path possible from the cells to the motor.

Cooling Many elements of a hydrogen car require cooling. The motor, controller and fuel cells will all need water cooling. The water cooling system can probably be integrated together so that only one circulation method is needed. Additionally, these systems will be used to heat the cabin when the driver requires it. The water can also be circulated through the radiator in the same manner as in a conventional car, venting the heat out into the air. Because both the motor and controller are far more efficient than the internal combustion engine in a regular vehicle, they do not need such a large radiator and cooling system. This will decrease the cost and complicity of a hydrogen vehicle as compared to a 50

conventional car. However, when converting a car to run off hydrogen, it is simply easiest to use the radiator and cooling system already there. It is important to ensure the motor in particular receives adequate cooling. As the wires in the circuitry of the motor heat up, they become more resistant. A higher resistance decreases the current flowing to motor (as given by the equation V = I * R), and so the motor becomes less powerful. Besides preventing the components from burning out, system cooling assures you will have maximum power. The specifics of the cooling system will be determined primarily by the final location of each component. As it is impossible to say at this point in time where the fuel cell will be located in the chassis, it is impossible to describe exactly how it will be cooled. If it is under the hood, cooling lines can simply be run over to the radiator. If it is under the vehicle, however, a different solution may be needed depending on how the cooling hoses can be run. Additionally, the fuel cell may (in the case of Ballard’s) have a cooling system already built in, and until the details on that system is fully determined, it is impossible to say if and how that system would tie into the rest of the car.

Performance Analysis Now that the various components have been determined, it is possible to perform some rough estimates on the vehicle’s performance. Before the vehicle’s acceleration can be estimated, the total weight of the car must be found. It is impossible at this stage to provide a perfect estimate of the vehicle’s weight, but a likely range can be determined.

51

mass

a conservative estimate:

an optimistic estimate:

kg

kg

lbs

lbs

h2 tank

110

242

110

242

fuel cell stack

220

484

96

211.2

motor

61

134.2

61

134.2

controller

20

44

20

44

ultracapacitors

16

35.2

16

35.2

cooling

20

44

20

44

1000

2200

900

1980

transmission

90

198

20

44

hydrogen

5.4

11.88

5.4

11.88

misc. components

50

110

100

220

1592.4

3503.28

1348.4

2966.48

body and frame

total vehicular weight

There are two different ways to determine the vehicle’s potential acceleration. First, we ran a few quick calculations based on the simple laws of physics and kinetic energy. It is possible to calculate how long it takes a 3500 lbs mass to accelerate to various speeds when 100 kW of power (from the motor) is poured into it.

weight

mass

v

v

KE = 1/2 mv^2

lbs

kg

mph

m/s

joules

kilojoules

max power of motor

theoretical time until velocity is reached

kW

seconds

3500

1588

30

13.4

142570.64

142.6

100

1.4

3500

1588

60

26.8

570282.56

570.3

100

5.7

3500

1588

100

44.7

1586483.46

1586.5

100

15.9

This estimation seems to indicate that our car should 60 mph in under 6 seconds, which would be extremely good. However, this estimation is a poor one because simply running a motor at 100 kW does not add 100 kW of mechanical energy to the car. Power is 52

wasted as heat because the motor simply can not accelerate the car at the maximum rate with no losses. A better way to estimate vehicular performance is through the motor’s torque (as torque is the key determinant of acceleration, not horsepower). We determined what torque is needed to accelerate the car from 0 to 60 mph in 10 seconds. The calculation can be done all at once (i.e. from 0 mph to 60 mph), but this yields a torque requirement higher than is really necessary, because it assumes a constant acceleration from 0 all the way to 60. No car is actually like this; the time in which it reaches 30 mph is significantly less than half the time it takes to reach 60 mph. Consequently, the best way to make this torque calculation is to use many short steps of speed change (we chose 5 mph steps) to reach 60. Each step takes a different amount of time, as a vehicle goes from 0 to 5 in far less time than it does from 55 to 60. We first determined the time that a 100 kW motor should need to accelerate the car each 5 mph step, and then calculated how much torque that would require. When considering weight, we erred on the heavy side, using an estimate of 3500 lbs. Note that these calculations do not yet provide an indication of how well the car will perform; they simply indicate the torque we need to aim for.

53

54

Using these rough estimates of the torque the motor needs to output, we chose our two motor options. Now, working backwards through the process above, we can find how fast each specific motor actually will accelerate the car. The Siemens motor is calculated on the following page. The Siemens can reach 60 mph in 12 seconds, a little below our hopes, but still perfectly reasonable.

55

56

Unfortunately, we were unable to acquire torque/rpm specs for the MES-DEA 200-250 motor. However, we did find a torque curve for a 21 kW version of the motor, and were able to calculate performance based on it. The next page details the calculations. The MES 200-175 can reach 60 mph in around 18 seconds. Our motor of choice, the MES 200-250, is approximately 150% as powerful. A direct proportion of the motors’ two powers (although this is not good science, it is the only method of approximation we have) indicates that the MES 200-250 should reach 60 mph in 12 seconds. This is a little longer than we had hoped, but considering that our estimation technique is poor we should not throw out the motor yet. Also important to consider is that the MES motor is slightly more powerful than the Siemens, which reached 60 mph in 12 seconds, and so the MES should in fact perform better than this.

57

58

Some other interesting calculations include air drag. Based on a Mazda RX7 body (see the Platform Vehicle and Modifications section), our car will have an air resistance at various speeds as described by the following table: P=ACV^3D/2

AIR DRAG Vehicle frontal

Coefficient

speed

area m^2

of drag

mph

air density m/s

kg/m^3

P=

(kW lost)

1.784

0.31

10

4.47

1.18

29.14279

0.0

1.784

0.31

20

8.94

1.18

233.1423

0.2

1.784

0.31

30

13.41

1.18

786.8553

0.8

1.784

0.31

40

17.88

1.18

1865.139

1.9

1.784

0.31

50

22.35

1.18

3642.849

3.6

1.784

0.31

60

26.82

1.18

6294.843

6.3

1.784

0.31

70

31.29

1.18

9995.977

10.0

1.784

0.31

80

35.76

1.18

14921.11

14.9

1.784

0.31

90

40.23

1.18

21245.09

21.2

1.784

0.31

100

44.7

1.18

29142.79

29.1

1.784

0.31

110

49.17

1.18

38789.05

38.8

1.784

0.31

120

53.64

1.18

50358.74

50.4

1.784

0.31

130

58.11

1.18

64026.71

64.0

1.784

0.31

140

62.58

1.18

79967.82

80.0

1.784

0.31

150

67.05

1.18

98356.92

98.4

kW of Air Resistance 120.0 100.0 80.0 60.0 40.0 20.0 0.0 4.47 10

8.94 13.41 17.88 22.35 26.82 31.29 35.76 40.23 44.7 49.17 53.64 58.11 62.58 67.05 20

30

40

50

60

70

80

90

100

Speed (m/s and mph)

59

110

120

130

140

150

Until the vehicle gets going above 60, the air resistance is very small. This is due in part to our choice in vehicular chassis; the RX-7’s coefficient of drag (how aerodynamically streamlined it is) is a low .31 and the car’s frontal area is also small. One of the interesting conclusions from this graph concerns top speed – with an 80 kW fuel cell running at max, the car would top out at a respectable 140 mph before air drag became too great. Driving at this speed, however, would quickly burn through the vehicle’s fuel supply.

Costs This section is here for curiosity’s sake only. Most of the prices listed here represent the cost of components bought off the shelf. Other components do not have “list” prices, and we could only estimate their cost at this time. In any case, these components are not mass-produced in nearly the volume they would be if hydrogen cars were built to replace gasoline vehicles. Their prices are several multiples higher than they could be given large-scale production. These estimates are not meant to scare people away from the technology; they merely represent how significant the economy of scale can be. It is impossible to say at this point how a fully developed hydrogen vehicle would compare in cost to today’s cars, but the major car companies would not be pursuing the technology if it could not be made cost effective. The chart on the following page describes the cost of each component.

60

Category Fuel Cell estimated at $3,000 per kW output Hydrogen Tanks these prices are pure speculation

Component 80 kW fuel cell

AC Motor and Controller (Siemens) quotes from metricmind.com AC Motor and Controller (MES-DEA) quotes from metricmind.com Ultracapacitors price is outdated; should be cheaper Platform Vehicle these prices could vary a lot, and are relevant only to our specific design

cost $ $240,000

DyneCell W 150 DyneCell V 74 (x2) gas lines

$2,000 $2,000 $200

1PV5135 WS14 Simovert 6SV-1 AC inverter

$5,581 $3,996

MES 200-250 MES DEA TIM 600 ac inverter

$3,820 $4,694

Maxwell BCAP0008 (x40)

$5,480

Mazda RX-7 (used) High Pressure tires Motor Mounts Modification to the suspension

$1,000 $500 $500 $1,000

supplied with MES 200-250

$1,194

Vacuum pump, water pump other

$500 $500

Gear Box Misc Electronics - needed to replace conventional systems previously powered by gasoline engine - other, such as wiring Other more speculation

cooling system drivetrain adaptors misc frame modifications

vehicle total (assumes MES-DEA motor system is used)

$1,000 $500 $1,000 $265,888

It is noteworthy that the vast majority of this ridiculous price tag comes from the fuel cell; as discussed in the Fuel Cell section, it is currently made from rare metals. Again, the future will hopefully be brighter and provide cheaper fuel cells.

61

Appendix 1: Sources of Hydrogen To be truly environmentally friendly, a hydrogen car must run off hydrogen produced in ways that do not pollute. Unfortunately, most of the cheap and common ways of producing hydrogen do lead to pollution. Hydrogen is easily gathered from fossil fuels. Fossil fuels are hydrocarbons composed of hydrogen and carbon. Most hydrogen today is produced from breaking down fossil fuels into their components and collecting the hydrogen. The remaining carbon is dumped into the atmosphere where it combines with oxygen to create carbon dioxide, the infamous greenhouse gas. Because fossil fuels are currently plentiful, this method for generating hydrogen is the cheapest. However, this strategy undermines the principle behind hydrogen vehicles – the idea that we can avoid harming the environment while we go about our daily business. This technique also will not eliminate all our energy problems, because we will still need large quantities of fossil fuels which may not be available in sufficient amounts in this country. For example, 48% of hydrogen produced today comes from natural gas, and 30% from oil. Because fossil fuels are not infinite, using them to generate hydrogen can only be a temporary solution. There is a cleaner way to create hydrogen. Through the process of electrolysis, water is broken down into its components, hydrogen and oxygen. The hydrogen can be stored for use in vehicles and the oxygen can be released into the atmosphere. The atmosphere is already approximately 21% oxygen, so the additional amount will not be foreign. There is no need to worry about changing the environment by increasing oxygen levels and damaging plant life. A hydrogen vehicle with a running fuel cell will draw oxygen back out of the air in the same quantity as was added during electrolysis. Using electrolysis of water to generate hydrogen creates a nearly perfect balance.

62

Figure 17: A balance is achieved. All water destroyed to create hydrogen and oxygen for the car is recreated in the fuel cell as the vehicle is driven. There are no environmental changes in the levels of any compounds.

Unfortunately, electrolysis of water is expensive. A lot of electricity is needed to break down water into its components. Essentially, this process is the reverse of running a fuel cell, so the high potential output of fuel cells per quantity of hydrogen now means that a large amount of energy is needed to break down water. Because electrolysis requires electricity, and most electricity if made in fossil fuel power plants, this strategy, if implemented today, does not reach a perfect “zero-emission” goal. The only way to have a completely pollution-free supply chain is to generate electricity for electrolysis from renewable sources. Perhaps in the future large arrays of solar panels will work to break down water to extract the necessary hydrogen. Harnessing wind and water power is also something we should be working towards today, regardless of the future of hydrogen vehicles. In the far future perhaps hydrogen fusion will become a viable way of

63

generating electricity, and our energy needs will be taken care of. There will be plenty of electricity to generate hydrogen cleanly and cheaply. Iceland is the perfect example of how hydrogen can be generated cleanly. The nation has decided to move towards a hydrogen-powered economy. Iceland has the natural advantage (in this case) of being located on the boundary of two tectonic plates. Consequently, there is a significant amount of geothermal activity that can be used to generate cheap electricity. By capping off geysers and using superheated water provided by the earth, Iceland can produce large amounts of electricity without harming the environment. This can be used in turn to produce hydrogen via electrolysis, effectively making hydrogen vehicles one-hundred percent green. Regardless of which method is used to generate hydrogen, it is estimated the vehicle fuel costs will either match or fall below that of current prices for gasoline vehicles. The possible higher cost per kg of hydrogen over gallon of gasoline is offset by the fact that hydrogen vehicles are far more efficient. A kilogram of hydrogen, although holding nearly the same amount of energy as a gallon of gasoline, can propel a vehicle far further. Hydrogen cars will be cheaper to drive.

Appendix 2: How Safe is Hydrogen? Hydrogen is a flammable gas, so safety must be a concern. However, hydrogen’s flammability must not prohibit its use; after all, gasoline is also highly combustible. Hydrogen nevertheless can be considered slightly more dangerous because unlike carbonbased fuels, it will combust in the presence of oxygen with little or no cause – no spark is necessary. However, several properties also make hydrogen safer. In a vehicle, hydrogen gas is by necessity stored in a very strong tank. A weaker tank could not handle the pressures (in excess of 5000 psi) that the hydrogen is stored at. In a collision, it is very unlikely that the tanks will rupture, especially when they are designed specifically for 64

automotive applications. A gasoline tank, on the other hand, can break open easily. It is also very unlikely that the hydrogen would cause an explosion, even given a leak in the tanks, because only a very rich and concentrated mixture is unstable. As hydrogen is literally the lightest element in the universe, it will quickly rise and disperse into the atmosphere. The chance that conditions for explosion would be met is extremely slim.

Additionally, in the event that the tank

hydrogen or

the

hydrogen

fuel

lines broke, the worst that the hydrogen might Figure 18: A demonstration of a hydrogen and a gasoline fire in a vehicle. The hydrogen fire burns upward, and is unlikely to ignite other parts of the car. The gasoline fire, on the other hand, spreads around the entire vehicle and is an obvious danger to anyone in it. This simulation was performed by DaimlerChrysler and the image comes from Scientific American Frontiers at PBS.org.

do is ignite. In this situation, it is unlikely that anyone would

be burned because a hydrogen flame radiates little heat. The result would be somewhat like a Bunsen burner – a small flame where the hydrogen met the atmosphere. There would be no risk of the flame following the hydrogen down into a tank or along a fuel line, because like a Bunsen burner, hydrogen needs oxygen to burn. Inside the tanks there is no oxygen, and therefore there can be no fire. Finally, unlike gasoline fires, hydrogen combustion does not produce any smoke (the result of hydrogen combustion is water). Smoke inhalation is the number one cause of death in gasoline fires. One event many skeptics point to is the Hindenburg disaster, where a large zeppelin caught fire and resulted in many fatalities. Because the Hindenburg was filled with hydrogen, some people believe that the hydrogen was responsible for the fire. It has been demonstrated that the fire was actually a result of flammable cloth surrounding the

65

hydrogen and electricity in the atmosphere. When the Hindenburg burned, the hydrogen that did ignite burned above the passengers. The 65% of the people who survived were able to avoid falling out of the gondola or getting burned by the flammable cloth or diesel fuel. They rode the flaming gondola down to earth. The accident could have happened just as easily if the Hindenburg had been filled with non-reactive helium. Finally, the fuel used in hydrogen vehicles bears little resemblance to that of hydrogen bombs – in the case of a hydrogen bomb an isotope of hydrogen (usually deuterium) is used. Even so, the only way to create fusion in H-bombs is through the use of several coordinated uranium A-bombs, forcing the deuterium to fuse. There is absolutely no way this is possible in a car. Hydrogen cars should match or surpass current gasoline vehicles with regard to safety.

Appendix 3: References Hydrogen Storage Brooks, Alec. “Fuel Cell Disruptor”. 7 Dec. 2002. EV World. May 2004 . Dynetek Industries Ltd. June 2004 .

Fuel Cells Ballard Power Systems. May 2004 . Fuel Cells – Green Power. Thomas, Sharon and Marcia Zalbowitz. Los Alamos National Laboratory. May 2004 . “The Online Fuel Cell Information Resource.” Fuel Cells 2000. June 2004 . FuelCellStore.com. 2004. June 2004 .

66

Motors and Controllers Metric Mind Engineering. 2004. May 2004 . "Direct Current Traction Motor Systems.” Railway Technical Web Pages. Trainweb.org. 11 Dec 2000. June 2004 . “AC Induction motor drive.” MES DEA. June 2004 . “Induction motors.” MES DEA. June 2004 . “Vehicle Systems.” Solectria. 2004. June 2004 . “AC-150 EV Power System.” AC Propulsion. 2001. June 2004 . “NetGain Motors.” NetGain Technologies, LLC. June 2004 . “D.C. Motors.” Advanced DC Motors Inc. June 2004 .

Ultracapacitors “BCAP0008 Ultracapacitor Product Information.” Maxwell Technologies. June 2004 . “Cell Balancing in Low Duty Cycle Applications.” Maxwell Technologies. June 2004 .

Misc. Lovins, Amory B. “Twenty Hydrogen Myths.” Rocky Mountain Institute. 2 Sept. 2003. 29 May 2004 . “Honda FCX.” Honda Corporate. May 2004 . Plugitin.co.uk - Tomorrow’s Transport Today. June 2004 . Electro Automotive. 2004. June 2004 . Cloud Electric Vehicles. June 2004 . EV Parts. 2002. June 2004 .

67

“Jerry’s Electric Car Conversion.” 2004. June 2004 . “Fuel Cell Grade Hydrogen.” Praxiar Technology, Inc. 2004. June 2004 . “HEVA Manual – Appendix A: Energy Balances.” Power and Propulsion Office, NASA Glenn Research Center. 03 May 2003. June 2004 . Mangini, Mike. Personal Interview. Sept 2003 – June 2004. Glidden, Steve. Personal Interview. Sept 2003 – June 2004. “Future Car.” Scientific American Frontiers. PBS. WCNY, Syracuse. 19 May 2004.

68