flywheel battery

8/3/2019 Flywheel Battery

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ECE 200-A1Prof. J. N. McMullin

Formal Report:

Flywheel Batteries

by

Denis Lachance

ID#: 1244466

Date due: November 27th 2010


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Date: Nov. 27, 2010

To: Professor James N. McMullin B.Sc., Ph.D., P.Eng.

From: Denis Lachance

Subject:Flywheel Batteries

Dear Sir:

Please find enclosed my report entitled "Flywheel Batteries" written in response to atechnical writing assignment. This report discusses the history, theory and applications ofrotational batteries and similar inventions. These batteries had gained popularityapproximately 30 years ago as alternative energy storage systems but until recently have

been left alone. I chose this subject for my report out of personal interest as well as a desireto familiarize the concept with others. The report is organized in the chronological style asit was important to note the lengthy history of flywheels and their many uses throughouttime. If you have further questions, I may be reached by e-mail or cellular phone.

Sincerely,

Denis Lachance

1244466

Cell: (780) 716-8315

Email: [email protected]


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AbstractFlywheels have existed since the stone age and appear in many forms. With a little

more development, flywheel systems could be the bridge between ultracapacitors andstandard batteries. While the chemical battery industry moves in bursts of innovation fromthe discovery of new chemical compounds with high specific energy (Lithium-Ion, Zinc-Air,etc.), the mechanical battery industry grows every time a stronger material is developed for

the revolving disk. As a result, we should not judge flywheels for its past failures as energystorage but rather envision new ways for it to be applied.

This technology is known for being a replacement to ultracapacitors and lead-acidbatteries as well. Even so, companies developing electric vehicles and other suchapplications are still waiting for enough advancement and public acceptance beforeincorporating flywheel systems. With these battery systems it is not necessary toconstantly tailor a new type of battery for each application encountered. Ironically,development in flywheel systems would put an end to the phenomena of "re-inventing thewheel" present in the chemical battery industry.


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Table of Contents

1.Introduction............................................................................................................. 1

1.1.Scope of Report........................................................................................ 1

1.2.Theory....................................................................................................... 1

2.History.................................................................................................................... 2

3.Applications............................................................................................................. 4

3.1.Railguns.................................................................................................... 4

3.2.Arc Welding............................................................................................... 5

3.3.Electric Vehicles........................................................................................ 5

3.4.Power Management.................................................................................. 5

3.5.Satellites.................................................................................................... 6

Conclusion................................................................................................................. 6

References................................................................................................................. 7


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List of Illustrations

Page 3, A logarithmic plot of specific energy (how much energy can be held per kilogram)in function of power density (how much energy can be outputted at once per kilogram).

Graph made by AFS Trinity in 2000.

Page 4, Porsches GT3 R, a flywheel hybrid (flybrid) racing car.

Page 5, 2 Graphs of a simulated Uninterruptible Power Supply shortage. The Yellow curveis the output voltage (the voltage that would be sent to the building) and the other curvesare the batteries current/voltage output. In the left graph the flywheel is in series with lead-

acid batteries and we see the yellow curve dip down quite a bit and the batteries arestruggling to support the load. In the right graph, the flywheel is in parallel and thusuninhibited by the chemical batteries. The flywheel picks up the slack quite nicely.


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1.Introduction

1.1.Scope of Report

In this report, we will cover the theory, history and uses behind the mechanicalbattery. This report is written in chronological order, first starting with the abstract theory ofa mechanical battery then moving on to its evolution through time. Also during the timeanalysis of the battery, it will be compared to other models in its time. Then after coveringwhat it is and where it has been seen we will go over similar technologies and theapplications of all of these.

1.2.Theory

A Flywheel Battery is essentially a spinning wheel. Because electric motors can bereversed to function as electric generators, a wheel can be spun up by inputting a voltageinto the motor and voltage can be outputted by decelerating the wheel using the generatorthis time [1]. Of course the motor and generator are both the same element. Normally withmost electric motors, AC voltages are inputted and outputted but if needed a homopolar

motor can be used to work with DC voltages instead. Because AC motors are both ACmotors and AC generators, the flywheel would lose energy from Back EMF caused fromthe generator operating at the same time as the motor. Of course because a homopolarmotor does not alternate its voltage, it cannot induce a magnetic field that counters theexisting "forward" magnetic field [2]. Thus DC homopolar motors are preferred whenconstructing a flywheel capacitor (or compulsator). AC motors are then used for largerstorage flywheels because their high inertia is less affected by Back EMF.

Essentially a flywheel is a wheel with high rotational inertia mostly used to decreasethe choppiness of the spinning of a shaft. For example when placed on the output shaft ofan engine, the pistons fire, causing the flywheel to spin but also the flywheel ensures a

smooth rotation of the shaft. This is why you dont feel the wheels move in "burst" from thepistons firing but rather an even monotonous motion. Without flywheels, the industrialrevolution would have suffered because their steam engines would be much less efficientand would require multiple pistons to function smoothly [3].

In electric motors, the strength of the magnetic field induced can be determined bythe current passing through the windings and and the number of turns in the windings. Thestronger the magnetic field, the stronger the torque [1,2]. Hence to achieve the fastestcharge/discharge rate, flywheels are built with many turns in their windings. In comparisonto chemical batteries which discharge at a rate determined by the speed and amount ofchemical reactions in the battery, flywheels can discharge much quicker and are much

more lenient when being charged. If for example, you have a chemical battery whichnormally accepts a trickle charge of 1A while charging and you accidentally use a 2Acharger, you will most likely damage the battery and possibly even cause it to leak acid.Meanwhile, the only thing restricting the charge rate of a flywheel would be the limits of thewinding itself and the strain on the flywheel's material. Because of this flywheels candischarge at rates of approximately 660V and charge at similar rates [4]. A typical flywheelspinning at 100,000RPM with a 0.7m diameter can discharge 1kw for many hours [5].

Because of basic electromagnetic laws the discharge rate of flywheels isdetermined by its speed and the strength of the magnets. Therefore to achieve high poweroutput, some systems use low inertia flywheels to be able to spin up faster and they useseveral turns on their windings for added current [24]. This creates a fast chargingcapacitor type system called a compulsator (compensated pulsed alternator).Compulsators can output more at once than ultracapacitors and are used in railgunresearch [6].

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Flywheels have many advantages over chemical batteries and chemical storage systemssuch as lead-acid and gasoline. Flywheel systems do not produce any toxic material overtime, do not contain any dangerous chemicals and thus they are very Eco-friendly. Theycan also be charged or discharged at almost any rate. But with these new advantages alsocomes a set of dilemmas. As a result the flywheels have a massive amount of rotationalmomentum, they act as a gyroscope in that they resist any rotation (other than the rotation

in the direction of the flywheel's rotation). This poses a problem for moving objectscontaining flywheels. The another big problem is that if the flywheels were to explode frombeing over-spun, it would "have the energy of a tank travelling at highway speeds" [14].

2.History

Flywheels have been around since the invention of the wheel (literally). The firstflywheels batteries could have been considered to be the potter's wheel because theystore kinetic energy in a flywheel [7]. The dilemma with the potter's wheel was that toachieve a smooth constant rotation, one needed to constantly peddle on the wheel. Thus,a flywheel was added to increase the time it took to spin up the spindle (the rotationalinertia) and also the time it took for it to spin down. This particular problem is muchrepeated in history.

The second example of a flywheel would be in a waterwheel used in watermills [8].The waterwheel uses multiple paddles which get pulled down by the weight of the water.Of course the more paddles it has, the smoother the rotation. But the second way toincrease the steadiness is to increase the rotational inertia of the waterwheel, the samesolution as the potter's wheel.

The next notable application is the steam engine, or even all internal combustionengines (ICE). The pistons of the ICE can be compared to the paddles of the waterwheelin that many pistons are needed for a constant spinning of the shaft and to avoid any

unwanted reverse motion. Without the steam engine, the industrial revolution might havenot have occured. And without the flywheel, steam engines couldn't function with just onepiston [3,9]. Simple clutches use flywheels to connect/disconnect the engine's output tothe main drive shaft [10]. Technically, this is a crude way to "store" energy in a wheel andrelease it when needed. Even though the energy is transferred by friction, the time theflywheel spends slipping on the clutch disk is quite small (depending on the driver).

The first "real" electrical flywheel battery was made by Michael Faraday in the formof a homopolar generator [11,12]. This flywheel system was and is used as a short termpulse power and generally not as a battery. Much like a capacitor, it can store energyaccumulated over time then release in a small amount of time. Though this is not exactly a

flywheel battery, it is a close cousin, the compulsator. Because a flywheel system can differin storage and output, it has a rather wide range of possibilities compared to other batterysystems (see below).

The interest in flywheels began in the 1950s when they had been placed in buses inSwitzerland. These were called Gyrobuses and could travel 3-6 miles at 30-40mph.Gyrobuses were powered solely by a 3-ton rotating steel flywheel spinning at 3,000RPM. Itcould be charged in 30sec-3min. To increase charging time the infrastructure had to berevamped to output more that the regular amount of voltage at the charging stations. Theflywheel of course, could handle almost any charging voltage [14].

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Figure 1:A Logarithmic plot of Peak Power and Specific Energy of various energy sources [13].

In the 1970s, materials such as carbon fibres were made that could hold 20 timesmore energy than flywheels. Later on in the 1990s, Jack Bitterly (an aerodynamicengineer) and his son Steve started a company, US Flywheel Systems, which created a110,000RPM composite (carbon fibre) flywheel weighing in at 50 pounds (90 with thecontainment). Each had 4.1kWh of energy, could be charged in a mere 10-20 minutes and

had an output of 25hp which can be bumped to 50hp for a minute. Bitterly claimed in orderto power a car, you would need 16 of these, giving the car 800hp in bursts and a 300 milerange. Each charge would cost about 5$ to 10$ and flywheels can handle anything from10,000 full charge-discharges to 100,000. To put that in perspective, thats a lifespan ofanywhere between 27 and 270 years! Flywheels also boast a round trip efficiency of 85-95% [15, 16, 17].

Bitterly has said that many other companies have been trying to build his flywheelsfor decades. Like a true mad scientist, Bitterly keeps solving all the problems heencounters with flywheels and yet no one seems to accept his ideas. All automobilecompanies are turning a blind eye because accepting flywheels would mean they wouldhave to abandon all previous technology. NASA, on the other hand, had no problem withthis. Bitterly had already written machine factory blueprints, patents and all the requiredred tape to mass-produce all of his equipment down to the last bolt. His magnetic bearingsalso included an auxiliary set of mechanical bearings in case the flywheels went beyondthe range that the regular bearings could handle. His other challenge was to reduce thegyroscopic effect of a flywheel. US Flywheels Systems has the most advanced flywheelsever built. Bitterly has stated that he has never personally broken a wheel yet.

Eric Sonnichsen, founder of Test Devices, tested flywheels to see what would happenswhen over-spun. Steel flywheels shatter as expected and send 10kg fragments flyingaround at the speed of a bullet. Meanwhile, composite flywheels melted into red dust or"lumps of coal" but could be contained much easier.

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They finally figured out how to blow a speeding flywheel apart by firing a bullet into it. "Itend to be the Cassandra of the high-speed spin world," he[Sonnichsen] says. "But at thispoint I am satisfied with the centrifugal safety of flywheels. In fact, they are much lesshazardous than other storage methods we have now. A can of gasoline can be dangerous.Even a car battery can blow up, if you reverse polarity."

-Direct Quote from [4]

In recent times, companies like Beacon Power, Pentadyne and AFS Trinity areusing flywheel storage for power management and UPS systems. Of course since they arenot dealing with moving objects containing flywheels, they simply use steel flywheels andbury them in large casings instead of taking the design challenge as Bitterly did. There hasbeen no recent news of US Flywheel Systems since 2000. Yet even though the flywheelcompanies seem to have abandoned cars for now, Porsche has come out with the GT3 R.Its first hybrid car, let alone racing car, in 110 years. It has a 480hp engine with a40,000RPM flywheel battery powering a 60kW motor delivering an additional 160hp to theexisting 480 for 6-8 seconds. The battery charges purely on braking power [18].

Porsches GT3 R Flybrid Car [19].

3.Applications

3.1.Railguns[20]

Essentially, a railgun is an electric linear motor which fires a metallic projectile. Tworails are put under current and when the projectile is placed between them, it completesthe circuit. The wires and the projectile create a magnetic field which oppose each other

causing the projectile to be repelled. As stated before, to achieve strong magnetic fields ahigh current must be produced. Compulsators can spin at ludicrous speeds and act asultracapacitors by outputting currents up to and above one million amperes. With the

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strongest gun being megajoules, it is no surprise that the projectiles can accelerate toMach 10 and have a range of 440 nautical miles.

3.2.Arc Welding[21]

Arc Welding uses high currents to meld two metals together. Normally most powersupply setups are gas powered and quite bulky (they take up the back of a truck). A steady

current supply is needed to achieve a nice weld. If gas power supplies were replaced withflywheel batteries, they could be more portable because of reduced size and could evenbe recharged by existing generators if needed for long uses. Flywheels are robust and aregood for heavy duty applications such as these. As with all electric components, flywheelsystems can be recharged by photovoltaic cells to extend the battery life.

3.3.Electric Vehicles[1, 22]

The biggest problems in electric vehicles are range, speed and charging time. All ofthese problems depend on the batteries used since electric motors can be superchargedsimply by having better batteries and range. Charging time also depend on the batteries.

With Bitterly's Flywheels, cars could absorb nearly all the energy released when brakingand could accelerate at much higher speeds. When GM released their EV1 it had 1,100pounds of lead-acid batteries giving it a range of 70-90 miles. The batteries neededreplacing every couple of years or so at a cost of $1,800. Bitterly's system would probablyoutlast the car and would most likely severely increase the acceleration. Of coursebecause of the gyroscopic momentum of the flywheel, the car would have some difficultyturning and the flywheel might "touchdown" on the bearings. Of course the back upbearings would take up the slack, but that didnt stop the public's fear of flywheels in cars.Mostly, the reason why no one has incorporated flywheels into a "standard" car other thana prototype or a racing car is because of the public's idea of "Better the devil you knowthan the devil you don't".

3.4.Power Management[4, 23]

In the power distribution industry, quality and reliability are key. Flywheels candeliver massive pulses of power when needed and can also absorb similar amounts. Thismakes them perfectly suited for an Uninterruptible Power Supply (UPS) or power qualitycontrol centre. Safety concerns are less serious with power management because theflywheels can be buried deep underground where they can cause no harm. Flywheel UPSsystems can usually react within 50ms or less and deliver constant power until largergenerators (diesel) can kick in. It has been shown that when flywheels are put in serieswith a string of lead-acid batteries, they must reduce their voltage so as not to damage thechemical batteries. This is not the case when placed in parallel.

Left: UPS with flywheel in series. Right: UPS with flywheel in parallel [23].

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3.5.Satellites[4]

Possibly the best fit for flywheels is with the space industry. They are both focusedon reducing the weight and size of things as much as possible and flywheels have a longlifespan which could possibly outlive the space station in which it was designed to be used.It was projected that the lead acid batteries would be replaced with 192 flywheels and saveNASA $260 million (projection from 1996). Of course another aspect would be to use thegyroscopic momentum of flywheels to their advantage. For example if 2 flywheels arepaired together in opposing directions, they have a total rotational momentum of zero.They can then transfer energy from one another which would give one wheel more energyand thus the total rotational momentum would be augmented in that direction. To conservetotal gyroscopic momentum, the satellite would then spin in the opposite direction of theovercharged flywheel. This can be undone in reverse order. With 6 flywheels, you couldorient a satellite any direction with minimal losses and without the use of thrusters.

Conclusions

In closing, flywheel batteries are a great technology stuck in the worst of places. It is

ridiculous to think that no matter how little exposure a technology has had, it will succeedif it is innovative enough. Some might say that current technologies could replaceflywheels in terms of specific energy (zinc-air batteries) or power density (ultracapacitors)but of course this is a biased statement. Humanity and especially automotive companiesare resistive to change and have to come to accept chemical batteries and all of theirflaws. Flywheel systems are not the single solution to all of the world's problems. Even so,everyone refuses to accept them until they become the utopic flywheels they hadimagined. I hope that this report will help with spreading awareness of flywheel batteriesand that soon enough we will hear some news from Mr. Bitterly to get things rolling again(literally!).

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References

[1]: Electric Motor Internet: http://en.wikipedia.org/wiki/Electric_motor , Nov. 2010 [Nov.19, 2010].

[2]: Inductor Internet:http://en.wikipedia.org/wiki/Inductor , Nov. 2010 [Nov. 19, 2010].

[3]: Steam Engine Internet:http://en.wikipedia.org/wiki/Steam_engine , Nov. 2010 [Nov.19, 2010].

[4]: C.Platt. (2000, may). Re-Energizer Wired. [Online]. Issue 8.05. Available:http://www.wired.com/wired/archive/8.05/flywheel.html [Nov. 18, 2010].

[5]: Flywheel Facts and Fallacies Internet: http://flywheel.esmartbiz.com/facts.htm, Jun.2010 [Nov. 18, 2010].

[6]: Compensated Pulsed Alternator Internet:http://en.wikipedia.org/wiki/Compensated_pulsed_alternator , Jun. 2010 [Nov. 21, 2010].

[7]: Potter's Wheel Internet: http://en.wikipedia.org/wiki/Potter's_wheel, Oct. 2010 [Nov.19, 2010].

[8]: Water Wheel Internet: http://en.wikipedia.org/wiki/Water_wheel , Nov. 2010 [Nov. 21,2010].

[9]: Internal Combustion Engine Internet:http://en.wikipedia.org/wiki/Internal_combustion_engine , Nov. 2010 [Nov. 21, 2010].

[10]: Clutch Internet: http://en.wikipedia.org/wiki/Clutch , Nov. 2010 [Nov. 21, 2010].

[11]: Homopolar Motor Internet: http://en.wikipedia.org/wiki/Homopolar_Motor , Nov. 2010[Nov. 23, 2010].

[12]: Homopolar Generator Internet: http://en.wikipedia.org/wiki/Homopolar_Generator ,Nov. 2010 [Nov. 23, 2010].

[13]: Flywheels for renewable energy and power quality applications Internet:http://www.bpa.gov/energy/n/Tech/energyweb/docs/Energy%20Storage/TRINITY.PDF,[Nov. 19, 2010]

[14]: The Mechanical Battery Internet: http://www.damninteresting.com/the-mechanical-battery , Oct. 2007 [Nov. 25, 2010].

[15]: Re-Inventing the Wheel Internet: http://www.mega.nu/ampp/bitterly.html , Aug. 2006

[Nov. 25, 2010].

[16] Bitterly, J. G., 1998, Flywheel Technology: past, present, and 21st centuryprojections, Aerospace and Electronic Systems Magazine, IEEE., V. 13, n. 8, pp 13-16.See: http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=707557

[17]: Post R. F., 1996, The Electromechanical Battery Science & Technology ReviewMagazine, IEEE, pp 12-19. See: https://www.llnl.gov/str/pdfs/04_96.2.pdf , [Nov. 25,2010].

[18]: Porsche 911 GT3 R Hybrid Does Good In 1st Race Internet:http://www.wired.com/autopia/2010/03/porsche-911-gt3-r-hybrid-does-good-in-1st-race/ ,

Mar. 2010 [Nov. 25, 2010].

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[19]: GT3 R preview Internet: http://auto.niot.net/post/geneva-preview-porsche-911-gt3-r-hybrid/ , Apr. 2010 [Nov. 25, 2010].

[20]: Railgun Internet: http://en.wikipedia.org/wiki/Railgun , Nov. 2010 [Nov. 23, 2010].

[21]: Arc Welding Internet: http://en.wikipedia.org/wiki/Arc_welding , Nov. 2010 [Nov. 23,2010].

[22]: "Who Killed the Electric Car?" (2006) Movie, Directed by Chris Paine.

[23]: Flywheel Technology Helps Life Spring Eternal for Battery Systems Internet:http://ecmweb.com/mag/electric_flywheel_technology_helps/ , Apr. 2004 [Nov. 25, 2010].

[24]: J. Irwin and R. Nelms, "The Ideal Transformer" in Basic Engineering Circuit Analysis,9th ed. Wiley, 2008, ch.10, sec. 3, pp 521-529.

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ECE 200 (2010)

Formal Report Marking Sheet

Name: ______enter your name here ______ ID#: __ __ __ __ __ __ __

Contains all the required parts? (1 mark each)1. Cover/Title Page (first page)2. Memo of Transmittal3. Executive Summary (aka Abstract)4. Table of Contents5. List of Illustrations and Tables6. Main body (5-6 pages)7. Intro, discussion sections, conclusions8. Reference list (separate page)9. Grading form (last page) /9Letter of Transmittal (1 mark each)1. Format (proper memo or letter format)

2. Why topic was chosen3. Mentions major points in the report4. Identifies pattern of organization /4Executive Summary/Abstract1. Approximately 150 words2. Reasonably summarizes content3. Avoids technical jargon4. Paragraph Format /4

Main Body of Report/ReferencesIntroduction (3)1. Purpose/reason for the report2. Scope of the report

3. Brief preview of sectionsDiscussion Sections (4)4. Headings and Subheadings5. Follows organizational pattern6. Proper use of lists, tables and illustrations7. Contains appropriate level of detailConclusions/Recommendations (2)8. Appropriate summary of content, conclusionsReference List (6)9. Has minimum number of references (book, article, web page)10. Correct IEEE format /15

General formatting, writing essentials (8)

1. Sans Serif Font and Single Spacing (2)2. Margins (1)3. Page numbers (1)4. Spell-checked (2)5. Grammar-checked (2) /8

Overall Impact on Reader (Was it a good report?) /10

TOTAL /50

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