Green Energy Design Project

By:Grace AyodeleEric HeckmanDrew Peden

Ryley Rosenfeldt

Mechanical Engineering 111Engineering Fundamentals II

College of Engineering and Applied SciencesUniversity of Wisconsin-Milwaukee

Milwaukee, WI 53201

5 May 2014

i

Executive Summary

The main object of this report is to explain the design process behind the windmill

prototype. The problem presented was to design and build a model of a quiet, roof mountable

green energy system. The system was to be used to recharge a home battery backup. Through the

design process, the following limitations were implemented: materials, cost, no internal

combustion engine, no use of lithium-ion batteries, and finally the prototype could be no taller

than two feet and must have a volume of four cubic feet or less. The conducted research showed

that viable production methods included solar power, micro hydro power, vertical blade drag

design and horizontal wind power. Each method was evaluated based on criteria outlined in the

design objectives and decision matrix. Horizontal power was the final choice for our green

energy system. The following report details the research process, green energy source selection,

design process, prototype development and the final design solution. A final recommendation

will be given based off of the projects results.

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Table of Contents

Title Page i

Executive Summary ii

Table of Contents iii

Conclusions and Recommendations 1

Introduction 2

Body of Report

Revised Problem Statement 3

Proposed Design Solutions 3

Contribution of Team Members 6

Economic Analysis 8

Bibliography 9

Appendices 10

1

Conclusions and Recommendations

In a wind with a velocity of 5 ms the final design had an output of 2.3 V and 35 mA (G1).

This was enough to overcome the forward voltage of the LED chosen (1.8 V f ¿ . At lower

velocities, the final design produced much less voltage. In the initial calculations several things

had to be assumed. One was the tip to speed ratio (TSR) of the design. Using a less than ideal

wind velocity (G2.1) and a TSR of 1.75 to determine the rpm (G2.2) the torque predicted was

100 Nmm (G2.3). Based on this modelling a generator was chosen with a torque rating of 39

Nmm with an operating range of 4.5-12 volts and max efficiency at 190 rpm. Gears were

purchased with a 3:4 ratio to slightly exceed the ideal rpm (G2.4). Therefore our predicted

voltage output was initially a minimum of 4.5 volts. Upon initial assembly and testing at

velocities of 2-3 ms it became apparent that the design did not produce enough torque to turn the

motor. Due to the exponential relationship between wind velocity and power (G2) and therefor

torque these were not ideal testing conditions. A lower torque motor was chosen that would

produce 12 V at an ideal rpm of 14,000. Although it easily produces small amounts of voltage in

low wind velocity conditions, the gear ratio could not be changed due to time and financial

considerations. Later experimental data with an air velocity of 5 ms indicated that the design

would achieve 400 Nmm of torque (G1.1), which is more than enough to turn the motor the

initial design called for. However with the new motor the design only produced 2.3 V (G1.4).

This was enough to light our LED, but under our initial expectations.

The design was, for the most part, successful. The prototype was capable of producing

power in the given test conditions. At this point it is recommended that the initial motor be re-

installed in order to produce a more appreciable amount of voltage and new experimental data

gathered in order to adjust the circuit as well. At low wind velocities the new recommended

design will not produce electricity, but in average to above average winds the voltage level will

be more useful and will take advantage of the gear ratio calculated in the initial mathematical

modelling. All other components of the design were successful and will transition well into the

production model.

2

Introduction

The goal of the project was to design a prototype that generates power from a green

energy source. From this problem statement, three design objectives were created. The main

design objectives implemented were efficiency, safety, and user friendliness. The project also

included several design constraints that restricted certain solutions. These constraints included

the physical limitations that the prototype had to be equal to or less than 4 cubic feet and no taller

than two feet. In addition, the design could not include lithium-ion batteries or an internal

combustion engine due to safety reasons. Ideally, the chosen design should be efficient, quiet,

and pleasant to the eye in case of installation in an urban environment. Using the design

objectives and decision matrix, viable power production methods were evaluated on a utility

point scale based on how close they fit the criteria. The following report will explain the process

behind choosing the current prototype design.

3

Body of Report

Revised Problem Statement

Design a prototype that generates power from a green energy source.

Proposed Design Solution

Through the research, the three main green energy types in consideration were solar,

wind, and hydro. After learning about possible solutions, a list of objectives was created to

determine which of the possible solutions best fit the problem statement. A weighted objective

tree was then created to summarize which objectives were most important (see Appendix B). A

larger weight was placed on the objective of efficiency (broken down into power and cost)

because it was deemed the most important part of the design. Each possible design solution was

then evaluated through the use of a detailed decision matrix that used a utility scale and relative

weights of the objectives to determine which proposed solution best fit the original problem (see

Appendix C). Popular solutions, such as solar panels, were disregarded due to their immense

initial costs. Hydroelectric generators, the other competing design, were removed due to its

requirement of a nearby water supply. The results determined that wind with a horizontal shaft

was the best design solution for the given criteria. This conclusion resulted from the outside

factors of cost, efficiency, sound, and safety presented in the weighted objective tree.

After a horizontal wind design was chosen, calculations had to be completed properly

before the prototype could be assembled. The required calculations were used to determine the

gear train, blade size, and power all routed back to one another. Due to the Betz Limit, a

windmill can only produce 60% of the energy provided. Using 60% as a stepping stone, working

backwards proved what RPM would be valid as well as the size of gears. Staying on the

conservative side, a 30% efficiency rate was used when calculating the blade speed. Using a

4

Milwaukee wind average of 3.15 m/s, an efficiency rate of 30%, and an estimated TSR of 1.75,

the blade length was calculated at roughly 0.29m (see Appendix G2 – figure 1). This blade

length was calculated to produce 107 Nmm of torque (G2.3) at 181 rpm (G2.2). The gear ratio

was then calculated to find that a ratio of 3:4 would achieve an ideal rpm for the initially chosen

motor.

The blades themselves were cut out of 1/8” abs plastic sheeting due to the strength and

light weight of the material. The blades are 10 inches in length and are in a teardrop shape that

comes to a sharp point (see Appendix A – figure 3). The blades are attached to the assembly

through the use of a threaded eye bolt. A hole is located at the base of each blade. A ¼-20 size

eye bolt is fastened to the back side of each blade using a nut, bolt and washer. Each blade

assembly is then screwed into one of three evenly spaces holes at 120 degrees apart on the nose

of the windmill (A.3). The current blade design is capable of harnessing enough wind energy to

produce a sufficient amount of power. After testing, it was found that the blades have a slight

flex. It may be beneficial to increase the thickness of the material used in order to reduce this

issue.

The blades assembly is attached to a ¼ aluminum shaft, due to its strength and light

weight. Two ¼” ball bearings attach the shaft to the housing and allow it to freely spin with

minimal resistance. The rotational energy from the shaft is transferred to a DC motor by two

small gears. The original design placed the motor parallel and directly below the shaft (A.4).

However, at the start of assembling the prototype, it was discovered that the outside gear

diameter was smaller than anticipated and that the motor could not lie against the shaft without

rubbing. An alteration was made that involved shortening the shaft, moving the rear bearing into

a new, internal wall and building a small platform for the motor to lie on (A.2). The new location

5

for the gear is now at the end of the shaft. This allows for the gears to rotate the motor without

the shaft rubbing. The new design works just as intended and does not seem to have an impact on

power production. For testing purposes, a 1.8v LED was attached to the back of the unit to

indicate power production. A 60 Ohm resistor was added to the circuit to prevent the LED from

being damaged.

After the model was confirmed to work, several safety analyses were conducted to

determine the security of the model. A Failure Mode and Effects Analysis (FMEA) report was

filled out to identify and prevent any problems (see Appendix D). It looked for all the possible

ways that the model could fail and established what actions to take to reduce the risk of priority

areas. The FMEA determined that components like snap rings and electrical wiring were a

relatively low risk priority. The eye bolts and motor, however, were identified as having high

risk priority numbers. Actions were taking by assuring that a high quality motor was used and

Loctite adhesive was applied to the threaded fasteners in the blade assembly.

6

Contribution of Team Members

Grace Ayodele – Semester Project Work Completed

Her contributions to the project included initial research that was used to narrow down

the selection of green energy production and some of the initial design work for the assembly.

For the decision matrix, she focused on assigning more weight to be allotted for safety over the

over objectives. She was also in charge of in the initial design for the base, shaft and housing in

the design assembly, although changes were made for the final design.

Eric Heckman – Semester Project Work Completed

Eric’s initial contributions included online research of green energy projects and

delegating work to the other team members. The majority of his contributions involved the oral

and written reports for the group. He was in charge of putting together the visual aids for all four

PowerPoint presentations and assigned sections to the group. For the initial prototype design, he

was in charge of researching blade types and the final result was his design. He drew the models

for the blades, blade assembly, and revised housing. He was in charge of assembling the

complete CAD assembly after the other team members finished some of the individual parts.

Eric completed both the safety and economic analysis of the prototype. This included the FMEA,

safety labels, and cost breakdown of the model. He assisted Drew in the overall construction of

the prototype and any experimental testing. Lastly, Eric wrote the majority of the body and

economic analysis within the final report, as well as attach all the images in the appendix. He

also assembled and formatted the final report after receiving individual sections from the other

team members.

7

Drew Peden – Semester Project Work Completed

Drew initially conducted online research into various forms of green energy in order to gather

metrics for the design choice. After the research was complete he compiled the team research

into a design matrix in order to determine the direction of the final design. Once the design

matrix determined that a horizontal wind generator would be ideal Drew contributed to initial

mathematical modelling for determination of component parts. He calculated electrical

component values as well. After mathematical modelling and electrical components were

determined Drew spearheaded prototype construction with team assistance due to having more

space available. He assembled the circuit on the prototype as well. Once the prototype was

complete he participated in final tests of the design. He contributed to the conclusions and

recommendations, overall report format, and operating instructions for the final report.

Ryley Rosenfeldt – Semester Project Work Completed

For the engineering analysis, he looked at the different ways that power output was possible

through gears, belts, and chains. He then used this data in order to calculate which gear ratio

would be most efficient as well as not having to worry about the slip that belts and chains can get

once in a while. For the assembly, he drew up all the shaft and bearing assembly along with the

gears. This was then passed onto the team and assembled as a whole.

8

Economic Analysis

Before moving on to a production model, an economic analysis of the design had to be

completed. A detailed spreadsheet of the cost breakdown can be found in Appendix D. The cost

breakdown of the model included both recurring and non-recurring costs of production.

Recurring costs must be paid for each model that is produced and included expenses such as

materials, parts and labor. The majority of the prices were based off of material costs for the

model. The acceptation to this is the housing, which was made out of wood for the model and

would be replaced with an aluminum paneling for the final product. Labor time is also predicted

to lower through the use of modern manufacturing techniques since the figures are based off of

the prototype and is likely to be more expensive than the production model. The overall

estimation for recurring costs was $420. Non-recurring costs include expenses for machinery and

non-labor related time spent on the design or research on the project. The non-recurring expenses

are evenly distributed over each model that is produced are have a smaller overall cost per unit as

more units are produced. The two main tools listed for this design are a molding and stamping

die for the production of windmill blades and paneling for the housing. The estimation for non-

recurring costs is at $46,000. Spread evenly over a 1000 unit run, the overall cost per unit would

be at $46, bringing the total production cost to $466. If the model is sold for a 20% rate of return,

the retail price of the windmill would be set at $560. This fits right into the $400 - $1,200

average range for household, consumer-grade windmills.

 

9

Bibliography

Fink, Dan. "Small Wind Turbine Basics." Energy Self Sufficiency Newsletter (July 2005): 12-16.

Web.

Gore, Jessica. "A Green Electricity Comparison." Suite. Suite.com, 8 Jan. 2010. Web. 11 May

2014.

"Grid-Tied Solar Power Systems." Whole Sale Solar. N.p., n.d. Web. 10 Apr. 2014.

Klemen, Michael. "Perfect Turbine." Turbines. North Dakota State University, 1 June 2009.

Web. 11 May 2014.

Kroh, Kiley. "Germany Breaks Its Own Record For Solar Power Generation."

ThinkProgress.org. Climate Progress, 22 Aug. 2013. Web. 27 Apr. 2014.

"Solar Water Heaters." Energy.gov. U.S. Department of Energy, 7 May 2012. Web. 10 Apr.

2014.

"Understanding Coefficient of Power (Cp) and Betz Limit." Kid Wind. Kid Wind Project, Mar.

2011. Web.

"Wind Power Your Home | Wind Energy Foundation." Wind Power Your Home. Wind Energy

Foundation, n.d. Web. 4 Mar. 2014.

10

Appendix A – CAD Drawings

Figure 1. Top, front, left and isometric views

Figure 2. Internal view

11

Figure 3. Blade shape and assembly

Blades

Drive and Gearing

Housing

Generator and Circuit

Figure 4. Initial design concepts

Appendix B – Weighted Objective Tree

Energy Source

1.0/1.0

Efficient

.40/.40

Powerful.40/.16

Cost.60/.24

Safe.30/.30

Installing.50/.15

Maintenance.50/.15

User Friendly

.30/.30

Installation.30/.09

Operation.70/.21

12

Appendix C – Decision Matrix

Solar Hydro

Horizontal

Wind

Vertical

Wind

Objective Weight Utility Score Utility Score Utility Score Utility

Power

Generation 0.16 6 0.96 5 0.8 5 0.8 4

Cost 0.24 3 0.72 5 1.2 6 1.44 5

Safety of

Installation 0.15 5 0.75 4 0.6 5 0.75 5

Ease of

Maintenance 0.15 5 0.75 4 0.6 5 0.75 5

Ease of

Installation 0.09 6 0.54 2 0.18 6 0.54 4

Operation 0.21 7 1.47 2 0.42 6 1.26 4

Total Score: 1 32 5.19 22 3.8 33 5.54 27

Appendix D – FMEA

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System/Component/Function

PotentialFailure Mode

PotentialEffect(s) ofFailure

Seve

rity

PotentialCause(s) ofFailure

Occ

urre

nce

CurrentControls

Det

ectio

nR

PN

RecommendedAction

Snap Rings Bend/Break

Loosen and misalign the shaft 4

Too much play/tension1

High tolerances1 4

Make sure tolerances are tight

ElectricalShort circuit/ Electrical Fire

Loss of power production/ Fire hazard 3

Water/ Circuit overload 1

Proper build quality and tolerences 2 6

Test for leaks and electrical current

Gears Chip Gears can slip 3

Over torque/ Corrosion 2

Higher quality materials 2 12

Use high quality gears

Bearings Wear/Rust

Loss of RPM/ Power production 2

General usage/ Moisture 4

Use high quality bearings and grease 2 16

Test wear levels for bearings

BladesCrack/Fracture from inpact

Loss of balance/ Power production 4

Impact/ Debris buildup 2

Use materials that do not crack easily 3 24

Proper maintenance by the user

DC Motor Wear

Reduction/Loss of power production 3

Over torque/ General wear 3

Use gear ratios to lower the torque 3 27

Make sure torque calculations are correct

Eye BoltsStripping/Loosening

Loss of balance/ Detachment of Blade 5

Improper installation of blades 2

Adhere with Loctite 3 30

Properly assemble blades

14

Appendix F – Economic analysis

Appendix G – Calculations

G1. Experimentally Determined Values of Final Design

Experimentally Determined Values with Wind Velocity of 5 ms

(1) Torque: 0.4 Nm

(2) RPM: 163 = 17 rad

s(3) Current: 35 mA (0.035 A)

(4) Voltage: 2.3 VSwept Area: 0.29 m2

Power Available in Wind: 12

ρ V 3 A= 12 (1.3 kg

m3 )¿23.7 W

Power Generated: Tω = (0.4 Nm)(17rads

¿=¿6.8 W

Percent Efficiency: 6.8

23.7x 100=28.7 %

15

TSR = ωrV

=(17 ) 0.3048

5=1

G2. Initial Calculations

Initial Calculations

(1) Velocity of Wind (5 ms

¿ (0.66 )=3.15 ms

The 5 ms is the yearly average wind velocity of Milwaukee 1948-90 taken from the Wisconsin

Climatology Office at 20 ft.http://www.aos.wisc.edu/~sco/clim-history/stations/mke/milwind.html

The 0.66 coefficient was added to account for less than average wind speeds.

Power Available in Wind: 12

ρ V 3 A=12 (1.3 kg

m3 )¿6.77 W

Including estimated efficiency of 30% (half of Betz Limit) P = 6.77(.03) = 2.03 WIn computing the angular velocity a Tip Speed Ratio (TSR) had to be guessed, we used 1.75

(2) ω=Vr

TSR= 50.3048

1.75=18.9 radsec

=181 rpm

(3) Torque = Pω =

2.03 W

18.9 radsec

= 0.107 Nm = 107 Nmm

(4) Nω=Nω(4)181

3=241 rpm

16

0 1 2 3 4 5 6 7 80

10

20

30

40

50

60

70

Power in Wind (Watts)

Wind Velocity (m/s)

Power Available in Wind (W)