Design of a Residential Wind Turbine System
By
Timothy J Pond Jr
A Project Submitted to the Graduate
Faculty of Rensselaer Polytechnic Institute
In Partial Fulfillment of the
Requirements for the degree of
MASTER OF ENGINEERING
Approved:
_________________________________________
Professor Ernesto Gutierrez-Miravete, Project Adviser
Rensselaer Polytechnic Institute
Hartford, Connecticut
May, 2012
i
© Copyright 2012
By
Timothy J Pond Jr
All Rights Reserved
ii
CONTENTS
Design of a Residential Wind Turbine System
LIST OF TABLES………………………………………………………………………..v
Symbols Used…...…………………………………………………………………….....vi
LIST OF FIGURES……………………………………………………………….…....viii
ACKNOWLEDGMENT………………………………………………………………..vii
ABSTRACT……………………………………………………………………...……...ix
1. Introduction…………………………………………………………………..……….1
2. Theory/Methodology of Design.………………………………………...…...………2
2.1
2.2
2.3
2.4
Verify Location…………………………………...……………………..……..2
2.1.1
Mount Location…………………………………………………..…….2
2.1.2
Wind Data………………………………………………………..…….3
Connection Style………………………………………………………...……..5
2.2.1
Off Grid…………………………………………………………….…..6
2.2.2
Direct Connect…………………………………………………………6
2.2.3
Battery and Grid……………………………………………….……….6
Turbine Style………………………………………………………………..….7
2.3.1
Horizontal Axis Wind Turbine………………………………………...7
2.3.2
Vertical Axis Wind Turbine…………………………………………....8
Component List…………………………………………………………….…..9
2.4.1
Rotor Blades…………………………………………………...……….9
2.4.2
Tower…………………………………………………………………11
2.4.3
Power Generator……………...………………………………………13
2.4.4
Inverter………………………………………………………………..14
2.4.5
Charge Controller……………………………………………………..15
2.4.6
Batteries………………………………………………………..……..15
2.4.7
Monitoring Devices………………………………………………...…19
iii
2.4.8
Grid Connection………………………………………………………20
3. Manufacture…………………………………………………………………………21
4. Results ……………….…………………………………………………………..….24
5. Conclusion…………………………………………………………………….…….28
6. References…………………………………………………………………………...29
iv
LIST OF TABLES
Table 1: Pole Sizing Results………...…………………………………………………..12
Table 2: Battery Sizing Calculations……...…………………………………………….17
Table 3: Battery Sizing Calculations for 2KWh load…………………………………...18
Table 4: Wind Speed Applied as Uniform Side Load…………………………………..21
Table 5: System Cost……………………………………………………………………23
Table 6: Payback Period………………………………………………………………...24
Table 7: Payback Period with Excess Wind and Tax Breaks………………………...…24
v
SYMBOLS USED
m………………………………..meters
ft………………………………..feet
MPH…………………………....Miles per Hour
In……………………………….Inch
M………………………………Moment (inch*lbs)
I………………………………..Inertia
sb……………………………...Bending Stress
t………………………………Shear Stress
Ap……………………………..Pipe Area
V……………………………...Volts
A……………………………..Amps
AC…………………………...Alternating Current
DC…………………………...Direct Current
AH…………………………..Amp Hour
W…………………………....Watt
Wh….. ………………….…..Watt Hour
KWh…………………………KiloWatt Hour
Hz…………………………....Hertz
CD……………………………Drag Coefficient
FD…………………………....Drag Force
P…………………………….Uniform Pressure
rair…………………………..Density of Air
VW…………………………..Velocity of Wind
VM…………………………..Von Misses Stress
Fp……………………………Force of Wind
Wt……………………………Total Watts Used
At……………………………Area of Turbine
Weu…………………………..Total Watts Needed for Given Time
N1……………………………Number of Lights
vi
SYMBOLS USED (cont.)
Nd…………………………….Number of Days Used
Hd…. ………………………...Hours of Use in Day
Ab…………………………….Amp Hours Required of battery Bank
Bv…………………………….Nominal Battery Voltage
Wbs…………………………..Wattage for Battery Bank
Nb……………………………Number of Batteries Needed
Dr……………………………..Rate per Day
Ye…………………………….Yearly Earning
PP1……………………………Years Till Payback
S………………………………Swept Area of Turbine
V1……………………………..Wind Speed
Cp………………………..……Power Coefficient
Pavailable………………………...Power Available
Pactual…………………………..Actual Power
s……………………………….Seconds
vii
LIST OF FIGURES
Figure 1: U.S. Department of Energy Wind Data………………………………………..2
Figure 2: Anemometer Used for Measuring Wind Speeds……………………………….3
Figure 3: Wind Speed Data Vs Weather Bug Recorded Speeds…………………………4
Figure 4: Wind Speed Averages………………………………………………………….4
Figure 5: Time of Day vs. Wind Speed…………………………………………………..5
Figure 6: Horizontal Axis Wind Turbine…………………………………………………7
Figure 7: Vertical Axis Wind Turbine……………………………………………………7
Figure 8: Component Layout……………………………………………………………..9
Figure 9: Turbine Design……..…………………………………………………………10
Figure 10: Rotor and Stator Layout..……………………………………………………11
Figure 11: Sine Wave, Square Wave, and Direct Current………………………………14
Figure 12: Average Energy Daily Usage...……………………………………………...16
Figure 13: Turbine Design………………………………………………………………20
Figure 14: Wind Turbine FEA Results………………………………………………….22
viii
ACKNOWLEDGMENT
I would like to thank my wife Rachel for her support of me while I pursue a Master of
Engineering degree.
ix
ABSTRACT
I have always been interested in adding a renewable energy source to my home. This
project will cover the necessary steps for designing and installing a wind turbine on my
house. The area will be evaluated to determine where I will mount a turbine and the
type of turbine best suited for the configuration of my property. A series of analysis will
be performed on standard and custom parts required to make this work. Standard
strength calculation will be performed to size required parts of the wind turbine and FEA
will be used when deemed necessary for any custom pieces. The cost of implementing
this project will then be compared to the money saved by using a free and renewable
energy
source
instead
of
purchased
electricity
from
the
grid.
x
1. Introduction
The global need for energy increases as our civilization ages. Homes that once were
powerless are now connecting to an electricity grid. New homes are being built as the
world population grows. These new homes also require power from an aging electricity
grid. People are buying more and more technology that require electricity. The growing
need for electricity strains an already taxed system.
In order to limit the dependence on an aging electricity grid, a supplemental system is
required. This system will offset cost required to power my home and in turn reduce the
load on the existing electricity grid. If this idea were to be adopted by others, then the
negative impact of additional energy plants on the environment can be reduced. This
project will determine the optimal size for a wind turbine to supplement power to my
home. The system design requirements for the desired wind turbine system will be
identified in this project.
This project will document the processes required for designing and implementing a
wind turbine system. I will first establish if my area is feasible to support this project.
Then I will list the components needed to complete this task. As the components are
listed, basic size requirements will be identified. Once the system is completed the
output will be used to calculate the cost savings.
1
2. Theory/Methodology of Design
2.1 Verify Location
2.1.1
Mount Location
The design of a wind turbine requires one thing most of all, wind. There is no point in
designing a wind turbine system for an area where no wind is present. Aside from a very
expensive form of yard artwork, it will be useless. My first step for determining the
feasibility of installing a wind tower on my property is to check the availability of wind.
I have observed a lot of wind in my time at my house but have never quantified the
speed. The U.S Department of Energy has posted general wind data for Connecticut in
2007, as seen in Figure 1. Even though this data was created from 2007 weather data, it
demonstrates patterns of high wind and these patterns can be expected to be similar for
each following year. My home is located 10 miles from the coast in the southeast corner
of Connecticut. This data tells me that I can expect wind speeds of approximately 12-14
MPH at my home; however, this data was collected at 50 meters above the ground and
may not reflect the wind speeds on my property at a much lower elevation.
Figure 1: U.S. Department of Energy Wind Data
Surrounding houses, trees, and changing ground elevation have severe affects on wind
speed and need to be considered before deciding on wind power. An anemometer was
2
used to measure wind speed on my property. The anemometer was a D2 rotor with
Cateye Velo8 display. The anemometer used is depicted in Figure 2. This was done
during windy conditions where weather data reported a 12 MPH average wind speed.
The choice of where to permanently mount a wind turbine is either to utilize several low
lying areas that were clear of obstructions or higher ground that was obstructed by either
my house or surrounding trees.
Standard rule of thumb for wind turbines is that your
turbine should be 30 ft above any surrounding obstructions in a 500 ft radius [1]. There
is no area on my property that meets these criteria, so measurement is needed to
determine if wind turbine installation is wise. It was determined that the highest point of
my property (i.e. the peak of my roof) was the optimal place for finding the highest wind
speeds available.
Figure 2: Anemometer used for Measuring Wind Speeds
2.1.2
Wind Data
Over a 3 week time frame, wind data was recorded from 4 ft above the peak of my roof.
The instantaneous wind speed was recorded at various times of the day. The data
recorded was the average wind speed for the day, and the maximum wind speed
occurring for the day. Figure 3 depicts the instantaneous wind speed and the given day.
This data is recorded against what the weather bug service [2] has reported for my area
at that given time.
3
Figure 3: Wind Speed Data Vs Weather Bug Recorded Speeds
Figure 4 depicts the daily average wind speed vs. the maximum recorded wind speed for
any given day. The maximum wind speed values recorded were found to be significantly
higher than instantaneous speeds recorded for the given day. The average wind speeds
recorded for the day are noticeably lower than the recorded instantaneous speeds for the
days recorded. This clues us to the fact that the inconsistent wind speeds atop my house
may not be steady enough to support a traditional wind turbine. The time of day at
which the winds speeds are recorded were determined to be a significant factor on what
was observed.
Figure 4: Wind Speed Averages
4
Figure 5 depicts the time of day and the wind speeds recorded on that given day. It can
be seen that if the instantaneous wind speed were recorded at the same time every day,
then the wind speeds recorded and what is truly experienced at a given site could be very
different.
Figure 5: Time of Day vs. Wind Speed
If data were only collected at 10:00AM every day, the wind speeds would be very low.
This would prevent the installation of a turbine because it would be perceived that no
wind exists. The opposite would be true if the only data recorded was at 9:00PM every
night. This would produce a number of 10.5 MPH, a number that is much higher than the
average wind speed at my location. It is for this reason that several data points are taken
during any given day. The average is then taken and used to produce the plots in Figures
3 and 4.
2.2 Connection Style
Three main styles of wind turbine configuration exist. Each has its reasons for and
against its use. It is important that before a turbine design is created, I select what the
turbine system is required to do. The main system designs are:

Off Grid

Direct Connect

Battery and Grid
5
2.2.1
Off Grid
The intent of an entirely off grid system is to provide all power for the home from the
wind turbine. This system will depend on a steady wind source of medium to high wind
speeds. This requires a large battery bank and is usually run in parallel with some other
power generation system to supplement power during extended periods of little or no
wind. This type of system requires the most amount of work to set up and maintain. It
is also the most expensive because it requires more supporting systems than any of the
other designs. However, this system is self sufficient when installed and is not affected
by grid power outages.
2.2.2
Direct Connect
This system requires the least amount of supporting equipment. The turbine is connected
directly, or by means of some components, to the grid. All power generated is fed
directly into the grid and none is saved. No batteries are required for this system. This
system requires the least amount of maintenance and initial assembly is simplest.
However, because there is no battery backup, direct connect turbines are unable to use
power when the grid goes down. For those residing in an area where the grid is pretty
reliable, this system may be a good option.
2.2.3
Battery and Grid
This system requires an intermediate amount of work to set up and maintain when
compared to the other two systems.
This system does connect to the grid. When
connecting to the grid, all excess electricity produced can be sold to the utility company.
This is an important fact to consider when figuring out costs and payback periods which
I do later in this paper. Excess electricity cannot be sold to the utility company when the
grid is down. Some maintenance is required for the batteries and supporting equipment.
Similar to an entirely off grid system, this system needs to be monitored to prevent
damage or fire by malfunctioning equipment. When the grid is out for this system,
battery backup can be used to power the home.
6
The three system designs all have their pros and cons, but given the goal of this project, I
have chosen to design a battery and grid system. This system is not as labor intensive as
an off grid system but requires some maintenance. For the purpose of this project I will
start small and work on increasing efficiency of the system. As efficiency is increased I
will expand the system to include more and more of my home systems.
2.3 Turbine Style
There are two styles of wind turbine that were considered for this project. They are
depicted in Figures 6 and 7.
Figure 6: Horizontal Axis Wind Turbine
Figure 7: Vertical Axis Wind Turbine
These styles have their strengths and weaknesses and needed to be evaluated before any
particular style was selected for my home. Each is expensive and it is important to
decide which will be a better fit for my location before any investment can be made.
2.3.1
Horizontal Axis Wind Turbine
Horizontal wind turbines are the most popular style of wind turbine on the market. They
are more efficient than the vertical axis turbines. The HAWT take wind energy from one
direction. Wind flows over the turbine blades and creates lift. The lift in the blades is
translated to rotational energy. Most HAWT are capable of rotating at much faster
7
speeds than the wind is travelling, rendering them capable of generating a lot of
electricity.
HAWT are more complex than VAWT because the main generators are located directly
behind the rotors, on top of whichever mounting tower is required for the system. Access
to this for maintenance or trouble shooting is difficult, so design tolerances are tight to
avoid as many problems as possible. This is part of the reason why HAWTs are more
expensive because there is a much smaller margin of error in these systems.
With
tighter design tolerances comes more cost. The more expensive turbines are very
elaborate but still very efficient.
2.3.2
Vertical Axis Wind Turbine
VAWTs are less popular styles of wind turbine because they are not as efficient.
VAWTs are however more effective at lower wind speeds. VAWT efficiently use wind
from all directions without the need for additional components to change angle of attack
like HAWTs.
There are two types of VAWTs and they are:
–
–
Lift dependent
•
Capable of rotating faster than available wind speed
•
Difficult to manufacture
Drag dependent
•
Only capable of going as fast as available wind speed
•
Easy to manufacture
It is for these reasons that I have selected a VAWT for this project. The wind traveling
over my house will be more turbulent than laminar and this is ideal for a HAWT. A
VAWT will operate better in this environment because it can use wind from any
direction to generate rotational energy without redirection. A HAWT would be required
to rotate and face the wind. This can be difficult if the wind is constantly changing
direction. Constantly changing direction can put a lot of undue stress on the system and
shorten its overall lifespan when compared to a HAWT design. Also, the gearbox for
the power generator of a VAWT system can be located at the base, or much lower than
8
the actual blades. This allows for easy access to the gearbox for maintenance and trouble
shooting. For house mounted systems like mine, it also allows for the gearbox to be
inside where checking the system during inclement weather is much easier to do.
2.4 Component List
Several components are needed to complete this power generation system. Figure 8
depicts the series of components needed for this system to be successful. They are all
described in greater detail below.
Figure 8: Component Layout
2.4.1
Rotor Blades
Rotors for this project have been selected to be lift and drag based. This style is more
difficult to manufacture than simply just a drag based system. However, it is more
efficient than that of drag based rotors. Lift based rotor design is capable of not only
matching wind speed available on site, but also have a slight additive effect and can
rotate faster than winds available. This makes a lift and drag system ideal for a low wind
speed application, like my house. The overall turbine design is depicted in Figure 9
below.
9
Figure 9: Turbine Design
The turbine design is made of eight stators (white) and 16 rotor blades (blue). The rotor
blades are mounted on the rotor assembly (red). The stators are mounted just outside of
the rotors. The stators provide support for the turbine design. The stators are mounted
on an angle so that they may affectively direct the wind inward toward the blades. This
blocks any wind that would otherwise counteract the rotation of the rotor blades. Figure
10 depicts the layout of the wind turbine rotors. The different parts of the assembly have
been color coded to differentiate where one part starts and the other ends.
A top view is depicted to display the relation of the stators to the rotors blades. As wind
is directed inward toward the turbine blades, it will rotate the rotor. One side of the rotor
blades will be pushed by the wind and the other side of the rotor blade will generate lift
as it rotates into the wind. This is what makes the turbine capable of rotating slightly
faster than the wind speed available. The efficiency of blade design greatly influences
the performance of the turbine. Angle of attack will also affect the performance of the
turbine. Ideally, blade design and attack angle would be experimented with to determine
10
the optimal design for a given location and generator. Due to the time constraints of this
project, a previously tested design was used to create my turbine.
Figure 10: Rotor and Stator Layout
2.4.2
Tower
The tower will be located 6 ft above the peak of my house. It will comprise of tubular
steel and be directly connected to the gearbox with in the house. The tower was sized
according to the calculations below. The effective area for a pipe is calculated using
Equation 1.
[1]
The moment of inertia and the acting moment can be calculated using Equations 2 and 3.
[2]
[3]
11
The bending stress and shear stress that the pole experience due to any given load is
calculated using Equations 4 and 5.
[4]
[5]
Combining these stresses is done with the Von Mises equation, as seen in Equation 6.
These equations are referenced below [3].
[6]
Table 1: Pole Sizing Results
12
Table 1 depicts the results of the pole sizing calculations. The force used is calculated in
section 3.0. Using a 6 ft pole and a force of 291 lbs, the resulting stress is 10820 psi. Any
pole material that is selected must have a yield strength greater than 10820 psi to
adequately support the turbine.
2.4.3
Power Generator
Electricity is generated by passing a magnet over a conductive wire. As the magnet
passes the wire it forces electrons through in one direction. The flow or current (Amps),
and charge (Volts) are directly related to number of magnet passes and number of wire
coils. As the wire is wound into more and more coils, the charge per magnet pass
increases. In the power generator used for this project, magnet passes are accomplished
by rotating a permanent magnet over coils of copper wires.
Generators for the VAWT will be located at the base of the tower. This will be in my
house and protected from the elements. There are several styles of power generation to
choose from. They can be boiled down to two main styles of alternator.
•
•
Permanent magnet alternator

Only efficient at certain speeds

Require no additional parts to generate electricity

Easy to manufacture

Very efficient
Wound field alternator (electromagnet)

Effective at many speeds

Require an outside voltage source to initiate output

Not as efficient as permanent magnet alternators
A permanent magnet generator has been selected for this project. The permanent
magnet generator will convert the rotational energy of the rotors into 3 phase electrical
energy. The generator used is a Cat 4 low wind speed Hurricane Wind Generator from
Hurricane Wind [4]. Power from the permanent magnet generator will be Alternating
Current (AC) and can be used by simple appliances, when needed. Any energy that is
13
not being used immediately will be stored in the battery bank or sold back to the power
grid.
2.4.4
Inverter
An inverter will be required to convert the electricity generated by the Hurricane Wind
Generator. The permanent magnet generator will create AC which will need to be
converted to Direct Current (DC) prior to being stored in the battery banks. This will be
done by a rectifier.
The inverter purchased for this project is an 800W Peak
Performance Model # PKCOBD. This inverter will convert the DC electricity from the
battery bank into AC to be used by the house.
AC electricity comes in two forms, sine wave and square wave. Square wave electricity
is commonly used by cheaper inverters that are primarily used for smaller appliances in
cars or boats. Electricity supplied by the grid is done so in sine wave form at a
frequency of 60 Hz. This form of electricity causes less interference with sensitive
electronics and is more favorable to use. It is, however, more difficult to produce than
square wave and therefore more expensive. The inverter used for this project will be
sine wave so that the electricity produced can be eventually sold back to the utility grid.
Figure 11 depicts the three types of electricity discussed above.
Figure 11: Sine Wave, Square Wave, and Direct Current
14
2.4.5
Charge Controller
A charge controller will monitor the charge of the battery bank. The charge controller
purchased for this project is a Xantrex C-35 Charge controller. It is used for both 12V
and 24V battery banks. If the battery bank is fully charged then excess energy will be
sold to the grid. If the grid is down this is not possible and the energy will need to be
dissipated via a dump load. The dump load for this application will be some kind of
heater that is capable of using the max electricity the wind turbine can output and
convert it to heat. With a dump load connected to the system, the batteries will not be
vulnerable to the damages that can occur by over charging. Batteries will lose charge
over time so this controller will also ensure that the bank is always ready to use and at
full charge.
2.4.6
Batteries
12V, 24V, or 48V batteries are recommended for home powering projects. 12V deep
cycle batteries will be used to support this system. They are the cheapest of the three
and also the easiest to obtain. Deep cycle batteries are primarily used in vehicles and are
built to support many loading and charging conditions. This is ideal for a residential
power generation application. Eventually my home will deplete the batteries several
times to support a small circuit when needed. The charge controller mentioned earlier
will ensure that the battery bank is full and that it does not become damaged by
overcharging.
As time passes and even without loading, the batteries charge will
naturally decrease. Close monitoring of the system will be required to ensure that the
batteries perform well. If the deep cycle batteries are depleted too low then they can be
damaged and this could result in a shortening of their life span.
Therefore, it is
important to closely monitor the battery performance. Batteries are one of the most
expensive components to this system.
The 12V batteries selected for this project can be stacked in series to increase the current
load to support a sufficient circuit in my home. There are two major types of battery
type to consider for this project. They are as follows:
15
o Sealed

Sealed batteries are more expensive

Require less maintenance
o Flooded

Flooded batteries are cheaper

Batteries require more monitoring than sealed batteries (fluids
replaced and seals checked)
12V, 100AH sealed batteries will be used for this project. These batteries require the
least amount of maintenance and are the best choice for quickly establishing a working
system.
Batteries will be sized based on the average usage in the house. My home uses on
average approximately 20 Kilowatt Hours (KWh) a day. Figure 12 depicts the average
energy usage break down for my home on a given day. This is assumed to be during the
colder months where heating would be a larger portion of the electricity cost. This is a
representative case of when the turbine will be used more because historically the winds
are greater during the colder months.
Figure 12: Average Energy Daily Usage
There are several types of battery banks to use in order to supplement power. Batteries
are the most important and expensive part of this system. It is for this reason that I will
be starting small with only enough batteries to run a lighting circuit in my home. The
16
lights in my home are Compact Fluorescent Lighting (CFL). This is a low power
alternative to regular incandescent light bulbs and there is no real difference in light
quality. Traditional incandesent bulbs run on 60W-100W. CFLs run on 13W. The
battery bank calculation below determines the required number of batteries to support
demand of one lighting circuit during extended periods of no wind. The lights are
assumed to run for 7 hours a day constantly. The actual run time may be less than this
but this time period was picked as a starting point.
The total wattage for any given number of lights in a given day of use is calculated using
Equation 7. The watt hours needed for any given time period is found by multiplying
the number of days by the total wattage as in Equation 8.
[7]
[8]
The total amp hours can then be found by dividing by the required battery voltage. In
this case that is 12 volts. This is used to determine the number of batteries because they
are often sized by amp hours instead of watt hours. Equation 9 is used to determine the
amp hours required of the battery bank.
[9]
Table 2 uses these equations to determine the sizing requirements of the battery bank.
Table 2: Battery Sizing Calculations
17
Table 2 determines that 2 batteries are needed to build a battery bank large enough to
support the desired load. Ideally the bank will be strengthened over time to support
more and more systems. However because this is a new system, it is better that all of the
bugs will be worked out on a smaller scale. Failure of 2 batteries and several lights is
much better than $700 of batteries and most of the electrical appliances in my home.
The battery bank above is sized for 4 lights being used for 3 days without wind to
recharge the batteries. Ideally the battery bank will be increased in size to use lights,
microwave, radio, and small fridge. This load is estimated to be about 2KWh for one day
of use. This should be a sufficient load to last my family for 3 days without assistance
from the grid. It will most likely last longer than 3 days if there is any wind during the
period of grid outage. Grid outage usually coincides with periods of high wind as this is
usually the cause of grid outage in the first place. It is often not recommended to use
deep cycle batteries to less than 50% charge. The more charge percentage of a bank is
used, the shorter life span it will have. If the battery bank is being used during a period
of high wind then the charge percentage of the total bank is not impacted much and this
helps prolong the life of the battery bank.
Table 3 below sizes the battery bank
accordingly.
Table 3: Battery Sizing Calculations for a 2KWh Load
18
The table determines that 10 batteries are needed for an appropriately sized battery bank
to support 2 KWh a day load for 3 days of no wind.
2.4.7
Monitoring Devices
Several points throughout the system will require monitoring devices. This will help
trouble shoot when problems arise. Additional metering will tell me what is working and
what is not. It is important to know how each system is performing when trouble
shooting a new set up. There will be a multi-meter measuring the current (A) and voltage
(V) coming from the wind turbine. This meter will tell me when the turbine is
performing normally and if there is a problem. The charge controller will be constantly
monitoring the status of the battery bank. This is required to ensure that it does not get
overcharged or damaged. A multi-meter will be measuring the output of the inverter to
monitor its performance as well. Once a connection to the grid is established a meter will
be used to measure the amount of electricity that is sent back into the grid. This meter
needs to be set up by the utility company because it will require the main line from the
house to be disconnected and reinstalled.
2.4.8
Grid Connection
The power supplied by the grid is AC sine wave power. The current alternates in a sine
wave pattern when supplied by the grid. Figure 11 depicts the difference of wave forms
for electricity. In order to sell power back to the grid it is required to be in the same
condition. The inverter mentioned above converts the power created by the turbine
above into an acceptable form of sine wave power. A meter on the outside of my house
provided by the power company will monitor the amount of power that I provide back
into the grid. A rate will be provided for the electricity provided and deducted from my
monthly electricity bill. The energy sold back to the grid will be small in comparison to
the energy used.
Electricity will only be sold back to the grid when the grid is
operational, the battery bank is charged, and there are no loads operating in the house.
Once all of the above conditions are met, electricity can then be sold back to the grid.
This is not expected to happen often but when it does, additional savings will be factored
into the total cost of this system.
19
3. Manufacture
The turbine is made primarily of plywood. This is a cheap and plentiful building supply
that is ideal for the main structure of this project. Plywood will be used for the main
structural members and poplar wood will be used for stators. Although this is already
suitable for outdoor use, the turbine will be painted to further protect it from the
elements.
The turbine rotor blades are made of fiberglass. They are in the shape of an aerofoil to
provide lift when rotating into the wind. This shape is crucial to efficiency because their
light weight allows for lower startup wind speeds. The design of the wind turbine is
depicted in Figure 9 previously and Figure 14 below.
Figure 13: Turbine Design
A Finite Element Analysis (FEA) was performed using the program ABAQUS [6], to
determine the areas of high stress. A uniform wind gust of 88 miles hour was assumed
to load one side of the assembly. A factor of safety of 4 was selected to determine this
wind load. The highest wind load recorded in Figure 3 was 22 MPH. Equation 10
determined that a wind load of 88 MPH shall be used for sizing all components.
20
[10]
The calculation below in Table 4 determines how to apply that wind speed as a uniform
load to one side of the wind turbine FEA. The results of this analysis are shown in
Figure 15. Equation 11 is used to determine drag force given several measured
parameters. The area of the wind turbine, density of air, drag coefficient, and wind speed
are all used to determine the force imparted onto the assembly during the worst case
wind loading. The drag coefficient, density of air, and force calculations are from
reference text [5].
[11]
Table 4: Wind Speed Applied as a Uniform Side Load
21
Figure 14: Wind Turbine FEA Results
The above analysis identifies the connection points of the stators and rotor blades as high
stress regions. These areas are marked in red and gray colors. Blue depicts a 0 psi stress
and gray depicts 900 psi. Re-enforcing blocks will be added to these areas to add
strength to the system.
22
4. Results
For the purpose of this project, the generator is expected to produce the desired amount
of electricity needed to run several small circuits. The cost of the system is calculated in
Table 5. When the total cost is compared to the performance numbers for this system,
the time required to payback the initial system costs can be determined.
Table 5: System Costs
The total cost to implement this system is approximately $1090 from Table 5. This is the
original estimation. Cost will most likely increase because as the system is integrated,
parts may become damaged or additional discoveries will be made.
There are several savings available to lower the cost of this wind power system. Several
states offer discounts and rebates for green energy programs. Connecticut does not
currently offer any state aid for residential wind power projects.
The federal
government, however, allows for 30% tax rebate against the cost associated with
implementing a wind power system. The return will be $327.
The current rate for power at my home is $0.15 per KWh. All of the power generated by
the residential system will generate savings because it is generating electricity that I will
not have to buy from the grid. Connecticut Light and Power does offer generation credits
for small time residential customers. Assuming that the learning curve for this system is
quick, I will have a 2KWh a day system up and running shortly. In a perfect world it will
generate enough energy every day of the year; however, this is not realistic because site
23
data does not yet exist for my home. Ninety percent of the days measured so far have
provided enough wind to generate some power. I have conservatively assumed for the
purpose of this project that this turbine will generate 2KWh for half the year. Table 6
calculates the payback period for this wind turbine without taking into account any
excess power generation or tax breaks. The yearly rate is calculated for this system and
applied to the total cost.
Table 6: Payback Period
According to Table 6 it will take nearly 20 years to generate enough electricity savings
to pay off this system. Out of the 183 days that I have assumed to generate wind to
power my battery banks, half of those have been assumed to fully charge the battery
banks, half of which (92) are assumed to be capable of selling excess electricity to the
grid. Assuming 1 KWh is generated in excess daily, the following savings will be
produced as depicted in Table 7.
Table 7: Period of Payback with Excess Wind and Tax Breaks
24
Given the assumptions made, the calculation above determines that it will take 11 years
to recoup the money spent on this turbine system. This is assuming that the turbine
survives that long without needing repair or replacement parts. As time goes by I will
improve the efficiency of the system and add additional energy generation methods to
add to my savings. However, this will also increase the overall cost.
The power extracted from any given wind speed can be calculated as indicated below in
Equation 12. This states that as wind speed increases so does available power. Due to
inefficiencies in any given system it is not possible to capture 100% of this power.
Gearing, Friction, and Drag are a few items that decrease the true available power in any
given wind stream.
[12]
The true power available in any given wind stream is dependent on turbine design. The
actual power extracted divided by the true power available is called the power
coefficient. This is depicted in Equation 13.
[13]
As efficiency increases, the power extracted from the wind can be expected to increase.
The ideal performance of actual wind mills can be expected to have a Cp of 59.3%. This
is otherwise known as the Betz Number. This was named after Albert Betz, a German
physicist and pioneer of wind turbine technology. Figure 16 depicts the power available
in a wind stream at several given wind speeds. Commercial windmills are expected to
have power coefficients at or very close to the Betz number according to reference text
[5]. Amateur windmills are expected to have a Cp of 25%. Hopefully my turbine design
falls close to this number. As time passes I will be able to increase the efficiency of my
system by identifying inefficiencies and eliminating them.
25
Figure 15: Power Available Efficiencies
26
5. Conclusion
My home has been evaluated for this project and been deemed an acceptable site for a
VAWT. For this system design, a VAWT will directly power a permanent magnet
generator. The generator will charge a 10 battery bank that I will use in my home and
managed by a charge controller. Excess electricity will be sold back to the grid or
discharged via a dump load. The results of this turbine design are expected to generate
2KWh per day. This is only 10% of my current daily usage. It will also take 11 years to
pay back the cost of this design. Many assumptions were made during the design of this
turbine. Once initiated, the actual output of this system will be compared to what was
assumed in this project.
Hopefully some of my assumptions are proved to be
conservative and more power is available then what I have assumed. This project also
provided the means to make my home more self sufficient. In the event of grid failure,
my home will still have enough electricity for some essentials if only for a short amount
of time.
This turbine will only have a small effect on my electricity bill. If more people were to
adopt similar power generation systems then they too could reduce their electricity bill
by a small amount. America used 3,962*1012 Wh in 2009 according to reference text [7].
If 10% of that power was generated by home systems, than 39.6*1012 Wh is no longer
required to be generated from an aging grid. As more people become educated about
renewable energy, commercial businesses are recognizing a demand for energy products.
If this trend continues, then communities can become less reliant on the need for
traditional sources of power which can harm the environment.
27
6. References
1. http://www.windpoweringamerica.gov/maps_template.asp?stateab=ct (04/13/12)
2. http://weather.weatherbug.com/ (04/13/12)
3. Eric Oberg, Franklin D. Jones, Holbrook L. Horton, and Henry H. Ryffel.
“Machinery’s Handbook 27th Edition”. Industrial Press Inc. 2004, New York,
NY
4. http://www.hurricanewindpower.com/servlet/the-Hurricane-Wind-Generators
(04/13/12)
5. Frank M. White. “Fluid Mechanics Fourth Edition”. McGraw-Hill Companies
Inc. 1999, Boston MA
6. Dassault Systemes, ABAQUS CAE software, 6.11 May 18 2011
7. http://en.wikipedia.org/wiki/Energy_in_the_United_States (04/13/12)
8. http://www.dsireusa.org/incentives/incentive.cfm?Incentive_Code=US37F
(04/13/12)
9. F.E. Powell. “Wind Mills and Wind Motors”. Skyhorse Publishing 2012 New
York NY
10. Ian Woofenden. “Wind Power for Dummies”. Wiley Publishing Inc. 2009
Indianapolis, Indiana
11. http://www.otherpower.com/otherpower_wind.shtml (04/13/12)
12. Ed Begley Jr. “Ed Begley Jr’s Guide To Sustainable Living”. Clarkson Potter
Publishers, New York NY 2009
13. George V. Hart, Sammie Hart “Ugly’s Electrical References 2011 Edition”.
Jones and Bartlett Learning Sudbury, MA 2011
14. http://www.cl-p.com (04/13/12)
28
29