2. i
Abstract
The Tunnel Turbine is a design for implementing the use of wind turbines in tunnels, specifically
subways, in order to harness the wind energy of the piston wind generated by the movement of objects
through enclosed spaces. Vertical axis turbines are housed within a metal casing that helps to channel
the air into the system, increasing variable wind speeds. Units will be installed in pairs, and attached
directly to the ceiling of the tunnel at set intervals throughout the length of the tunnel. The electricity
generated by the ceiling-mounted turbines will be tied directly back into the existing power transformer
and will be used to help make the transit system more self-sufficient and less grid dependent.
3. ii
Executive summary
With a goal of incorporating green energies into the existing infrastructure, Bare Energy has met our
goal of developing an aesthetically pleasing wind turbine system, capable of installation in a variety of
subway and transportation tunnels, that is both economically and energy efficient. Bare Energy has
come to a conclusion that a vertical axis turbine with a funnel component to direct the wind from the
subway drafts is the best option. This solution was chosen from a variety of options which also included
pinwheel and auger shaped blades.
After the general design of the blades was chosen, further design of the product was broken down into
five subsystems: funnel, casing, blades, alternator, and electrical. The design was made to fit the
specifications of the subway tunnel at DIA, but can be made to fit other tunnels as well.
The funnel was designed to gather the train’s draft from a larger area and direct it to a smaller area,
thus causing a higher wind velocity for heightened energy production. The funnel, made of 6061
aluminum, is composed of two components, one that gathers the wind from above the train and a
second component to gather wind from beside the train.
The casing was designed to house the alternator as well as the blade system. It has an upper
component to contain the alternator and some wiring, and a lower component to hold the blades.
Inside the blade housing, the casing is designed to provide as much of a seal for the blades as possible
for maximum efficiency. Made mostly out of aluminum, the bottom face of the casing is made of
Plexiglas for viewing of the blades, thusly increasing aesthetic appeal.
The turbine is a vertical axis blade system composed of three blades which taper to a point at the
outside edge. The blades have a total diameter of about four feet. The blades are attached to an axle
that rests on a bearing. The axle threads onto the axle of an alternator.
The alternator is a purchased permanent magnet alternator which converts the rotational energy from
the blades into electric current to be sent to the electrical subsystem. The electrical system, a will then
convert the direct current into alternating current at the same frequency and voltage of the grid for a
grid tie in.
All of these will be assembled into a single unit and then fastened to the top and side of a subway
tunnel.
Bare Energy estimates a cost of $12,098 for the first unit in any given tunnel and then a cost of $2,827
for each subsequent unit in a tunnel, assuming a 30% profit margin. Bare Energy believes that sales of
at least 2,500 units can be sold, coming out to a total revenue of $10.4 million and a gross profit of $2.4
million. Because Bare Energy does not have the resources to continue the research and design needed
to complete the project, we seek to hand over the design to a company or group that can continue the
project to completion and implementation on the market.
4. Table of Contents
Abstract..................................................................................................................................................i
Executive summary....................................................................................................................................... ii
Table of Contents..........................................................................................................................................0
Introduction ..................................................................................................................................................1
Vision and Goal.........................................................................................................................................1
History and Research................................................................................................................................1
Alternate Solutions .......................................................................................................................................2
Design Options..........................................................................................................................................2
Criteria......................................................................................................................................................2
Final Decision............................................................................................................................................2
Sub-System Analysis......................................................................................................................................2
Funnel.......................................................................................................................................................3
Casing........................................................................................................................................................4
Turbine......................................................................................................................................................5
Alternator .................................................................................................................................................7
Electrical ...................................................................................................................................................9
Overall Dimensions.................................................................................................................................10
Product Assembly...................................................................................................................................10
Cost-Benefit Analysis ..................................................................................................................................11
Business Plan...............................................................................................................................................12
Description of Business and Vision.........................................................................................................12
Description of Product and Service ........................................................................................................13
Definition of the Market.........................................................................................................................13
Financial Plan..........................................................................................................................................13
Implementation Plan..............................................................................................................................14
Conclusions and Recommendations...........................................................................................................14
Bibliography ................................................................................................................................................15
Appendix .....................................................................................................................................................17
Sample Calculations................................................................................................................................17
5. 1
Introduction
Vision and Goal
At the Denver International Airport (DIA), the subway tunnels have an artistic display of pinwheels lining
the tunnel walls that spin when hit by the draft created by the oncoming trains. This simple observation
raised the question: what if there was a way to capture energy from the drafts of passing vehicles in
tunnels around the world? If the harnessing of subway drafts proved to be economically and physically
feasible, we had found a previously untapped source of an immense amount of energy which could be
used to power appliances, computers, and even aspects of the train itself. If this project proved to be
possible, it would have the potential to help the transportation sector reduce its carbon footprint while
stimulating the renewable energy sector.
We here at Bare Energy believe that in order to meet growing energy demands, new and efficient ways
of incorporating green energies into the existing infrastructure must be implemented. Our vision is to
develop an aesthetically pleasing wind turbine system, capable of installation in a variety of subway and
transportation tunnels, that is both economically and energy efficient.
History and Research
For scope of work see Chart 1, 2.
In order to develop a product of this magnitude, extensive research on variable wind speed and turbine
designs was conducted. In addition to analyzing natural wind velocities, a better understanding of the
effects of train drafts in various subway tunnels was acquired. Using calculations based off of Betz’s
limit, which states that the most energy that can be captured from a wind turbine of any type is 59.3%
of the energy of the wind that is being captured [1], it was determined that for a turbine to begin
turning, there must be a wind speed of at least 3 m/s. Research conducted in China indicated that wind
speeds in tunnels with a top train speed of 70 km/h approached 14-15 m/s [2]. Based off of these
results, it was determined that the wind speeds generated in highway/freeway tunnels were
insufficient, and therefore focus should be placed on the design of wind turbines specifically for use in
tunnels with high, consistent vehicle speeds, such as subways. [3]
After deciding to focus on the design of turbines compatible with subway tunnels, several initial blade
designs were proposed. These ideas included a traditional horizontal axis, or “pinwheel” design (Figures
1,2), a double helix, “auger”, design (Figure 3), and a vertical axis, “revolving door”, design (Figure 4). A
design for a mechanical “kick-start” (Figure 5), that would help to reduce the wind speeds needed to
overcome the turbines initial static friction, was also considered as a way to help increase the systems
6. 2
overall efficiency. Conceptual sketches, provided in the appendix, were produced for all four of the
initial designs.
Alternate Solutions
Design Options
The decision making process was fairly straight forward for most of the casing and funnel designs, as
they had stringent size and function constraints, limiting design flexibility, while the blade design proved
to have much greater variability. To start the design process, a SWOT (Strength, Weakness, Opportunity,
and Threat) analysis was performed on the top three initial blade designs: vertical axis blades
(resembling a revolving door), auger-type, and a pinwheel style blade (Table 1). The SWOT analysis
provided a general overview of the basic pros and cons of the three possibilities. After completion of the
SWOT, a comparison between each design’s advantages and disadvantages was performed to help
develop a better understanding of the best option to pursue. For example, while the pinwheel proved to
be efficient, its complicated design, and its many different parts give the design more points of failure
and may cause the system to break easily. The auger would be more durable, but less efficient, and at a
much greater cost than the other designs. The vertical axis blade appeared to be the most realistic
option, due to its relatively simple, inexpensive, and energy efficient design.
Criteria
Five major final design criteria were determined based off of the results of the initial design analysis:
cost, efficiency, feasibility, aesthetic appeal, and durability. These criteria were then used to re-examine
each design in a more critical and detailed manner, giving a numerical ranking to each design based off
of deeper analysis, and further scientific research (Table 2). This process allowed a broader body of
information to be gathered about each proposed design solution before a final design was decided on.
Final Decision
After completion of the SWOT and numerical decision matrix, it was clear that the vertical axis blades
were the most compatible with the project’s design criteria. Although the vertical axis design, while
efficient, proved less so than the other designs, its relatively low production cost, aesthetic appeal and
durability made it a much more feasible design than both the auger and pinwheel.
Sub-System Analysis
7. 3
With a final decision on the overall design approach, the vertical axis turbine was split into five sub-
systems: the Funnel, Casing, Blades, Alternator, and Electrical set-up. Each system was developed and
analyzed in great detail to ensure the collaboration of each component would contribute to the final
product in a manner that was efficient, consistent, and within reasonable budget constraints. In addition
to clarifying the specified product assembly and set of dimensions, the specific purposes and materials
of each system are outlined in the following assessments.
Funnel
Function Analysis:
The purpose of the funnel is to be added onto the outside of the turbine unit to increase the
amount of wind captured and therefore add to the energy produced from the collected wind.
The general idea is that the more air that is flowing through a smaller area will make the turbine
turn faster and, therefore, produce more energy. This is displayed in the fluids equation that
states that the initial cross section multiplied by initial velocity will equal the final cross sectional
area multiplied by the final velocity. The intent is to block off half of each turbine (Figure 6) to
prevent this wind energy form being lost all together we have designed a gradually sloped
surface to channel the wind into the open portion of the turbine. This will increase the flow of
wind and therefore increase the speed of the turbine. The funnel can also extend outward and
down below the level of the subway roof in order to collect wind that could be lost on the sides
of the subway because there are things such as access paths and other empty space on the
sides.
System Function:
This system will not have any moving parts but is designed to be attached to the outside of each
turbine unit. Its function is to cut into the wind and gradually direct it into to turbine without a
great loss of energy. It does this by having a sharp edge that faces into the wind and then a
gradual slope that guides the collected wind into the open potion of the turbine.
We designed each turbine unit to be a set dimension in height, width and length. The funnel can
be designed to fit dimensions of tunnels that may have more unused space than others. The
funnel can then be enlarged and designed to fit onto our unit and therefore create more wind
collection and not lose energy because a tunnel has dimensions that do not fit our turbine unit
exactly.
Materials:
The part will be made out of 6061 Aluminum. This was chosen because plastics are too fragile
but it needed to be sturdy enough to support its weight. In order to keep it relatively light an
aluminum alloy will be used. The total weight of the turbine unit will be about 125 pounds. This
is with the aluminum sheets being 0.1875 inches thick [4]. This will cost about $250 [5]. With the
8. 4
optional side component fitted for the DIA tunnel that will maximize the power collected the
total unit weighs about 440 pounds and will cost about $800 [5]. This does raise the price quite a
bit but if tests are show for it to increase the wind speed by a significant amount it will more
than pay for its self. There will also be around a $10 cost for the bolts that attach it to the roof
[6].
Assembly:
This part can be installed in two separate parts. The main part that will be a part of every unit is
the smaller funnel that is fitted to match the casing of the turbine unit (Figure 6). The outer,
larger funnel unit, Figure 7, is an optional portion. This part will have to be dimensioned on a
tunnel to tunnel basis depending on the measurements of the tunnel and the size of train going
through it. This specific one was designed to fit into the DIA subway tunnels.
There are one inch diameter bolt holes in each corner of the top of the product. The intent is to
attach the funnel directly into the roof of the tunnel and fit it so that there is no space between
the part and the walls. The funnel with the side component is designed to fight tightly into the
top right corner of the DIA subway tunnel as shown in Figure 8. This part can also be easily
mirrored to fit into the top left hand corner as well when installing two side-by-side units.
Dimensions:
The dimensions of the funnel will be 48 inches wide by 48 inches deep and 7 inches tall at its
shortest point. At the highest point, the funnel will be 18 inches tall. The sides will be smooth
curves, so that the air that is being channeled will not become too turbulent. For full
dimensions, see Figure 9.
For the side component, the total depth will be 108 inches, and the total depth will be an
additional 50.50 inches. The side component will then extend 48 inches down at the tallest
point. Much of the mass inside these dimensions will be gone, due to the purpose of the system.
The sides will then be smooth curves, so the fluids will not be too disturbed during the
channeling. For full dimensions, see Figure 10.
Casing
Function Analysis:
The function of the casing is to house the alternator as well as the turbine, and to increase
overall efficiency by controlling the airflow. The casing will have two layers; one layer will house
the alternator, with the exact shape and size of the bottom of the alternator. This will minimize
the possibility of the alternator moving throughout the life of the system. There will be a hole
drilled through so that the threaded axle of the alternator can be attached to the turbine. The
bottom layer of the casing will house the turbine. The front opening will be large enough that
9. 5
the air only hits one side of the turbine, thus causing the highest possible force to be imparted
on the one blade, causing a higher rotational velocity of the turbine. As well, there should some
edge that will prevent the air from flowing out when the turbine is at an angle (Figure 11). This
will be accomplished by a quarter circle piece of metal that prevent air from escaping, and will
push the air back onto the blade, thus creating higher efficiency (Figure 12). The bottom of the
casing will be made of Plexiglas. This will preserve the aesthetic quality by allowing passengers
to see the turbine spinning as they pass in the train.
Dimension:
The casing will be 48.25 inches wide by 48.25 inches deep by 25 inches tall (Figure 13). The
bottom layer will be 17.5 inches tall, with the top layer being the remaining 7.5 inches tall. The
walls will be made out of 1/8 inch sheet aluminum. In the front right, there will be an opening
17.5 inches tall by 24 inches wide (Figure 14). This will allow the air to flow into the casing in a
more controlled manner. In the bottom layer, there will be a circle with a diameter of 48.25
inches in the side opposite the casing, as well as the quadrant adjacent to the opening. The floor
between the top and bottom layer will be 1 inch thick. This is so that the alternators weight can
be fully supported (Figure 15). In this floor, there will be a .669 inch hole through all, as well as a
custom cut to fit the bottom of the alternator. The very bottom of the casing will be made out of
3/8 inch Plexiglas. In the Plexiglas there will be a .669 inch diameter hole drilled .079 inches
deep. This will house the bearing necessary for the turbine.
Turbine
Function Analysis:
The function of the blades is to be turned by the draft of the passing subway. Since the drafts
come in short bursts, the amount of energy that can be transferred from the drafts to the blades
must be maximized. In order to do this, there needs to be a larger surface area on each blade
than on the traditional turbine. This energy would then be transferred to electrical energy in the
alternator, which is not the matter of this report. To maximize the angular velocity, the amount
of friction on the axle as well as resisting drafts must be minimized.
System Function: Optimizing Performance
The blades need to be easily moved by the draft, but at the same time, they cannot be too light
to be buffeted by stray drafts. As well, with each passing of an individual blade, there will be
turbulent drafts behind it. To minimize the effects of this draft, the blades will be placed 120
degrees from each so that the draft is gone by the time the next blade comes into contact with
the pushing of the draft. This would lower the negative reactions of the drafts on the revolution
of the turbine. As well, the blades will be shaped like a revolving door, rather than the
traditional turbine. This would maximize the area the draft can push against, causing a higher
angular velocity of the turbine. However, the drawback to this design is that there will be a drag
10. 6
force due to the area of the blade cutting through air. However, this will not be a big issue, since
the density of the air behind the blade will be very minimal, due to the pressure differentials
between the inside of the casing and directly outside of the back of the casing.
The blade must spin on an axle that is connected on both sides of the blade compartment of the
casing. This would create a significant amount of friction on the blade. In order to minimize this,
there must either be a lubricant or ball bearings. In order for the turbine to be basically
maintenance free, the grease is not feasible. Since grease needs to be reapplied, this would
require the disassembly of the entire construction. As well, grease will allow for more friction
than bearings. This means that the turbine will accelerate slower as well as hit a lower top
speed. To avoid this, ball bearings are a better, more efficient, as well as more economical
decision. The ball bearings are a one-time expense with very occasional lubrication costs, which
would not require disassembly. Grease, on the other hand, is a more regular price.
There are two options for the ball bearings. One is the standard metal ball bearing. These are
cheap, and very easy to find. The other option is a needle roller bearing. These are cylindrical
rollers, rather than the standard spherical rollers. The needle roller bearings will support a
greater axial load than a ball bearing would. An axial load would be a force in the direction of
the height of a cylinder. [7] In fact, the bearing that will be used has a maximum rotation speed
of 7000 revolutions per minute, able to carry a dynamic load of over 3000 pounds. [8] This will
be sufficiently enough, considering the turbine weighs only 30 pounds. The type of bearing will
be a thrust bearing, a bearing that will allow rotation in one direction, but will provide a force
contradictory to that of gravity, allowing the turbine to stay in place, but be able to rotate freely.
See Figure 16.
Materials:
For the turbine to perform optimally, the turbine must be of certain materials. The turbine must
be light enough to be accelerated easily by the draft, but also heavy enough that any pressure
differentials or stray winds will not hinder the turbine too much. As well, the material must be
durable in all conditions it is submitted to. Wood will rot; plastic will wear out, and will be too
light. The ideal material is Aluminum 6061 T6. It is lighter than most metals, and will not corrode
easily. As well, it is light enough that it can rotate with the draft speed. As well, the aluminum
will give an aesthetic pleasure with the reflection as it revolves. [9]
Dimensions:
The turbine will be 17.5 inches high from the bottom of the axle to the top. The blades will be
17.2 inches tall giving .05 inches on either side of the blades and the casing. As well, each blade
will be 23.9 inches long, measured from the center of the axle. The blades made out of 1/8 inch
thick sheet aluminum, then will be welded onto a solid cylinder of aluminum with a diameter of
2 inches. There will be a threaded female end, one inch deep that fits directly on the top of the
axle. This will be cut through starting on the top of a 1 inch flange, extruding from the top of the
11. 7
axle by one tenth of an inch. See Figure 17. On the bottom there will be a triangular flange that
will increase from a diameter of 1 inch to that of 1.653 inches over a distance of .2 inches. See
Figure 18. The bottom of this flange will rest on the thrust bearing. See Figure 19 for the
dimensions of the bearing. All dimensions will have a tolerance of .025 inches. See Figures 20
and 21 for more detailed dimensions of the blades and axle
Assembly:
To assemble the turbine from the sheets and pipes of aluminum, they must be machined and
welded from sheets and pipes of aluminum. The blades will be assembled from 1/8 inch thick
Aluminum cast sheets. They will be cut into triangles, with the thickest end then welded onto a
central piece of piping. The blades will be welded at an angle of 120 degrees from each other.
The axle will then be made of a solid cylinder of Aluminum, welded on the top and bottom of
the central pipe of the blades. The axle will then have two small disks welded perpendicular to
the axis of the axle. These disks will be placed into the thrust bearings, which will be attached to
the casing, whether by welding or adhesive is yet to be determined. The threaded female end
will then be attached to the alternator’s male end. This will allow for the transfer of energy. See
Figure 22.
Alternator
System Function:
The permanent magnet alternator works to convert the rotation in the axle to current that can
be passed on to the electrical system and used. When the axle rotates, it also rotates internal
permanent magnets along an axis. This magnet and its respective magnetic field passes by and
through a series of coil windings. As the magnetic field fluctuates inside of each coil winding, it
induces a current in that wire. By having multiple coils with multiple windings, the induced
current and voltage can be maximized. As the magnet makes a revolution and induces current
into the wire loops, an alternating current is created in the wire. An internal rectifier is also
included inside the alternator, which converts the alternating current to direct current using
diodes in a bridge form. The wire carrying the current then comes out the back of the alternator
which is then sent on to the electrical subsystem.
Decision Making:
There were a few different options for the alternator. The three options were to use a car
alternator, to use the DC-540 Low Wind Permanent Magnet Alternator by WindBlue Power, or
to design and develop a new alternator unlike others out on the market already. Because car
alternators are optimized for high rotational speeds that will not be reached in this unit, the
WindBlue alternator and a new alternator turned out to be better options [10]. The WindBlue
alternator is also optimized for use at low rotational speeds, like in this project, which makes it a
good option [11]. Most alternators on the market are generally the same design. If a new
12. 8
alternator was designed, it would likely be similar to existing systems, and although it may cost
less than systems that can be bought, it would need research to optimize output, which would
detract from the research needed for the turbine project. The final decision was made to simply
buy the WindBlue alternator for $299.99 per unit.
Function Analysis:
The WindBlue alternator is optimized for function at low RPMs. The manufacturer provides a
data on the current and voltage that the alternator supplies at different rotational velocities.
The data and general trends are seen in Graph 1. The chart shows that both voltage and current
increase as the rotational speed increases.
The power output can also be found using these graphs, and is found by multiplying voltage and
current. A plot of power and RPMs is provided in Graph 2. Power also increases as RPMs
increase.
The rotational speed of the system is dependent on the time that the wind applies a torque and
what the torque is. The higher torque and the longer the time that the torque is applied, the
faster the rotational speed will be for the blades and subsequently the alternator. The power
that could be extracted from the spinning blades, assuming 100% efficiency, is the torque
multiplied by the angular speed [12]. This system will not be operating at perfect efficiency, but
this relationship does explain how the output will be based on the speed of the blades and the
air being moved by the train.
Technical Specifications:
The alternator is driven by a 303 stainless steel shaft. This shaft has a diameter of 5/8 x 18
threads per inch for one inch, which threads directly on to the axle of the blades. The axle then
turns to a diameter of 0.669” (17 mm) which then runs through the full length of the unit, a total
length of 7.25” (Figures 23, 24). The axle runs through and mounts directly to the magnet rotor,
which is a disk with 14 neodymium magnets. The outer diameter of this disk including the
magnets is 4.40 inches.
The stator is a ring made of iron, a material optimal for electromagnetic induction. Made up of
52 pegs connected to a ring, the stator holds the coils of wire for induced current [13]. The
outer edge of the stator fits snugly inside the casing while the inside edge of the stator fits
closely to the magnet rotor (Figures 25, 26).
The casing has an overall diameter of 6.00” and a height of 5.50 inches. The casing is broken up
into two pieces, a top piece with a height of 2.5” and a bottom piece with a height of 3.00 inches
(Figures 27, 28). There are four pieces with bolt holes to connect the top and bottom parts of
the casing. Two flanges on the sides each have bolt holes at a distance of 3.30” from the center
13. 9
of the part. Both halves of the casing have a thickness of 0.10 inches. For full dimensions and
assembly, see Figures 29, 30, 31.
Assembly:
The alternator part used in this design is a design that is bought and installed as is. Using 2
screws through the 2 flanges on the casing, the alternator can be attached to the top of the
blade casing by aligning the holes and putting the axle into the hole in the blade casing. The
blades are then threaded onto the alternator by threading the axle of the rotor into the axle of
the blades.
Electrical
System Function:
In order to feed the power created by the wind turbines directly back into the buildings main
transformer, the 40V direct current (DC) produced by the alternator must be converted to a
alternating current (AC) with a voltage and frequency compatible with the existing power grid.
Due to the nature of wind power and its variable wind speed and consistency, the current
created must be regulated in order to maximize output. This will be achieved through the use of
a three-phase rectifier, load resister and inverter. The alternator is connected directly to a
rectifier which feeds excess voltage from the alternator to a load resistor, protecting the
inverter from power surges. The invertor then converts the variable voltage and frequency
produced by the turbine/alternator into a fixed frequency and voltage compatible with the grid.
Decision Making:
There were a couple different ways to handle the grid-tie in. One such way is to use a system
similar to that of a Doubly-Fed Induction Generator (DFIG),[14][15] implementing a transformer
and a back-to-back inverter-converter circuit with Rot-Side (RSC) and Grid-Side (GSC) converters
connected by a DC-link capacitor[16] (Figure 32) which functions as energy storage, keeping
voltage variations to a minimum between the AC-DC-AC conversions. This system converts the
variable voltage and frequency produced by the turbine/alternator into a fixed frequency and
voltage compatible with the grid while also acting as a buffer between the generator and grid,
protecting the system from energy surges while maximizing wind energy capture [17].
However, it is very complex and requires many components, adding to overall cost.
Another option is to implement a pre-existing grid-tie system [18] such as the Windy Boy[19].
With a maximum efficiency rating of 97%, grid monitoring, and a programmable characteristic
curve, the Windy Boy 1200 (Table 3) is perfectly suited for small wind energy plants and
optimized for fast and frequent load changes. The compatible Windy Boy Protection Box 400
(Table 4) with an integrated rectifier protects the inverter from voltage surges and includes a
three-phase array connection.
14. 10
Due to its one-time cost of roughly $4,900, and its overall efficiency and ratings, the Windy Boy
grid-tie system will be used.
Function Analysis:
Before the current is manipulated, each set of turbines will be wired in parallel and connected
into a unified line for the entire system or “wind farm” (Table 5). Next, the pooled current will
be fed through the Windy Boy Protection Box 400, which protects the inverter from the
possibility of voltage surges by feeding any excess array voltage to a load resistor, before being
channeled through the Windy Boy 1200-US. The Windy Boy 1200-US is a grid-tie inverter
developed specifically for small wind turbine farms. With a 97% peak efficiency rate and
automatic grid voltage detection, the Windy Boy converts the DC current to AC while regulating
the output frequency and voltage to be compatible with the public grid (Figure 33).
Dimensions:
Windy Boy Protection Box 400: 11x9x8 inches
Windy Boy 1200: 18x12x9 inches
Overall Dimensions
The overall dimensions without the side components will be 48.25 inches wide by 96.25 inches deep,
and 18 inches tall at the tallest point. The overall dimensions of the unit with the side component will be
98.75 inches wide by 156.25 inches deep by 48 inches tall at the highest point. In the funnel with the
side component, there will be an opening of about 98.5 inches by 48 inches, channeling down into an
opening of 17.5 inches by 24 inches. Inside the 48.25 by 48.25 inch casing will be a turbine with 3 blades
of 22.55 wide and 17.20 inches tall attached to a 2 inch axle, which will then be attached to an
alternator, resting in the top of the casing.
Product Assembly
The Tunnel Turbine is designed to be assembled on site with two units side by side on the ceiling of the
tunnel. Each unit consists of a funnel, a side component for the funnel, a casing, a blade system, an
alternator, and the first unit in each tunnel must be also be equipped with a Windy Boy grid tie inverter.
Assembly begins with the blades and alternator being installed into the casing (Figure 34). The
alternator will first be put into the electrical housing of the casing. The axle of the alternator will be
dropped down through the hole in the casing and the alternator will be bolted on to the casing through
the bolt holes. The blades will then be put in through the bottom of the casing and the threaded end of
the blade axle will thread on to the axle of the alternator. Before the piece of Plexiglas is put on to cap
the bottom of the casing, a bearing must be adhered to the center of the piece of Plexiglas, which will
15. 11
reduce friction on the turning blades. With the bearing put on, the Plexiglas will be fastened to the open
bottom of the casing and the bottom of the axle of the blades will contact the bearing. The funnel
consists of a standard funnel component and an additional side component. The side component will be
attached to the standard component so that they will match up. The assembly of the two will then be
bolted to the side and roof of the tunnel (Figure 8). The casing housing the blades and alternator will
then be lifted up and attached to the roof of the tunnel as well as the funnel so that the opening on the
casing lines up with the area that the funnel directs the air to (Figures 35, 36, 37).
The direct current from the alternator will be wired to the Windy Boy grid tie inverter which will be
located wherever there is room, whether in the tunnel or outside the tunnel. The wires to make this
connection will be attached to the ceiling of the tunnel. The inverter will be connected to the wiring
from the alternator as well as the grid that it will be connected to.
Cost-Benefit Analysis
Overall Cost
The cost for the system will be more expensive for the first unit for every 25 units, due to the need of a
transformer. One unit includes one casing, one funnel, one alternator, and one turbine. Table 6 shows
the manufacturing cost and final market price for each unit with a transformer, as well as each unit
without the transformer. Each tunnel will need a different number of units, depending on the length
and/or width of the tunnel. If a custom sizing is needed for a specific tunnel, then the dimensions of
each unit can be altered so that they can be implemented in that tunnel. Cost changes due to those
specific needs will be evaluated on a case-by-case basis. Table 7 shows the market price for differing
quantities of units.
Benefits
For a 30 mph tunnel, the turbine will spin at a peak of about 1300 rpm, and at an average of about 900
rpm. The turbine will spin at this average for around 9.5 seconds, producing around 1000 Watts in that
period. This means for each passing of a train, one unit will create . For a 100 unit
tunnel, this means will be produced with every passing of a train. This means in a tunnel
system where 4 trains pass per hour for twenty four hours, then in one day, there would be a
production of 22.74 kWh for every day of operation, meaning in one year, 8300 kWh will be produced.
Currently the price per kWh in the United States, according to the Energy Information Administration, is
10.11 cents per kWh. [20] This means in the course of 1 year, a 100 unit tunnel, with 4 trains an hour,
24-7, would be generating $839.19 equivalent of electricity. It would take around 500 years at this
operation rate to break even financially; however, this is a low usage tunnel. For a tunnel where there is
a train passing every 3 minutes, there would be 46,235 kWh produced in 1 year, which would be
equivalent to $4,674.39 of electricity produced, which would require about 90 years of operation to
16. 12
break even. For a 30 mph train system, this system tunnel is not economically practical; however, the
fact that the company who owns the tunnel is implementing a clean energy technology can generate
good publicity, and can produce a higher profit if people are swayed to ride the subway to support the
energy initiative.
For a 50 mph tunnel, the turbine will spin at a peak of about 5,800 rpm, and at an average of about
4,400 rpm. Each pass of the train will cause the turbine to spin at this average rpm for around 4.5
seconds. This means in this period, one unit will create 9495 Watts. For one pass of the train, there will
be kWh produced per unit. A 100 unit tunnel will create 1.187 kWh with each pass of the
train. For a system where 4 trains pass per hour for 24 hours, in one day, there will be 113.952 kWh
produced in one day. In the same system, there will be 41,592 kWh produced in one year. This is
equivalent to $4,205.00 dollars of electricity produced. This means this system would pay for itself in 99
years. In a busier system, say one with a train passing every 3 minutes, 24-7, then in one day, a 100 unit
system will generate 569.76 kWh per day. In one year, the system would generate 207,962 kWh, which
is equivalent to $21,025 worth of electricity. The system would then pay for itself in 20 years. In higher
speed tunnels, the system is much more economically practical than a lower speed subway system.
However, this cost is the high end of the spectrum, since if they are to be mass produced; the sheet
metal will be cheaper, since a roll of aluminum can be bought, as opposed to each individual sheet that
was used. This would dramatically reduce the cost. As well, the energy produced is based off only the
average revolutions per minute, not taking the peaks into account. However, these calculations above
did not take into account the fact that wind energy apparatuses can only harvest a maximum of 60% of
the energy in the wind, according the Betz limit [1]. These figures should be about accurate, since the
cost would be about 60% lower with the bulk purchasing of the aluminum.
Business Plan
Description of Business and Vision
We here at Bare Energy believe that in order to meet growing energy demands, new and efficient ways
of incorporating green energies into the existing infrastructure must be implemented. Our vision is to
develop an aesthetically pleasing wind turbine system, capable of installation in a variety of subway and
transportation tunnels, that is both economically and energy efficient. We believe that the Tunnel
Turbine has the potential to be implemented in the tunnels of all major cities in the continental United
States, as well as Europe and Asia. We at Bare Energy would love to see our vision realized, even if that
means handing the reigns to another company with the resources and capabilities needed to make our
initial designs a reality.
17. 13
Description of Product and Service
The Tunnel Turbine is a wind turbine system developed for tunnels, specifically subways, in order to
harness the wind energy of the piston wind generated by the movement of objects through enclosed
spaces. The electricity generated by the ceiling mounted turbines will then be used to help make the
transit system more self-sufficient and less grid dependent. Vertical axis turbines are housed within a
metal casing that helps to channel the air into the system, increasing variable wind speeds. Pairs of side-
by-side units will be attached directly to the ceiling of the tunnel at set intervals throughout the tunnels
length.
This product is revolutionary in the fact that its implementation is unlike that of any other product on
the market. Currently, there are no other wind turbines on the market designed to convert the piston
wind from a train into usable electricity, which makes the Tunnel Turbine a groundbreaking piece of
machinery, competitive in the fact that it is one of a kind.
Definition of the Market
The target market for this design, at this point, is primarily full-service engineering firms, which can take
the design from its current state to completion and implementation. After the design is researched
further and revised by a firm, the target market for sales of the product expands. This market includes,
but is not limited to, the Department of Energy, State Departments of Transportation, private
companies involved in public transit such as Amtrak, and other companies that own transit tunnels, such
as DIA.
The transportation sector needs energy. Subways use a lot of power, and other systems near to subway
systems also draw a lot of energy. By implementing this design, grid dependency and energy costs of
subway systems and nearby systems can be reduced.
Bare Energy anticipates that the Tunnel Turbine can be sold and implemented in up to 10% of the
subway tunnel systems in the continental United States.
Financial Plan
Bare Energy hopes to sell the design for the Tunnel Turbine to a company that will complete the product
and bring it to market.
It is estimated that for each tunnel, the first full unit will cost $12,098 and each following unit will be
$2,827. We estimate that the revenue generated for a tunnel with 25 units would be about $103,924,
assuming that profit is 30% of the sales price. Assuming implementation in 100 different tunnels at 25
units per tunnel, the revenue generated is $10.4 million with a gross profit of around $2.4 million.
18. 14
Bare Energy is seeking to sell the design at a negotiable price along with a royalty of 2.5%.
Implementation Plan
After further research is conducted, Bare Energy recommends that the final design be patented. Any
necessary licenses from relevant departments of transportation or other organizations that control
tunnels should be acquired to enable installation of the units according to safety standards, security
standards, and other standard protocol.
With a final design, a manufacturer and distributor should be arranged for. After final pricing
information is acquired, the product should be marketed directly to all stakeholders that may be
interested. After a general idea of interest in the product is acquired, we then recommend that final
arrangements be made for manufacturing, distributing, and installation of the product.
Conclusions and Recommendations
The product developed by Bare Energy accomplishes the vision of the project. The Tunnel Turbine
successfully converts kinetic energy in drafts from trains to electrical energy that can be used in a grid
tie. Bare Energy has limited resources and therefore cannot manufacture the product, but we
recommend that any company that continues the project market the product, sell the product, set up a
manufacturing plant, and set up installation services.
The vision of this project is to create another source of renewable energy by means of trains in tunnels
and their respective drafts. This can be accomplished by developing the product and bringing it to
market. The business is to fully develop the product, make a prototype, and then begin marketing,
sales, and manufacturing of the product. Because Bare Energy is limited in resources at the present
time, all of these services must be done by an outside company.
From here, Bare Energy primarily recommends that more research be done on the project. The research
that needs to be done is currently beyond the capabilities and resources of the team. Potential different
designs for the funnel must be researched to investigate whether there is another design that will better
harness the wind’s energy. Alternate solutions should also be investigated for the electrical system as
well. Research must be done into efficiency of the system and potential output of the system at
different wind velocities and with different trains. A prototype should also be made after the research.
A prototype is also beyond the capabilities of Bare Energy at this time. Because of the multiple
restrictions on the capabilities of the group, we recommend that the project be sold to a company or a
group that has the resources to continue the project to completion and implementation on the market.
19. 15
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![2013
Bare Energy
Jacob Draper
jadraper@mines.edu
1811 Elm Street 21E-A
Golden, CO 80401
[THE
TUNNEL
TURBINE]](https://image.slidesharecdn.com/9fe364d0-4b7a-43cf-a52d-2155464a09bd-150602191600-lva1-app6891/85/Bare-Energy-Final-Report-1-320.jpg)
