Piezoelectric Energy Harvesting Brian Doyle, Materials Science and Engineering ‘12 An opportunity exists at Rutgers University to implement a piezoelectric energy harvesting floor in the Busch Campus Center. The volume of foot traffic in the main hallway provides a great opportunity to promote energy awareness, while harvesting energy normally wasted. The main goal is to increase awareness of sustainable practices, which is accomplished through the floor itself and the two demonstration events through the first year. The harvested energy is on the order of 7 kWh per day, which is enough offset of the energy associated with the television displays that track the cumulative energy generate. This proposal suggests a three-­‐phase adoption strategy beginning with rental of floor tiles and continuing on with expansion through the student center and other well traveled areas on the New Brunswick campus. The estimated costs are on the order $50,000 for the rented tiles and $800,000 for the full permanent installation. 9 pages Major: Materials Science and Engineering Minor: Psychology Graduation: May 2012 575 Easton Ave, Apt 14E Somerset, NJ 08873 bdoyle08@eden.rutgers.edu 862-­‐432-­‐7457 Opportunity
As Rutgers University grows through the era of sustainability, there is an increasing need
to find alternative sources of energy. This presents an opportunity to implement a piezoelectric
energy-harvesting floor in the Busch Campus Center. A piezoelectric floor generates electricity
through the deformation of the material under a load. Due to the high foot traffic of the campus
center throughout the weekday, the energy harvested potential and energy awareness can be
recognized.
Such an energy generation source must be something easily implemented and utilize
property that is already developed. Both of these issues are successfully addressed by the
installation of piezoelectric floor tiles. These tiles would be installed in the main walkway
portion between the main entrance by the bus stop and the back exit next to the post office. The
tiles can be installed on top of the current floor and will be connected to an inverter, which will
connect the energy generated to the electrical system in the building or any peripheral electronics
like a television display.
Promoting energy awareness is an integral part of this proposal. The fact that the
piezoelectric floor will be seen and physically walked on provide constant reminder of the
sustainable practices going on at Rutgers University. This physical reminder will be
supplemented signage and electronic displays in and around the campus center displaying
information about the system and the energy harvesting capabilities.
This opportunity constitutes a pilot program that upon its successful completion will
provide a model for implementation throughout the entire New Brunswick Campus. Piezoelectric
energy harvesting floors could be incorporated into the floors of the student centers as well as in
Piezoelectric Energy Harvesting 1 the sidewalks along College Ave, for example, in the future. This proposal will allow Rutgers
University to confirm the benefit of the project and be able to make a more informed decision
about future investment.
Research
The energy harvesting aspect of these piezoelectric floor tiles lies in the unique proeperties of the
crystal structure. Certain ceramics, such as lead zirconate titanate shown in Figure 1, form a
tetragonal structure with a small atom in the
center. When the crystal is strained, the center
atom displaces from its lattice site and creates a
potential. In our case, this displacement allows
for energy harvesting of the depression caused
during foot strike. The energy output of these
Figure 1. Lead zirconate titanate crystal structure. Image from: types of energy harvesting tiles depends upon the
http://open.jorum.ac.uk/xmlui/bitstream
/handle/123456789/1022/Items/T356_1
_section17.html applied force; a larger stress corresponds to a
larger potential difference and thus more energy.
In order to estimate the power output of a single person walking through the campus center, it is
important to determine the magnitude of forces experienced by the ground during walking.
While walking, the force exerted on the ground is approximately 1 – 1.5x the individual body
weight[1] (Ground Reaction Forces). Using the assumption that on average, the body mass of a
student is around 80 kilograms (including men, women, and the carrying books, etc) the force
felt by the floor is on the order of 800N. This force translates into about 5 Watt-seconds per step
Piezoelectric Energy Harvesting 2 harvested by the tile[2]. Using a displacement of 0.01 cm under the 100 N force yields a 10.4
J/step capable of being harnessed. The top of the line modules used in this proposal are able to
harvest 50% of this energy[3]. Two companies offer this type of product:
POWERleap Inc
This company is new to the energy harvesting market. They offer a
product called the PowerFloor, shown in Figure 2, that comes with
an integrated LED bar and has the ability to wirelessly transmit
power and energy data. This recorded data, which includes number
of steps, energy, and change in temperature of the room, can be
shown on an television monitor to raise awareness of the energy
Figure 2. PowerFloor Module. Taken from: http://powerleap.net/?page_id=32 generated
Sustainable Dance Club
A bigger player in the energy-harvesting field, this company set out on the self-titled mission to
create sustainable dance clubs. While their main focus in sustainability is dance club
management, their top of the line product is the energy harvesting floor tile. Their product,
known as the Sustainable Energy Floor (SEF) and seen in Figure 3, can be incorporated into any
floor arrangement and can be ordered in pure black or
with an LED display. They offer customization in terms
of top design for an additional fee. These tiles have
already been implemented successfully in many
different venues. The most successful in terms of energy
Figure 3. SEF Floor Tile Taken from: http://www.sustainabledanceclub.com/
products Piezoelectric Energy Harvesting generated has been their dance floor model, which at full
3 capacity can mitigate upwards of 30% of the dance club’s energy usage. Sustainable Dance Club
has had experience in projects ranging form permanent installations at museums in Miami and
Philadelphia to one-time events in Vancouver, Shanghai, and Abu Dhabi.
Both companies offer an opportunity to purchase and rent the energy harvesting tiles. For
this proposal, the first step would involve renting the units in order to better understand the
realistic benefit that can be realized. These tiles would be implemented between the front
entrance to the student center by the bus stop and the exit near the post office. The distance
covered by walking from one end to the other takes approximately 250 steps per person. Using
an estimate of 20,000 people walking through the campus center throughout the day, the top of
the line tiles previously mentioned are able to harvest 7.23 kWh per day. The detailed
calculations are broken down and shown in the Calculations section.
This walking path contains an area of nearly 4,000 ft2 that would be covered by the tiles.
The estimated material cost for permanent tiles is on the order of $700,000 with subsequent
installation and maintenance costs. The total implementation costs would be around $800,000.
Detailed monetary data can be found in the Financial section. Because of the high installation
cost, it seems more practical to implement a rented floor tile system to determine the feasibility
of the system. A 50-tile system rented over a 1-3 year period would cost $35,000 in product with
an additional $30,000 in installation and maintenance. This possibility would generate 173 Watts
per day, which would go toward the low power energy needs of monitoring and displaying the
harvested energy. The rental period will allow for the realistic expectations of a full floor. After
that period, the higher cost of the full-time tiles can be well reasoned if it makes sense for the
university. At the very least, it is an less expensive method of introducing awareness for energy
consumption and the impact of sustainable practices.
Piezoelectric Energy Harvesting 4 Energy Awareness
The purpose of this project is to raise energy awareness in the student population. This is
accomplished through installation of the floor tiles as well as installation of a television
displaying current and cumulative energy harvesting. The floor tiles themselves will be a
physical reminder of the technology and will likely provoke conversation concerning this hightech energy harvesting method. For those students that are more interested, the television will
display specific data regarding the energy harvested per day, week, and year as well as
information about the company and product employed in this project.
In an attempt to create more attention for the installation, two awareness events will take
place during the one-year rental period. One time in the Fall and one time in the Spring of the
rental period, an energy-harvesting station will be turned into a game platform. This energy
harvesting station will be connected to a game console to turn the floor tiles into a larger version
of the popular dance game, Dance Dance Revolution, as exemplified in Figure 4. This is
technically feasible because each tile exists with the ability to act as a sensor as well as an
Figure 4. An example set up of an energy harvesting interactive event. In this proposal, the event would incorporate the popular Dance Dance Revolution game. Figure taken from source [3]. Piezoelectric Energy Harvesting 5 energy-harvesting unit. The sensor output can easily be utilized for the gaming system in a
similar set-up to the actual game. The event would take place in the open area by the Cove and
the Help Desk in the Busch Campus Center. It is these two opportunities that will expose
students to the technology behind the energy-harvesting unit. It is an interesting opportunity
because it combines a popular game with the knowledge of sustainable energy practices
The exciting aspect of this proposal is the ability to combine energy awareness with
energy generation. While energy awareness is the major effect of this program, there is still a
considerable amount of energy generated that can be utilized. Low power applications such as
powering the television that displays the harvested energy are available and will enhance the
visual impact of the program.
Plan
Phase I
During the first phase, the 50 energy-harvesting tiles will be rented for a one-year period starting
in the Fall 2012. The installation can be completed in one weekend directly on top of the existing
floor. During the ensuing one-year period, the energy statistics are recorded. As previously
mentioned, two awareness activities will be held with one in each semester. The set up of these
Dance Dance Revolution gaming areas requires the movement of the tiles into the area near the
Help Desk and the Cove. This time period is long enough to gain an accurate representation of
the full investment. If further investment were not desired, the project would end after Phase I
with an increase in student awareness for energy harvesting possibilities.
Piezoelectric Energy Harvesting 6 Phase II
The successful completion of Phase I leads to the purchase of the energy harvesting floor tiles.
At this time, the total square footage and number of tiles will be determined by the given walking
area. Because the rental period will have presumably gone off without major problems, the
installation can occur over a 3-week period. The longer time relative to the initial installation
takes into account the permanent nature of the new tiles versus the temporary nature of the
previous phase. The major expense in this phase is the tile installation, i.e. the tile and labor cost.
the total square footage needed for the installation is determined.
Phase III
During this phase, future expansion opportunities will be considered. Successful completion of
Phases I and II will begin the planning of future implementations, most likely within 18-24
months of the beginning of Phase II. Future opportunities include implementation of energy
harvesting floor tiles in other campus centers on Livingston, College Ave, Cook, and Douglass.
These new destinations can follow the same progression as this proposal or skip straight to Phase
II.
Calculations
1.3! 80kg ! 9.8 m s2 = 1019.2N
1019.2N ! 0.01m = 10.19 J step
The calculation assumes that the exerted force is equal to 1.3x the mass of an 80kg individual
multiplied by the acceleration of gravity. This force applied over the 0.01m depression of the tile
results in 10.19J for every step a person takes. The advertised efficiency of each unit is 50%,
Piezoelectric Energy Harvesting 7 meaning 5.10J are harvesting for every step a person takes. Using the approximation that the
distance from the entrance to the back exit is 250 ft and that the average stride allows 1.5 feet
between steps, the associated energy harvesting potential is:
5.10 J step !
375 ft
1kWh
kWh
x
= 0.000354
6
ft
1.5 step 3.6x10 J
person
0.000354 kWh person ! 20, 000 persons day = 7.07 kWh day
The number of 20,000 students per day takes into account many students that walk through the
campus center more than once. This estimate was based off of visual count done during a
weekday. The estimate for the rental unit of 50 tiles assumes a 18 foot by 6 foot rectangular area.
Assuming the student will walk the 18 foot length and relying on the previously stated
assumptions:
5.10 J step !
18 ft
1kWh
kWh
x
= 0.000017
6
ft
1.5 step 3.6x10 J
person
0.000017 kWh person ! 20, 000 persons day = 0.34 kWh day
The weekly and semester long totals are based on a 5-day week and a 15 week semester.
Energy Harvested
50 Tiles (Phase I)
1400 Tiles (Phase II)
Piezoelectric Energy Harvesting Daily
0.34 kWh
Weekly
1.7 kWh
Semester
25.5 kWh
Daily
7.07 kWh
Weekly
35.35 kWh
Semester
530 kWh
8 Financial
Phase I Cost
(Rental)
Expenses
Material
$666.90
per tile
Phase II Cost
(Purchased)
$33,345
$500.00
per tile
Phase III Cost
$500 per
tile
$700,000
$1.5+
million
Installation
$5,000
$30,000
$50,000+
Service Contract
$10,000
$40,000
$50,000+
Two Awareness
Events
$5,000
$2,500
per event
$2,500
per event
Total Cost
$53,345
$782,500
$1.6+ million
The decrease in per tile cost is due to discount for bulk ordering. The installation and service
contract costs are estimates. The awareness events take into account the labor and costs for small
appliances used (television, game console, etc).
References
[1]
Nilsson, J., Thorstensson, A. Ground reaction forces at different speeds of human
walking and running. Act Physiologica Scandinavica. Vol 136, Issue 2, pages 217-227,
June 1989
[2]
POWERleap Website: http://powerleap.net/?page_id=32
[3]
Energy Floors Limited (Sustainable Dance Club Subsidiary). Sustainable Energy Floors
Information Leaflet
Piezoelectric Energy Harvesting 9