Development, Characterization, and Optimization of a Thermoelectric Generator

Development, Characterization, and Optimization of a Thermoelectric Generator

Development, Characterization, and Optimization of a Thermoelectric Generator System
Lindsey Bunte, Jonny Hoskins, Tori Johnson, Shane McCauley
School of Chemical, Biological and Environmental Engineering
Sponsors: Perpetua Power Source Technologies & ONAMI

Objective

Heat Transfer Fundamentals

Experimental

Design of an outdoor, wireless monitoring system that is powered by a
thermoelectric generator (TEG). The design of the generator will consist
of a solar absorber and a reservoir in the soil. The absorber will capture
the sunlights energy during the day and the reservoir will provide a heat
sink. In the evening, the reservoir will act as the heat source and the
solar absorber will act as the heat sink.

Thermocouple

Heat Source

Absorber
Rubber Stopper
Thermocouple
Thermocouple

Thermocouple

Background

TEG

ENERGY IN
Radiation

Hot side

Battery life is currently the biggest limitation to wireless sensors.
Thermoelectric power can harvest renewable energy from virtually
any source of temperature difference.
Key benefits of incorporating self-powered wireless sensors:
Reduced battery replacement labor costs
Ability to take more measurements and collect more data
Maintenance-free solutions
Network autonomy
Environmentally-conscious choice

Conduction
through
plates

ENERGY OUT
TEG

Convection
in water

Solar Absorber

ENERGY OUT
Conduction

Earth

Acknowledgements:

High T
60

Absorber
Top TEG
Bottom TEG

60

Absorber

30

Top TEG
Bottom TEG

Low T

Water

Conduction
through
stake

0

Qradiation=QTEG+QConduction

System Boundary

Conduction down the stake can be calculated using Fouriers Equation, where k is
thermal conductivity, L is the stake length, T1-T2 is the difference between the inner
and outer wall, R2 is the external radius, and R1 is the internal radius.
Qcond

2k L T1 T2

ln R2 ln R1

0

6

12
Time (hr)

18

24

The graph above is a 24 hour
day/night cycle of our current
reservoir design. The current
design needs modification
because the bottom and top TEG
should have a larger temperature
difference during the night cycle.
A possible solution is to insulate
the reservoir better.

0

0

12

24
Time (hr)

Qconv
h Tsurf Tsurr
A

The energy stored in the water can be found using sensible heat change, the
amount of energy it takes to change the temperature of the material. The energy is
shown in terms of the mass of the material m, heat capacity Cp, temperature
difference dT , and time difference dt.
dT
dt

Water was chosen to be our reservoir liquid material because it can store a large
amount of energy before changing temperature in comparison to other liquids
because of its high volumetric heat capacity value.

Dennis Bowers
Marshall Field

36

48

The graph above shows a 48 hour
day/night cycle of a thermos. During this
test the bottom TEG thermocouple
failed. The bottom TEG should follow the
temperature of the water closely as seen
in the 24 hour test. If this were the case
this would have produced a workable
temperature difference capable of
creating a large voltage.

Future Plans

Heat loss due to convection is represented by Newtons Law of Cooling where h is
the heat transfer coefficient, Tsurf is the temperature of the exposed surface, Tsurr is
the temperature of the surroundings, and A is the exposed surface area.

Q mC p

Reservoir

90

30

Qrad
T 4 TC 4
A

The TEG will use the temperature difference between the water and the solar
absorber to create renewable energy.

90

Water

Radiative heat transfer in the TEG system from sunlight can be modeled with the
Stefan-Boltzmann Law for non-ideal, or gray bodies, where is emissivity, is the
Stefan-Boltzmann constant, TC is the temperature of the colder surroundings.

Thermoelectric generators (TEGs) work using the Seebeck effect, which converts
temperature differences across dissimilar metals into an electrical potential, or
voltage.

The greater the temperature difference between the top and
bottom of the TEG the more voltage can be produced.

Temperature (C)

Power
Output

Energy is always conserved. The energy into the system from radiation from
the sun leaves the system through the TEG and the energy lost to the ground.
Temperature (C)

Cool Side

Data
Logger

1. Optimizing Design
1. Stake length for optimized heat transfer
2. Perforation to increase surface area and convective mixing
3. Improve insulation of reservoir for decreased heat loss
2. Outdoor Tests Questions
1. What is the sunlight exposure for energy harvesting within the
reservoir?
2. How will rain/wind/weather effect the convective heat loss to the
system?
3. How suitable is the system for extended field use?
3. End User Application Considerations
1. Seasonal demands of agriculture in relation to energy gathering
capabilities
2. Voltage requirements and sample rate of sensors
3. Sensor types and placement
Dr. Philip H. Harding
Andy Brickman
Spencer Bishop

Lea Clayton
Manfred Dittrich
Stephen Etringer

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