Generating Unit

1
Sung Hoon Bae1, Daniel Rim2,
Chris Zachara2 Advisor David Owens3 Dept. of
1Biomedical, 2Chemical Engineering, 3Owen
Graduate School of Management, Vanderbilt
University, Nashville, TN
Third World Electric Generator Electricity from
Excess Heat
Introduction
Design Performance (continued)
Design Components

• Problem Statement
• Third world countries, though some of the most
  populated regions on earth, suffer from abysmal
  electricity distribution
• Manure-to-biogas digesters are a great source of
  renewable fuel for families off the grid, but use
  of biogas is largely inefficient
• Design Approach
• Utilize excess heat wasted by gas appliances
• Stored electricity is needed for its portability
  and ease of use
• Thermoelectric Generation (TEG)
• Temperature difference creates electric potential
  described bywhere and are Seebeck
  coefficients and and are temperatures at
  junctions (Figure 1)
• Typical application is thermoelectric cooling
  (TEC)
• - Theoretically reversible process
• Specially doped semiconductors (ex. Bismuth
  Telluride)
• Current technology only 10 energy efficient

• Generating Unit
• TEG (TEC1-12706)
• Vmax 16.4V Qmax 57W
• Heat sink
• Thermal grease (Arctic Silver)
• - Maximizes contact area
• Storage Unit
• NiMH Battery (Sanyo Electric)
• - Voltage 1.2V
• - Capacity 2000mAh
• Controllers
• - Voltage regulator
• - Charging controller
• LED (Figure 4)
• - Vforward 2.4V Iforward 20mA
• - R 1.8Ohms
• - Luminous 6000mcd

• Storage Unit
• Not enough power was generated to charge the
  batteries
• Unrealistic theoretical charging time with given
  performance
• Cost Analysis
• Cost of the prototype 57.86/unit
• Battery life is approximately 4 years (limiting
  factor)
• Visible monetary benefit in 6 years at most

Usage Hours Usage Hours
1 hour 2 hours 3 hours 4 hours
Energy used (mAh) 180 360 540 720
Capacity Used 9.0 18.0 27.0 36.0
Expected Charging Time (hrs) 16.7 33.3 50.0 66.7
Figure 3 Overall design of the prototype
Table 2 Required charging time for each various
usages hours (1,2,3, and 4)
(Eq.1),
Average Money Spent for Lighting Average Money Spent for Lighting Average Money Spent for Lighting
Year 1.00/mo 1.50/mo 2.00/mo
1 -45.86 -39.86 -33.86
2 -33.86 -21.86 -9.86
3 -21.86 -3.86 14.14
4 -9.86 14.14 38.14
5 -3.36 26.64 56.64
6 8.64 44.64 80.64
7 20.64 62.64 104.64
8 32.64 80.64 128.64
Component Unit Price (/unit)
TEG 5.50
Heat sink 24.00
2 NiMH Batteries 14.99
Thermal Grease 0.87
6 LED lights 6.00
Miscelleneous 6.50
Total 57.86
Figure 4 Circuit diagram of LED component
System Verification

• Generating Unit
• Short-term drift and long-term drift
• Characterized actual specifications
• Heat source boiling water (100C)
• Storage Unit
• Monitored charging process over time

Table 4 Expected savings by usage years for
different energy consumptions
Table 3 Material cost of the prototype I without
economic scale
Figure 1 Diagram showing Seebeck effect
Figure 5 Experiment set up
Conclusions
Figure 2 Discharging graph of a NiMH battery
Design Performance

• Thermoelectric cooling (TEC) and thermoelectric
  generating processes are not completely
  reversible
• Current prototype cannot provide sufficient power
  to charge 2 NiMH batteries or light 6 LED lights
• Failed to meet the required product
  specifications under the price constraints
  (mainly due to quality of TEG)

• Generating Unit (Figure 6 and Table 1)
• Steady electric generation after 50 seconds
• Higher electric generation from prototype I
  (2.5V)
• Prototype I withstood 30 minutes of operating
  period
• Not enough power was generated for both prototypes

Project Goals

• Design a household scale electric generator
• Integrate with biogas systems
• Utilize thermoelectric technology to recover
  energy from excess heat
• Power 6 LED lights for 2 hours per day
• Incorporate a battery charging system for
  portable electricity
• Achieve low selling price, ideally between 40
  and 60

Future Directions
Further investigate ways to increase output
voltage and power Experiment with larger TEGs
and TEGs in series Analyze performance of
various TEGs from multiple manufacturers Invest
igate advanced cooling methods, like fluid or fan
cooling Finalize method of implementation and
develop housing. Assess feasibility of market
success
Figure 6 Short-term (left) and long-term (right)
drift measurements of prototype I (blue) and
prototype II (red)
Design Criteria

• Must be easy to use and require no training
• Must be portable for flexible uses
• Must be economically feasible
• No additional energy should be used to generate
  electricity
• Should effectively use excess heat to generate
  electricity
• Charging process should be safely and
  automatically monitored

Acknowledgements
Type Rise Time Falling Time Avg. Amp. Power Generated Power Needed
I 47 sec 30 min 2.50 V 6.25 mW 500 mW
II 46 sec 11 min 0.62 V 0.38 mW 500 mW
We would like to thank the Dr. King, Dr. Bonds,
Dr. Walker, Alex Makowski, Kurt Hogan, Stephen
Songy, and the ME mechanics shop for making this
project possible.
Table 1 Various specifications of prototypes I
and II. To charge NiMH batteries.