Generating Unit TEG (TEC1-12706) V max = 16.4V; Q max = 57W Heat sink

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 Components Design Performance (continued) 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 by:where 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 Nickel Metal Hydride (NiMH) Battery • Relatively constant discharged voltage (Figure 2) • More current compared to other batteries • Various capacities available 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 Figure 3 Overall design of the prototype Table 2 Required charging time for each various usages hours (1,2,3, and 4) (Eq.1), 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 (100°C) 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 Figure 2 Discharging graph of a NiMH battery Conclusions 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 TEG’s and TEG’s in series • Analyze performance of various TEG’s from multiple manufacturers • Investigate 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 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.