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Design, Development, Theoretical and Experimental Analysis of Advanced Hybrid Solar Thermoelectric Generator

"Due to the fact that much of the world’s best solar resources are inversely correlated with population centers, significant motivation exists for developing the technology, which can deliver reliable and autonomous conversion of sunlight into electricity. Thermoelectric generators (TEG) are gaining incremental ground in this area due to its extensive use in solar thermal application as power generators, known as solar thermoelectric generators (STEG). STEG systems are gaining significant interest in both, concentrated and non-concentrated systems and have been employed in hybrid configurations with the solar thermal and photovoltaic systems. In this dissertation, mainly studies of Hybrid Solar Thermoelectric Generators (HSTEG) configuration are presented.
 HSTEG systems are much less studied both experimentally and theoretically, despite their clear techno–economic advantages. There is a scope for significant improvement in the performance (efficiency) and a need for detailed performance analysis to understand the fundamentals of the energy transfer process. HSTEG systems (conventional) reported till date, initially the solar energy is utilized by the TEG for generating electricity and then transferred to other low-temperature thermal cycles (heating or cooling). As an alternative one can design an advanced HSTEG system, in such way to first utilize the solar energy in the heat transfer fluid (HTF), which can run high-temperature thermal cycle for heating or cooling or power generation and then generate electricity by using TEG. Further, there is no advanced HSTEG system available in the literature, which could deliver high-temperature heat output from the hot side of the HSTEG system.
 This dissertation proposes a novel and advanced HSTEG system, based on previous limitations. The innovative driving concept of the advanced HSTEG system is its tri-segmented geometry, in which the thermoelectric generator module is sandwiched between two semi-cylindrical tubes (termed as “Semi-cylindrical Parabolic Trough Thermoelectric Receiver”, SC-PTTR). In this geometry, both the hot side and the cold side of TEG are utilized for harvesting useful heat, simultaneously. Thus, the TEG generates electricity by utilizing the operational temperature difference created between the heat transfer fluid (HTF) on the hot and cold sides. The operational temperature of the hot side HTF is above 300°C, thus the majority of the heat is still available to drive a steam turbine or other thermal cycle. The cold side HTF can be used for preheating the feed water or running other low-temperature thermal cycles. One-dimensional theoretical model, which investigates the high-temperature performance (both thermally and electrically) of the advanced HSTEG system, is established. A laboratory scale advanced HSTEG system is developed and its performance (open-circuit voltage, current, power output, electrical efficiency and thermal efficiency) is analyzed experimentally.
This thesis also examines the potential of conventional HSTEG (with/without vacuum enclosure) system with forced convection cooling for combined cogeneration of heat and power generation through theoretical/experimental investigation. Theoretical analysis of the HSTEG systems (conventional/advanced) are conducted by varying the parameters such as geometric solar concentration ratio (CR), solar insolation, figure of merit (ZT) of the TEG module, hot side tube inlet fluid temperature (THfi), cold side tube inlet fluid temperature (TCfi), mass flow rate (ṁ) and wind speed (Ws).
Experimental investigations show that the maximum electrical and thermal efficiency achieved by the conventional HSTEG is about (1.2 and 61%) and advanced HSTEG is about (0.1 and 63.5%), respectively. The electrical efficiency of the advanced HSTEG system is low due to relatively low ZT and ΔT (average temperature difference across the hot and cold side values). Theoretical analysis shows that the maximum electrical and thermal efficiency achieved by the advanced HSTEG is about (5.9 and 69%) and conventional HSTEG is about (11.6 and 65.4%), respectively for ZT = 1. Conventional HSTEG system shows higher electrical efficiency, but, it can run only low-temperature thermal cycle (<100°C), whereas, the advanced HSTEG system can drive high-temperature thermal cycles (>300°C). Theoretical results are in good agreement with the experimental observations.
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Department: 
Mechanical Engineering
Year: 
2017
Student Name: 
Pradeepkumar S
Faculty Advisor: 

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