POWER MANAGEMENT OF THERMOELECTRIC GENERATOR IN A PARABOLIC DISH SOLAR COLLECTOR

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 6, June 2018, pp , Article ID: IJMET_09_06_095 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed POWER MANAGEMENT OF THERMOELECTRIC GENERATOR IN A PARABOLIC DISH SOLAR COLLECTOR K. Barkavi Department of Electrical and Electronics Engineering, SRM Institute of Science and Technology, Kattankulathur, Chennai, India R. Senthil Department of Mechanical Engineering, SRM Institute of Science and Technology, Kattankulathur, Chennai, India ABSTRACT A parabolic dish solar collector is used to producing a medium temperature at the focus of the reflector. A thermoelectric module is attached to the focus plate and the hot and cold junction temperatures are maintained using phase change material on the source side and the forced circulation of water through the sink. The differential temperatures maintained across the thermoelectric module are 120 C, 150 C and 180 C by varying the fluid flow rate through the phase change material. Hence, a maximum power point tracking and voltage regulation are required to harvest the optimum energy. The overall solar to the electrical conversion efficiency of 2.7% is achieved and the salient points of operating TEG modules are discussed in this article. Keywords: Parabolic dish, solar collector, thermoelectric module, solar receiver, Phase change material, maximum power point tracking. Cite this Article: K. Barkavi and R. Senthil, Power Management of Thermoelectric Generator in a Parabolic Dish Solar Collector, International Journal of Mechanical Engineering and Technology, 9(6), 2018, pp INTRODUCTION Solar energy is one the options to generate heat and electricity for our needs. Several solar collectors are used to produce hot water or steam. Photovoltaic (PV) is the option to generate the electricity using solar energy. PV technology promises the solar light to electricity conversion efficiency up to 20%. The thermoelectric power generation (TEG) works on the thermoelectric effect while maintaining a temperature difference across two terminals. This is due to Peltier-Seebeck effect. TEG produces the heat to electricity overall efficiency around one-fourth of PV technology. However, the thermo-electrical management of TEG at the editor@iaeme.com

2 Power Management of Thermoelectric Generator in a Parabolic Dish Solar Collector outdoor integrated environment has to be optimized to become as one of the efficient and economical energy conversion technology. Shanmugam et al. [1] fabricated a low-cost parabolic dish collector. Commercial thermoelectric modules made of bismuth telluride for electricity generation was tested on the focus of trough collector. The energy end exergy efficiencies were determined. Muthu et al. [2-4] demonstrated the hot-side temperature reached the optimum value, the conversion efficiency was reduced, even though an increase of the power. Lertsatitthanakorn et al. [5] investigated a finned heat sink coupled with a fan to release heat from the cold end of TEG. They used a tracking system to continuously track the sun. Shanmugam et al. [6] modelled a thermoelectric power generator driven by a solar parabolic dish collector. The solar collector and TEG were modelled by a set of steady state energy balance equations of first law of thermodynamics. The effects of fan orientation and air flow rate were investigated. Eswaramoorthy and Shanmugam [7] estimated the standard efficiencies of TEG over the average solar radiation data at the site. A parabolic dish collector is used to drive the TEG. The proposed system had shown generating 24% and 7% of excess electricity at maximum and minimum radiation data respectively. An effective cooling technology using nanofluids are not only improves the overall performance of TEG but also the heat recovered for further process heating applications. The effect of maintaining the temperature gradient across the TEG module with the effective thermal management is studied. The effective temperature gradient across the thermoelectric module is vital to improving the heat to electricity conversion. The generation of constant electricity irrespective of the variation of solar intensity over the solar collector is investigated and the salient points are reported in this article. The practical challenge is the maintaining of the temperature difference across the module for the varying beam solar radiation at the site. 2. MATERIALS AND METHODS A parabolic dish collector (PDC) having effective aperture area of 14.8 m2 is used to produce the high temperature in the range of C at the receiver plate made up of copper (diameter 400 mm and 2.5 mm thick). The parabolic dish is tracked by two-axis using the PLC controlled DC motors. The focus point of the receiver is 2.7 m [8-11]. The thermoelectric module is bismuth-telluride and having 127 p-n cells. The size of the TEG module is 56 mm by 56 mm and depth of 4 mm. The maximum stable temperature limit of TEG is 300 C. The heat sink of the TEG is fitted with thin fins of aluminum and a solar PV operated DC water pump is used to regulate the heat transfer fluid (HTF) to maintain a colder temperature. The schematic diagram of PDC and TEG is illustrated in Fig. 1. The optical efficiency of the PDC is vital to achieving a higher temperature at the focus [12]. The high temperature side is maintained uniform with the phase change material (PCM). The sugar alcohols are preferred over its phase change enthalpy during the heating to supply the required temperature to the source of TEG. The selected PCM is D-Mannitol and it has a melting temperature of 166 C and phase change enthalpy of 320 kj/kg. The effect of PCM in the solar receiver provides the uniform temperature distribution and provides the continuous supply of heat to the HTF to respective applications [13-19]. The module energy efficiency depends on the hot and cold junction temperatures (T h and T c ), Figure of merit (Z), Seebeck coefficient (S), electrical conductivity (σ), electrical resistivity (ρ), average temperature (T avg = 0.5 (T h -T c )) and thermal conductivity (k) of TEG materials. TEG module efficiency is expressed in Equ editor@iaeme.com

3 K. Barkavi and R. Senthil Where, Z = S 2 σ /k 1 Figure 1 Schematic diagram of PDC and TEG experimental setup Figure 2 Thermoelectric module From Equ. (1), the maximum power is possible at the unity figure of merit. The left side term indicates the Carnot efficiency and right side denotes Seebeck effect of TEG. The use of multiple PCM for the thermal management in TEG is reported by Ahmadi et al. [20]. Further, Ravita et al. [21, 22] investigated the solar concentrated TEG operating around 600 C and the they optimized the cooler of TEG using a genetic algorithm. Cui et al. [23] investigated a concentrated PV-TEG using PCM. Figure 3 Maximum power point tracking editor@iaeme.com

4 Power Management of Thermoelectric Generator in a Parabolic Dish Solar Collector Figure 2 indicates the schematic diagram of TEG. The p-n junction and the DC current flow is indicated. The copper plates are used in hot and cold junctions. The maximum power point tracking on the P-V characteristics of TEG is illustrated in Fig. 2. When the power to voltage gradient reaches zero, the power generation reaches the maximum value. The operating parameters of TEG is maintained at the MPPT produces continuously uniform electrical output. The outdoor experiments are conducted as per the ASTM standards of concentrated solar collectors. The operating conditions and TEG performance are discussed in the following section. 3. RESULTS AND DISCUSSION The outdoor experiments are conducted and the real time experimental observations are noted and the thermal and electrical performance are evaluated. Figure 4 shows the average solar radiation of around 800 W/m 2 on both test trials. The similar radiation data are considered for the thermal and electrical performance calculations. Figure 4 Solar radiation on test days Figure 5 Average ambient temperature and wind velocity on test days Figure 6 Power characteristics of TEG over the load resistance editor@iaeme.com

5 K. Barkavi and R. Senthil Figures 6 and 7 show the power characteristics of TEG under the load resistance and output voltage respectively. The maximum power of 5.6 W is generated at the load resistance around 4 Ohm. This point is useful to maintain the power output of the TEG. The higher the temperature gradient, the power generation is higher. Hence, the thermal management on the hot and cold side are vital to produce uniform power. Table 1 indicates the accuracy of the measurements. The measurements are reliable and within the allowable limit. The electrical output voltage and current are measured to determine the power output from the TEG. The overall heat input was determined based on the solar radiation, aperture of PDC and operational duration. Figure 7 Voltage variation over the output voltage Table 1 Uncertainty analysis Property Uncertainty Temperature ± 1% Solar radiation intensity ± 3% Wind speed ± 1% Mass flow rate ± 1% The overall efficiency of the PDC-TEG is the product of optical efficiency of PDC, receiver efficiency and efficiency of TEG. While the optical efficiency of 0.8 and receiver efficiency of 0.72 and thermoelectric conversion efficiency of 4.7%, the overall efficiency is around 2.7%. The electrical power management includes the MPPT and stabilizing the output voltage of TEG. Several topologies and algorithms are used and the simultaneous regulation of MPPT and output voltage regulation is the effective option due to lesser components in the circuit and economically. 4. CONCLUSIONS Thermal and electrical power management of TEG are discussed in this article. The uniform temperature is maintained by varying the flow rate of HTF on the source or sink side. Use of PCM in the source side is useful to maintain the uniform temperature as well as storing the heat for the lean solar radiation periods. The overall solar to electricity efficiency is around 3%. The electrical power management includes the MPPT and stabilizing the output voltage of TEG. Several topologies and algorithms are used and the simultaneous regulation of MPPT and output voltage regulation is the effective option due to lesser components in the circuit and economically. The proposed cooling medium is nanofluids to effectively maintain the cold junction closer to the ambient conditions editor@iaeme.com

6 Power Management of Thermoelectric Generator in a Parabolic Dish Solar Collector REFERENCES [1] Shanmugam S, Veerappan AR, Eswaramoorthy M. An experimental evaluation of energy and exergy efficiency of a solar parabolic dish thermoelectric power generator. Energy Sources Recovery Util Environ Eff 2014; 36(17): [2] Muthu G, Shanmugam S, Veerappan AR. Energy and exergy analysis of solar parabolic dish thermoelectric generator. Appl Mech Mater 2014; : [3] Muthu G, Shanmugam S, Veerappan AR. Numerical Modeling of Year-Round Performance of a Solar Parabolic Dish Thermoelectric Generator. J Electron Mater 2015; 44(8): [4] Muthu, G., Shanmugam, S., Veerappan, A.R., Solar parabolic dish thermoelectric generator with acrylic cover. Energy Procedia; [5] Lertsatitthanakorn, C., Jamradloedluk, J., Rungsiyopas, M. 2014, Electricity generation from a solar parabolic concentrator coupled to a thermoelectric module. Energy Procedia; [6] Shanmugam S, Eswaramoorthy M, Veerappan AR. Modeling and analysis of a solar parabolic dish thermoelectric generator. Energy Sources Recovery Util Environ Eff 2014; 36(14): [7] Eswaramoorthy M, Shanmugam S. Solar parabolic dish thermoelectric generator: A technical study. Energy Sources Recovery Util Environ Eff 2013; 35 (5): [8] Senthil R, Sundaram P., Effective utilization of parabolic dish solar collectors for the heating and thermo-electric power generation. International Journal of Mechanical Engineering and Technology, 9(2), 2018, pp [9] Senthil R, Cheralathan M., Effect of non-uniform temperature distribution on surface absorption receiver in parabolic dish solar concentrator. Thermal Science, 21(5), 2017, pp [10] R. Senthil, Enhancement of heat absorption of parabolic dish solar receiver using tapered surface cavities, JP Journal of Heat and Mass Transfer, 2018, 15 (2), [11] Senthil R. Recent developments in the design of high temperature solar receivers. International Journal of Mechanical Engineering and Technology, 8(8), 2017, pp [12] Senthil R, Nishanth AP., Optical and thermal performance analysis of solar parabolic concentrator. International Journal of Mechanical and Production Engineering Research and Development, 7(5), 2017, pp [13] R. Senthil and P. Sundaram, Effect of Phase Change Materials for Thermal Management of Buildings, International Journal of Civil Engineering and Technology, 8(9), 2017, pp [14] Senthil R, Cheralathan M. Simultaneous testing of a parabolic dish concentrated PCM and non-pcm solar receiver. International Journal of Mechanical and Production Engineering Research and Development, 7(6), 2017, pp [15] Senthil, R., Cheralathan M., Effect of the Phase Change Material in a Solar Receiver on thermal performance of parabolic dish collector, Thermal Science, Vol. 21, No. 6B, 2017, pp [16] Senthil R, Senguttuvan P, Thyagarajan K. Experimental study on a cascaded PCM storage receiver for parabolic dish collector. International Journal of Mechanical Engineering and Technology, 8(11), 2017, pp [17] Senthil R, Thyagarajan K, Senguttuvan P. Experimental study of a parabolic dish concentrated cylindrical cavity receiver with PCM. International Journal of Mechanical Engineering and Technology, 8(11), 2017, pp editor@iaeme.com

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