Power generation from solar pond using thermoelectric generators

Abstract

Renewable energy is becoming an important source of energy due to the rise in crude oil prices and the increase in greenhouse effects due to burning of fossil fuels. With only finite source of fossil fuel and exponential increase in the demand of power because of increase in human population, power generation from renewable energy promises a sustainable future for the mankind. Currently, solar thermal technologies convert energy from the sun into useful thermal energy. Solar energy is intermittent in nature and most solar thermal technologies require separate collectors and storage systems. This makes them expensive to operate. Furthermore, power generation from low grade heat is currently restricted to vapour compression cycles with low reliability and high maintenance cost. There is a need to explore low cost integrated solar thermal collector and storage system and an alternative technology to convert this low grade heat into electricity. A salinity gradient solar pond is a low-cost solar collector with long term thermal storage capability. It utilizes a large body of saline water with increasing density gradient from top to bottom that absorb solar radiation and stores the thermal energy. Solar ponds have been simple and low cost solar energy system for a relatively longer period of time and very stable with the intermittent supply of solar energy. A thermoelectric generator (TEG) has the advantage that it can operate from a low grade heat source such as waste heat energy. Heat is supplied at hot side of the thermoelectric cell while the other end is maintained at a lower temperature by a heat sink. As a result of the temperature difference, Seebeck voltage is generated that result in current flow through an external load resistance. There are no moving components in the TEG and this will lead to a reliable, quiet and maintenance free operation for power generation. Although Organic Rankine Cycles (ORC) engine is currently used to generate electricity from solar pond using low grade heat, it still requires a certain threshold in the temperature difference of the system. The TEGs however works without any temperature difference threshold needed for its operation. The main aims of this project are to develop a system for conversion of low grade heat (< 100 ºC) to work and effective utilisation of low driving temperature differences from low grade heat for heat to work conversion. This thesis examines the potential of power generation from solar pond using TEGs with innovative new designs. Theoretical analysis was developed to investigate the performance of TEGs with low grade heat input. The thesis also explains the systematic procedure of design and manufacturing of TEG heat exchangers. Experimental test rigs and instrumentations used for testing the prototypes are explained in detail. The effect of thermal adhesives on power output from TEGs without any mechanical fixtures presented shows remarkable potential for large scale TEG heat exchangers. The effect of thermal variation on the performance of TEGs are also studied and highlighted in the thesis