Development of an advanced nano-satellite (VELOX-IV) : solar energy system

Abstract

In this report, a Concentrated Photovoltaic (CPV) cell is used to convert solar energy to electrical energy. The output power of the CPV cell is increased by using a concentrator with optical lens to focus solar intensity to 40 times the original amount. However, the CPV cell will experience an increase in temperature and this lowers the output voltage of the CPV cell, hence reduces the output power of the CPV cell as time goes by. In order to recover the waste heat and to compensate the energy loss, a thermoelectric Generator (TEG) is added in this project to convert the waste heat into electricity.

Tests have been conducted on the prototype CPV cell system to study the energy loss issue. The power loss of the CPV cell is quantified and modelled using the power loss factor multiply by the change in temperature of the CPV cell. The test is able to extract the output characteristics curves of the TEG and the power loss is quantified to be 1.5W. In order to find out the optimal environmental condition of the combined TEG and CPV cell system, the power equations of the TEG are modelled in relation to the quantified power loss and studied. With this modelling, a simulation study has been conducted and there are 3 findings which have been tested using different TEGs.

To validate the simulation findings, a TEG system has been developed to test the TEG. It is able to measure the temperature difference on both sides of the TEG as well as to record the output voltage and current. Three different methods have been experimented for different TEG configurations. Method A is tested using TEG with high Seebeck coefficient and is able to recover 16% of power loss. Method B is tested using a TEG with low R_int and 32% of power loss could be recovered. Method C uses 2 TEG connected in series and 77% of the power loss has been recovered. Method C proves to be the best in recovering the power loss of the TEG but using 2 TEG is actually not ideal as it will take up the precious space in nano-satellite. The highest recovery ratio for single TEG is 32% at 〖 T〗_h =120℃ and 〖 T〗_c to 20℃. Overall the project objectives are met in developing a more efficient energy harvesting power system by using the TEG.