Development of Shape Memory Alloy Based Heat Engine for Solar Energy Harvesting

Solar energy is the most ubiquitous and abundant of various types of environmental energy available on the earth. Conventionally photovoltaic cells are used to convert solar energy to useful electric power, where available commercial technologies ensure efficiency of 10-25%. In this paper an investigation has been performed to use Shape Memory Alloy (SMA) for harvesting solar energy to electric power. SMA exhibits large deformation with change between martensitic region of low temperature and the austenitic region at the higher temperature. Employing this characteristic, we demonstrate SMA based heat engine to convert solar energy into useful mechanical work, which further has been used to generate electric energy. Nitinol wire has been used as the SMA material to absorb the solar heat and covert the same to mechanical work and electric power. The SMA wire has been initially in bending mode which exhibits large deformation when is heated by solar energy. Further, the deformation of the wire has been used to drive a custom-made micro-generator to utilize the wire deformation to electric energy. Theoretical calculations have been presented to discuss the energy balance of input solar energy, mechanical work done, and electric energy harvested. Experimentation of the prototype ensured 2.08% of efficiency to deliver average power of 4.86 µw.