An energy harvesting system comprises a first region and a second region having a temperature difference therebetween. A heat engine is configured for converting thermal energy to mechanical energy. The heat engine includes a first discrete element of a shape memory alloy having a crystallographic phase changeable between austenite and martensite in response to the temperature difference between the first region and the second region. The first discrete element of the shape memory alloy expands and contracts in response to the phase change to exert a linear force. A motion conversion mechanism is operatively connected to the first discrete element to be driven by the linear force and a component is driven by the motion conversion mechanism.