This is an example application of the FemtoGen Electronics energy harvesting module EH2D. The solar cell produces voltages in the range of 20mV to 200mV where the voltage is converted up to 5V by the EH2D module. Since the solar cell can produce voltages of 100s of millivolts, EH2D is more efficient for this application where EH1D would be best for thermoelectric generators at 20mv to 50mV.
With the low input voltages in the mV range, the energy harvesting module continues to capture energy even with dim light environments such as indoors.
The harvested energy is stored in a 1F super capacitor. The wireless node continues to operate from the super capacitor stored energy even when there is no light!
The low duty cycle of the wireless sensor node means it sleeps most of the time and periodically wakes up to report temperature. The low quiescent current draw of micro controllers and sensor node wireless radio devices makes them ideal for energy harvesting projects. The wireless sensor module is EZ430-RF2500 from Texas Instruments. The FemtoGen energy harvesting module replaces the 2 AAA batteries.