System Design and Energy Management for Indoor Solar Energy Harvesting Under Consideration of Spectral Characteristics of Solar Cells

A standardized characterization method for solar cells is only available for outdoor use. For the supply of wireless sensor nodes with energy harvesting also indoor applications are of interest. Without comparable values it is difficult to select the proper cell for defined environmental conditions. Therefore it is necessary to make an investigation on their behavior individually to be able to make a selection. The work presented here shows the characterization of solar cells according to their spectral behavior, the influence of illumination and the usage of this information about the maximum power to design an energy management. Therefore a test structure with a monochromator, different light sources, source measure units and instruments for measuring intensity and spectra has been developed. The measurements help to select the best solar cell out of a repertory for indoor energy harvesting applications. As for indoor applications also the ability to make use of weak light and a high efficiency is important, the energy management has been improved using a dual DC/DC strategy that allows it to make efficient use of solar cells within difficult situations.