In this position paper we summarize our achievements and discuss some important aspects and challenges for future advances and realization of energy harvest- ing from solar antennas. The enhancement of the rectification and the impedance matching between nano-antennas and the rectifier stand out as major tasks in the pursuit of research in this field.

We have achieved lab scale technology validation at the system level, at least in the low THz regime for rectennas, and in the visible regime for nanoantenna structures. The GreEnergy nanoantenna-diode-storage concept could also be of future interest for local harvesting in self-powered units, e.g., for Internet of Things applications.

Still the challenges related to bringing this technology to useful systems, especially of the optical regime, are enormous. Single components and nanomanufacturing must be further developed, development of materials and materials with dedicated properties is necessary, insertion losses must be reduced, and in particular, the nanoantennas must be perfectly impedance-matched to the rectifiers, to avoid losses. The GreEnergy project has made several important steps forward in this area, even though much research and development remain in the coming decades.