Rod-shaped semiconductor nanowires provide today highly promising materials for applications in areas like energy scavenging as well as in energy conservation. The ability to form each nanowire into a designed three-dimensional device structure, and ways in which such units can be combined into ideal arrays thus forming a complete device, lends great promise for many areas of applications. The ability to control the crystalline structure in-between the cubic zincblende and the hexagonal wurtzite structures lends another handle to optimize performance, and may sometime also be an issue in the ability to control things. In this talk I will concentrate on two such examples: (a) one in which III-V NWs, like InP or GaAs and ternaries based on these, can form the basis for a highly efficient photovoltaic technology, one that can easily constitute an add-on to standard silicon solar cells, and (b) one based on the GaN family of hexagonal materials, in which one aims to master and control the effect of piezo-electric effects in axial and radial LED device structures. I will conclude by discussing how one may take advantage of the built-in piezo-electric fields in specially designed tunnel device structures to increase the interband tunneling probability.