A system combining photovoltaic (PV) and solar thermal approaches is designed to convert solar energy to electricity with high efficiency across the full solar spectrum. Concentrated solar spectrum is split into two parts: PV and thermal. The PV part of the spectrum is further split into several subbands directed to bandgap appropriate solar cells on an inexpensive Si substrate. Epitaxial Ge on Si is used as a virtual substrate for III-V semiconductor growth. At long and very short wavelengths where PV efficiency is low, solar radiation is directed to a high temperature thermal storage tank for electricity generation using heat engines. The potential of using PV waste heat due to thermalization of high energy photoelectrons for electricity generation is also investigated. Detailed optical and thermal analysis show that with optimized design and neglecting optical component loss, system power conversion efficiency can reach 56%, including more than 16% absolute contribution from thermal storage.