Photoelectrochemical cells (PEC) can be used for the absorption of solar light as energy source for the production of solar fuels such as hydrogen, and for the conversion of other species into chemical products. The principles of semiconductor photoelectrochemistry are at the heart of a future PEC technology and economy. There it is important to realize and understand that the conversion of the light energy takes place predominantly in the bulk of the photoeletrode, whereas the chemical conversion takes place at the surface of the electrode, when in contact with the electrolyte. We are dealing therefore with a complex interplay of physical and chemical processes between photovoltaics and electrocatalysis. I will present a suite of ex situ, in situ and operando studies with synchrotron x-rays which helped to elucidate these processes and how they impact on the electronic structure and molecular structure of the photoelectrode, exemplified with iron oxide and tungsten oxide. It is not surprising that we find that the photoelectrode itself participates in chemical reactions which can constitute parasitic reactions which are recorded as photocurrents, but which do not contribute to hydrogen production, for example.