Photovoltaic semiconductors convert light directly to electricity. Individual photovoltaic cells may be used for detecting and measuring light, and arrays of the cells can produce useful electric power. Considerable investment has gone into improving the efficiency of their power generation, so they can move from expensive and specialized applications to becoming a significant renewable energy source.
The Sun is the energy source for large-scale photovoltaic power generation. There is obvious potential in using them for local building service power, mounting them on roofs and other building surfaces. Of course, there needs to be either storage of the photovoltaic-generated power, or supplemental power sources, to continue providing electricity during darkness.