When sunlight hits certain materials, sufficient energy in the photons striking the material is absorbed to allow electrons to move, and this is especially true for silicon, a semiconductor.  Solar cells made from silicon are treated and processed to enhance this effect, and have a wire grid attached to gather the electrons produced when sunlight strikes the silicon.  In a typical solar module many cells are wired together in series and parallel configurations to deliver the desired DC voltage from the module.  Solar modules are then wired together in series (call a "string") to deliver the desired voltage to an Inverter.  The Inverter receives the DC electricity from a large number of solar modules and converts the DC current to Alternating Current (AC), precisely matching the voltage and frequency characteristics of the electricity being supplied by the local electric distribution company. Different photovoltaic materials react differently to the spectrum of light, as well as to temperature, and thus produce different amounts of electricity under the same light conditions.The AC electricity produced by the inverter displaces electricity normally supplied by the electric grid, reducing how much electricity is purchased.  Depending on the size of the solar electric system relative to the site's consumption, excess electricity produced during the sunny part of the day will flow out to the electric grid, spinning the utility electric meter backwards. The excess electric generated registers as a credit on the meter, and is applied to electricity supplied by the electric utility or carried forward and spplied to a subsequent billing period.