You have seen photocells (solar cells) in calculators, garden lights and bus stops, while the last few years (for Greece 2005 onwards) appeared the first photovoltaic parks.
Photocells convert solar energy into electricity.
In simple terms we could say that the light is absorbed by a special material inside the photocell. This results in the creation of free electrons with high energy. An electric field present in the photocell forces them to move to a certain direction. This directed movement of the electrons is the electric current.
The conversion is achieved due to the photovoltaic effect which causes the cell to transform solar energy into electricity.
It is obvious that photocells cannot produce electricity during night, or cloudy days.
Photovoltaic parks produce direct current. This is transformed to alternate current and then normally is given to the electricity company's network. The owner of the park is paid according to the electricity given to the electricity company.
In the cases the solar panels are used for a certain purpose, part of the electricity produced during the day is stored for use when there is no light. A method to store this electricity is charging batteries. A battery is sufficient to illuminate a house, or power a refrigerator for a few hours. The machines of a factory, however, cannot be powered using batteries.