The photovoltaic effect is the transformation of light into electrical energy, as in solar cells.
The economics vary considerably around the world, resulting in widespread selling prices, e.g.
Primary cells, such as the common zinc–carbon batteries, act as power sources directly, but secondary cells (i.e.
rechargeable batteries) are used for storage systems rather than primary generation systems.
A characteristic of electricity is that it is not a primary energy freely present in nature in remarkable amounts and it must be produced. Electricity is most often generated at a power station by electromechanical generators, primarily driven by heat engines fueled by combustion or nuclear fission but also by other means such as the kinetic energy of flowing water and wind.
Other energy sources include solar photovoltaics and geothermal power.