A photovoltaic cell is a light absorbing device which converts light energy
into electric energy.
When the photons in the light are absorbed by a semi conducting material like silicon
negatively charged electrons are knocked loose from their atoms and when they flow through the semi conducting material, they produce electricity.

The maximum output power of a solar cell is influenced by different factors,
some of them are:

• Temperature
• Weather
• Environment

One interesting point in alternative energy sources is the “Energy payback” time.
This is the time an alternative energy source needs to generate the total energy used
for it’s own production.
Back in the 1990’s the production of solar cells took more energy that the cell would generate in its entire lifetime due to shorter lifetimes of the cells and other factors.
Today the energy payback time varies between 1 and 20 years depending on the net energy gain and type.

The output power is usually measured in Watts and depends on the amount of incoming light and the efficiency factor of the cell.
A solar cell with a surface of 1 square meter can under optimal weather conditions produce up to 120 Watts peak power.