The following response was provided by one of NASA's Heliophysicists
(which means a scientist who studies the Sun).
Most of the energy from the Sun that reaches the Earth comes in the
form of light (photons). The Sun is really bright. This light
includes visible light (the stuff we can see), infrared light, and
ultraviolet light. Some of that light gets absorbed by the Earth's
atmosphere, some gets reflected back into space, and some gets
absorbed by the ground or things on the surface of the Earth.
Chlorophyll is the green chemical in plants that converts the Sun's
energy to chemical energy that the plant can use. Solar cells convert
the light from the Sun into electricity. The total amount of light
that reaches the Earth is about 1360 Watts per square meter. That
means that to power a 100 Watt light bulb would require a perfect
solar array about a square foot in area. Because real solar cells are
not perfect, you really need a solar array four or five times that.
We hope this helps.
Please let us know if you have any questions.
Warm Regards,
Michelle
NASA Langley ASDC User Services