|
What's a Watt?
A Watt
is a unit of power--the rate of energy usage or production with respect to time.
We use
Watts to express how much energy an electrical device consumes in
a certain time, how much energy an electrical
generator produces in a certain time, or the amount of energy being
transported through power lines in that time.
The Big Light
Bulb
Watts can
express the energy output of the Sun as well as a light bulb. The
"Wattage" of the Sun, if you think of it as the biggest light bulb
around, is about 386,000,000,000,000,000,000,000,000 Watts--386
million billion billion!
Of that
incredible amount of solar energy constantly shining into space,
lighting up the "living room" we call our Solar System, the
Earth intercepts only a tiny fraction: less than half a billionth
of the Sun's total output!
That solar
energy is spread out over half of the Earth's globe, so that the
strength of solar energy in Earth's vicinity is about 1000 Watts for
every square meter. This amount of solar power is the maximum
amount available to the Earth, whether it is utilized by photosynthetic
life forms (plants), human-made solar energy collectors, or just to warm
the Earth's surface, oceans, and atmosphere.
Irradiance
Though the amount of solar
power reaching Earth works out as about 1000 Watts per square meter,
that doesn't necessarily mean that every square meter of Earth's Sun-lit
surface receives that amount. The "irradiance," or the amount of
solar energy received by a surface sunlight shines on, also depends on
the angle at which the sunlight strikes it.
The amount of solar energy
that a given surface area collects depends on the strength of the
sunlight and the angle at which the light strikes.
The
farther the Sun is from being directly overhead, the less the amount of
sunlight striking each square meter of the Earth's surface--or the lower
the irradiance. On a daily basis, a given location receives the
most solar power at astronomical noon, when the Sun is at its highest
point in the sky for the day. On a yearly basis, the irradiance at
any given time of day changes with the season. In winter, the Sun
is lower in the sky and its rays strike the Earth at a sharper angle, so
there is less solar energy for life forms and for heating both dry land
and water surfaces. In summer, of course, sunlight strikes more
directly and, we experience higher irradiance, and there is more solar
energy available to the environment. |
The
Solar Radiation
value (or "irradiance") shows the strength of sunlight, in Watts per
square meter, striking the Earth at Chabot's location
(Latitude: 37.789 N Longitude: 122.182 W).
