The sun's energy on earth - Wonders of the Solar System - BBC

So how much energy does fall
on the surface of the Earth from the Sun?

You can work it out with a beautiful simple experiment

using only thermometer,
tin full of water, and an umbrella.

Basically, you let the water heat off in a tin
to an ambient temperature,

which here in Death Valley today
is about 46°C.

And then you put thermometer in the water

you take the shade away
and let the Sun shine on the water.

In direct sunlight
the water temperature begins to rise.

By timing how long it takes the Sun to raise
the water temperature by one degree Celsius,

you can figure out exactly
how much energy the Sun has delivered
into the can of water.

And from that, how much energy is delivered
to a square metre of the surface.

It turns out on a clear day,
when the Sun is vertically overhead,

that number is about a kilowatt.

That's ten a hundred watt bulbs
can be powered by the Sun's energy

for every meter squared of the Earth's surface.

In an audacious leap of imagination,
Herschel used this figure to calculate

the entire energy given off by the Sun.

So imagine adding up those kilowatts
over this entire landscape

and then imagine, following the Sun's rays,
as they cover the entire surface of the Earth.

But then, imagine this:

The Earth is 150 milion kilometres away
from the Sun.

So actually, the Sun is radiating the energy out
across a giant sphere

with the radius of 150 milion kilometres
surrounding our star.

And how much energy does that make?

It's four times π
times the distance to the Sun squared

which is about three times...

It's four hundred million million million million Watts.

That is a million times the power compsumption
of the United States

every year radiated in one second.

And we worked that out by using some water,
a thermometer, a tin, and an umbrella.

That's why I love physics.