Thames & Kosmos Solar Mechanics handleiding

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THE ANGLE OF SOLAR RADIATION

The sun is so far away from Earth, that the sun’s rays hit Earth in virtually parallel lines. So

when the sun is directly overhead, its rays hit Earth perpendicular to the ground (at a 90° an-

gle). When the sun is low in the sky relative to your position on Earth, the sun’s rays hit the

ground at an angle. They also pass through more layers of atmosphere coming in at an angle.

The greater the slant at which the

sun’s light hits the ground, the

larger the area that the same

amount of light, or photons, are

distributed across. Because the

same amount of energy is spread

over a larger surface area, the en-

ergy per unit of area is lower. This

is why the sun feels hotter when it

is high in the sky in summer than

when it is low in the sky in winter.

Even at a distance of 150 million kilometers,

where Earth orbits the sun, the power of

this radiation still amounts to 1.4 kWh/m

Only a portion of that energy is absorbed by

Earth, while the other half is reﬂected back

into space.

The sun’s radiation is highly variable in dif-

ferent regions of the world. That has to do

with cloud cover and Earth’s tilt. In New

York, about 1,000 kWh/m

of solar energy

are available per year, while the ﬁgure is

about 1,700 in Los Angeles, 2,000 kWh/m

the Caribbean, and 2,200 kWh/m

in the Sa-

hara desert. Compare these numbers to the

fact that the average American uses only

about 13,500 kWh in a whole year.

In total, Earth gets about 1.1 x 10

kWh of

energy from the sun every year. To put this

in perspective, the amount of energy pro-

duced and consumed in one year by every-

one on Earth is only about 1.3 x 10

kWh.

Thus, the sun gives us 8,000 times more en-

ergy than we consume in a year! This means

that in about an hour, the sun delivers as

much free energy as all of Earth’s inhabit-

ants combined use in an entire year.

When light rays hit a surface at a

lower angle, the energy per unit

of surface area is lower.

Light rays

CHECK IT OUT

Powering Up: Solar Cells | 23

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