How Energy Is Produced - The Renaissance of Renewable Energy - page 94

containing matter (like water in an ocean wave or air in a sound wave), these waves are
composed of pure energy.
Like waves in water, electromagnetic radiation comes in varying wavelengths: radio
waves are long, comparable to waves in the ocean; light waves have a medium length,
comparable to ripples in a lake; and X-rays are very short, comparable to tremors in a
glass of water. The shorter the length of a wave, the greater its concentration of energy.
This is why prolonged exposure to certain short waves, such as X-rays and gamma rays,
is so dangerous; they have sufficient energy to penetrate our bodies and interfere with
our cells, causing our genetic material (DNA) to split. This, in turn, may lead to cells
'malfunctioning', forming tumours.
About 40 per cent of solar radiation is visible (what we experience as light); another
50 per cent is infrared (what we experience as heat). The rest is at higher and lower
frequencies, such as gamma rays, ultraviolet, microwaves and radio waves (Arvizu et al.
2011a ) . Visible light is the aspect of the sun's radiation that which most crucially supports
life, through photosynthesis. However, the other forms of electromagnetic radiation are
also essential to life; ultraviolet radiation, for example, is used by insects to navigate, and
infrared rays transmit heat.
Since any object exposed to sunlight will absorb heat, the process of converting solar
energy to heat is relatively straightforward and can be achieved either actively or passively.
Passivesolarheatinginvolvesadaptingarchitecture tomaximiseheatcaptureandminimise
heat loss. This is the cheapest and most convenient way to take advantage of solar energy.
Active solar heating involves the use of devices, usually roof-mounted panels, to collect
solar radiation to heat water or other liquids.
Passive Solar Heating
The ancient Greeks were probably the first to design buildings that took advantage of the
fact that, in the Northern Hemisphere, south-facing façades receive far more sunlight than
thosefacingnorth,eastorwestdo.Theydesignedentirecitiessothatallhomeswouldhave
south-facing façades. Later, the Romans improved on Greek solar architecture, adding two
other innovations: glass windows to trap the sun's rays and black roof tiles to absorb more
heat. Glass allows solar radiation to enter a building, but because in doing so it loses some
of its energy, some of the radiation remains trapped inside. Black roof tiles heat up on a
sunnydaybecause,likealldarkmaterials, theyhavethecapacity toabsorbelectromagnetic
radiation (a white surface reflects about 80 per cent of the light, a dark surface absorbs
about 90 per cent). Consistent with the first law of thermodynamics (law of conservation of