This light, formed by billions
of particles called photons, is a huge mass of energy,
which, every day,
for hours, arrives on our planet warming it and allowing
the continuation of the vital cycles. The sun is essentially
formed by helium and hydrogen and, inside, the temperature
reaches 20 million degrees while the pressure hundreds
of tons per square millimetre. Solar energy is produced
through an atomic reaction called “nuclear fusion”,
i.e. an hydrogen bomb in continue explosion on the surface
and inside the sun.
Every second 4.3 tons of solar mass are destroyed and 600
million tons of hydrogen are transformed into helium. Despite
this gradual self-destruction, the sun will continue to
spread energy to the Earth for at least other 10 billion
In a sunny summer day, without clouds and in good geographic
conditions, we can calculate that more than 1000 Watt of
energy arrive from the sun in a square metre of Earth surface.
1000 Watt are sufficient to supply, during that hour and
with a conversion of 100%, 10 lamps of 100 Watt each.
The total solar radiation captured by the Earth is about
173 x 1012 kW, a value which is 13000 times more than the
energy consumption of our planet.
THE PHOTOVOLTAIC CONVERSION
The optimum system for the conversion of the electromagnetic
energy (solar light) into electrical energy is the photovoltaic
cell. The word PHOTOVOLTAIC comes from the name of the
particles called PHOTONS composing the light of any nature.
In the photovoltaic conversion the capacity of some materials
to spread electrons thanks to a light beam is exploited.
These electrical charges are collected through some conductors
placed on the surface of the tapping material and they
are then carried to the terminals.
The photovoltaic cells are not a very recent invention,
they exist for more than 40 years, during which they
have changed their form and performance. From round they
became square, with an improvement in their efficiency
from 8-10 to 15-16%.
If we connect some cells in series and/or in parallel
we have the photovoltaic module (it is usually composed
by 36 or 72 cells according to the voltage of the system,
12V or 24V).
If we use a lot of photovoltaic modules and if we combine
the connections properly, it is possible to produce electrical
energy with desired values of voltage and current.
In fact the modularity of the photovoltaic technology
always makes possible the adaptation of the generator
to the electrical charge and its adjustment to the users’ needs
as the years go by.
When the electrical energy is needed in no-sun conditions,
i.e. during the night or when the weather is bad, an
accumulator is used. In fact, thanks to a battery the
photovoltaic systems are able to spread electrical energy
24 hours a day.