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 years.
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.