Alternative energy

Solar energy the foundations: (photovoltaic)

The direct convertion of solar radiation  into electric energy happens thanks to the photovoltaic effect. The photovoltaic technology doesn't use any combustible and it can supply little instruments such as the watch, the calculator, the street illumination systems or very big such as the power stations. The photovoltaic makes use of the sun which is the most widespread energy, free and avaible.
There is enought  to make of the photovoltaic the clean energy of the future.

The first forms of an efficacious exploitation of the solar energy go back to the far East, where the convertion of he solar energy allowed the diffusion of the ceral  intensive cultivation and the development of the first urban centers.

The first exemples of solar achitecture  were born in the ancient Greece: houses with porticos exposed towards  the South to mantain the cool during the summer and to make the sun penetrate during the winter; black stone floor and thick walls to keep the sun heating and to release it during the night. The Romans introduced the glass to mantein the heat, still in the Middle Ages and untill the Industrial Revolution the sun energy, used only for vegetable convertion, became the indirect energy source, in aid to the Animal energy and to the 3 great energy sources of that time: he water, the wind and the wood.During the Industrial Revolution the biolocal supremcy stopped and that of the fossil energies established.

The photovoltaic effect, was  discoved by Antoine-César Bequerel in 1839 , but only during the 50 years of the last Century the first working systems were made perfect.

Different systems had been studied  to realise the sun  energy convertion into electric energy : today  silicium cells  (monocrystalline or policrystalline) and thin film of CdS-Cu2S are avaible for generators of a few Kw. The efficency energy convertion of these cells varies between the 8% and the 15%.The gallium arseniuros cells, together with concentration systems, can reach efficiencies of 25%.The photovoltaic generators  that produce untill 1  kw of power , can be used for communication systems, lighting and water pumping; for  powers untill 100 kw, such as power-stations for isolated villagesand for agroindustrial   purposes.

Some exemples:
The small Vanguard satellite, launched in 1958 from the Cape Canaveral base, was the first complex object to work thanks to the direct convertion of the  solar energy in electric power. In 1977 the English physicist sir Nevill Mott invented a type of more economic silicon, even if with lower yields, obtaining, for its studies, the Nobel award.

In the  Ninety  the technology has made still remarkable progresses,   both regarding the use of the silicon both for the experimentation of new semiconductors like the  arseniuro of gallium. The more used  cells  remain those of   policristallin silicon, but in the United States  cells realized in thinnest silicone films  are developping to lead electricity and plastic details that could change the perspective of the photovoltaic technology  rendering it cheaper. But there are still some problems. The technology today concurs to gain an electric  energy  equal  to 20% of the avaible energy.  This can represent a limit: if the power that we want to  obtained is remarkable, great spaces are necessary in order to install all the pannels  that are necessary. The search is, however, trying to obtain improvements of the  convertion efficiency, to reduce the costs of the departure material and to reduce the fabrication cost. In 20  years all this has carried to a discouragement of ten times of the cost of the  photovoltaic energy. But this figure remains however nine times higher regarding that of the  energy obtained with the traditional sources.

How many types of system do exist?
The extreme modularity of the photovoltaic systems determines the detail flexibility of employment in many applications, also much various between them.
The  photovoltaic systems can be divided according to  their electrical configuration  in:

The indipendent systems are characterized by the necessity to supply the  electric power to the  user also in bad conditions of insolation or dark; it becomes necessary then to accumulate the  electric power produced by the cells and not used at the moment of the production. A system of batteries guarantees the  distribution of current also in these conditions. It is opportune to preview therefore a dimentioning of FV field in a position to allow, during the hours of insolation, both the  feeding of the cargo than the  recharges  of the batteries. The current generated by the photovoltaic system is a continuous current. If the cargo is constituted by an  equipment that demands a  current alternated feed  a converter is necessary that is an inverter continuous/alternating current.
These systems are used in multiple applications, that are economically  favorable in the cases in which the net electrical worker is difficultl to reach or absent.

The systems connected to the net do not need of system of accumulate because they are always  connected to the net electrical worker. In the hours in which the photovoltaic generator does not produce sufficient energy in order to cover the electricity question is the net to supply the demanded energy. Viceversa, if the photovoltaic system produces  more electric power than how much  it is demanded from the cargo, the surplus comes transferred to the net. In a system two counters count  the exchanges between the customer and the net.
An inverter  transforms the electric power from continuous current, produced from the photovoltaic system in alternating current. In this case the quality of marks  in escape  of the  inverter  must be very high  because the produced current must be able to be introduced in net and therefore to have the same requirement of that supplied from the same net. The inverter  is  the most important BOS  member in the systems connected in net, because, it not only  transforms the electric power from continuous current in alternating current, but it also controls and optimizes the passage of energy between the photovoltaic module and the cargo.

Which is the environmental impact them?
The photovoltaic is probably the best one among  the energy production methods that we  known. It is  silent, it does not produce emissions, it does not use fuel (with the exception of the sunlight). The photovoltaic technology is based on the silicon,the second  more common element and not toxic present on the surface.