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The photovoltaic system: From the solar surface to the heart surfase
The structure of a photovoltaic system can be very varied; in its most general form, a block system is shown here. Even if, in general, the most practical realizations use only some components. The systems are usually composed of components assembled on a fixed carrying structure, generally at angle equal to the latitude of the site, so that the ratio of the energy to the pannel and the global cost of the system is optimum.
Solar cell
characteristics
A photovoltaic cell is substantially a big diode behaving like a current
generator when exposed to solar radiation. The maximum suppling power in
specific conditions of lighting and temperature is measured in watt of peak
(Wp). A junction temperature of the 25° C and a 1000 W radiation, are
considered international conventional values [m²]. A photovoltaic cell
efficiences, results from the ratio of its maximum power to the radiation on
its surface (a cell):
h = P max /1000 x A ceII
PV cell
operating block.
Components
of a complete PV system.
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Examples of
elements on the market.
PV block
connected to the net.
Photovoltaic
station composed of pannels arranged in parallel lines.
The photovoltaic
block
The photovoltaic block is composed of photovoltaic elements connected in series
and in parallel so that the operating conditions you desire are possible the
string is formed by: More components or panels electrically connected to get
the nominal generation voltage. Finally the electric connection more laces
constitute the block.
In the planning phase of a photovoltaic block must be effects some choices.The
block operation depends on them.
A fundamental choice is, surely, the series-parallel configuration of the
components of the photovoltaic block; such a choice, in fact, determines the
electric characteristics of the block.
As soon as the size of the photovoltaic block is over some kilowatts of peak,
the sizes and the whole weight of the components are such to require the
subdivision of the block in to panels. The panels in can be arranged parallel
lines with the desired inclination. In this case the least distance among the
lines of panels can not be accidental but must avoid that the shade of the
anterior line covers those of the back line. It is therefore, necessary to
calculate the least distance among the lines in accordance with the panel
sheight, the place latitude and the inclination angle of the panels, morder
that shading doesn`t take place at 12 o`clock of the winter solstice.
Accumulators
In the
isolated photovoltaic system the energy is generally, stored by means of
electrochemical accumulators. The presence of accumulation batteries allows to
pace points of load, without the generators, as well as to guarantee the
continuity of energy, supples also in the case of low radiation generator or
temporary breakdown of the generators. Besides the accumulation battery, often
effects, the excellent joining between the photovoltaic generator and the rest
of the system.
The technological development in this sector, tied up to the auto industry, has
permitted to get acid lead accumulators with low auto discarge, long life (over
6 years) and reduced maintenance.
Electrochemical accumulators
Isolated village
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