been created a power system’s pattern inside this room, to be utilized as base for the
various tests performed. Afterwards, have been selected the photovoltaic modules
main manufacturers operating on the market, selected some models for each
manufacturer (different in cells typology and power, in order to cover the entier
range), and have been performed the simulations for the performances analysis of
each one of the modules adopted for examination, in terms of energy quantity
produced in a year period, module and power system efficiency.
At this point the results obtained have been elaborated concerning the different
modules behaviour, and have been selected, with the aim to optimize the system,
those modules showing the energy’s highest quantity produced in a year, per
surface’s unit, and it has been designed their lay-out on the roof covering, whose
available area is entierly exploited, and such a solution is feasible if aren’t existing
constraints regarding the amount to be invested for the power system realization. On
the contrary, namely if the capital available for the investment is limited, it is
preferable to utilize those modules characterized by the highest ratio value between
the energy produced in a year and price, in order to maximize the productivity,
exploiting in the best manner the capital available.
Then both the situations considered have been analized, and for each one of them the
main results have been evaluated, such as the costs and yields related, the energy
quantity produced, and the investment’s pay-back time. Additionally it is performed a
comparison among the results obtained by the simulations based on the system
pattern realized by the TRNSYS calculation code, and other valuation models of a
photovoltaic system productivity, which are traceable free of charge in several
websites.
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Chapter 1
Energy and energy sources
The power is defined as a system’s capacity to perform a work. The unit of
measurement derived from the power , in the international system is the joule [J],
which expresses the quantity of power equal to the work performed by the force of 1
N to move of 1 m the application point. Another measurement’s unit largely utilized
for the electric power is the kilowatt-hour [kWh] which represents the quantity of
energy supplied by a power source of 1 kW, working at costant power for one hour
time (1 kWh = 3600 kJ). Then in order to measure large quantities of energy, it can be
utilized also the measurement’s unit tonnes equivalent of petrol [tep] (1 tep = 11,630
kWh).
1.1 Energy sources classification
It is defined primary energy source a resource directly available in nature and
utilizable by the man, it means that from this one it is possible to obtain useful energy
in a direct manner, while the secondary sources are those needing a transformation, to
be utilized like sources. Among the primary energy sources are considered:
● Radiant energy: energy radiated in continuos manner by the Sun on the
terrestrial orbit (equal to roughly 1.35 kW/m2). It can be utilized like heat
flow (thermic solar energy), or in order to produce directly electric power
(photovoltaic solar energy).
● Fossile sources: energy obtained by hydrocarbons combustion (for instance
oil, natural gas, coal) that is vegetables absorbing carbon dioxide and water,
and capable to accumulate energy in chemical form. From the anaerobic
degradation of these organic substances, are obtained the fossile
combustibles, but the transformation is extremely slow. (it requires millions
of years times).
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● Biomasses: organic substances of animal or vegetable origin, non fossile,
from which it is possible to obtain other substances to be utilized like
combustibles, by means of different processes, like for example the
fermentation. Besides it is existing the dry biomass (Wood) which doesn’t
need particular treatments. There are also under experimentation fast-
growing vegetable cultivations, to be utilized expressively for energetic
purposes. The biomasses don’t generate CO2 net emissions, because the
quantity emitted during their combustion is virtually equal to the one
absorbed by the substance during its growth, therefore the carbon cycle is
closed.
● Nuclear energy: energy released by reactions involving the atomic
nucleuses, where it isn’t checked the mass conservation. In the fission
reaction (commonly utilized in the nuclear reactors), atoms of elements
bearing high atomic number (Uranium 235 or Plutonium 239) are striked by
a neutron, and are generated nucleuses bearing lower atomic number, with
total mass decrease, and other neutrons to continue the reaction. Instead
during the fusion’s reaction, atoms of elements bearing low atomic number
(Hydrogen or its isotopes, like for instance deuterium) melt togheter to
produce heavier nucleuses, releasing a higher quantity of energy compared
with the fission’s case. But to start a fusion reaction are needed very high
temperatures (in the order of magnitude of millions of degrees) and it isn’t
yet available a method to obtain controlled fusion’s reactions..
● Water energy: potential energy of a defined water mass located at high
altitude; the energy production takes place by exploiting an elevation head.
It bears the advantage to be already in mechanical form, therefore it can be
converted into electric power with low losses. But the exploitation’s
potential of this resource, has the tendency to the saturation in the time,
because the power globally installed has a growing trend, but having the
tendency direction an asymptote in the time, because the suitable sites where
it is possible to exploit such resource, have been gradually utilized, and the
industrialized countries are already in this phase.
● Eolian energy: kinetic energy owned by the winds and airstreams, which is
exploited by suitable aerogenerators, which are machines equipped with a
bladed rotor, assembled on a tower support top. It is a discontinuous form of
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energy, because it isn’t always and everywhere available, but predominantly
in some locations, and in addition the winds direction and speed could be
strongly variable. The rotor’s rotation energy can be utilized directly in
kinetic form or (more frequently) converted into electric form. The elevation
at what it is placed the rotor should be the maximum possible, in order to
avoid the dynamic boundary layer, with the aim to exploit airstreams in
motion at higher speeds, because the power obtained depends on the
airflow’s speed third power.
● Geothermal energy: energy generated by heat’s geologic sources,
which could take place in presence of particular conditions, for instance
when the subsoil temperature is, in some zones, higher than the average, it
can happen steam outburst under pressure from the subsoil. In some cases it
is adopted the cold water immission in depth, with the purpose to increase
the steam’s production, and to obtain a continuos flow. The steam can be
utilized as thermal energy’s source, or piped to suitable steam turbines, for
the electric power conventional production.
● Tidal energy: energy obtained from the water displacements caused by the
tides. This natural phenomenon exploitation is based on a suitable basin
filling (obtained when the water level raises), which is drained afterwards,
exploiting the elevation head created by the tidal range caused by the tides;
during the draining phase, large water flows cross suitable turbines for the
electricity production. The energy obtainable by this resource can be
forecasted with a high degree of accuracy, because the tides cycles are
known and recurring, but it can be exploited with a determined efficiency
only at some suitable sites, those where the tides create high tidal ranges.
● Sea currents and sea state energy: the sea currents water flows kinetic
energy, which can be utilized to put into rotation a bladed rotor, a
component of an underwater turbine, placed on the soundings. The sea
currents speed has generally a cyclic trend in the time, which can be
assumed as sinusoidal, therefore the rotors must be able to function in
presence of a water flow having both positive and negative speed, that
means coming from a determined direction or from the opposite one.
Also the electric power production itself follows the sea currents trend, and
so it isn’t constant in the time, but it is easily foreseeable, and the problem
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can be solved by installing more turbines in parallel, in points where the sea
currents trends are conveniently out-of-phase. Some techniques exist for the
sea state energy exploitation, installed for instance on floating tubolar
structures, bearing some turbines installed in their inside, activated by the
water flowing in-and-out, following the sea state’s trend. But such
technologies are still in the initial experimentation phase, and their costs are
very high.
● Seas thermal gradient: energy obtaineble by exploiting the temperature
differences between the see water at the surface, and the one at the depths.
The optimal conditions for such resource exploitation, can be found at very
hot seas and having a determined depth. Also in the best conditions, these
temperature’s differences are anyway low, and therefore (due to the fact that
the maximum efficiency of a cycle operating between two heat’s reservoirs
at different temperatures, is the Carnot cycle one, defined as :
ηc = 1 – TMIN ∕ TMAX ) the efficiency of a cycle of this type is extremely low.
A further classification can be performed distinguishing the renewable energy sources
from the non-renewable ones. Are generally defined renewable energy sources those
regenerating themselves or those non-exhaustible in the “human” scale times, or
better, those regenerating and refeeding themselves, in times comparable to the
consumption’s ones.
For instance, based on this principle, therefore aren’t to be considered as renewable
the combustibles obtained from fossile sources, also if they derive from
transformation’s processes which occur in nature in regular and continuous way,
because these transformation’s processes require extremely long periods (millions of
years), if compared with the utilization’s times of these combustibles. The same thing
happens also for the Uranium, utilized like base combustible for the nuclear energy
exploitation.
The renewable energy sources are those allowing the sustainable development, for an
undetermined time and with a minimum environmental impact. Some of these
energy’s forms, can be microgenerated, that means produced in small domestic
systems, which are able to satisfy the energy’s requirements of an individual house or
of a group of houses. Besides this allows to avoid the transportation’s losses, which
commonly occur during the electric power distribution.
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