Which are the renewable energy sources
An energy source is renewable when its exploitation time is comparable to the time needed for its regeneration. The law no. 10/91 considers the following renewable energy sources (RES): sun, wind, hydropower, geothermal resources, tides and wave motion. This definition should be completed by adding the biomasses (e.g. wood), by precising that those resources can be considered renewable only if managed properly, that means by making sure that their exploitation is compatible with their growing time. It is important to consider that the energy forms on our planet originate from the solar radiation, except for the nuclear energy, geothermal and tides: the hydroelectric power, that exploits the falling of water, would not exist without the “solar” cycle of evaporation and rain. Without the sun there would be no wind, due to the unequal warming of the air masses, and so the wind power. The energy of the biomasses is solar energy stored chemically, through the photosyntesis.

Why using renewable sources?
The RES provide many advantages, among which one of the main ones is, with no doubts, the absence of polluting emissions during their use (“clean” sources) and their endlessness. Those positive characteristics make them much more preferable than the fossil sources currently used, such as oil, natural gas and coal.
What is a photovoltaic system?
A photovoltaic system directly transforms the solar energy into electric power. It is essentially composed of:

• modules or photovoltaic panels;
• an inverter, that transforms the direct current generated by the modules into alternating current;
• electrical panels and cable leads.

The modules are composed of cells made of a semiconductor material, of which the most used is crystalline silicon. Those are the active part of the system because they convert the solar radiation into electric power. The photovoltaic systems can be grid-connected or stand-alone.

Which are the advantages of the photovoltaic technology?
This is a summary of the advantages:

• absence of any type of polluting emission;
• saving on fossil fuels;
• reliability of the systems since there are no moving components;
• low maintenance and operational costs;
• modularity of the system, (to increase the power of the system it is sufficient to increase the number of modules) It is important to take into account that the photovoltaic systems has an high initial cost (mainly due to the high cost of the panels) and has a discontinuous production caused by the unpredictability of the solar source.

What is the difference between a photovoltaic system and a solar thermal system?
Both technologies use the sun as energy source, capturing the radiation though collector surfaces: but while the photovoltaic modules directly transform the solar radiation into electric power, the solar thermal panels use the thermic energy of the sun to heat the water for fixtures and heating.

Where can a photovoltaic system be installed?
The photovoltaic modules can be placed in any building appurtenance (roof, façade, terrace) or on the ground. The decision should be made according to the presence of the following requirements in the installation site:

• necessary space availability to install the modules;
• the right exposure and tilt of the modules surface.

The best conditions in Italy are:

• SOUTH exposure ( also SOUTH-EAST and SOUTH-WEST are acceptable, with a reduced production loss);
• The tilt of the modules should be between 25° (southernmost latitudes) and 35° (northernmost latitudes);
• Absence of obstacles that could cause shading.

How much space does a photovoltaic system take?
Referring in particular to small systems and modules in crystalline silicon, an estimated amount of surface occupied is of about 8-10 kW/ m² of electrical nominal power installed 

On what does the electricity production of a photovoltaic system depend?
The annual electric production of a photovoltaic system depends on several factors:

• The solar radiation incident on the installation site;
• Orientation and tilt of the modules surface;
• Absence/presence of shadings;
• Technical performance of the system components.

For example, let’s take as a reference a system with a nominal power of 1kW, optimal orientation and tilt and no shading present, not equipped with a solar tracking array, in Italy, it is possible to estimate the following maximum annual productivity:

• Northern regions: 1100 kWh/year
• Central regions: 1400 kWh/year
• Southern regions: 1600 kWh/year

It is important to highlight that the average annual energy consumption of an Italian family is of about 3000 kWh.
How much does a photovoltaic system cost?
An indicative estimation goes from 7000 Euros per kW for the systems till 10 kW and a bit less than 5000 Euros per kW for larger systems (500 - 1000 kW).

How much are the maintenance costs of a photovoltaic system?
The annual maintenance cost is fairly low: usually it is estimated of about 1% of the system cost.

How long will a photovoltaic system last?
In the technical and economic analysis it is usual to find references of an estimated lifetime of 20-25 years. In particular the modules, that are the most expensive component, have an average lifetime of 25 years guaranteed by the manufacturers.

What is the nominal power of the photovoltaic system?
The nominal power (or maximum, peak, or rated) of the photovoltaic system is the electric rating of the system determined by the sum of the individual ratings (maximum, peak, nominal) of each photovoltaic module of the same system, measured at standard conditions (temperature of 25 ° C and radiation of 1000 W / m²).
It is important to underline that the average annual energy consumption of an Italian family is of about 3000 kWh.


The photovoltaic system works even in cloudy weather?
Yes. The photovoltaic system works at its best with direct solar irradiance (clear sky, south-oriented modules temperature of 25°C) but some electricity will be produced even under partly cloudy conditions.

The installation of a photovoltaic system requires to modify the existing electrical system?
No, it is not necessary to modify the existing system. The photovoltaic system has its own autonomous power line that should be connected to the main electrical panel and two meters installed by the electricity supplier: one incoming, to register the electricity taken from the national network, and one outgoing, to register the electricity injected into the network by the photovoltaic system. (Or a bidirectional meter that counts both the incoming and outgoing electricity).

Why the energy issue and the renewable energies are so much of topical interest?
To face the energy issue means to start from those phenomena that are more worrisome to the citizens: atmospheric pollution, the oil getting expensive and the negative effects of climate change.
From here the need of a long-term energy planning, characterized, on one hand by the centralization of the regulation and, at the same time, by a localization of the intervention measures.

What is the photovoltaic technology?
The photovoltaic technology allows to directly transform the solar radiation into electric power. This exploits the so called photovoltaic effect that is based on the properties of some semiconductor materials, (the most used is silicon, a very common element in nature) that, properly processed, are able to generate electricity if stricken by solar radiation. The most elementary device able to carry out this conversion is the photovoltaic cell that is able to produce a power of 1.5 Watt. The basic component, available in the market, is, instead, the module, composed of more cells linked and encapsulated. More photovoltaic modules connected in series and in parallel, form the sections of a system, of which the power can vary from a few hundreds to millions of Watt.
The correct exposure to the solar irradiance of the photovoltaic modules represent a key factor in order to achieve an optimal performance of the system in terms of production feasibility of electricity. For example in Italy the optimal exposure if towards South with a tilt of about 30-35° degrees. In the map it is shown the production feasibility of a photovoltaic system of 1kWp in Italy, optimally oriented and tilted, installed in a fixed structure (indicatively from Northern to Southern Italy the specific production can vary from 1000 to 1400 kWh for every kWp installed). Moreover, every kWp installed needs a net space of about 8-10 m² in case the modules would be installed in a coplanar way to the buildings surfaces; while it would need more space if installed in more subsequent rows or on titled support structures placed on flat surfaces.
The system configuration includes the insertion of an inverter downstream of the photovoltaic modules that transforms the direct current generated by the cells into alternating current directly usable by the users. At last, the system is completed by a support structure to fix the modules to the installation surface: ground, roof, façade, wall, etc. The structure can be fixed or movable, able to follow the daily sun path during the year.
The main applications of the photovoltaic systems are:

• Systems with a storage system for users not connected to the grid;
• Systems for users connected to the grid in low voltage;
• Power plants connected to the grid in medium or high voltage (Source: GSE).