What is a photovoltaic plant?
A photovoltaic plant is a system composed of several complementary elements that allow the transformation of solar energy into electrical energy.
It's essential components consist of:
- the photovoltaic panels, composed in turn of semiconductor modules and cells;
- the inverter, which transforms the direct current generated by the modules into alternating current;
- electrical panels and connecting cables.
The photovoltaic plants can be directly connected with the electrical grid (grid-connected) or may be isolated utilities (stand-alone), typically to ensure the availability of electrical power in isolated zones.
What are the benefits associated with photovoltaic technology?
The main benefits deriving from the use of this type of technology are:
- the absence of any type of polluting emission;
- the savings of fossil fuels;
- the reliability of the plants, there being no mechanical parts, except when systems to track the trajectory of the sun are used;
- the reduction of operating and maintenance costs;
- the modularity of the system: the plant is designed and installed according to the specific energy needs, lending itself to possible subsequent expansion in the number of modules, with a correlated increase of rated power;
The installation of the photovoltaic plant has a high initial cost, due to the cost of the modules, with a discontinuous production of energy, due to the variability of the energy source (the sun).
What difference is there between a photovoltaic plant and a solar thermal plant?
In both plant types, the sun is the power source exploited. Nevertheless they differ from each other in the technology used to exploit the solar radiation: whereas photovoltaic modules directly transform solar radiation into electrical energy, the thermal solar panels utilize the thermal energy of the sun to heat water to be used for sanitary purposes or to heat the surroundings.
Where can a photovoltaic plant be installed?
Photovoltaic modules can be placed on any real property fixture (roof, facade, terrace, etc…) or on the ground.
The choice depends on the presence of two prerequisites at the site;
- sufficient space available for the installation of the plant;
- the correct exposure and inclination of the module surfaces.
The optimal installation conditions in Italy are:
- SOUTHERN exposure (also acceptable are SOUTH-EASTERN, SOUTH-WESTERN exposure, with a small loss of production);
- inclination of the modules between 25° (more southern latitudes) and 35° (more northern latitudes);
- the absence of obstacles capable of creating shadowing.
How much space does a photovoltaic plant require?
Referring especially to small applications (photovoltaic roofs) and to crystalline silicon modules, an approximate value of the surface area employed is about 8-10 sqm per kW of rated power installed.
How much electrical energy is a photovoltaic plant capable of producing?
The quantity of electric power produced annually by a plant depends upon:
- the solar radiation incident upon the installation site;
- the orientation and inclination of surface of the modules;
- the absence/presence of shadowing;
- the technical performance of the plant components (modules, inverters, and other equipment).
If we want to provide figures for the sake of reference, it is possible to consider a plant with 1 kW of rated power installed under the best possible technical conditions (the best possible orientation and inclination, the absence of shadowing) and not equipped with a sun “tracking” device; for this purpose, the following maximum annual production capacities can be estimated for Italy:
- northern regions, 1,000 – 1,100 kWh/Year
- central regions 1,200 – 1,300 kWh/Year
- southern regions 1,400 – 1,500 kWh/Year
It should be mentioned that the average annual consumption of an Italian family is equal to approximately 3,000 kWh.
The map of annual solar radiation over the territory of Italy is shown on the site http://re.jrc.ec.europa.eu/pvgis/countries/europe/g13y_it.png.
What are the total costs for the installation of a photovoltaic plant and those for maintenance?
The start-up costs can be estimated between approximately 7,000 and 5,000 €/kWp, if dealing with a small or large plant, respectively.
The maintenance costs are very low and may be quantified on the order of 1 – 1.5 % of the start-up costs.
How long can a photovoltaic plant last?
From tests conducted it was found that the average life of a photovoltaic module, the most economically significant component, can be estimated to be about 20 years. It should be specified that the other components, especially the electronic ones having greater sensitivity, demonstrate a shorter average duration.
To whom is the request to connect a photovoltaic plant with the grid forwarded?
The responsible party who intends to build the photovoltaic plant forwards the request to connect with the grid to the local grid operator.
As regards the plants to be connected to the Enel Distribuzione grid, the information for the application to connect and trade can be found in the following web address:
For what type of plants is it necessary to request a license from the Ministry of Finance Engineering Department [UTF]?
Plants with a power capacity greater than 20 kW (law 133/99) are subject to the Electrical Works Notification and require an operating license from the Ministry of Finance Engineering Department.
It is not necessary instead to provide notice of the opening of the electric works to the Ministry of Finance Engineering Department if the plant emits all the energy produced into the grid (circular letter 17/D of May 28 2007 of the Customs Agency: enforcing provisions of Legislative Decree no. 26 of February 2)