“Photovoltaic” solar energy systems serve the purpose of producing electricity that can be partially or totally integrated into the energy network and sold to the Electricity Board GSE .

Generally, “domestic” photovoltaic systems (less than 20 KWp) are developed on a scale that allows them to use all the electricity they produce annually based on the “on-site exchange” method, whilst large scale systems (industrial) are generally designed on a scale that allows them to sell the electricity they produce.

The basic elements required for a photovoltaic system are essentially the following:

• Photovoltaic module, the purpose of which is to capture solar energy and transform it into a continuous electricity supply. The most commonly used photovoltaic modules are made up of mono or polycrystalline silicon cells, and more recently developed, CIS thin-film cells (copper and indium diselenide or other material)
• Low electrical resistance wiring
• Electricity inverter transforming direct current to alternate current to make it suitable for use
• Network connection equipment, where necessary, for large scale systems (transformers, control panels)
• Monitoring system to control operating conditions of system (energy produced, operative anomalies, etc.)
• Electrical accumulator battery where systems operate autonomously
• Meter to measure electricity produced by system.

Since September 2005, an incentive mechanism has been operative in Italy known as the “Energy Account” to promote the production of electricity using photovoltaic systems.
The Ministry for Economic Development and Minister for the Environment, Land and Sea Conservation issued a new Ministerial Decree on 19th February 2007 (DM of 19/02/07, published in the Official Journal (G.U.) on 19 February 2007, introducing radical amendments and simplifying the original framework (Ministerial Decrees of 28/07/2005 and 6/02/2006).

The most significant amendments, compared with the previous framework, relate to:

• abolition of the preliminary investigation stage required for eligibility to be granted favourable tariffs (there is no longer any need to make an application to be granted favourable tariffs before installing the system);
• abolition of the annual limit to capacity on favourable terms, replacing it with a maximum accumulated limit of power on favourable terms;
• improved structuring of tariffs, which aims at promoting small-sized applications that can be architecturally integrated into structures or buildings;
• introduction of a prize for photovoltaic systems, where efficient use of energy has been shown.

Electricity produced by photovoltaic systems which start functioning prior to 31 December 2008 have the right to favourable tariffs, as indicated by the values in the following table:

The highest tariffs are granted to the small domestic systems up to 3 KWp, which are architecturally integrated and can be increased by a further 5% in certain special cases, as foreseen by the Energy Account (for example, in systems where the party in question is a state/non-state schools (with equivalent status) or a public health structure).

The tariffs are issued by the Electricity Board (GSE) for a maximum period of twenty years commencing from the date the system becomes operative, and they remain constant without being subject to any standard-of-living-indexed adjustments for the entire period.

Mention should also be made of the fact that the tariffs are issued in relation to the total energy produced by the system, independently of the amount consumers by the person installing such a system.

More detail can be obtained by consulting the Ministerial Decree and clarifications published on Electricity Board website.

As regards thermal solar energy systems, on the contrary, economic advantages relate substantially to the possibility of detracting 55% of the costs sustained in setting up the system (fiscal deductions foreseen by the current Annual Budget Act) and the possibility of being granted access to so-called White Certificates if the party setting up the system satisfies the eligibility criteria for the same (these certificates are worth approximately €100 for each tep (equivalent tonne of petrol saved).

White Certificates are tradable coupons that can only be purchased by companies with specific requisites, such as “ESCO” (for further detail about the “White Certificates” mechanism, consult the information provided by the Authority).

These systems are usually used to produce hot water; they are connected up to the main system and are basically made up of:

• solar (collector) module, the purpose of which is to capture and transfer solar energy to circulating fluid
• accumulator boiler, used for storage of water to be heated (hot water for sanitary or heating purposes).

Moreover, in most cases the systems also have a heat exchanger which allows heat to be transferred from the circulating fluid in the panel to the water contained in the storage boiler.

The way in which stored water is heated depends on the type of system; there are basically two different circulation methods:

• natural: the system in which the boiler is compulsorily placed in a higher position than the panel so that the liquid present rises by convection when heated. In this case the circulating fluid can be
  a. water actually present in the boiler
  b. a vector fluid (usually non-toxic propylene glycol) that transfers its heat to water in the boiler through a heat exchanger.

The circuit is said to be open if the water is replaced as it is used though an external inflow. The system, which is a simple construction, is subject to a high degree of heat loss and consequently loss of efficiency in addition to the external position of the boiler, and it is not therefore recommended in cold climates with snow, or in any case where the night temperature is low.

• pressurised: a pump, known as a circulator, introduces the fluid vector, propylene glycol, in to the heat exchangers positioned inside the boiler only if the first is higher than the temperature of the stored water. In this case, the circuit is more complex, and requires an expansion chamber, temperature regulator for the various fluids and other components as a result of additional needs, and in addition, it consumes electricity because of the pump and the control panel, which is however compensated for on account of its considerably higher thermal efficiency, since the boiler is positioned inside and there is less heat dispersion during the night or under particular climatic conditions. However, by integrating the system with a photovoltaic system, electricity costs can also be reduced.