Photovoltaic effect is related to the properties of certain materials (semiconductors) to convert light directly into electricity.
The discovery of photovoltaic effect dates back to 1839, and it was made by Edmond Bequerel, a French scientist during an experiment. He observed that when platinum was hit by solar radiation it produced electricity, thus he started to think how to use this phenomenon. The first solar cell was built in 1889 by Charles Fritts in New York. The photovoltaic panel consisted of a thin layer of selenium lying on a metal plate covered with a semitransparent film of gold. Its efficiency was just about 1%. Since the19th century many advances have been done in photovoltaic technology, the material used, and their efficiencies (nowadays close to 15%) The photovoltaic cell is the simplest element of photovoltaic technology. It comprises a series of layers of properly treated materials, and it is connected with other cells to form a photovoltaic (PV) module (or panel), which is the basic unit commercially available.
Strengths of PV systems are:
- no pollutant emissions during operation;
- fossil fuels saving;
- high reliability (there are no moving parts);
- low operative and maintenance costs;
- plant modularity (in order to increase the plant power you just have to add other PV modules.
Weakness of PV systems are:
- variability and randomness of the energy source (i.e., solar radiation);
- high cost of PV plants because the PV market that has not yet reached the technical and economical maturity.
In order to overcome the last weakness point in many countries (i.e., Germany, France, Spain, Greece, Italy) development of PV systems is supported by national incentives, which have triggered a strong market growth.
PV systems are divided into two main categories: grid-connected and stand-alone. The former are connected to the national, regional or locale electric grid, whilst the latter are used for isolated systems (i.e., when a connection to the electric grid is not possible or too expensive). Grid-connected PV plants are more flexible and less expensive than the stand-alone ones, which need a battery pack to stock the unused electricity.
The structure of grid-connected PV systems (the only ones subjected to the ‘Conto Energia’ national incentive) is very simple: they are composed by the PV field, the inverter, and a meter. The PV field: it is composed by the set of PV modules properly connected together, which captures solar energy and convert it into DC. Inverter: it is an electronic device which transforms DC into AC compatible with the local grid. Meter: it counts the electricity produced by the PV system, hence allowing to receive the appropriate incentive, and that possibly exchanged with the grid. In the best position a PV system in Italy has the modules facing South and forming an angle of about 30-35 ° from the horizon. However, exposures and different inclinations, within a certain limit, do not reduce the system performance significantly. In any case, the PV system configuration has to be studied and adapted case by case.
The ‘Conto Energia’ incentive provides an incentive for each kWh of electricity produced by a grid-connected PV system. The incentive is paid for 20 years, varying depending on the plant size (the bigger the size the smaller the incentive) and its degree of architectural integration (the better the integration the larget the incentive). The electricity produced can be used directly or fed into the grid, giving a choice between net metering (for plants smaller than 200 kW) and selling to the grid operator (for all systems). The gain is therefore twofold: in the case of net metering, in addition to the incentive rate, there is a saving in electricity bill because part of the electricity consumption is provided by the PV system; in case of grid operator selling, it has the additional gain from the sale of ‘electricity.
As for the PV thecnology, Aires Tech provides a comprehensive support: from consultancy to plant sizing, and request for the incentive. Aires Tech also is connected to a network of banking and insurance companies which can provide customized financing programs.