Flat photovoltaic (PV) systems using single-junction cells, thanks to their small size and high acceptance angle of solar radiation, have had a huge dissemination in the building sector, favoring the widespread diffusion of distributed generation. The PV modules of these systems usually feature a conversion efficiency of about 20%, while new modules have reached 22%.
On the other hand, modules used in concentration photovoltaic (CPV) systems, featuring multi-junction cells, can offer higher efficiencies (currently 35%). Current concentration systems, however, are usually rather bulky and require a two-axis solar tracking system. Due to these limitations, they are unsuitable for use in the architectural-residential sector.

The research carried out in this Line of Activity aimed to find suitable solutions to promote the use of concentration systems in the architectural-residential field by addressing two different aspects of this problem.

The first concerns the size of the module. In this regard, some new optical configurations have been designed, studied and simulated, capable of drastically reducing the thickness of the solar concentrator, from tens of centimeters to a few centimeters, while maintaining a high concentration level (over 500 suns).

The second aspect addressed concerns the problem of solar tracking. In this regard, two different solutions have been studied. One solution exploits the optical transition properties of some materials to allow for solar disk tracking without having any moving parts. This solution has been tested only in a very preliminary phase and the concentration level that can be achieved is presumably between a few suns and a few dozen suns, a value that is in any case decidedly higher than that (<1) of luminescent concentrators based on a similar principle.

The second solution involves the development of a new solar tracking system integrated inside the CPV module. The state of the art of solar trackers consists of electric motors with gears and various ancillary components that involve high costs and reliability problems related to wear, aging and atmospheric agents. To overcome these limitations, the development of a tracking system has been started that uses low-cost actuators based on shape memory alloys (SMA), which do not use joints, gears, and bearings, but which, when heated for example by the passage of electric current, deform by stretching or contracting with considerable excursions in relation to their size and weight. In addition, a new pointing sensor has been developed, also low-cost, based on LED technology, that allows to detect the position of the sun within a wide viewing angle (up to 60°). The combined use of the new sensor and SMA actuators has allowed to significantly simplify the control scheme used in conventional trackers, which resulted in cost reduction and greater reliability.

Finally, the first results related to the development of the new tracking system integrated into the CPV module are presented, as well as some case studies on the energy producibility and economic advantages that can derive from the development of hybrid photovoltaic modules (i.e. based on Si PV cells and CPV cells) that integrate the tracking system designed by RSE.