The optical system is composed of the lens parquets and the secondary optical element (SOE) which is mounted on the PV receiver. The optical system determines the key performances of the high concentration module since it determines the three following fundamental parameters:
– Transmission factor;
– Angular acceptance;
– Irradiance uniformity on the cell’s surface.
The higher the transmission factor, the higher the module’s output power. The higher the angular acceptance, the higher the tolerance with respect to manufacturing errors and defects and with respect to tracking errors and the higher the energy yield (since a higher acceptance enables the capture of a bigger amount of solar energy, particularly the so-called “circumsolar radiation”). The higher the electromagnetic field’s uniformity on the cell, the better cell’s conversion performance.
It is therefore clear that the important objectives are the maximizations of all the parameters:
– The angular acceptance and the field uniformity can be increased by designing the primary and secondary element as a whole with non-imaging optic design methods, obtaining free form optical elements. For example a method like the Köhler integration method can be used for synthesis.
Other important objectives are:
– The realization of a refractive optic system with a concentration of at least 1000x to demonstrate the feasibility of a high concentration solution based on lenses;
– The realization of a high throughput SOE manufacturing line able to demonstrate the feasibility of a low cost free form SOE;
– the demonstration of a high reliability and low cost anti-reflective multifunctional coating process for secondary optics and front glass.