Maximum energy yield of PV surfaces in France and Italy from climate based equations for optimum tilt at different azimuth angles

In the present paper, the problem of the determination of yearly maximum energy producibility in terms of optimum tilt angle for solar surfaces is addressed with reference to 216 locations in France and Italy. Original correlations are proposed to calculate the optimal surface slope as a correction parameter to be applied to the local latitude angle. The correction factor formulas are based on local climate conditions and have been inferred from local monthly insolation data (12-year global and diffuse irradiance, PV-GIS-SARAH platform). An optimization problem is solved aimed at maximizing the yearly collectable energy by a sloped surface, in a range of azimuth values (from South Facing to East Facing), for all the selected locations. Different equation forms have been investigated and compact and accurate formulas have been developed able to provide the optimal tilt as a function of latitude, surface azimuth and clearness parameters. The accuracy of the proposed formulas resulted in a correlation coefficient with respect to the "exact" tilt angles higher than 0.93 for azimuth angles till 60 degrees. Proposed formulas allow up to a 4% increase in collectable solar energy, corresponding, as an example, to a virtual increase in PV module efficiency from 21% to 21.8%.