Irradiance treatment: circumsolar
The treatment of the irradiance has indeed been improved.
We now distinguish a new irradiance contribution: the circumsolar (enhanced irradiance in a crown around the sun).
This contribution was previously included in the Diffuse component, and treated as such in the shading calculations (i.e. isotropically).
It is now evaluated from the Transposition models (i.e. proportional to the beam component) so that we have now 4 irradiance contributions:
Beam component, circulmsolar, isotropic diffuse and albedo.
In the shading calculations and IAM, the circumsolar is now treated in the same way as the beam (i.e. coming from the direction of the sun). This means that the Shading loss on isotropic diffuse is lower, and the shading loss on beam + circulsolar is higher. For the linear losses, these loss contributions approximately compensate each other.
But the Electrical shading losses are only related to the beam, and are therefore increased.
NB: These improvements are not so important in usual systems. They become crucial in vertical bi-facial systems modelling, for the evaluation of the back side irradiance.
This explains the differences of the simulation, in the optical contributions in the losses (shadings and IAM).
The default values of the Rserie and Rshunt PV module parameters is assumed to ensure a low-light relative efficiency of -3%@200 W/m2, with respect to the STC.
However in the Version 6, this value was not always attainable (sometimes -4 or -5 %).
This may be improved by încreasing the Rshunt, which was not done correctly in the version 6. The new version 7 ensures that the low-light performance is -3%@200 W/m2 in any case.