PV*SOL Expert 6.0 - Manual - Valentin Software

4.1 Radiation Processor
In the supplied climate files, radiation to the horizontal plane is given in watts per square
meter of active solar surface (radiation to the horizontal plane). The program converts this
to the tilted surface during the simulation in the radiation processor and multiplies it by
the total active solar surface. Possible shading reduces the irradiation.
The radiation processor must split the radiation into diffuse and direct radiation. The
splitting is carried out according to Reindl's radiation model with reduced correlation.
[Reindl, D.T.; Beckmann, W. A.; Duffie, J.A. : Diffuse fraction correlations; Solar Energy;
Vol. 45; No. 1, p.1.7; Pergamon Press; 1990]
When converting the irradiation onto the tilted surface, the anisotropic sky model by Hay
and Davis is used. [Duffie,J.A.; Beckmann, W.A.: Solar engineering of thermal process;
John Wiley & Sons, USA; second editions; 1991] This model takes into account an
anisotropy factor for circumsolar radiation and the ground reflection factor entered in the
program (Albedo).
To convert the direct share of solar radiation in relation to the PV array, taking into account
the active solar surface from the direct solar radiation to the horizontal plane, the position
of the sun relative to the PV area must be calculated from the height of the sun, solar
azimuth, PV array tilt angle and PV array azimuth. The height of the sun and the solar
azimuth are determined on the basis of the date, time and latitude. The tilt angle and
azimuth of the PV array are entered in the program.
The radiation without shading results from the direct and diffuse share together.
The radiation to tilted PV array surfaces takes into account possible shading of the array.
The shading is also split into diffuse and direct radiation. The diffuse share is determined
proportionally to the shaded area independent of the height of the sun and the solar
azimuth. The direct irradiation to the PV area is reduced by the duration of shading in each
calculation step.
The radiation to tilted PV array surfaces is reflected at the module surface. The direct
radiation share is reflected depending on the position of the sun and the incident angle
modifier of the module. The incident angle modifier for diffuse radiation is set in the
program. The resulting radiation is the radiation minus reflection.
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