<< Click to Display Table of Contents >> Navigation:  Project design > Shadings > Calculation and Model > Treatment of the Albedo component

We can consider that for a given azimuth, the albedo  (ground reflection of "far" terrain) is visible by the collectors only if no close obstacle is present at the ground level.

Far shadings

With far shadings, you can manually choose the fraction of albedo to be taken into account, according to the distance of the "horizon" obstacles.

If the obstacles are far enough, like a mountain, the sun has the opportunity to illuminate the terrain in front of the horizon. If the obstacles are rather close (forest, buildings, etc), the terrain between the obstacle and your system will  receive (and re-emit)  less irradiance for the albedo contribution. PVsyst gives the opportunity to reducing the albedo contribution manually.

Moreover, the albedo contribution will diminish with the height of the obstacles, and become null for an horizon line higher than 20° (value adjustable in the Hidden parameters).

Near shadings

For the near shading, we use an analogy with the albedo calculation in the transposition models  (see Hay model).  We suppose that for a given azimuth, the albedo contribution is proportional to the part that would be "seen" below the azimuth point, between the horizontal plane and the prolongation of the collector plane.

Therefore, we integrate the shading factor at zero height (presence of an obstacle or not), over the portion of the sphere "under" the horizon, comprised between the horizontal plane and the plane of the collectors. This is of course a questionable hypothesis. By the way, please remember that for non-vertical planes, the energetic contribution of the albedo is weak in the global incident energy, and that errors in its estimation will therefore only have secondary repercussions.

As for the diffuse, this integral is not dependent on the sun's position, and therefore constant over the whole year.

Albedo contribution in big systems

For sheds (rows) arrangements, this evaluation is quite realistic: only the first row is "seeing" the albedo, so that the albedo shading factor will be  (n-1)/n  (n = number of sheds). The albedo loss is a significant contribution to the global shading losses.

Now many people have doubts about the albedo coefficient for their site. For big systems, we understand that this contribution is negligible on the yield result.

However the albedo is part of the transposition (GlobInc) value. As the Performance Ratio is referenced to GlobInc, a higher albedo value will not change the Yield, but reduce the PR !