Backtracking Performance Ratio
With the backtracking strategy, even with a comparable yield, the PR is significantly higher than with a similar system without backtracking.
Remember the definition of the PR for a grid-connected system:
PR = E_Grid / (GlobInc * PnomPV)
With a backrtracking system, the incident energy GlobInc is decreased, due to the misalignment of the tracking orientation. Therefore the PR is "boosted". The reason is that the loss due to the misalignement is not accounted in the PR.
As a contrary, with non-backtracking systems, the GlobInc is optimal, so that the PR is lower. A part of this irradiance is lost due to the mutual shadings; the shading loss is accounted as a global loss of the system, included in the calculation of the PR.