One of the thorniest issues that seemed to be facing large, utility-scale PV systems was sudden changes in PV system output due to the movement of single clouds on an otherwise sunny day. Now it seems that this issue has been resolved favorably, in an economical manner.
Figure 1 shows a particularly excruciating example of solar variability.
This kind of sunlight graph put chills down the spine of utility engineers and caused a major setback for the deployment of large-scale PV systems. PV output responds instantaneously to such changes. Such variability also compares unfavorably to solar thermal electric (STE) systems, which have natural thermal inertia, which damps out the sudden changes. STE system installers gladly took note and publicized the PV problem to everyone making a choice between STE and PV.