How Much Power is Lost from a Solar PV System when Clouds Block the Sun?

The following graphs of half hourly measurement of the energy generated by a large shopping centre rooftop solar PV array, in Johannesburg, South Africa, taken during the recent very rainy/cloudy period over November/December 2022, show just how much clouds affect the energy generated, from one moment to the next, and also how erratic that can be.

During normal full, uninterrupted sunshine, a solar system should produce a very characteristic sinusoidal (bell shaped) curve, over each day, which is only evident in one instance in the snapshots shown above.

The area under each curve is the accumulated energy which will be available for use. Clearly on some days, during that very cloudy period, a lot less energy was produced than is possible under ideal conditions from such a system.

One can compare that to an obviously relatively cloudless period earlier in the year, where the distinctive sinusoidal shape of solar energy generation is much more evident.