The power output from PV arrays usually changes from moment to moment, albeit by only small amounts in relatively steady sunlight. Every minute a snapshot of the chosen PV array's instantaneous power output is taken and shown when you chose "Power-Instantaneous" to display . The unit used for power is kW. A technical definition of "Power" is given in a section below. On sunny days the power curve for flat PV panels will adopt a symmetrical bell shape.

If clouds move to block the sun the power output will drop immediately and this is shown by a sharp dip in the power curve. Having clouds blocking the sun does not mean complete loss of output though. Flat PV panels can make use of scattered or diffuse light and consequently useful power can still be produced in haze, uniform light cloud or broken moderate cloud cover. On days with heavy cloud the power output can, however, remain very low and close to zero.  The concentrating array relies on direct sunlight. If the concentrating array cannot see the sun then power output will drop to zero.