The diesel engine must be able to follow the variation of
loads and PV power. The size of frequency variation indicates
how well the diesel and its governor maintain the balance of
active power in the system, and the size of voltage variation
indicates how well the gen-set and its voltage regulator maintain
the balance of reactive power through the generator excitation.
Under transient conditions, the frequency and the voltage will
not be absolutely constant because PVpower and load variations
change constantly.