In this paper, a power system with an automatic generation control (AGC) in two contiguous areas are studied to demonstrate speed deviation of a generator due to photovoltaic (PV) power fluctuation in both time and frequency domains. The system is linearized and modeled in state-space representation. The change of the PV power is defined as the input of the system, and the change of speed deviation is defined as the output of the system. The analysis using a unit step function input illustrates that increased change of PV power can affect the speed deviation of generators. Changed PV power on another side can lower overshoot of the change of speed deviation in the study area. Moreover, the system is excited with the sinusoidal waveform input signal imposed on dc signal, and with the scaled solar irradiance data, respectively. In the case of using sinusoidal waveform input, the results show that the magnitude of change of speed deviation can be a function of amplitude and frequency, but is not a function of biasing. In case of the system which has been inputted by using scaled solar datasets, the changes of the speed deviation arc observed when the PV power fluctuation occurs.