This paper describes power modulation of a photovoltaic (PV) generator for frequency regulation. The generator has a small electric double-layer capacitor. The capacitor absorbs rapid fluctuations of PV generation, and allows the generator to change its output at a limited ramp rate. The capacitor voltage is kept at a specified value to maintain adequate energy storage. The generator output is modulated in proportion to the frequency deviation. The responses to step and periodic changes of the frequency are examined. The voltage control is modified so as not to affect the frequency control. It is shown by numerical simulations that the PV generator cooperates well with conventional generators. Some experimental results are demonstrated to validate the proposed method.