In response to the high market deviation penalties caused by the intermittency and uncertainty of photovoltaic (PV) power generation, while avoiding the high investment and operational costs associated with self-built energy storage, this paper proposes a robust optimization strategy for time-of-use leased energy storage participating in the frequency regulation market for photovoltaic power plants. This strategy aims to enhance the market revenue of PV power stations through a light-asset, low-risk approach. First, a time-shared capacity leasing mechanism is designed according to the diurnal intermittency characteristics of PV output. Then, a two-stage robust optimization model is established to account for the multiple uncertainties of PV output and market prices. By introducing a budget conservatism parameter, the leased capacity configuration is dynamically optimized. Subsequently, duality theory is applied to transform the two-stage robust optimization model into a mixed-integer linear programming problem, which is solved using the CPLEX solver to obtain the optimal leased energy storage capacity plan, thereby providing operational decision support for plant operators. Finally, validation using measured data from a PV power station in Ningxia, China, demonstrates that by adopting the proposed operation strategy, the PV power station can achieve net comparable to the self-build model after covering its energy storage leasing costs, while also reducing deviation penalty fees. Additionally, it significantly lowers initial investment pressure and operational risks, highlighting its significant value for engineering applications.