Future energy networks face the significant challenge of integrating inherently intermittent and variable renewable power generation while maintaining a high degree of security of supply. The increasing penetration of renewables in electric power generation aims to lessen dependence on fossil fuels and reduce carbon dioxide emissions. In this paper we formulate and study a stochastic model for large scale fast response storage and slow-to-moderate ramping generators with high wind penetration. We define a strategy for operating the storage facility and investigate the system-wide long-term effects of fast response energy storage in reducing the amount of conventional power used. In particular, we study the trade-offs between various system performance quantities, including wind spill and the loss of load probability.