The variable nature of wind and solar generation could exploit the economic potential of bulk electric energy storage (EES) systems. This paper presents an optimal planning model, a dc optimal power flow (OPF) based multi-period optimization formulation, and its software implementation. The model co-optimizes the investment in all resources including EES while taking their optimal operation into consideration. Condensed hourly profiles of wind and solar output are applied to preserve their variable nature in terms of production. In this study, a 3-bus test system is constructed to demonstrate and test the sensitivity of the planning model. The relevant economic data are compiled for different types of generators and EES technologies. The potential impact of CO2 emission price, renewable incentive, natural gas price, and energy storage cost to the future grid are demonstrated by employing the proposed optimal planning model.