The electric sector is expected to grow substantially into the future, although electric power supply technologies and demand patterns may evolve in significant ways. Changes in the composition of electric supply, such as deployment of variable renewable energy (VRE) technologies, are a key component of studies of future energy system transitions.  In addition, long-term analyses of global energy transitions often involve major changes in the extent and temporal patterns of electricity demand, such as electrification of passenger vehicles and building heating/cooling services. The emergence of modular, flexible electricity storage technologies may have a profound impact in managing temporal variability of electricity supply and demand introduced by these drivers. A comprehensive analysis of long-term energy sector transitions requires a multisector model that considers the electricity sector in the physical and economic context of the rest of the energy system. The simple approaches used by multi-sector models for representing electricity supply and demand, such as meeting average annual demand or meeting an aggregated demand profile with a combination of baseload and flexible peaking capacity, are not adequate to represent these changes.  More complex models of the electric power sector often lack the interconnections to explore the dynamic interplay between co-evolving electricity supply and demand sectors.  Here we present recent work to incorporate grid-based electricity storage into electric sector dynamics of the Global Change Analysis Model (GCAM).  When then use this new capability to explore key drivers for electricity storage deployment and operational outcomes for the power sector, taking advantage of our integrated modeling approach.  Finally, we quantify the value of grid storage in these alternative futures.