This ars technica article on energy storage provides a concise summary of the challenge of energy storage and the current technology options. Focusing on the power needs of datacenters, the article describes the intermittency problem associated with renewable sources (in normal language, the sun doesn’t necessarily shine and the wind doesn’t necessarily blow at times that coordinate naturally with electricity demand).
Energy storage is the Holy Grail of the electricity system. Even if we did have dynamic pricing to enable decentralized coordination between supply and demand, it would be highly unlikely to match up perfectly all the time. Storage bridges that gap. Storage also changes the market power dynamic; if I have a storage option I can buy more when it’s cheaper and use it when it’s pricier. That alternative creates a substitute for generated on-demand peak power.