You are conflating the electricity producers with the grid. The grid itself actually saves money by installing storage, when compared to upgrading links, and do

You are conflating the electricity producers with the grid. The grid itself actually saves money by installing storage, when compared to upgrading links, and does so when it can. As to, if they do not need the power, why should they buy it? Well, there are two reasons, one is that everyone else on the grid already gets to, so it would be anti-competitive to not allow it for the little guys, and the other is that someone will always want power, so it makes economic sense to buy the power and build storage to offset it and make money through arbitrage.