Why can't we store excess electricity from power plants?

Your question is very good. Since electricity is always a product that is produced, supplied and sold at the same time, i.e. the charge determines the electricity production, there are no such large batteries yet. If one day there was a very large capacity battery in the world, then the generator could produce electricity at full charge when needed and store the excess electricity. In this way, the generator charging rate reaches 100%, the power consumption rate of the factory will also be reduced, as well as the consumption of coal and water, which is the greatest benefit to the business, the environment, and humanity. As an electrician, I really hope that one day!