Comment by mrb

Read the article. They explain exactly how batteries can replace (yes, replace) the coal plant. In short: renewables have a hard time matching real-time demand. Clouds come. Wind dies down. What do you do? So in the past they needed that coal plant to add extra generating capacity, when needed. But now, with the batteries, the battery can store the surplus of renewables not instantly needed. Then when clouds come or wind dies done, the energy flow reverses and batteries deliver this surplus, hence smoothing supply.