This is fantasy. Electric car battery production is 0,3 terawatt hours a year. Britain uses about 1650 twh of energy in a year. There isn’t enough raw materials, like cobalt, in the whole word to have any meaningful battery buffering. And any large electricity storage would make electricity very expensive = you couldn’t build it. The best and only way is to store energy before generation, like all current coal, gas, nuclear and hydro do.