You have to account for increasingly frequent continent-scale weather patterns which can last for weeks in extreme cases. "Weeks" is a figure I heard a few time

You have to account for increasingly frequent continent-scale weather patterns which can last for weeks in extreme cases. "Weeks" is a figure I heard a few times in the media, but even "days" is a herculean task considering we're presently at "minutes" or worse. Note also that part of solving for emissions means "electrifying more applications" which means it's not sufficient to store days or weeks of today's energy demands, but rather days or weeks of future energy demands which will be much higher (e.g., today our entire transport industry isn't electrified--in the future our grid will need to supply the energy to move cars and trucks and trains which means the overall demand is much larger and consequently we'll have greater storage demands).