In addition to what the sibling comment says, a few minutes is fine for predictable changes like sunset, but you also need enough dispatchable power online to d

In addition to what the sibling comment says, a few minutes is fine for predictable changes like sunset, but you also need enough dispatchable power online to deal with unexpected changes. What if a transmission line goes down and cuts off a big solar farm? Other plants must respond within a literal second to fill the gap and prevent a cascading failure of the whole grid like what happened in Spain recently. That doesn't have to be natural gas, batteries and hydro and even other curtailed solar plants can fill this role if there are enough of them, but we're not there yet.