That's not how renewables work. They don't produce electricity on demand (at least not solar and wind), their energy output is dependent on the weather. If there's no wind and no sun, they won't cover any demand spikes. Which is why baseload power like nuclear is pretty much useless in combination with renewables.
What is actually needed is flexible power that can be quickly adapted to the varying output from solar and wind. This is currently mostly done with natural gas, which we're trying to get away from. In the future, biomass, water and storage will cover that part, while demand response strategies will help reduce demand peaks during times of low energy production.