The case study that demonstrates this is Denmark, which has about 50% of its energy produced locally from renewables, mostly wind. They plan to increase this to 84%. They hardly had to overbuild, and they sell the excess capacity to their neighbors. Even if the overcapacity wasn't sold and was wasted, it's still much cheaper than nuclear.
This shows us that a bigger country could easily get >80% from renewables without storage. Two reasons. First, more terrain means more variability cancelling from wind. Second, solar cancels out wind, and Denmark has very little solar. Solar and wind are significantly negatively correlated, because it's less windy in Summer.
You can do even better by having a network of countries, each selling overcapacity.
Storage or gas makes up the small remaining shortfall. Luckily battery costs are declining on a super-linear learning curve.
I'm all for nuclear power, it works fine and is far better than fossil fuels. But I'm more for renewables as a mass scale solution. It's cheaper and we can have it sooner.