> The odds of it being neither everywhere (grid) for an extended period of time (storage) is astronomically low.

The problem isn't that production is literally zero, it's that production is non-trivially below average for an extended period of time.

Continent-spanning grids mitigate that to a certain extent, but they're also a) expensive (purposely-idle high capacity very long distance transmission lines), and b) are essentially a scheme to trade frequent localized shortages for less frequent continent-spanning ones.

Making the grid larger to make it more reliable is also inconsistent with incentives. You install the long-distance transmission line because you're supposed to be using it to get power from far away in an emergency but then it turns out that one end of the transmission line has power which is less expensive, e.g. it gets more sunlight or has more favorable regulations or subsidies. Soon your generation is concentrated in the place where it's cheaper to build and the line gets used to average out long-term prices instead of short-term prices, leaving you with the short-term volatility but now it will affect even more people.

Then you're in more trouble. You get a month of unfavorable weather in the place where generation was concentrated, or an extended period of elevated demand at the same time as total supply is on the low side of average, and instead of a shortfall in Massachusetts you now have one in the Eastern Grid containing everything on the New York side of the Mississippi river.

And the US is one of only a few countries that spans something on the scale of a continent to begin with. Is the UK inclined to be reliant on power from the EU? Is Japan supposed to rely on China? How about India and Pakistan or Israel and any of its neighbors?

> You don't build solar plants and windfarms where prolonged periods of non-production are to be expected.

Prolonged periods of low production happen as a result of weather, e.g. Florida is suitable for solar because it's at a favorable latitude, but it also gets a lot of rain, and sometimes the rain continues for several weeks at a time.

Moreover, suppose there are places that are expected to experience prolonged periods of non-production from solar and wind. What are they supposed to do for power?

> The once in a century black swan event where distributed power production across a continent all goes down at the same time is basically the same as a blackout from damage to the power grid, which you need to be ready to deal with on those timescales anyways.

Having the same weather system affect most of a continent at the same time isn't really that uncommon. You also get nasty correlations like cloudy and still weather in the heart of the summer, causing simultaneous low generation and high electricity demand for air conditioning over wide areas.