It's the same problem at any scale, from a house in Las Vegas to a regional electric grid.
The average household in Las Vegas uses about 30 kilowatt hours of electricity per day.
If we are being generous, the capacity factor of solar is 33%.
Las Vegas solar panels produce daily, on average, in kilowatt hours, eight times their nameplate wattage. A 4 kilowatt solar array will produce 32 kilowatt hours of power on an average day. Bingo. Enough for a house. (Your mileage may very. Probably for the worse.)
Making a house that gets half its power from solar energy is easy. You get enough solar panels to cover your household at it's maximum demand, say when the air conditioner is running flat out, you are cooking lunch on your inductive stove, you are doing your laundry, and the heat pump water heater is running. That's more than 4 kilowatts, but go with it. Solar panels are inexpensive these days, or so I've heard.
Then you size your batteries to carry you through the evening and into the next morning until the sun is high enough in the sky to start generating electricity again. 26 kilowatt hours ought to do it. Last I looked, $22,000 is about right for those batteries if you have an electrician friend.
When that solar system can't carry you, especially on the colder, cloudier days of winter, you simply rely on fossil fuels to keep you going.
Getting to at least 98% reliable 100% solar power (which isn't that great as it means seven days a year of extreme electricity shortages) is another problem entirely, requiring ludicrous amounts of storage, whatever that storage medium is, be it batteries, hydrogen, magic beans, whatever you've got.
The wretched reality of solar and wind power is that outages occur over large areas as do large surpluses. When you've got baskets full of zucchini your neighbor has baskets full of zucchini too, more than you or they can use. When you don't have zucchini neither does your neighbor.
You've got a similar problem with grain, but grain can be stored for a year without too much fuss. Put it in a silo. It's not so simple with zucchini or electricity. Or hydrogen, for anyone who cares.
Coal and nuclear power don't work that way. When one power plant goes offline other power plants continue on and it's possible to obtain near 99.9% grid reliability. The zucchini is always available, all year.
That's not quite the case with natural gas, which depends upon pipeline supplies. When the pipeline fails so do all the gas plants attached to it., including the gas plants propping up those solar and wind follies. Ask Texas.
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