Solar power, obviously, is greatest during midday and you get nothing at night.
Wind power, in most of North America does the opposite. In midday, wind is down to very little. But wind starts picking up around 7pm, reaches peak levels just before sunrise, then goes back down to very little by midday.*
This means that the power provided by a good mixture of solar and wind power in combination is fairly constant on a 24 hour basis. You can check this out on the various real time graphs published by ERCOT in Texas. Conveniently, they have a graph showing Combined Wind and Solar for both the current day and the previous 24 hours and projected 24 hours. These data are available to power plant operators for them to make daily plans. The combination of the two sources averages above 15Gw, reaching above 20Gw at midday (because solar power is peaking, and so are air conditioning needs).
As I'm writing this, it peaked today at noon at 23,850 Mw. Last night at 1am, it was up to 22,034Mw at 1am. The low point was in between at 8am at 14,012 Mw because the wind had ramped down but the solar hadn't kicked in. Tomorrow they are projecting a similar combined low of 12,225 Mw at 8am. The evening low point at 9 pm is similar, they are projecting 13,465 Mw tonight. In between the low points it appears as a fairly smooth graph, no doubt the result of averaging enormous numbers of inputs, and biased toward the high side. Mostly above and around 20 Gw but with two predictable dips daily below 15 Gw around 8am and 9pm where solar and wind don't perfectly mesh. That they mesh at all is some kind of miracle. Without wind power there would be nothing* at night, and without solar there wouldn't be much to help with peak loads. (*Except other renewable sources that haven't been well developed yet, including geothermal power and tidal power.)
At night, wind power carries more and more of the electric load in Texas, often reaching above 50% at wee hours 1-5am when the electric load is at its lowest. Texas has 40Gw of installed nameplate wind capacity, so if the wind is really blowing we get all that.) This isn't very useful for handling the midday air conditioning peak loads (solar power is best for that) but nevertheless it does save fuel as gas and coal power plants regularly burn much less at those times when wind is really cranking, which is handled by regulations, technical means, and a competitive electricity market. Wind is the cheapest power source so it underprices everything else when there's lots of wind, saving fuel and reducing CO2 emissions. The fuel and emissions savings don't depend on when the fuel is being saved. If the wind isn't blowing 1-5am, dirtier sources must be used instead.
*Many many people don't understand that wind picks up at night in the central continental plain. You see lots of articles saying that wind is stronger during daytime. That may be true in a lot of places, but not in central North America.
Here is one authoritative source.
Here is a graph from that study. Wind power is clearly greatest from midnight to 5am.
The complementary nature of wind and solar is something that I would never have expected. For quite awhile I had been worried that wind wouldn't be all that useful, and that the whole RE paradigm might fail for lack of energy storage.* I had often been cowed by the oft repeated statement that wind is intermittent. But it's clear that the massive amount of wind power in Texas is being used quite effectively. Wind Power is Real. I still think it's a kind of miracle too. The actual power source is a force of nature we are merely tapping.
(*We should be using only (or using much more) energy storage and demand reduction to deal with regular gaps in Renewable Energy (RE), instead of fossil power, and then even larger gaps. Using fossil power more and more as just backup is much better than using it all the time. We may need fossil backup for a long time. It's imponderable to think of energy storage good enough to last for weeks of useless weather. But the better fossil plants can be maintained or mothballed for typical or extreme emergencies as we meet more and more needs from low polluting technologies, like wind and solar power.)
We could use even more wind power effectively by shifting more energy uses (eg EV charging and energy intensive manufacturing) and even human activity to the late night hours. That would especially make sense in Texas summers, having triple digit temperatures midday, meanwhile it's quite nice after midnight, typically upper 70's. We should be sleeping in the daytime and stay up all night. This is not a new idea. (Nor, for that matter, is wind power. It predates coal, gas, and nuclear. It powered ships in 4000 BCE.)
Opening up the Texas grid to the rest of USA would also help utilize even more wind power, for those areas which aren't lucky enough to have fairly consistent winds at night.
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