The simple answer is BATTERIES. I live near a "battery" surrounded by wind farms in western Michigan https://en.wikipedia.org/wiki/... . It is a 1.3 Square mile reservoir -- 110 feet (34 m) deep, 2.5 miles (4.0 km) long, and one mile (1.6 km) wide which holds 27 billion US gallons (100 Gl) or 82859 acre-feet of water. It is up-hill along the bluffs / bank of Lake Michigan. When the wind is blowing, water is pumped uphill, and when the grid needs energy, water flows downhill through reversible turbines producing over 2,000 Megawatts even if the wind is completely calm. Of course there are other kinds of batteries to buffer power demand, and wind isn't the only kind of power that needs buffering. This "battery" finished in 1973 to buffer nuclear power in the grid that includes Chicago.

Slowing down from top speed does, indeed, save fuel in jets when in no-wind or a tail-wind situations. The squared-function you mention (energy to overcome drag vs speed) is most true toward the higher end of the speed range (at the low end, a different kind of drag begins to dominate and it increases as you slow down -- allowing for the nose to rise without climbing while the aircraft slows down for landing for example). But (with no wind or a tail wind) at cruise air speeds -- slower saves fuel. This is not usually true when flying into headwinds, because the time to destination can easily increase beyond any fuel savings (think of a 100 knot True Airspeed flying into a 100 knot headwind. The ground speed would be zero. If you could go 200 knots, even at 4x the fuel burn per hour, your total fuel consumption for the trip would go down (in this case infinitely) by speeding up. Pilots and airlines and dispatch teams and flight planning software knows all of this, and generally do slow down in tailwinds and speed up (as appropriate) in headwinds to both arrive "on time" and save fuel. After all, fuel not burned is not just good for the profit for the airline.