It doesn't have to exceed the power purchased rom the utility. Many grid tie systems don't, and some meters even charge customers in both directions.
Nearly every utility user puts electricity back in to the grid at 100 or 120 times per second, in the form of bad power factor. It's a less extreme version of using the grid for energy storage, or slow response time from a generator. Putting extra electricity in during the day and using more at night is a much greater burden on the utility company than bad power factor or slow generator response, but it is really the same concept.
Wouldn't the induction motor when used as a generator work against the bad power factor from existing induction motors in appliances like refrigerators? Or does it not work that way? I once read that an induction motor will work as a generator with an exactly right sized capacitor used with it. All loads must be non reactive for this to work.