The term of art is "frequency response" for "stabilization." This is the system's ability to respond to shocks. Though, the need for frequency response is driv

The term of art is "frequency response" for "stabilization." This is the system's ability to respond to shocks. Though, the need for frequency response is driven primarily by very large "traditional" power plants. For example, in WECC, the single largest contingency is the loss of a 4GW large nuclear complex. So, should the cost of maintaining this frequency response be borne by the system, or by that specific contingency? Smaller power plants, and smaller transmission lines have smaller contingencies. Following demand is a different function called frequency regulation. Regulating frequency down (curtailing output) is easy for solid-state inverters (including solar), though regulating up (increasing output) is, as you note, more difficult for generation (but very easy for load).