Once upon a time I ((Eric Dobbs)) worked in the electrical power industry. I improved the deploy code, test automation, and continuous integration for the software in a software/hardware/services company that ultimately turned air compressors off for millions of air conditioners on the hottest days of the year. The complexities offer a compact example to illustrate how adaptive systems operate in tangled layers with different tempos and how each layer has its own needs to be able to change tempos. Moreover, the layers and tempos interact and require coordination.
A system as complex as the power grid needs slow-rolling changes. The risks of sharp changes can fry consumer electronics or trigger cascading failures in the grid itself. But the grid cannot control how high the ambient temperature will go on a given day.
Grid operators have to anticipate the need to begin a load reduction in time to accommodate peak demand.
They will also be anticipating the need to start up secondary generators.
There are combined pressures of regulatory limits on consumer electricity pricing while there are no such limits on the spot market prices for natural gas and diesel fuel which are the other most common tools for coping with peak demand.
Change has to be fast but slow, or slow but fast.
...Demand Response... wikipedia 
Demand response is a change in the power consumption of an electric utility customer to better match the demand for power with the supply. Utilities have traditionally matched demand and supply by throttling the production rate of their power plants, taking generating units on or off line, or importing power from other utilities. There are limits to what can be achieved on the supply side, because some generating units can take a long time to come up to full power, some units may be very expensive to operate, and demand can at times be greater than the capacity of all the available power plants put together. Demand response, a type of energy demand management, seeks to adjust in real-time the demand for power instead of adjusting the supply.
Residential and commercial electricity use often vary drastically during the day, and demand response attempts to reduce the variability based on pricing signals. There are three underlying tenets to these programs:
1. Unused electrical production facilities represent a less efficient use of capital (little revenue is earned when not operating).
2. Electric systems and grids typically scale total potential production to meet projected peak demand (with sufficient spare capacity to deal with unanticipated events).
By "smoothing" demand to reduce peaks, less investment in operational reserve will be required, and existing facilities will operate more frequently.
In addition, significant peaks may only occur rarely, such as two or three times per year, requiring significant capital investments to meet infrequent events.
...Utility Frequency... wikipedia
Usually 60 Hz in the US.
In practice, the exact frequency of the grid varies around the nominal frequency, reducing when the grid is heavily loaded, and speeding up when lightly loaded. However, most utilities will adjust generation onto the grid over the course of the day to ensure a constant number of cycles occur.
Modern alternating-current grids use precise frequency control as an out-of-band signal to coordinate generators connected the network. The practice arose because the frequency of a mechanical generator varies with the input force and output load experienced. Excess load withdraws rotational energy from the generator shaft, reducing the frequency of the generated current; excess force deposits rotational energy, increasing frequency. Automatic generation control (AGC) maintains scheduled frequency and interchange power flows by adjusting the generator governor to counteract frequency changes, typically within several decaseconds.
...Operating Reserve... wikipedia
In electricity networks, the operating reserve is the generating capacity available to the system operator within a short interval of time to meet demand in case a generator goes down or there is another disruption to the supply. Most power systems are designed so that, under normal conditions, the operating reserve is always at least the capacity of the largest supplier plus a fraction of the peak load.
...Peak Demand... wikipedia
Peak demand may exceed the maximum supply levels that the electrical power industry can generate, resulting in power outages and load shedding. This often occurs during heat waves when use of air conditioners and powered fans raises the rate of energy consumption significantly. During a shortage authorities may request the public to curtail their energy use and shift it to a non-peak period.
...Energy Spot Market... wikipedia
The spot energy market allows producers of surplus energy to instantly locate available buyers for this energy, negotiate prices within milliseconds, and deliver energy in a short-term timeframe. Spot markets can be either privately operated or controlled by industry organizations or government agencies.