Electric Grid Frequency Regulation

There is a market for electric grid frequency regulation.

http://www.miller-mccune.com/environment/vehicle-to-grid-a-new-spin-on-car-payments-36697

Regulation fine-tunes the balance between supply and demand to make sure that the electricity in outlets has a frequency of exactly 60 hertz at all times. ...
To provide regulation, an electricity generator must adjust output up or down based on a hard-wired electronic signal that grid operators send out 400 times a day. ...
The world market for regulation services is $6 billion — $1.5 billion in the United States and $4.5 billion overseas ...

http://www.energycentral.com/reference/whitepapers/contact_vendor/103334/Grid-Scale-Frequency-Regulation-Using-Flywheels

The grid frequency regulation function addresses the balance between the network’s load and power generated. The intent is to maintain the grid at the target 50Hz or 60Hz operating point. When there is more load than generated power, frequency drops, and vice versa. The system operator generates a signal, Area Control Error (ACE), based on the difference between load and power.

... open bid auction markets for frequency regulation services. A large part of the United States and some countries utilize such markets.

Regulation Service requires the abilities of a sophisticated network -- because there are over 5 million Regulation requests per year.

Current RTO and ISO Compensation Practices Article in Federal Register.

Frequency regulation service is the injection or withdrawal of real power by facilities capable of responding appropriately to a transmission system operator’s automatic generator control (AGC) signal.