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intermittency
Intermittency
Some renewable resources, particularly wind and to some extent solar power, present special challenges to utilities because they are intermittent, that is, their precise production levels at any given moment cannot be reliably forecast (but often their production levels can be forecast with substantial predictability hours or days in advance). All utilities are required by law or contract to keep their systems in exact balance: that is, load must exactly balance resources at all times. Utilities have, or make arrangements for, a variety of tools to ensure that the system is balanced. It should be noted that the intermittency of a generating resource does not “look” any different to a utility system than the intermittency of a given load, which is likewise not possible to predict with perfect reliability. However, utilities have many more years of experience dealing with, and therefore forecasting, intermittent loads.
A utility and renewable developer can enhance the value of a renewable resource by making arrangements to have the resource “firmed” up, typically by arranging to have it twinned to another more flexible (dispatchable) resource. In most parts of the country, wind power projects are firmed through very flexible gas fired turbines. In the Northwest, hydropower can be used to a certain extent to firm wind power. The hydropower system is not quite as available although, for firming as was originally thought due to other competing needs.
