Operating reserves comprise which of the following?

Operating reserves are crucial for maintaining the reliability and stability of the power grid. They refer specifically to the available capacity that can be deployed quickly to meet unexpected demand or loss of generation.

Synchronized reserves are the most immediate form of reserve, typically provided by resources that can respond within minutes, allowing for rapid dispatch capability. Non-synchronized reserves can respond in a longer time frame, offering additional backup once the immediate demand is met. Supplemental reserves serve as further contingency measures that can be tapped into if both synchronized and non-synchronized capabilities are unable to meet the requirements.

In contrast to the selected answer, the other options refer to various aspects of power generation and load management that do not directly encompass the definition of operating reserves. For instance, base load and peak load capacities refer to the minimum and maximum output levels of generation facilities, rather than reserves held to respond to fluctuations in demand or generation losses. Demand-side resources focus on consumer-side measures to reduce or shift energy consumption, while efficient units pertain to the performance and optimization of generation, rather than the reserve capacity necessary for reliable grid operation. Thus, the combination of synchronized, non-synchronized, and supplemental reserves represents a comprehensive understanding of the operating reserves necessary to support grid reliability.