What is included in secondary reserves?

Secondary reserves are typically characterized as resources that can be deployed to meet demand after primary reserves have been exhausted. They are designed to be available within a certain timeframe to ensure grid reliability. In this context, the correct answer identifies the 30-minute operating reserves as part of secondary reserves.

This 30-minute timeframe is critical because it represents the resources that can be made available quickly after the primary reserves respond to fluctuations in demand or contingencies such as sudden generator failures. These reserves can be brought online in a relatively short period to maintain the balance between supply and demand.

Conversely, other options like 15-minute, 1-hour operating reserves, and emergency reserves represent different categories of resources with specific response times or operational purposes. For instance, 15-minute reserves are typically classified under primary reserves due to their rapid availability, while 1-hour reserves may be regarded as a different tier of backup that has a longer response time. Emergency reserves serve a different role, mainly activated in crisis scenarios rather than for routine operational support.