What can the Blue System operate to provide electrical power during flight?

The Blue System on the A320 is designed as part of the aircraft's electrical distribution system, and its ability to operate during flight is critical for maintaining electrical power when needed. The emergency generator is specifically engineered to provide electrical power in essential situations, such as during an in-flight failure of primary power sources. When the aircraft's engines are running, the emergency generator can be activated, allowing it to supply power to important systems and components. This capability is crucial for ensuring that the aircraft can continue to operate safely and efficiently, even in the event of a failure in the main electrical sources.

In contrast, conventional batteries and solar panels are not used as primary sources of power during flight for the A320. While auxiliary power units (APUs) can provide power when the aircraft is on the ground and when starting the main engines, they are not a primary electrical source for in-flight operation. Thus, the emergency generator stands out as the correct answer due to its role and functionality within the aircraft's electrical architecture.