Which of the following is a type of alternative source used with UPS systems?

The correct answer encompasses all the listed options because each one represents a viable alternative source that can be used in uninterruptible power supply (UPS) systems.

Batteries are the most common component of UPS systems, providing immediate, reliable backup power during outages. They store electrical energy and release it as needed, ensuring that critical devices remain operational without interruption.

Flywheels offer another innovative form of energy storage, utilizing mechanical energy to provide backup power. They work by spinning a rotor at high speeds, storing energy in mechanical form and releasing it quickly when needed. This method is often lauded for its ability to handle short-term power outages with high efficiency.

Fuel cells convert chemical energy directly into electrical energy, providing a clean power source that can be sustained over longer periods. They only require a constant supply of fuel and can be used to support various types of loads alongside conventional battery systems.

By including all these technologies, UPS systems can enhance their reliability and adapt to various energy needs, making it effective to recognize that all the options listed are applicable.