stand-by power source

例句：

1. 1. The generator is a stand-by power source for the hospital.
   发电机是医院的备用电源。
2. 2. The solar panel is a stand-by power source for emergency lighting.
   太阳能板是紧急照明的备用电源。
3. 3. The backupgenerator is ready to provide power in caseof an emergency.
   备用发电机随时准备提供电力，以防万一。