This Solar On Demand fountain runs in direct sunlight, but has a battery unit as well which will power the fountain on overcast or cloudy days. On the solar powered mode, the fountain will run directly from solar energy; however, the pump will only work in bright and sunny conditions. On the battery mode, you can power your fountain for up to 4 hours on cloudy days or at night. A fully charged battery will power the fountain up to 4 hours. When the battery power is depleted, the system will automatically change back to solar powered mode and start again when there is sufficient sunlight. You can operate the fountain daily using the battery technology for consistent performance even in cloudy conditions, or leave your fountain off, charging the batteries for use when you want it. A wonderful combination of solar energy and consistent performance. Dry Run Protection Pump Technology – Typical pumps continue to run when the fountain is low on water or runs dry causing the pump to burn out and need to be replaced. This fountain includes new dry run protection technology so if the fountain runs low on water the pump will automatically shut off to save the life of your pump.