Backup Power Systems
Adding energy storage (a battery) to a solar power system increases functionality by keeping power on even when there is a grid power outage.
Backup systems are not the same as an off-grid system, but are similar in principle. Most backup power systems have the capacity to run a home autonomously for one to two days. In some cases backup power can last continuously, depending on the season, weather and power users.
Back-up power systems are generally configured in one of two ways:
To backup essential loads like refrigeration, lighting, and most 120V appliances and outlets, a partial-house backup configuration separates these loads from larger loads, requiring less battery power for operation.
To backup a whole house, including larger 240V appliances like water heaters, air-conditioning, and well pumps, the main electric panel can be supported by additional battery capacity.
In either configuration, the duration of backup power depends on the users, load management, capacity of the solar array, and the availability of sunlight.