Batteries - DC Power Storage

We need electricity at night and on cloudy days as well as on the sunny days. If tapping into the utility grid is not an option, a battery backup system is necessary for energy storage.

However, batteries do lower the efficiency of a PV system, because only about 80% of the energy that goes into them can be reclaimed. They also usually need to be replaced every 5 to 10 years, take up considerable floor space, pose a few possible safety problems, and require periodic maintenance.

Nevertheless, batteries provide a reliable way to store PV electricity for later use. Like PV cells, batteries are direct-current devices that are directly compatible only with DC loads. Batteries can also serve as a power conditioner for these loads by regulating power. This allows the PV array to operate closer to its optimum power output.