Quality inverters provide sine-wave electrical output that conforms to utility power quality standards in terms of harmonic content and voltage and frequency stability established for the power grid. Utility-interactive inverters incorporate precise control circuitry to ensure power quality and quick disconnect of the PV system from the grid in the event of a utility outage to protect service personnel. And, some inverters now include dc ground-fault protection, which disables the PV array in the event of a short to ground. Batteries are needed in stand-alone systems to store electricity for use at night and during periods of low sun. Batteries are connected in series to provide the necessary system voltage, and in parallel to provide the required amount of storage rated in amp-hours at the system's voltage.
Charge regulators manage the flow of electricity into and out of the storage batteries.
These electronic devices prevent damage to the batteries by protecting against both overcharging by the PV array and over-discharging by the load. String combiners are prefabricated junction boxes that are useful to facilitate the parallel connection of the series strings of PV modules, called source circuits, which make up the PV array. Disconnect switches are needed for system servicing and personnel safety. They are typically installed on the inverter's input and output, at the array output and on the battery bank's output. Most disconnect switches also include overcurrent protection, either as fuses or circuit breakers.