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. Many new battery technologies are being investigated for use in electric vehicles. When commercialized, these new batteries will benefit PV systems as well.
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. A number of different models are available, from basic to sophisticated. Desirable features include low-voltage load disconnect, field adjustability and provisions for a finishing charge. 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, as set forth in NEC Article 690.