These systems store the energy until it is needed, for example, in powering navigational aids at night. The simplest version drives DC loads only, and may require a battery system with charge control if the loads are variable. These systems have an inverter and charge controller to drive connected AC loads. A hybrid version has one or more energy sources such as a wind or motor generator set to supplement battery charging. The PV power is delivered first to the load.
Any excess power is fed back into the grid.
These systems require synchronous inverters that not only convert DC into AC power, but also match the output power to the phase and frequency of the grid. However, the facility must pay for the interconnection. Storage systems for PV arrays provide the owner the capability of using the captured energy at night or at other off-peak times. The typical storage system is a set of batteries sized to accommodate the PV input as well as the load demand. When selecting a battery system , the designer needs to consider size and weight, cost, warranty, availability, reputation of the manufacturer, maintenance requirements, cyclic and calendar life, daily depth of discharge, temperature and environmental conditions, off-gassing characteristics, and terminal configuration.