Two ways exist to couple energy storage with an existing rooftop photovoltaic (PV) solar array. AC-coupled systems involve installing a PV inverter to charge the batteries. A direct connection between the PV array and a charge controller or other DC–DC converter is required for DC-coupled systems. DC coupling is more efficient if your home’s electricity load is heavier during the evening and night hours. If your home’s load is higher during daylight hours, an AC system makes sense. This is because it allows solar energy to be used directly, with any excess routed for storage in the batteries.