Coupling modes

The main types of grid-tied battery systems are AC coupled, DC coupled and hybrid.

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AC coupled requires an additional rectifier/inverter that converts power from the AC power source to DC power in order to charge the battery. This is the most common type for a retrofit.

When it is time to discharge the battery, the battery uses the inbuilt inverter to convert the battery’s DC energy back to AC so that it can be used again by the appliances in your home.

So, an AC coupled solar battery uses three stages of conversion therefore making it less efficient. It is easier to install as a retrofit to an existing solar system and can be flexible in the location. It can also be charged from the grid or your solar.

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In contrast, DC coupling a solar battery only requires power conversion once rather than three times. It uses DC power from the solar panels to charge the battery. It then converts the DC power from the battery back to AC power to be used by the home.

Both of these steps normally happen by what is commonly called a hybrid inverter. A hybrid inverter is simply a battery charger, and a solar inverter put together in one box. This will make it more efficient since there are less conversions. However, it is not ideal for retrofits and only surplus PV can store energy in the battery.

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Hybrid systems are neither AC or DC. Instead, they take the benefits of both. The inverter is applicable to both on-grid and off-grid PV systems and can control the flow of energy intelligently. During the daytime, solar generation can provide electricity to the property, charge the battery, your EV or export to the grid. At night the inverter can discharge energy from the battery to support the load.