Solar Battery Energy Storage System: AC-Coupled or DC-Coupled

Solar battery energy storage system has two protocols, AC-coupling or DC coupling. Each has its advantages and disadvantages.

What is DC-coupling Energy Storage Systems?

In DC-coupled energy storage systems, solar components and storage batteries are connected to the module of charge controller and multi-mode inverters directly. Usually, this two modules can be replaced by the solar inverter with MPPT charge controller. In DC-coupled energy storage systems, the electricity flow is as the followings

DC to DC: The DC current generated by solar panels is stored by batteries through MPPT solar charge controller.

AC to DC: The AC current from the utility grid is alternative to DC current by the solar inverter, then stored by the batteries.

What is AC-coupling Energy Storage Systems?

In AC-coupled energy storage systems, there are two inverters. One inverter is connected to PV components, turning DC to AC. Another inverter is connected to battery, turning the DC current exceed battery to AC current.

The solar power system and energy storage system is divided into two independent parts.

Comparison between AC-coupling and DC-coupling?

Efficiency: DC-coupling ESS is better than AC-coupling ESS. Because AC-coupled system, the flow of DC current generated by solar panel to battery needs two conversion, DC to AC and AC-DC. When the power released from the solar battery, there is a DC-AC conversion again. Three times of current conversion make much more energy loss.

In general, for DC-coupled energy storage systems, the efficiency is up to 97%. For AC-coupled, only around 90%.

Costs: DC-coupling Energy storage system is lower than AC-coupling. DC-coupled system only requires one inverter. Meanwhile, there is all-in-one energy storage inverter can be optional.

Flexibility: AC-coupled energy storage system is more flexible than DC-coupling system because for the former, the solar power system and energy storage system are independent from each other. It is easy to add the new PV system or energy storage system. 

SVC POWER Smart Series All-in-one Energy storage system 

STACKED RPS SERIES Hybrid inverter with built-in batteries and MPPT solar controller   Stackable LiFePO4 battery modules and hybrid inverter module, easy capacity expansion Selectable priority between solar batteries or mains to feed the output Wide range of selectable mains input voltage Protection for over-discharge, overload, over tempearture, short circuit protection, ets Support communication interface RS232, RS485, CAN, Bluetooth

RPS SERIES Built-in batteries and MPPT solar controller Selectable priority between solar batteries or mains to feed the output Wide range of selectable mains input voltage Protection for over-discharge, overload, over tempearture, short circuit protection, ets