AC Coupled V DC Coupled
Battery Storage Solutions Compared
AC Coupled Battery Systems
AC-coupled batteries are a very popular choice when retrofitting a battery storage system to an existing solar panel array.
This is because the battery effectively sits on its own circuit with its own inverter / BMS (Battery management system).
As a lot of people who decide to retrofit a battery are signed up to the government’s Feed-in Tariff scheme, using the AC-coupled battery allows them to have a battery installed without affecting their feed-in tariff.
Although there are a lot of merits to the AC coupled system there are also some drawbacks/trade-offs for the convenience.
Batteries store power in DC and Solar panels generate DC electricity, it is the job of the inverter to convert this, with an AC coupled system the solar panels generate DC electricity which is then converted to AC, the AC power will then need to be converted back to DC power by the battery inverter / BMS to be stored and then converted back to AC when the battery discharges power to be used in the home.
This creates unnecessary conversions, each time you convert the electricity you will lose a bit of power.
The inverter/s is the component within the solar and or battery system that will fail regardless of manufacturer warranty and need replacing usually around year 10, therefore it makes sense to install as few as possible for your solar panel array.
Based on the above we would therefore only recommend AC-coupled batteries on retrofit projects.
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DC Coupled Battery Systems (also known as a hybrid inverter)
DC coupled or Hybrid batteries as they are also called, have become very popular in recent years, especially on a new project where the client does not already have solar panels installed.
A DC-coupled battery installation means that the battery is on the DC side of the Solar inverter and therefore the DC power generated by your solar panels can be stored as DC until you need to use it.
This cuts out the unnecessary conversions that an AC-coupled system causes thus improving the efficiency of the solar panels.
The DC coupled system also requires less hardware so it can be cheaper to install and comes with less potential maintenance costs in the future.
Should you decide you would like the option of power in the event of a power outage the DC coupled system can offer much simpler solutions and usually the opportunity to keep the solar running through the outage enabling it to keep the battery topped up.
The DC coupled system does have a couple of drawbacks, one of them is the requirement for the batteries to be relatively close to the inverter.
It’s also worth checking the inverter and battery are universal in the sense that they work with other brands, this means should you change the inverter manufacturer for example in the future the battery cells will still work.
We would recommend where possible the use of DC-coupled batteries on new installations and existing ones if there is no Feed-in tariff.
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