AC or DC Coupled: What is the best solution for your Battery Storage?

Rather than write an enormous article on this complex subject we are going to try and provide a summary to from the basis of a more in depth conversation where you can learn the best solution for you if you are considering Battery Energy Storage Systems.

Key Points

• AC-coupled batteries are best if you want to add a battery to an existing solar panel system.

• AC Coupled Systems are best if you are planning to take advantage of arbitrage energy tariffs without adding solar panels. In Summary, buy from the grid when power is cheap, fill battery, use and/or sell back to the grid when prices are high, usually during peak periods.

• AC systems are less efficient due to the need to convert power between AC and DC 3 times,

• In DC systems, electricity only needs to be inverted once, making them more efficient.

• DC Systems are usually significantly cheaper due to only needing one inverter.

• DC Systems are gaining in popularity as more manufacturers develop inverters that can invert power from both the battery and the solar panels: they are known as hybrid inverters.

So whats the Difference?

In simple terms in a DC System, your solar panels produce electricity in DC. Conveniently, batteries store electricity in DC so any power produced can flow into the battery if it's not required in the home or workplace. Your house or workplace requires AC, because that is what is provided by the National Grid and if you want to sell back to the Grid it must also be in AC. So your DC stored from your battery or power produced from your Solar panels must be converted from DC to AC using the inverter.

In an AC coupled system the battery receives energy from solar panel after they have been converted to AC. The problem is batteries can only store in DC so a second Inverter is required to convert the energy back from AC to DC. However when your home or workplace requires power it must be in AC, so the inverter has to convert the power back to AC . All this changing from AC to DC, back to AC results in an efficiency drop of about 9% over a DC Systems

Pros and cons of AC coupling

• The main advantage of AC-coupled solar battery systems is they are much easier to install on an existing system. The reduced labour makes this a better and cheaper solution in the vast majority of retrofit cases

• AC batteries can charge directly from the Grid. This allows you to take advantage of some demand response tariffs where you can buy energy when its cheap (late at night for example) and either use it or store it and sell back to the Grid when prices are high. You can now buy Batteries linked to AI Software that does this automatically.

• The main disadvantage of AC coupling is that inverting electricity multiple times results in a loss of deficiency of around 9%.

• In an AC Coupled system the battery energy storage system has an additional inverter which leads to higher upfront purchase cost than an equivalent DC coupled system of the same size.

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Pros and cons of DC Coupling

• DC-coupled solar energy systems have the advantage of being more efficient than AC-coupled systems.

• DC coupled systems often make a lot of sense for new installations as they are cheaper to purchase.

• DC coupled systems are hard to retrofit to an existing system.

• You might not be able to take full advantage of some energy providers variable rate tariffs

If you are interested in an new solar installation or have an existing solar array and want to add some battery storage why not give one of our experts a call to see how we can help you. We fit quality storage solutions from manufactures such as Enphase, Solar Edge and Give Energy.

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