Solar Power Battery Systems – AC vs DC coupled and grid network restrictions
You may be considering solar and battery storage and the Tesla Powerwall 2 is one of the most famous battery solutions on the market. A fantastic product in its own right but due to its built in battery inverter it may restrict your system design.
When installing batteries, what’s the difference between a hybrid Inverter (DC Coupled) VS an AC Coupled solution (Adding battery to non-hybrid inverter e.g., Tesla Powerwall 2)?
Solar panels produce DC power and this is the power batteries also store. A solar inverter converters this DC power to AC which we need for our appliances and devices. With an AC coupled solution you are converting the AC power back to DC to store into the battery and then back into AC so you can use it. Essentially you are double handling the power and there are some losses with this conversion of around 2%. With a DC coupled solution using a hybrid inverter you are using the DC power directly from the solar panels to charge the batteries and then converting what is required into AC power.
AC coupled battery solutions such as the Tesla Powerwall 2 are convenient options for those with an existing “standard” or “non-hybrid” inverter. Although great for retrofitting, you should know that this type of battery could restrict your options in the future and a hybrid inverter solution could be a better option.
For singe phase properties (Most common power supply for residential and very small commercial)
If you are installing solar on a single phase property and want to add batteries in the future, we strongly recommend a hybrid inverter. Especially if you are considering a system that needs a solar inverter larger than 5kW. If you install a standard 8kW inverter and you have single phase power it may be very difficult/expensive to add a battery without replacing your inverter.
If you are thinking about installing solar and may want to add a battery now or in the future one of the biggest potentially limiting factors is the networks distributers 10kW inverter capacity limit allowed on single phase properties. This is pretty much universal across Australia now and it may make you reconsider AC coupled battery options such as the Tesla Powerwall 2. This is because these types of batteries have a built-in inverter which can restrict the amount of solar panels you can install.
AC Coupled example – Single Phase
With a an AC Coupled solution such as a Tesla Powerwall 2 the maximum size solar system you can have and claim the STC rebate is typically a 6.66kW. This system produces approximately 27kWh per day and the battery stores up to 13.5kWh so for a lower user with a bill around $500 per quarter and conservative energy consumption at night, this may well be an adequate solution. If you have no more available roof space for additional solar panels then it could be the most viable option. Alternatively, if you are a larger user or thinking of adding additional appliances in the future e.g., Pool, AC, Electric Vehicles. This system may not be enough and as you are up to the inverter capacity limit there is very little you can do to cover the extra load. This is why you might consider a hybrid inverter (DC Coupled) solution instead so you can add more solar panels (See below).
Hybrid Inverter example (DC Coupled) – Single Phase
For three phase properties (Most common power supply for commercial and large residential properties)
Three phase power gives you much more flexibility and essentially three times the capacity allowance for adding solar and battery storage. If you are lucky enough to already have three phase power, providing you have the roof space you can have up to 40kW of solar PV and battery storage of 90kW+ with three phase hybrid inverters. These larger residential systems can cater for power bills of over $3000 per quarter. Not everyone will want or require a system that large but we can tailor a solution to your exact needs. We may be able to offer a three-phase upgrade for clients currently on single phase power, this typically costs around $3000.00
AC Coupled solutions are less restrictive with three phase supply but the same principles apply. Only if you are a very high user or intend on maximising your saving potential (and renewable energy contribution) would an AC coupled solution be particularly restrictive, but it is certainly still worth considering. For example, a three phase property could have a 15kW solar inverter with 19kW of Solar PV (Panels) and still have 3 Tesla Powerwall 2’s (40.5kWh capacity).
We hope this information has been helpful. For more information and advice, contact our friendly team today.