Do You Really Need A 3-Phase Battery To Backup Your 3-Phase Home?

Today’s post explains that no matter how hard you pedal, if you take two wheels off your tricycle, it won’t go anywhere.

In other words, a single-phase battery won’t power a three-phase appliance.

So whether you have a large ducted air conditioner, medium-sized bakery machinery or small industrial roller door, the most common battery backup systems simply can’t run a synchronous 3-phase load.

And, of course, there are always some exceptions I’ll detail later…

What The Hell Is Three Phase?

You may have heard people mention electricity in phases. They’re talking about whether you have 1, 2 or 3 active supplies coming from the street. While almost everything inside your house runs on single phase, there may be a few big-ticket items, like air conditioning or EV chargers, using all three supplies; they’re 3 phase appliances.

It’s one of the first things a savvy solar salesperson will ask you, and to help answer the question, we put together this handy guide in our even handier FAQ section.

We should rename it the CAQ for Commonly Answered Questions because these aren’t inane filler for a website. They are real queries from real people we wrote real answers for.

Single Phase Batteries Are Easy.

Market leaders like Fronius, Sungrow & GoodWe all offer very solid grid-connect solar battery systems.

Single-phase offerings cover the broadest variety of models and brands. In fact, top-quality brands like Enphase batteries and Tesla Powerwalls don’t offer three-phase units at all.

The primary advantage of a single-phase battery-backed system is good power surge capacity. Whatever the specified capacity, all of the firepower is aimed at one output, which is important when you’re trying to start a motor like a fridge compressor or rainwater pump.

To be honest, most people with a 3-phase home will be quite happy only backing up a single “essential” phase during an outage.

Three Phase Batteries Are Less Common.

While they used to be quite rare, as we recently outlined a much broader range is now available.

Generally, people don’t want to back up three-phase appliances. They are, by nature, large energy users for which you’d need a massive and expensive battery capacity.

However, the arrangement of your buildings or switchboard location might dictate that you need a three-phase battery system because rewiring the whole house is not an option.

Most 3-phase battery systems have a limited surge rating because roughly one-third will be available to run any given single-phase circuit. For example, a 10kW nameplate will only deliver 4kW for 5 seconds to an unbalanced load.

A Single-Phase Battery Will Not Backup A 3-Phase Solar Inverter

If you have a 3-phase solar inverter and the single-phase Tesla Powerwall, an extended grid outage will still be problematic because the Powerwall, even if you buy three of them, cannot form a synchronous 3-phase supply to reboot the solar inverter. This is true of any single-phase battery that’s AC coupled to a 3-phase solar system.

When the grid goes down, you have whatever energy is stored in the battery, and it won’t be replenished until mains power is restored.

However, if your solar power is provided from a single-phase inverter, Powerwall will happily keep the power on to that solar inverter, provided the equipment is sized under 5kW or controlled correctly by the commissioning electrician.

A Single-Phase Battery Can Backup All The Single-Phase Loads On A Three Phase House

If you have a 3-phase house but you’re happy to lose the use of your 3-phase loads in an outage, a clever electrician can set up a contactor arrangement that can parallel all your wiring to be backed up by a single-phase battery system.

Imagine taking the back wheels off your trike and putting them beside the front one, even though you’ll need to balance things carefully, it’s possible to ride it like a unicycle.

The same approach can be used for a 3-phase EV charger. It would be possible to top up your EV when it’s sunny, although I would suggest a manual changeover arrangement for this, as it would be too easy to just drain the house battery into the car.

But it’s easier to just put all your essential loads on one phase and simply back up that phase.

Do You Really Need A 3-Phase Battery System?

Even though Australia’s grid is 99.998% reliable by law, many people are investigating batteries for both economic and security reasons.

If you have a 3-phase house, seriously consider whether you need a 3-phase battery. Can you put your essential loads on the same phase and happily ride through outages with only that phase backed up?

Your choice will depend on whether your solar inverter is single or three-phase, how critical your 3-phase appliances really are and how much money you’ve got to spend.

Original Source: https://www.solarquotes.com.au/blog/3-phase-battery-trap/