What is 3-phase power?

What is 3-phase power?

Source for this info: https://www.solarquotes.com.au/blog/home-batteries-3-phase/

Three-phase is a type of grid connection. It describes how your home is physically connected to the grid. All grid connected homes in Australia are either:

  • single-phase
  • two-phase, or
  • three-phase

Single-phase: Most Australian homes have ‘single-phase’ electricity. This means that they have one live wire to their home carrying all their electricity. If you have single-phase, you can ignore this post and carry on with your day.

Two-phase: Two-phase supplies are rare, but some people have them. Two-phase means there are two live wires going into your home. If you have two-phase, 2-phase battery systems have similar issues to 3-phase battery systems.

Three-phase: As people get bigger homes and more powerful appliances, such as large air conditioners and pool heaters, they may need more power than can flow down a single wire. For this reason, more and more homes are getting ‘three-phase’ connections. three-phase means that you get three live (or active) wires instead of one. It follows that you can have three times the power coming into your home. If you have three-phase power, the phases are red, white and blue. Your single-phase appliances run off one of those phases. Any large, three-phase appliances connect into all three-phases. As electric cars become common, more people will start to upgrade to three-phase so they can charge the car more quickly.

If you buy the wrong battery system for your three-phase home your electricity bill will not go down nearly as much as you expect. And with the economic return of battery systems being pretty marginal in even the best case scenario, it is super important that your battery gives you the best returns possible.

The bad news is: The wrong (or misconfigured) battery system on a three-phase home will only reduce grid electricity use on the battery’s phase. It is therefore essential that you buy a battery system that is capable of offsetting your grid electricity consumption charges on all three-phases.

The good news is: Most battery systems can do this. You just need to check that the one you buy works optimally with your three-phase supply. The difference between a 3 phase battery system that reduces your bill on all 3 phases and one that doesn’t is often 2 current transformers (CTs). They cost about $30 each.

In his article on Solar Quotes (https://www.solarquotes.com.au/blog/home-batteries-3-phase/) Finn Peacock warns to dig deeper if a supplier tells you that the battery system will work just fine on your three-phase supply. But you need to dig deeper. You need to make sure that the battery will work optimally on your three-phase supply.



Summary

If you have a three-phase supply and want to install batteries your options are vast.

Finn Peacock's advice If you are starting from scratch:

  • If you  want to install as much solar PV and battery power as possible, then consider configuration 1.
  • If you are starting from scratch and are happy with 5kW of solar inverter power and 5kW of battery power, then a single-phase battery inverter, AC coupled with 3 consumption CTs is a good choice.
  • If being able to charge the batteries from the solar during a grid outage is important to you, then you need a single-phase solar inverter (configuration 7). Otherwise I always recommend a three-phase solar inverter (configuration 5), as they handle voltage rise issues better.

Advice If you are retrofitting batteries to an existing system:

  • When retrofitting, your choices are constrained by what you already have installed (unless you want to throw your existing solar inverter in the bin). For most people a single-phase battery inverter with 3 consumption CTs like configuration 5, or configuration 7 is a good choice.
  • If you are retrofitting a battery and want bags of battery power available to export because you believe it is your duty to support the grid, then a three-phase battery inverter is for you (e.g. configuration 9).

Or if it all looks a bit too much, simply engage an experienced solar+battery installer, who can decide  the best design for you. Just make sure you are clear in your requirements. Tell the installer:

  1. If you want self consumption on one or all phases
  2. If you want backup on one or all phases
  3. If you want to charge your batteries from your solar panels when the grid is down
  4. How many batteries and solar panels you want now or in the future

Then your installer will know which of the 16 configurations to work with (refer to https://www.solarquotes.com.au/blog/home-batteries-3-phase/,) or might invent a whole new one just for you.