Can You Add A Battery To Your Existing Solar? Here’s How To Tell

With all the interest created by Australia’s shiny new Cheaper Home Batteries Program, we’ve seen enquiries soar for everything electric. One of the most common questions is: do I need to replace my existing solar system to get a battery? Here’s how to tell if it is possible to stick with your legacy solar, and how to add a battery to it if so.

As early adopters, Australians are finding themselves at a new cutting edge with the federal battery rebate prompting a rethink, rejig or total replacement of their existing solar power.

There are 4.136 million solar power systems in Australia and to be honest, about 12 million different options for adding a battery. Getting the right answer for your place will involve a trained expert visiting before install day.

A call centre sales numpty, using an aerial photo, simply cannot assess a battery location, existing solar wiring or your switchboard.

Saving Good Investments

Roughly speaking, I’ve noticed $12,000, 12-year-old solar systems turning up second-hand for twelve hundred bucks. Realistically they’ll sell for half that.

While panels that originally cost $1000 each really shouldn’t go to waste, as prices fell, lots have proven to be poorer quality.

If yours was a cheap basic system then it’s not likely worth saving, especially if the array is taking up prime real estate.

If you recognise these units then yours is likely junk too.

However, if it’s working, the greatest value in your old solar power system is simply that it’s already there. In most instances, the paid labour required to remove and/or reinstall costs more than the used gear is worth.

This arrangement was never any good to begin with, particularly given LG Chem’s issues.

I’ve always maintained that the best quality equipment and installation is the best value, because it’ll prove reliable in the long term. When Australian labour rates for installation are such a large part of your outlay, bolting cheap gear to your roof, or cheap batteries to your wall, is a fool’s errand.

What About New Systems

If your solar is only a few years old, there’s a good chance you can just add a battery, but like any solar system, it’ll need an inverter, which is where things can begin to get tricky.

Whether it’s inside or adjacent, the inverter’s main function is to turn DC electricity from solar or battery into AC, which is useful to your house and the broader grid.

However with rooftop solar now Australia’s largest generator by installed capacity, AEMO are imposing rules, so inverters must respond to external network controls.

The federal battery rebate calls for inverters and batteries that are on Clean Energy Council approved lists, but don’t worry, if yours doesn’t appear it may just have fallen off. So long as it’s not been delisted, a legacy inverter will suffice.

There comes a time when a salad of cheap gear like this may need to be unified.

With Great Power Comes Great Responsibility

Whether it’s using emergency backstop or flexible exports, we occasionally have to put a lid on our roaring renewable success.

So new systems must have a consistent internet connection or be choked off with a default low fixed export limit, which frankly doesn’t help anyone.

Depending on network rules you may be obliged to bring all your equipment up the latest standards. While Victoria allows existing systems to be grandfathered, SA wants tighter control, sadly creating more e-waste because of it.

If you have a faithful old SMA workhorse for instance, it’ll likely get a bullet, but at least Fronius have the ethics to make their last ten years of production retrocompatible with a simple firmware update.

The other possibility is a smart device like CatchControl with a quick and dirty shutdown to make any old equipment behave. 

Without external controls, sadly these incredibly reliable SMA Sunny Boys are all rendered obsolete.

Inverter Capacity Counts

With 17 different electricity networks to comply with, there’s no consistent answer, but generally speaking you’re allowed 10kW of inverter generation capacity connected to each phase of your supply.

For some, this is a ceiling. Others allow a further 10kW of battery inverter (20kW total) but then they still have an overarching 30kVa site limit.

A hybrid inverter may count toward both allowable totals for generator and battery inverter, or you may get even more capacity with a network investigation and special agreement.

What Are The Options?

Dumb fixed export limits have been the standard for years so cheap installs simply used a 5kW inverter instead of a smarter, larger system with a customer consumption meter to impose a limit.

So let’s assume you have a single-phase supply, 5kW inverter with 6.6kW of solar. Here’s a few scenarios:

Add a 5kW hybrid inverter with battery and DC-couple more solar

• This fills your 10kW maximum permissible
• Utilises your existing inverter (and monitoring if you keep the same brand)
• More solar yield
• More solar oversizing on the existing inverter too¹
• Black start ability if there’s a prolonged outage
• May run your legacy solar as a minigrid, so it’ll help during a daytime outage
• Backup capacity will be limited to 5kW – lower surge rating, so backup for essential circuits only.

Add an AC-coupled battery

• Feasibly more than 5kW peak capacity
• Simply stands between your existing system and the grid.
• Allow you to add more panels to the legacy solar inverter.²
• No black start – you’ll need the grid to recover if the battery goes flat.

Add a hybrid inverter, with battery, configured as an AC-coupled system

• Feasibly more than 5kW peak capacity
• Utilises your existing inverter (and monitoring if you keep the same brand)
• Offers more surge rating for “whole home” backup
• Permissible under the 10kW ceiling
• No black start

Replace your 5kW inverter with a 10kW unit

• Can use the existing solar array as an input
• Add a further 8 to 13kW of solar on the roof
• Black start capable
• Excellent surge rating for “whole home” backup.

If you have a Sungrow system it may be eligible for Sungrow’s trade-up program.

For 3 Phase Customers

The range of new hybrid inverters available in 10, 12, 15 and more kilowatts, mean you don’t have to rewire the whole place to have things connected to a single-phase backup circuit.

If you have single-phase solar, a 3-phase battery hybrid isn’t out of the question, however keeping things balanced across phases may present a problem.

Get Professional Help

I have shorter hair now, arguably because I’ve been tearing it out over increasingly complex energy systems.

The best way forward is to get a package that plays well together. Usually this means solar, monitoring, battery, EV charging and hot water control from the same manufacturer ecosystem.

However there are systems which can be built from components and integrated together. The main thing you’ll need is a savvy installer to connect all the network approval dots, cross the technical tees, terminate the wires and do the testing.

Click here, add some notes about your existing system and we’ll find you someone who’s just the ticket.

For more on the federal battery rebate, read about the finalised rules.

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