Adding a battery to an existing solar system is achievable through three main methods: AC coupling, storage-ready systems, and DC-coupled systems. AC coupling is the most flexible and cost-effective, requiring an additional off-grid inverter to work alongside your existing grid-tied inverter.
Storage-ready systems replace your grid-tied inverter with one optimised for battery storage, while DC-coupled systems require a new hybrid inverter to directly charge the battery with DC power from solar panels. Before adding a battery, consider your goals such as energy arbitrage, blackout protection, or participating in a Virtual Power Plant.
Also, assess your solar system's winter performance to gauge its capacity to charge the battery year-round. Consulting multiple reputable solar companies for customised quotes is recommended.
How can I upgrade my solar system?
If you have recently purchased a home with a smaller solar system or have had a 3 to 5 kW system for a few years and loved it, you may want to upgrade your solar system and add even more panels or a battery. But can you do this easily? Unfortunately this is not as straightforward as adding some palings to a backyard fence. You definitely need an experienced solar installer to assist you in this endeavour.
Overall this journey is like renovating a house, often it is easier to build a new solar and battery system, than trying to upgrade your solar system, adding bits and pieces to an existing design. However, it is possible and here are the explanations.
How to add more panels
When did you get your original panels installed?
Over time solar technology and designs have developed, as have technical standards and rules. This means that some older solar systems are not compatible with modern solar installation rules.
The period of time of concern is from 2007 to 2013. The solar panels made during this time have nothing wrong with them, but more modern solar panels are not allowed to be integrated with these panels. This means that if you bought the solar system during this time or the system, you will run into issues.
While the Government allows older systems to operate, unfortunately, these solar systems can’t be upgraded. There is one way to overcome this issue. You can create an entire new system on your roof with the modern panels, and run it separately to your old system. This approach will not make a singular system, but you will have two independent solar systems providing electricity to your home.
Sometimes the visual appearance of 2 different solar systems can look ugly on one roof – and in such a case, if your original system is more than 10 years old and was relatively small, often the suggestion from professional installers is to start from scratch.
What if I have Enphase microinverters?
Should you have microinverters, and your system is relatively new (less than 5 years) then upgrading your solar system is no issue at all, and you can add more newer watt class panels and more microinverters.
What if I have a string inverter?
You will most likely have to upgrade your inverter if you expand your solar system. The reason is either technical, meaning your inverter is not conforming to the latest technical rules if older than let’s say a few years, or it will not be able to handle the capacity to add too many extra solar panels.
Contact the manufacturer of your inverter, or a local installer or study the product datasheet to work out how much the inverter can be oversized. For example, some inverters can be oversized by 133% of what it was originally rated as. This means if you had an inverter rated at 5 kW or 10 kW, the absolute maximum wattage of panels all added up can be 6.66 kW or 13.33 kW. In many cases the inverter has already reached its maximum capacity – so unfortunately you need a new and bigger capacity unit.
On the other hand, if you expand your solar system and the total kW fits within your inverter’s power spectrum, you will not have to replace it. In this case the power class (wattage) of the panels you add needs to be very similar to the original panels.
While adding panels looks already a little bit complicated – it all gets even more technical when it comes to upgrading your solar system with a battery. So one learning from all this is to purchase the correct sized solar system initially.
Do I actually generate enough solar electricity production to charge my battery all year round?
If you have an existing solar power system, the first thing to do is to look at how much electricity the system is producing that could be supplied to charge the battery. This would be the amount of electricity the solar system is currently exporting to the grid daily.
We would recommend working this out based on the amount of power that you export in the winter months when your solar system is least productive, this will enable you to ensure your battery can be charged regularly, year-round.
If you simply look at average daily exports or peak summer exports, you will likely find that your solar system will not have the capacity to charge the battery during the winter months.
For example, if you would like to get a Tesla Powerwall (13.5kwh capacity), you would be best to ensure that you have around 15kwh of exported electricity in a day through winter. It can be ok with a bit less, but should be aware that there may be days when the battery does not get fully charged from solar (particularly rainy days). In this instance you could still charge the battery from the grid during times tariffs are low, and then discharge it when tariffs are high (peak demand period).
There are a number of smaller and modular battery solutions that may suit your situation better based on the amount of excess electricity your solar system produces from batteries as little as around 2kwh through 4, 6, 8, and 10kWh batteries with expandable options up from there as well.
What do you want the battery to do?
You will also want to consider what you actually want the battery to do when the battery is installed. What is the desired outcome or result from having a battery then consider if adding a battery to the existing solar system will achieve this or whether you need to consider other options such as increasing the capacity of the solar system to have a larger battery to suit the desired result that you are looking for.
If you just want to make use of the existing power you are generating by your existing solar system, that’s great. It is worth considering what the best solution is for your home, family and living arrangements now and in the future as batteries can be of use in a number of ways.
That is storing your excess solar power generated in the day to use during peak demand periods and overnight. For this case, it is best to consider how much power you use at night and size the battery according to this.
If you experience blackouts you may want to have the batteries provide power to the home during a blackout. If this is something you want, make sure you specify this to your solar company when they quote as not all battery solutions are able to provide blackout power.
Virtual power plant (VPP)
This is an emerging option with many innovative solar retailers where you can sign up to your energy company for them to be able to supply power from your battery to the grid and pay you a fee for the use of that electricity.
Typically, systems much under 5kw capacity do not have the excess capacity to charge even a modest battery of 6kwh on a daily basis. Most solar systems will be at least 6.6kw of panels with many solar systems of up to 10kw or larger being installed with batteries.
We would recommend getting design quotes from 2 or 3 reputable solar companies to compare options for your specific requirements and a customised solution rather than an off-the-shelf cooky cutter solution.
Do you really need solar battery storage?
A solar battery acts as an electricity reservoir. Surplus electricity from your solar panels will be held in the battery, and deployed for use when needed. While this process sounds great, it may not be needed for you. The need for a battery is influenced by solar exposure, electricity consumption patterns, grid tariffs and nuances of the solar system. The best option is to contact a trustworthy solar professional to get their opinion.
The return on investment with a battery is completely unique to each household. This is due to how much you use the electricity stored in your battery being determined by your consumption patterns. Also, do you put EV charging into the ROI calculation? In such a case, a battery’s ROI comes down significantly.
Influences on investment
There are three main influences that make investing in a battery very enticing. These are your geographical location, fluctuating electricity tariffs and government incentives. If these three factors are in your favour in your current situation, the investment is likely worthwhile. As previously mentioned, if you believe you are in the right situation, contact a trustworthy solar professional. They can provide some insight into the decision.
So how can I upgrade my solar system with a battery?
Before you worry about all the technical aspects determine your needs and have your system’s compatibility with AC and DC batteries assessed. It is definitely an area that should be researched so you understand your energy storage needs and what kind of batteries would suit them. There are two battery technologies to consider:
- AC batteries, which are usually easier to retrofit to existing solar systems as they can be connected directly to the AC wiring of the house.
- DC batteries, which require a compatible inverter to convert DC electricity from the solar panels and battery to AC electricity for use in the home.
The easiest step forward is to select an AC-coupled battery solution. There are a number of brands and options available on the Australian market including the popular Tesla Powerwall, Qcells Senec, Enphase and Sonnen.
The good news is you don’t have to touch your solar system to add an AC-coupled battery. This is a fancy way of saying you connect the battery to the 240V wires in the switchboard, add a separate battery inverter (which in many AC-coupled batteries is built into the unit), and keep your current solar inverter. A quality installer should have no problem adding an AC-coupled battery without touching your solar.
Let’s get a little bit more technical
In the AC-coupled battery solution, your PV system still uses your traditional grid-tied inverter. However, your original inverter is then paired with an off-grid inverter or ‘storage inverter’ (sometimes like in the case of Tesla – built into the unit) that works to charge the new batteries.
Grid-tied inverters (the one you already have on your existing solar system) work hand in hand with the grid. They monitor the electrical frequency and voltage of the grid and shut off if it lowers, for example in the event of a blackout. Moreover, grid-tied inverters allow you to feed energy back into the grid. As the name suggests, this type of inverter is optimised for grid usage and as the grid, as well as appliances in your home utilise AC power. A grid-tied inverter is NOT designed to charge batteries, for this, you need a hybrid inverter.
Storage-ready solar system
An approach that works for all grid-tied inverter systems, yet an approach that is the most costly, is to replace your grid-tied inverter with a storage-ready inverter. This type of inverter is optimised for a battery bank and if a consumer knew that they wanted to have batteries with their solar system from the onset, but wanted to wait a little this is the type of inverter, known as a hybrid inverter that should have been installed. Then when the customer is ready to get the battery, it simply gets added and all should work well. In such a scenario it’s important not to wait too long for adding the battery to the inverter, as sometimes technologies change.
I heard about DC power and DC batteries
Then there is also DC power, the power that is generated by your solar panels. DC power is also used to store power in batteries. If you seek to use the DC technology in your batteries the inverter is removed and replaced with one that is compatible with a battery, being a hybrid inverter. The battery is charged with the DC power generated by your solar panels. The power then goes through the hybrid converter, which converts it into AC electricity. You can then use the AC power in your home, or business, or export it to the grid.