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What Size Battery Do I Need For My Solar System?

Solar battery storage is becoming an increasingly popular investment for homeowners looking to make the most of their solar-generated energy. While the cost of the technology is keeping many Australians on the fence, data shows that the combination of low feed-in tariff rates and a growing interest in greater energy independence is making battery storage a more attractive option.

If you’re considering taking the leap, you’ll have to make a few decisions. A very important decision is the size of your solar battery. There are a number of factors that will influence the size of your solar battery, but we’ve broken it down into four main categories: why you want a battery, your electricity usage, your budget constraints and your new or existing solar system size.

Table of Contents
battery size or solar system - Tesla Powerwall

Why do you want a solar battery?

Not everyone wants a solar battery for the same reason. The main reasons people invest in solar batteries are to:

In many cases, its a combination of these reasons.

If you want to significantly reduce your reliance on the grid or go off grid, you’ll need a big battery. In this instance, the benefits of energy independance should be your major motivating factor as it might not stack up financially.

On the other hand, if you want a solar battery mainly for backup power to store energy for use in emergencies, a smaller battery will do.

If you want to store energy to maximise your solar energy consumption when the sun isn’t shining during the night, on cloudy days or during peak demand times (when electricity prices are higher), then it’s really a matter of how much usage you want to cover. If you want to save money on your energy bills, then you should expect to still buy some electricity from the grid at certain times of the year.

How much electricity do you use and when do you use it?

The average Australian household uses 16-20kWh of electricity per day. A typical solar household might use a third of their electricity during daylight hours when their solar panels are producing electricity, while the remaining two thirds are purchased from the grid.

In this represents your household and you want to cover the electricity you purchase from the grid, you would need a battery with a capacity of at least 10kWh.

Some families use considerably more electricity than this, especially if they have large homes with reverse cycle air conditioning or a pool. On the flip side, other homes – particularly newer homes, are far more energy efficient, using far less than the typical household.

The simplest way to estimate your energy usage is to check your energy bill. On your latest bill there is often an average daily usage figure in kWh.

battery & solar calculator - calculate system size

What is your budget?

One of the deciding factors for many people when it comes to solar batteries is the cost. While prices are slowly dropping, a battery still a sizable investment.

As a rule of thumb, residential solar battery storage prices are currently around $1,000 per kWh including installation and GST. Variables to consider include the size and brand of battery, the solar installers used to complete the works and whether additional works are required to make the battery compatible with your system (like installing an additional inverter).

While this isn’t always the case, anecdotal data largely suggests that solar + battery storage bundles offer the best value.

Some state governments offer solar battery rebates and incentives to assist with the upfront cost of solar batteries.

If you’re looking for a return on investment, many battery systems are approaching the break even point when it comes to their warrantied life but few are currently paying for themselves in energy cost savings.

While the return on investment might not be quite there yet, a solar battery can offer benefits in other ways, like peace of mind during a power outage, less reliance on the grid and a reduced carbon footprint. Afterall, many investments, like holidays, a new TV or security system offer no ROI but instead offer benefits like happiness, entertainment or security. It comes down to your personal preferences and choices—what makes sense for you might not make sense for the next person.

What size solar system do you have or are you planning to buy?

The final factor to consider when sizing your battery is the size of your solar panel array. The steps to calculate your battery size will differ depending on whether you’re looking at adding a battery onto an existing system, or installing one with a whole new system.

Adding a battery to an existing system

If you already have solar panels on your roof and want to add a battery, then the capacity of that existing array should guide your battery size needs.

If your current system only generates enough solar power to meet a small portion of your energy needs, it may not be worth purchasing a battery. After all, if you’re consuming the vast majority of your solar generation, there will be very little solar power leftover to store in your solar battery storage. Instead, it might be worth considering expanding your solar power system.

In any case, it’s best to consult an accredited solar installer to get an accurate assessment of your solar system and what size battery would be suitable.

Adding a new solar + battery storage system

If you’re starting from scratch then you can tailor both your solar pv system and battery storage system to suit your exact power needs.

Energy Matter’s solar and battery storage calculator is simple to use. It can help estimate not only the size of your solar and battery storage system, but also your weekly and annual savings. You then have the option to send this information to accredited local installers for up to 3 obligation-free quotes.

calculator battery & solar system size

It’s worth shopping around

As you can see, there’s a lot to consider when it comes to sizing a solar battery. If you have a good idea of your goals, energy usage, budget and any other potential limitations ahead of time, you will be able to discuss these with your installer to find the best outcome.

At the end of the day, deciding to buy a solar battery storage system is a significant financial commitment so it’s worth shopping around. Remember, Energy Matters can help you get quotes from multiple accredited installers to save you time and money.

So, what size solar battery do you need? It really depends on your specific needs and situation. If you have any questions or want some help sizing a system for your home, we can put you in touch with accredited solar and battery storage installers in your local area.

Get a quick solar quote, or contact us today toll free on 1800 EMATTERS or email our friendly team for expert, obligation-free advice!


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