So, you’ve decided that a solar battery is the perfect companion to your solar panel installation. The next step is determining what size battery you’d need. But with so many variables coming into play, like home energy usage, solar system size or backup capabilities, it can be daunting trying to pick the right option.
That’s where this guide comes in handy. Read on to see what you should consider before choosing a battery size, as well as a quick comparison on system sizes.
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Do I need a solar battery?
If you have a solar system and are looking for a way to utilise your unused energy, then a solar battery is a way to do that. It can also reduce your carbon footprint, as you’re relying less on energy from the grid, which may in turn; help to reduce your energy bills.
To make sure that you get the most out of your investment, though, it is important to get the correct solar battery sizing for your usage and panel system.
What size solar battery do I need? 
Deciding which size battery would be best for your solar system can be tricky. Here are a few questions that need to be considered before deciding which size would be best for you:
- Why do you want to get a solar battery?
- How much energy does your solar system produce?
- How much electricity do you use?
- How much are you looking to spend?
- Do you already have a solar panel system set up or would this be in addition to a new installation?
Why do you want to get a solar battery?
Motive is incredibly important. Some purchase batteries in the hope of saving money, while for others it is about having backup power in the case of an emergency. Knowing why you want to purchase a battery is useful to your decision in which one to get.
For example, if your goal is to have backup power, then a solar battery with backup capabilities would be more important than one with heaps of storage. If this is your goal, make sure to let the installer know that you want a battery that is capable of running during a blackout.
How much energy does your solar system produce?
Knowledge is power when it comes to choosing a battery. Because the battery’s only job is to store energy, its usability entirely depends on the energy available to charge it. Therefore, knowing how much energy your solar system produces can assist in deciding how much storage space is required.
Having a solar monitoring system can assist with understanding your usage and habits to make the most out of your investment.
Compare Solar Plans & Prices
Here are some of the cheapest solar-specific deals from the retailers on our database. These costs are based on the Ausgrid network in Sydney but prices will vary depending on your circumstances. We show one product per retailer, listed in order of lowest price first. Annual price estimates assume general energy usage of 3911kWh/year for a residential customer on a single rate tariff. Price estimates exclude solar feed-in tariff credits. These are products from referral partners†. Our database may not cover all deals in your area, and please check retailer websites for up to date information.
Here are some of the cheapest solar-specific deals from the retailers on our database. These costs are based on the Citipower network in Melbourne but prices will vary depending on your circumstances. We show one product per retailer, listed in order of lowest price first. Annual price estimates assume general energy usage of 4000kWh/year for a residential customer on a single rate tariff. Price estimates exclude solar feed-in tariff credits. These are products from referral partners†. Our database may not cover all deals in your area, and please check retailer websites for up to date information.
Here are some of the cheapest solar-specific deals from the retailers on our database. These costs are based on the Energex network in Brisbane but prices will vary depending on your circumstances. We show one product per retailer, listed in order of lowest price first. Annual price estimates assume general energy usage of 4613kWh/year for a residential customer on a single rate tariff. Price estimates exclude solar feed-in tariff credits. These are products from referral partners†. Our database may not cover all deals in your area, and please check retailer websites for up to date information.
Here are some of the cheapest solar-specific deals from the retailers on our database. These costs are based on SA Power network in Adelaide but prices will vary depending on your circumstances. We show one product per retailer, listed in order of lowest price first. Annual price estimates assume general energy usage of 4011kWh/year for a residential customer on a single rate tariff. Price estimates exclude solar feed-in tariff credits. These are products from referral partners†. Our database may not cover all deals in your area, and please check retailer websites for up to date information.
How much electricity do you use?
After you’ve considered how much energy your solar system produces, the next step is to look at how much of that energy you use in the home. If you use all of the energy produced by the solar system then there may not be any left to charge the battery. At the same time, there is no point buying a battery with a huge storage capacity if you’re not going to use it.
How much are you looking to spend?
Generally, the more energy a solar battery can store, the more expensive it will be. Therefore, if you have a tight budget, a solar battery with a huge storage capacity may not be the best financial decision.
This is not to say go and buy the cheapest battery available, because this could potentially leave you with a low-quality product. It is just a good idea to figure out how much money you’re looking to spend and shop around until you find a good quality battery in that price range. There is no point going bankrupt just to get the most energy storage the industry has to offer.
It is really important to get multiple quotes before making a purchase decision. The only thing worse than getting an unreliable battery is paying a ridiculous amount of money for said unreliable battery.
Let’s take a Sydney household with a 5kW solar system already installed. The standard four-person Sydney household consumes 20kWh of electricity a day on average. Now let’s assume this property pays an electricity usage rate of 30c/kWh, meaning it’ll cost the home $6 a day in electricity costs. The home’s 5kW solar system produces about 20kWh of electricity each day, if conditions are optimal. So, for each kWh of power that’s generated from the solar system, the household will be saving 30c/kWh. To complement its current solar system, let’s say the household decides to purchase the Tesla Powerwall 2, which costs around $14,500 for the unit plus installation (excluding the cost of an inverter). The Powerwall 2 can hold 13.5kWh of electricity, but will take around 15kWh of the solar system’s generated 20kWh to fully charge the battery, according to SolarQuotes. Of the household’s 20kWh of electricity use each day, 13.5kWh would be stored in the Powerwall 2 as opposed to relying on the grid, meaning the house would save about $4 a day, or approximately $1,500 each year. Given that the Powerwall 2 has a 10-year warranty and 15-year life expectancy, this means that the household in this particular situation would be right on the money with their purchase. If you don’t currently have a solar system installed and paid off, then you will also need to factor in the costs of solar panels as well as their potential savings from feed-in tariff credits.Case Study: Solar Battery Storage
If this household were to add a solar battery…
The payback time would be around 10 years…
Do you already have a solar panel system or would this be an addition to a new installation?
Generally, it’s cheaper to install everything all at once, as opposed to adding a battery onto a pre-existing installation. This is because all of the wiring can be done at the same time and the installer can make sure that everything is compatible. However, it is not impossible to retrofit a new battery into an existing system.
If you do already have a system installed, then you may need to check that the battery is compatible first.
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How much solar battery storage do you need?
According to SolarQuotes, the average Australian home uses about 30 per cent of their total energy consumption during the day (when their solar panels are generating energy). This is assuming that they work a 9-5 job and are not home for most of the daylight hours. Therefore, you’d likely want a solar battery storage capacity that can handle the remaining 70 per cent.
Using this data and different sized solar panels, we’ve calculated how much energy you may use during the day and how much is leftover that could potentially go towards charging a battery to then be used at night time, or during a blackout (depending on the capabilities of the battery you get).
| Solar panel size (kW) | Average daily solar energy production (kWh) | Average home solar energy use (assumed 30% of daily use kWh) | Leftover solar energy (kWh) | Suggested solar battery size (kWh) |
| 3kW | 12 | 3.6 | 8.4 | 8-9 |
| 4kW | 16 | 4.8 | 11.2 | 11-12 |
| 5kW | 20 | 6 | 14 | 13-15 |
| 6kW | 24 | 7.2 | 16.8 | 16-17 |
| 10kW | 40 | 12 | 28 | 27-29 |
General guide only. Assumes 1kW solar panel produces 4kWh electricity a day and households use only a third of the energy produced by solar panels a day.
The information above should be treated as general only in nature. For a personalised assessment for your home solar system, it is best to get in contact with a reputable installer who can take your individual energy usage data into consideration. Remember, the best battery option is going to be the one that works to your needs, budget and lifestyle so be sure to compare a couple of quotes before making a purchase decision.
To see some of the solar installers that may be available in your area, check out our guide below. Here, we show the best-rated installers as voted by everyday consumers in our annual satisfaction survey.
Compare Best-Rated Solar Installers
Image credits: anatoliy_gleb/Shutterstock.com, petovarga/Shutterstock.com
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