Whether you currently own or are looking to invest in a solar panel system, adding a solar battery is a good way to maximise the amount of solar energy you can use. But with so many different solar batteries on the market, how do you decide on the right size for your system?
To choose the right sized solar battery, you’ll need to consider your average energy usage, the size and output of your current solar system and your budget. When deciding on a solar battery, you should also consider the number of people and appliances in your home and whether that number will increase in the future.
To help you decide on what battery size to get, this guide contains information and recommendations to help you decide on a solar battery size based on your own needs.
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What to Consider When Choosing Your Solar Battery Size
There is no one-size-fits-all solar battery size. You have to consider your household’s energy usage, the size of your solar system or array, your motive for adding a battery, your budget (and even the rebates and incentives you’re eligible for), and your location.
Let’s talk about each one in detail.
Your Budget
Budget is naturally your first consideration when investing in solar batteries. Although solar batteries are a great way to generate long-term savings with an existing solar system, the upfront costs are still a consideration for many, even with rebates and incentives available.
Many states in Australia do have rebates for solar batteries to help offset the upfront costs and reduce how much solar batteries cost. Check your state’s policies concerning solar battery rebates and incentives.
Your Energy Usage
Your current energy usage is one of the biggest contributing factors when deciding whether or not a solar battery is for you. If you have points of high energy usage during the weekend, for example, a large solar battery storing energy during the week can help offset the amount of power you draw from the grid.
Average daily energy consumption for Australian households is between 8kWh (single person household) and 20kWh (multi-family household) according to the CSIRO. Electricity usage varies according to household size, as well as energy usage habits and choice of heating and cooling appliances.
Homes with solar power usually use around one-third of their electricity during the day, when their solar array is running. The other two-thirds is drawn from the grid during peak energy periods, coinciding with evening and night-time. That two-thirds from the grid is what you typically want to base your solar battery size on.
Another way to get an idea of your energy usage is to look at your energy bill and compute your average daily usage (divide your monthly bill by the number of days in that month). If you have an smart energy meter at home, you can also get a more accurate picture of your electricity consumption.
Some devices and home appliances which consume more electricity are swimming pool pumps, electric hot water systems, electric heating, and large air conditioning systems. If there are over five people in the house, and you’re running several high-consumption appliances, your average energy usage may be up to 50 kWh per day.
Your Motive for Adding a Battery
Your motive for adding a battery to your solar system can help you decide on what battery size to get because not all households with a solar PV system actually get or need a battery. Only those who want to store the extra energy from their array install solar battery storage.
For instance, if you simply want to maximise your solar energy consumption or make some savings, you just have to match the energy you’re getting from the grid. However, connecting to the grid at certain times of the year may still be more cost-effective. A smaller battery may do if you have limited daylight or sunlight hours due to location.
On the other hand, if you want to reduce dependence on the electricity grid or go off-grid completely, a larger battery is the way to go. Another reason to use a solar battery is to provide backup power for blackouts or emergencies, which doesn’t require a large battery unless blackouts are frequent in your area.
The Size of Your Solar System
One of the main indicators for your battery storage size is the size of your solar system. This is because the batteries can only store the energy available to them, which is dependent on the size of your solar array.
When customers ask if a solar battery is worth it, one of the leading factors influencing the answer is your solar system’s size.
Here are some approximate figures for the maximum recommended solar battery size:
| Energy Usage | Solar System Size | Maximum RecommendedSolar Battery Size |
| 11-15 kWh | 2 kW | 4 kWh |
| 11-15 kWh | 3 kW | 7 kWh |
| 11-15 kWh | 5 kW | 9 kWh* 40 kWh** |
| 11-15 kWh | 7 kW | 8 kWh* 65 kWh** |
| 11-15 kWh | 10 kW | 8 kWh* 65 kWh** |
| 16-20 kWh | 2 kW | 3 kWh |
| 16-20 kWh | 3 kWh | 6 kWh |
| 16-20 kWh | 5 kW | 13 kWh |
| 16-20 kWh | 7 kW | 12 kWh* 55 kWh** |
| 16-20 kWh | 10 kW | 11 kWh* 90 kWh** |
| 21-25 kWh | 2 kW | 2 kWh |
| 21-25 kWh | 3 kWh | 5 kWh |
| 21-25 kWh | 5 kW | 12 kWh |
| 21-25 kWh | 7 kW | 16 kWh* 23 kWh** |
| 21-25 kWh | 10 kW | 15 kWh* 70 kWh** |
*most cost-effective option
**maximised energy independence (will yield 3 or 5 days of energy autonomy for 11-15 kWh and 16-20 kWh energy consumption respectively)
A solar energy professional can give you a customised estimate of the best solar battery size for your unique system, so it’s always best to get an individual calculation performed. However, this gives you a guideline on what size solar battery to consider.
Your Location
Location will also affect the size of the solar battery you should purchase because environmental factors can affect the efficiency of your solar system, including your battery. If you live in a constantly shady area, your panels may not generate enough energy to warrant the cost of solar battery storage.
Solar batteries may seem like a de facto great idea, if you have solar panels, a solar battery is great too. Unfortunately, this isn’t the case, and there are a lot of factors to consider. Depending on the location of your home, the direction of your solar panels and your general climate will all affect how efficiently your solar panels work and how helpful a solar battery will be.
If you are unsure if a solar battery is worth it where you live, it’s best to ask for help. Contacting a solar energy specialist will give you a better understanding of whether a solar battery will make its money back and be worth the investment.
How to Calculate What Size Solar Battery You Need
You can calculate your average daily energy consumption by dividing your monthly bills by 30 for each day of the month on average. You can use a solar battery calculator to determine how big your battery needs to be to offset your electricity usage based on your solar panel system or roof size.
The first part of the process is estimating your daily energy usage. You can use an energy monitor if your home has one, or you can manually calculate it by checking your monthly bill and dividing that amount by the number of days in that month.
So that will usually look like:
average daily consumption = monthly bill ÷ 30 days.
From there, you can use a solar battery calculator to determine exactly how big your solar PV system and battery needs to be. These calculators use information like the size of your solar system and your roof in combination with an average daily energy consumption to recommend how big your battery needs to be to reduce the amount of energy you are drawing from the grid.
How Many Solar Batteries Does Your System Need?
Most homes will have between 2 to 3 solar batteries; however the number of solar batteries your system needs depends on factors such as your energy usage, motive, and size of your solar system.
Another factor that will affect how many solar batteries you need is the type of solar batteries you have. There are two main types of solar batteries: lead-acid and lithium-ion batteries.
DoD stands for Depth of Discharge or the amount of charge used up by your battery, and you never want it to go to 100%. Different types of solar batteries have different depths of discharge. The depth of discharge affects the life of the battery as well as the amount of energy it can store in its lifetime.
Lead-acid batteries have 50% DoD, while lithium-ion batteries have 80% DoD. In short, a high DoD equals more energy. That means you will need more lead-acid batteries than lithium-ion batteries because of the former’s lower DoD.
Solar Battery Size Guide
Here is a size guide for the more common solar PV systems in Australia. Here we have outlined the most common kW size solar systems and approximately what size solar battery will offer the best value (or best energy autonomy).
Note that these figures are estimates only, and the right solar battery size for you will always depend on your unique circumstances.
What Size Solar Battery Do I Need for a 3kW System?
For a 3 kW solar PV system with 5-10 kWh daily energy consumption, you can use a 4 kWh battery to maximise returns or a 22 kWh battery to maximise energy independence (and yield about three days of energy autonomy).
For 11-15 kWh daily energy consumption, use a 4 kWh battery. For 16-20 kWh (the average daily energy consumption in an Australian household), you need a 3 kWh battery.
What Size Solar Battery Do I Need for a 5kW System?
For a 5 kW solar PV system with 5-10 kWh daily energy consumption, you need a 4 kWh battery to maximise the returns or a 35 kWh battery to maximise energy independence. For 11-15 kWh daily energy consumption, choose a 7 kW battery.
For 16-20 kWh (the average daily energy consumption in an Australian household), you need a 6 kWh battery.
What Size Solar Battery Do I Need for a 10kW System?
For a 10 kW solar PV system with 5-10 kWh daily energy consumption, you need a 4 kWh battery to maximise returns or a 35 kWh battery to maximise energy independence. For 11-15 kWh daily energy consumption, you need an 8 kWh battery to maximise returns or a 65 kWh battery to maximise energy independence.
For 16-20 kWh (the average daily energy consumption in an Australian household), use an 11 kWh battery to maximise returns or a 90 kWh to maximise energy independence.
Related Questions
What Is kWp in Solar?
kWp stands for kilowatt Peak. It is the nameplate rating of solar PV systems. It refers to the amount of power produced in bright sunshine or under standard laboratory test conditions.
Disclaimer:
This article is published in good faith and for general informational purposes only. JFK Electrical does not make any warranties about the ongoing completeness and reliability of this information. Always seek personalised advice on solar energy to ensure any recommendations suit your property and scenario.
John Lyons, the owner of JFK Electrical Solar & Air, started his career in the electrical industry in 1997. With years of experience gained in the industry across multiple continents, he relocated to Australia and decided to specialise in solar and air conditioning. After deciding he wanted to be closer to his family, John began his own local electrical business in Mandurah, using his extensive knowledge and training in the industry. At JFK, John’s number one goal is to provide tailored solutions to his customers. And thanks to his experience and commitment to his customers, JFK Electrical is now one of the most trusted local businesses in Mandurah for solar and electrical services.
