For modern solar systems, batteries are emerging as must-have devices. Especially in Tasmania, where the sun isn’t always shining, batteries can allow you to store valuable solar energy for later use. Getting the correct solar battery size for your household will allow you to maximise your investment. Although choosing the right size can be complex, once you consider your budget, personal energy usage and solar system, you can be in the best position to make the correct choice. Keep reading to also discover our strategies for finding the perfect size, including the key calculations to help you get it right.
Why Does Solar Battery Size Matter?
Selecting the correct battery size for your solar system is crucial to its overall effectiveness. A battery that is too small won’t have the capacity to store enough energy to meet your household’s needs when the sun isn’t shining. This means you’ll have to draw additional power from the grid for more electricity.
On the other hand, if you purchase a battery that is too large, you may be left with excess stored energy that you won’t use. However, many solar batteries can be charged from the grid during off-peak hours, helping you make better use of their larger capacity and minimise costs. Additionally, larger batteries also qualify for higher government rebates, helping to offset the initial investment.
Ideally, a perfectly sized battery will achieve all of your energy goals. It will allow you to store excess solar energy generated during the day for use at night or during power outages, ensuring a continuous supply. Every household has different energy needs depending on various factors, and it’s important to understand how to choose the right solar battery size for you.
Image credit: Sofar Solar
How to Choose the Right Solar Battery Size?
Deciding which battery size is perfect for you can be complicated. To understand the right capacity for you, it is important to address the following factors:
Budget
Assessing your budget should be one of your first considerations. Solar batteries are a major investment, and although they are a great way to save money long-term, they have significant upfront costs. Particularly as you think about their size, with larger batteries commanding higher installation costs. Below is a table representing the average battery cost by capacity.
| Battery Capacity | Cost |
| 1-5 kWh | $1,380 – $6,900 |
| 6-10 kWh | $6,780 – $11,300 |
| 11-15 kWh | $11,550 – $15,750 |
| 16-20 kWh | $16,000 – $20,000 |
Luckily, there are rebates available for Tasmanians that can help lower the cost. The Australian Government’s Cheaper Home Batteries Program is available to all eligible Tasmanians and can reduce your new battery installation by 30%. More information on the program can be found here.
Energy Usage
Your energy demands will significantly impact your chosen battery size. If you have low energy demands during the day, you may not even need a battery, because you are using all of the electricity your panels produce. On the other hand, a larger battery may be needed if your energy consumption is high, reducing the need to rely on electricity from the grid, and allowing you to use your solar power, particularly at night.
When discussing energy usage, it is also helpful to recognise the different times of the year. For instance, if you check during summer, you may not account for the added consumption during winter, when more frequent heating appliances are used. You may also need to consider your future energy consumption. For example, installing a new air conditioner may require you to increase your daily kWh.
Motive for adding a battery
Understand your reasons for adding a battery. This can help guide your decisions and the battery size to suit your needs. If you want to save money, but are also comfortable using the occasional electricity from the grid, then choosing a smaller battery could be a smart decision. However, if you want to use as much energy from the sun as possible and reduce your reliance on the grid, then you may need to spend more on a larger battery.
You may also have other motivations for getting a battery – such as its ability to power your home during a blackout. Depending on the frequency of blackouts in your area, you may only need a smaller battery.
Size of the solar system
Because your solar battery is storing energy directly from your panels, you should be aware of how the size of your solar system factors in. Larger solar systems generate more electricity, meaning a larger battery is usually needed to store all of the excess energy for later use. Conversely, if you have a small solar system size, then there’s no reason to buy a larger battery if you’re only producing low levels of electricity.
Location
Different weather conditions can affect how well your entire solar system is operating. For instance, if you are somewhere with excessive sunlight, you may choose to buy a smaller battery because your panels generate more consistent electricity.
Conversely, if you live in a house heavily impacted by shade or cloud, you may need a bigger solar battery. This is because you will be more reliant on your storage when your panels receive less sunlight to produce energy. It will be important to assess all of these environmental factors with your local installer when deciding the best solar battery size for you.
How To Calculate Your Solar Battery Capacity?
If you are looking to calculate the right battery capacity for you, then follow our four steps below:
Step 1: Understand your daily energy consumption.
You will typically be able to find this statistic on your electricity bill, displayed in a bar chart with your usage in kilowatt-hours (kWh) per day. The average Tasmanian household has a daily energy consumption of approximately 23.61 kWh.
Step 2: Determine the number of days the batteries should sustain the load without solar input.
This refers to the period you expect to rely solely on stored energy. You might only need enough storage for overnight use, or you may want to depend more heavily on your solar battery system.
For example, if your goal is to store enough energy to power your home overnight (around 12 hours), that would account for approximately 0.5 days.
Step 3: Understand the depth of discharge (DoD).
This is the metric indicating the percentage of a battery’s total capacity that can be used before you need to recharge. For instance, a battery with a 50% DoD can only use half of its capacity before a recharge is required.
Your Depth of Discharge will depend upon your solar battery type, with the majority of lithium-ion batteries (the most commonly-used type) having a DoD of 80%.
Step 4: Make the calculations.
Use the following formula with the values you’ve identified:
- Battery storage capacity = (Total Daily Energy Consumption)/(DoD × Days of Autonomy)
Using the example above:
- Total Daily Energy Consumption: 23.61 kWh
- Days of Autonomy: 0.5
- Depth of Discharge (DoD): 80% (or 0.8 in decimal form)
- Battery Storage Capacity = 23.61 / (0.8 × 0.5) = 9.4
So, based on this example, you would need a battery capacity of approximately 9–10 kWh.
Solar Battery Size Guide
If sorting through calculations isn’t for you, then you can also refer to our handy guide below to help simplify the process:
- Smaller 10-15 kWh: Suitable for smaller homes or light energy users. It can be great for those who want to offset some daytime energy consumption.
- 15-20 kWh: Appropriate for average-sized homes with moderate energy usage
- 30+ kWh: Larger homes with higher energy usage. Suitable for households that have significant backup power requirements.
Can You Increase Your Solar Battery Capacity Later On?
It is possible to increase your battery’s capacity later on. However, the ease and cost of your expansion will depend on your type of battery system, making it important to plan.
If you may need to upgrade your capacity in the future, then choosing a “stackable” battery could be a great choice. These systems allow for future expansion, with their “stackable” modules allowing you to slot in extra capacity at small increments, typically at around 2kWh.
If you don’t opt for these systems, then increasing your battery capacity can be more cumbersome. This will require you to completely remove your existing battery and reinstall a larger one. This makes choosing the right battery storage vitally important, with the significant costs associated with completely reinstalling a new system. Therefore, if you may need to upgrade your battery capacity in future, considering a stackable system could be a great option.
Choosing the correct battery capacity can make or break your solar system. It allows you to maximise your investment, with the right amount of storage to suit your needs. Making the right capacity decision is dependent on a variety of factors, from your location, solar system size and household usage. With our calculations and guides, you can ensure you make the right decisions going forward. Please reach out to our trusted team at Tasmanian Safer Solar; we’re always happy to answer any questions you may have about solar batteries.
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