What Size Solar Battery Do I Need?

what size solar battery do i need

Selecting the right solar battery size is based on two factors: your solar system’s output and your home’s energy usage. Ideally, your battery should store enough energy to cover the nighttime and cloudy days.

We don’t want to make the simple mistake of investing in a battery purchase only to find there is insufficient excess solar power to charge the battery.

It all starts with assessing your energy needs and aligning them with the battery’s capacity. Here are some simple steps to help determine the best size for your solar battery:

Assess Daily Energy Usage

Understand your household’s energy consumption patterns. Review past electricity bills to gauge your average daily energy usage in kilowatt-hours (kWh).

Consider seasonal variations and any changes in usage habits. For example, does your home use a lot of overnight air conditioning in the summer but almost no overnight heating in the winter?

Calculate Nighttime Energy Consumption

Figure out how much the average energy your home uses at night. Let’s say your home uses 25 kWh of electricity each day.

During the day, about 60% of this, or 15 kWh, is used. The other 40%, which is 10 kWh, is used at night. The overnight usage usually comes from the grid, not your solar panels.

So, if you want to use a battery instead of the grid at night, you’ll need one that can handle at least 10 kWh to cover your nighttime usage.

Consider Solar Output

Now, let’s think about your solar panels and the energy they make. You want to know how much power they create during the day and how much of that power you actually use in your home.

This is where we talk about the ‘solar self-consumption ratio.’ It’s a way to measure how much of the solar energy you produce is used up by your own home’s activities. We aim to use most of the solar power we produce because it’s free energy after the cost of installing the panels.

Here’s a general idea of what solar self-consumption might look like, although it will vary from your actual consumption.

If you’ve got a 3 kW solar setup and your daily power use is between 16-20 kWh, you might be using about half of the solar energy you make. The rest can either go back to the power grid or you can store it in your battery for when the sun’s not shining.

It’s smart to use at least 30% of the energy your panels generate. It means you’re really taking advantage of the solar power and saving more on your bills.

Battery’s Depth of Discharge (DoD)

Next, it’s key to get how much energy your battery can really give you. This is where the ‘Depth of Discharge’ (DoD) comes in.

While the solar output can help determine how much energy you can store, the DoD is crucial for knowing how much of that stored energy is actually usable.

Think of DoD as a battery’s energy tank. If a battery’s DoD is 90%, that means you can use 90% of its power. So, a 10 kWh battery would actually give you 9 kWh before it needs recharging.

Now, if the power goes out a lot where you live, and you want to make sure you’ve always got some electricity saved up, you might set your DoD lower, like 80%. This way, you keep more power reserved in the ‘energy tank’ just in case.

Just remember, the lower you set the DoD, the less of that stored solar energy you can use daily. Because you’re keeping more aside for emergencies or backup.

Estimate the Cost

When choosing a solar battery size, you also need to consider your budget. If spending over $10,000 is beyond your limit, options for large-capacity batteries might be limited.

Generally, solar batteries are priced at around $1,000 per kilowatt-hour (kWh) of storage capacity. Therefore, for a 10 kWh battery, the investment would be close to $10,000.

For those with lower energy usage, a smaller battery, potentially less than 5 kWh, could suffice and be more affordable.

However, it’s important to remember that the cost of a solar battery isn’t just the purchase price. Installation costs also play a significant role.

So the final cost can vary depending on the complexity of your solar energy system, the size of the battery you choose, and the specifics of the installation process. Be realistic for the budget estimation.

Battery Size Selection

Once you have an estimate of your daily energy consumption, required overnight usage, and any minimum backup requirements, choose a battery size that comfortably accommodates these needs.

If your average overnight consumption is 10 kWh and you want at least a couple of hours of backup power in reserve, then you’d ideally aim for a battery with a capacity of at least 12 kWh of usable energy (factoring in efficiency and DoD).

Consider Scalability

If your energy needs might change in the future, consider a battery system that allows for expansion or adding additional units to meet increased demands.

Consult a Professional

For precise calculations and to ensure the right fit, consult with a solar energy expert or installer. They can conduct an energy audit of your home and provide specific recommendations based on your unique circumstances.

Remember, choosing the best size for a solar battery involves balancing your energy needs, budget, available space for installation, and the battery’s technical specifications.

Careful consideration and, if needed, expert guidance can help you select a battery size that optimally meets your requirements and enhances your solar energy system’s performance.

As a solar expert, we can get you tailored solar battery quotes from CEC-accredited installers to power your home efficiently.

Contact us for personalised solutions that meet your energy needs.

Reviewed by

Tom Ransome
Tom Ransome

Co-Founder of Renewables4U and renewable energy advocate. He has experience and extensive knowledge in the field, including a groundbreaking academic thesis and a significant role in Australia's solar industry since 2016. With a BA in Business Studies, focusing on finance and management, Tom merges business acumen with technical expertise to deliver economically and eco-friendly projects.

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