Solair World

How Many Solar Batteries Do You Need?

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When planning to harness the power of the sun to energize your home, one of the crucial considerations is determining the number of solar batteries required.

The table below will give you a rough idea of what size battery you might need, depending on the size of your property:

Property size
Battery size (kWh)
Two bedroom
Three bedroom
Four bedroom

Determining the number of solar batteries needed is not a one-size-fits-all answer.

It varies based on your goals for using a battery system with your solar panels.

If your main aim is cost savings, the size of the battery system will depend on your electricity rate plan.

To save as much money as you can, you should have enough batteries to store energy for times when your solar panels aren’t making electricity. Usually, this means having about 2 to 3 batteries.

If your main goal is to have power during a blackout, typically one solar battery should be enough.

But, if you’re looking to live completely off-grid and not rely on public utilities at all, you’ll need a lot more batteries. For this setup, you might need around 8 to 12 batteries.

By assessing your daily power usage, understanding the capacity of solar batteries, and considering factors like weather patterns and energy goals, you’ll be equipped to make an informed decision about the quantity and type of batteries that will best suit your solar setup.

How Are Solar Battery Sizes Measured?

Battery sizes are determined by how much electricity they can hold, however, it’s important to consider the usable electricity rather than just the total capacity.

Usable capacity reflects the actual amount of electricity you can reliably use without harming the battery’s lifespan.

The capacity of a battery to store electricity is measured in kilowatt-hours (kWh), but the key to practical use is the ‘usable capacity’.

This is typically less than the total capacity because you should avoid depleting the battery completely to prolong its life.

This is where Depth of Discharge (DoD) becomes important, as it tells you what percentage of the battery’s capacity is actually available for use without adversely affecting its lifespan.

For most modern batteries, you can expect a DoD of around 90 to 95 percent, meaning that is the portion of the total capacity you can use.

How to Choose the Right Size and Capacity for a Solar Battery?

Depth of Discharge (DoD)

The DoD indicates the percentage of the battery’s capacity that has been used.

For example, if a battery has a DoD of 90%, and its total capacity is 10 kWh, its usable capacity is 9 kWh.

Choosing Capacity

When selecting a battery, consider your daily energy usage.

Batteries with capacities of 1–13 kWh are common for residential use, and the right capacity for you will depend on how much electricity you use during the peak hours when solar isn’t available or during an outage.

Cost Considerations

Generally, the more capacity a battery has, the more it will cost. It’s about finding the balance between meeting your energy needs and staying within your budget.

Power Output

This is a measure of how much power the battery can deliver at one time, measured in kilowatts (kW).

If you have a battery with a large capacity but a low power output, it might not be able to handle simultaneous demands from multiple appliances.

It’s like having a large water tank with a small tap. Even though you have a lot of water, you can’t fill a bucket quickly if the tap is too small.

Balancing Capacity and Power

You may need to strike a balance between the capacity and power output.

A battery with a high capacity and high power output will be able to run your home longer and support more appliances simultaneously but will be more expensive.

What Size Solar Battery Do You Need for Your Home?

If You Aim to Save Money

For a flat-rate electricity plan, your goal should be to minimize reliance on the grid by storing as much solar energy as possible for later use, enhancing your savings over time.

For a time-of-use or variable-rate plan, your battery system should at least have enough capacity to cover your energy needs during periods when electricity prices are highest.

For the greatest cost savings, you need a battery system that can power your home through periods of peak electricity prices, which vary based on your location and specific plan.

Typically, around two to three average lithium-ion batteries, similar to the Tesla Powerwall, could allow you to largely avoid using grid electricity during these peak price hours and when your solar panels aren’t generating electricity.

This approach doesn’t make your home fully independent from the grid; instead, it’s about leveraging your solar installation to the fullest by utilizing as much self-generated solar energy as possible.

For Power Outage

Solar batteries offer increased reliability for homeowners by providing power during grid outages.

The number of batteries you’ll need for this purpose depends on how long and how fully you want to power your home during an outage.

For basic resilience, such as keeping essential appliances running during short-term power failures, one average-sized lithium-ion battery may suffice.

If you anticipate or live in an area with more prolonged outages, you may require a larger system with additional batteries to sustain your energy needs over several days.

In essence, for most homes, a single standard lithium-ion battery should be sufficient to power the essentials through the majority of power outages.

For Off-Grid Living

Designing a solar-plus-storage system for complete off-grid living requires a substantial battery bank to ensure that your home can maintain its energy needs without any grid support.

The size of the battery bank is largely determined by the energy consumption of your home and the need to compensate for days with low solar production due to weather conditions or during the night.

To achieve off-grid self-sufficiency, a significant amount of battery storage is necessary.

You might consider having a system that includes multiple batteries, typically ranging from 8 to 12 units comparable to the average lithium-ion battery like the Tesla Powerwall, depending on your energy requirements and geographic location.

This setup should be capable of sustaining your home’s power needs through extended periods without sunlight, ensuring a consistent energy supply.

What Factors Impact Solar Battery System Sizing?

1. Electricity loads

These are the appliances and systems within your home that consume electricity, such as refrigerators, air conditioning units, and lighting.

Understanding the total electricity consumption of these loads is critical because it influences the amount of storage capacity you’ll need.

If you aim to power a large number of appliances, especially those with high energy demands, you’ll require a battery system with a larger capacity.

2. Size and production of your solar panel system

The amount of solar energy your panels can generate directly affects how much energy you can store in your batteries.

The solar system should be sized adequately to charge the batteries during daylight hours.

If your energy needs exceed what your solar panels can generate, you may need to expand your solar array to ensure your batteries are fully charged for later use.

3. Your individual needs

What you expect to achieve with your solar-plus-storage system plays a significant role in deciding the number and size of batteries required.

If your goal is to have a completely off-grid setup, you’ll need a much larger battery bank compared to a system designed primarily for emergency backup or to reduce electricity bills.

Off-grid systems must account for multiple days of autonomy to ensure sufficient power during periods of low solar production, such as during extended cloudy weather or in the winter months.