What size solar battery do you need?

A solar battery (or storage battery) pairs perfectly with a set of solar panels, and means that you’ll use a lot more of the electricity that your panels generate - as opposed to sending it to the grid. This is pretty important, given the high upfront cost of solar panels.

However, it’s essential that your battery is an appropriate size. If it’s too small or too big, you won’t be using your battery properly and it may deteriorate pretty quickly. 

In this article, we’ll take you through the basics of solar battery sizing, and explain how to keep your battery alive for as long as possible.

If you’re wondering how much a solar & battery system could save you, just answer a few quick questions below and we'll immediately generate an estimate for you.

How to work out the right solar battery size for you

In an ideal world, we'd all have solar panels and batteries large enough to mean we’d never have to rely on grid electricity again. But this would require an enormous amount of space, as well as a hefty price tag.

The smart move is to aim for a battery that's just the right size 80% of the time, while depending on the grid for the remaining 20%. If your battery is too big, it can lead to chronic undercharging and eventually long-term battery damage.

As a general rule of thumb, you need a battery that is:

• Big enough to cover your electricity needs in the evening
• Small enough to be filled up by your solar panels in the daytime

Fortunately, you will not need to work out what size battery you need - this calculation should be done by a professional installer.

If you're thinking of getting a battery when you install solar panels, check out our guide to whether solar batteries are worth it.

How will an installer work out what size battery I need?

There are several different areas that an installer will focus on in order to determine what size solar battery you need. These are:

• Your electricity consumption
• Your solar panel system size
• Battery capacity and depth of discharge
• Your future electricity requirements

Here’s a bit more detail on each factor.

Your electricity consumption

When it comes to finding the ideal home storage batteries for your UK household's PV system, there's no need to dive into the nitty-gritty details of energy consumption patterns yourself. That's because a professional solar installer (like Sunsave) is here to guide you through the entire process and make sure you get the perfect home battery solution tailored to your needs.

A reputable installer will follow these steps:

1. Review your utility bills to identify average daily energy usage in kilowatt-hours (kWh)
2. Analyse the periods when you consume the most energy – usually mornings and evenings
3. Consider seasonal fluctuations in energy use, such as increased heating during winter months

So, don't worry about crunching numbers or deciphering utility bills. Leave that to us, and rest assured that with Sunsave you'll enjoy a seamless solar experience and a brighter, greener future.

Your solar panel system size

A crucial aspect of selecting the right solar battery is for your installer to assess the capacity of your solar panel system. The objective is to ensure compatibility between the solar panels and the chosen battery while maximising energy storage and efficiency. Your installer will keep in mind:

• The total output of your solar panels should be compatible with the input capacity of the chosen battery
• A larger solar panel system may require a larger battery or multiple batteries to store excess energy generated during sunny days
• Smaller solar PV systems might not generate enough power to fully charge a large-capacity battery

Your solar panel system installer will consult with experts or refer to solar PV system manufacturer guidelines when determining the appropriate sizing for both home battery systems and related components.

Battery capacity and depth of discharge

Your solar installer will take into account the battery's total usable energy by considering its capacity and depth of discharge (DoD) when designing your system. This is important because:

• Battery capacity indicates the amount of electricity a battery can store, measured in kWh
• DoD signifies the portion of a battery's stored energy that can be utilised before needing recharging, expressed as a percentage

For instance:

• A 10 kWh capacity battery with an 80% DoD enables the use of up to 8 kWh of energy before recharging.
• A 7 kWh capacity battery with a 90% DoD also offers up to 6.3 kWh of usable energy.

At Sunsave, our expert team will analyse your daily energy usage patterns, taking into account peak and off-peak hours, as well as seasonal fluctuations in energy consumption, to find the best solar battery for your home.

Your future electricity requirements

Finally, your solar installer should anticipate potential changes in energy consumption in the future. This allows for appropriate solar battery sizing adjustments to accommodate future needs. They will consider the following:

• Whether you plan on adding rooms to your property, your installer will estimate their additional energy usage and factor this into the battery sizing calculations
• Whether you intend to switch to electric heating at some point in the future, such as heat pumps or infrared panels 

By taking these factors into account when selecting a solar battery, your installer will help you be better prepared for any changes in your household's energy requirements and maintain optimal efficiency as your needs evolve.

How to prolong the lifespan of your solar battery

Efficient energy usage reduces the strain on your solar battery, leading to a longer lifespan and fewer replacements needed over time. Solar batteries can be expensive, so it's essential for your installer to maximise their longevity.

To prolong battery life, your installer will:

• Make sure it’s set up to avoid deep discharging (draining the battery too low)
• Install the battery in a temperature-controlled environment

At Sunsave the batteries we provide all use the latest generation of battery technology (LiFePo⁴ for the chemistry geeks reading), which basically translates to much longer battery lifespans, and fewer issues with hot or cold.

If you want to learn more, read our complete guide: How long do solar batteries last?

Summary

Wrapping things up, pinpointing the ideal solar battery size to suit your needs is all about grasping the various elements at play, such as energy efficiency, solar panel types, and working out your specific needs.

Solar battery sizing: FAQs