Sizing Up Solar Batteries: How To Determine The Right Size For Your UK Home

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More and more people are adding solar batteries to their solar panel systems and this is a great way to save the power you generate and a lot more money on your energy bills.

But there’s one thing that people seem to keep getting confused over; the size of solar batteries. If you’ve never had any experience with solar batteries, this can feel intimidating but once you know what you’re looking for, you’ll be able to choose batteries that are perfect for your home.

In this post, I’ll explain how to determine the right size solar batteries for homes in the UK.

What Does The Size Of A Solar Battery Mean?

When we talk about the size of a solar battery, we’re not referring to its physical dimensions. Instead, the size refers to the capacity of the battery in terms of how much power it can store.

With that in mind, solar panel users should remember that it’s never a good idea to buy a battery that has just the right capacity because it’s never good to fully drain it. Rather, it’s better to consider the usable capacity which suppliers often refer to as the depth of discharge or DoD, for short.

Typically, a battery will have a DoD that sits somewhere between 90 and 95 percent and solar batteries usually come in sizes between 1kWh and 13kWh. Of course, the larger the capacity, the more expensive the battery will be. However, you don’t necessarily have to spend a fortune and there are several things to consider before buying your battery which I’ll discuss throughout this guide.

Average Battery Size Depending On Home Size

The size of your home can be a determining factor in your choice of solar battery size. But don’t rely entirely on this as there are many other things to think about.

For a 1 bedroom property, you’d typically need a 2kWh battery whereas a 2 bedroom property would likely benefit from a 4kWh battery.

For larger homes with 3 bedrooms, an 8kWh solar battery would be best and 4 bedroom properties may need something as large as a 9.5kWh battery.

Considering Your Solar Panels

While the information I have provided above regarding house size in comparison to battery size is reliable, there are other factors to consider. One of the most important is the size of your solar panels as this will play a significant role in which battery size you choose.

In each of the following cases, it is important to keep in mind that I am assuming you will not use any of the power generated during the day and that all of it will be going towards charging the battery and storing power. Otherwise, you would need to size up.

  • 4kWh solar panel system – for this size solar panel system, you would more than likely need an 8kWh battery as this system would be able to generate the same amount of power each day which would fill the battery to capacity and keep it charged.
  • 5kWh solar panel system – if you have a 5kWh solar panel system then a battery between 9.5 and 10kWh would be most suitable. However, I wouldn’t recommend using these larger capacity batteries alongside a smaller system as there’s a good chance the system wouldn’t generate enough energy to power it.
  • 6kWh solar panel system – when using a 6kWh solar panel system, you’ll need an even larger battery, typically with a capacity of around 12kWh.
  • 8kWh solar panel system – generally speaking, for this size solar panel system, you’ll want a battery that has double the capacity of around 16kWh. This will ensure it stays sufficiently charged.
  • 10kWh solar panel system – some of the larger solar panel systems will naturally need a much higher capacity battery. Normally, this would mean going for something between 20 and 21kWh if you want to ensure that the battery receives enough power to fully charge it each day.

Other Things To Consider

While the size of your home and your solar panel system will have a significant impact on which size batteries you choose, there are a few other things to keep in mind which will help you make the best decision.

Your Energy Usage

Before you buy a solar battery, it’s important to think about how much energy your home typically uses in a day. One of the easiest ways to do this is to check your smart metre as this will save you from having to make unnecessary calculations.

However, if you don’t have a smart metre then your energy bill will have a breakdown of your usage which you’ll then simply need to divide by the number of days within the month (or however long the bill covers.)

Power Output

Another important consideration when choosing a solar battery is its power output. You might have a battery with a very large capacity but a low output and this really isn’t going to serve you. The problem with batteries with a lower output is that they simply won’t have the capacity to supply enough energy to the devices and appliances within the home.

Battery Life

Batteries are not designed to last forever and a typical solar battery may last anywhere between five and fifteen years. Since solar panels are designed to last around 30 years, this means you will need to purchase two batteries during the system’s lifespan, so you want to get the best bang for your buck.

The lifecycle of a battery is related to how many times it can be drained and charged before it stops performing as it should.

This is why it’s a good idea to look for batteries that have a high number of charging cycles as it’ll simply last much longer.

Are You On Or Off-Grid?

Another important consideration when choosing solar battery size is to look at how you power your home.

A lot of solar panel users will continue to rely partially on the grid and there’s nothing wrong with that. However, it will likely mean that you require a smaller capacity battery compared to a home that’s completely off-grid.

Buying Oversized Batteries

It’s really important not to buy a battery that’s so much bigger than your solar panel system that the system won’t be able to deliver enough energy to charge it. However, in some cases, it is possible to purchase something slightly oversized if you think this will benefit you.

For example, you might have a particularly high daily energy consumption or you might just want something bigger as a backup.

Another good reason to choose an oversized battery is if you plan to install advanced technology in your home like an electric car charger or a heat pump. In these cases, your energy consumption will go up significantly and you’ll need to make sure your battery has the capacity to keep up with this.

That said, there’s really no point in going over the top and buying a massive battery that you’ll never make full use of. A lot of people fall into the trap of thinking that this will save them more on their energy bills but it probably won’t as the investment will vastly outweigh what you save each month and it’ll take years to break even.

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