What Size Solar Battery Do I Need?

Choosing the right solar battery size is just as important as choosing the right solar panels.

A battery that is too small may leave you relying on the grid when your solar system is no longer generating. A battery that is unnecessarily large can increase the upfront cost of your installation without providing enough additional savings to justify the investment.

So, what size solar battery do you actually need?

The answer depends on more than the size of your solar PV system. Your household’s electricity consumption, when you use energy, how much solar energy you generate, whether you have an electric vehicle, your electricity tariff and whether you want backup power all need to be considered.

At SolarTherm UK, we design battery storage around the way your home actually uses energy. We currently offer Hanchu ESS as our main battery storage solution, alongside Tesla Powerwall 3 and Sigenergy SigenStor, giving homeowners a choice of systems depending on their property, energy requirements and budget.

What Is a Solar Battery?

A solar battery stores electricity generated by your solar panels so that you can use it later.

Without battery storage, any solar electricity you don’t use immediately is normally exported to the grid. A battery allows you to store more of your surplus generation during the day and use it when your solar panels are producing little or no electricity.

This can be particularly useful in the evening, overnight and during periods of poor weather.

Battery storage can also work alongside smart electricity tariffs, allowing some systems to charge from the grid when electricity is cheaper and discharge when electricity prices are higher.

The aim isn’t simply to install the biggest battery possible. It’s to install a battery that is appropriately matched to your energy generation and consumption.

How Is Solar Battery Size Measured?

Battery capacity is measured in kilowatt hours (kWh).

For example, a 10kWh battery can store considerably more energy than a 5kWh battery.

However, the number shown on the battery isn’t the only specification that matters. You should also consider:

• Usable capacity – how much of the stored energy you can actually use
• Depth of discharge (DoD) – the percentage of the battery’s capacity that can be discharged
• Charge and discharge power – how quickly the battery can take in or supply electricity
• Round-trip efficiency – how much energy is retained through a complete charge and discharge cycle
• Scalability – whether additional battery capacity can be added later
• Backup capability – whether the system can provide power during a grid outage
• Warranty and expected lifespan
• Compatibility with your solar PV system and inverter

For example, Hanchu’s 9.4kWh battery has a 95% depth of discharge and uses LiFePO4 (LFP) battery chemistry.

What Size Solar Battery Do I Need?

There isn’t one battery size that is right for every home.

As a general starting point, many UK homes may benefit from somewhere around 5–15kWh of battery storage, but the correct size depends heavily on individual circumstances.

A typical household might consider:

Household situation	Potential battery size
Lower electricity usage	5–7kWh
Average household	8–10kWh
Higher electricity usage	10–15kWh
High usage, EV or larger home	15kWh+
Larger or more complex energy system	Bespoke design

These figures are only a starting point. Installing a 10kWh battery doesn’t automatically mean it will be the best option for a home using 10kWh of electricity per day.

The important question is when that electricity is being used.

Your Daily Electricity Usage

Your annual electricity consumption is one of the most useful figures when sizing a battery.

You can find your usage on your electricity bills or through your energy supplier’s online account.

For example, if your home uses 12kWh of electricity per day, that doesn’t necessarily mean you need a 12kWh battery.

Some of that electricity may be used while your solar panels are generating. A battery is primarily there to shift surplus solar generation from periods of high production to periods when your household needs more energy.

This means a battery should be sized around your generation and consumption patterns, rather than simply matching your daily electricity consumption.

Your Solar Panel System Matters Too

The size of your solar PV system is another important consideration.

A larger solar array will generally produce more surplus electricity that could potentially be stored.

For example, a home with a 3.6kWp solar system may not generate enough surplus electricity to justify a very large battery in the same way that a home with a 6kWp or 8kWp system might.

However, solar generation varies throughout the year.

Your system may produce considerably more electricity than you need during sunny summer days, while winter generation can be much lower.

This is why we don’t recommend sizing a battery based solely on your panel capacity.

What About Self-Consumption?

One of the biggest benefits of battery storage is increasing the amount of your solar electricity that you use yourself.

Without a battery, you may generate a lot of electricity during the day while you’re at work or out of the house. That surplus electricity can be exported to the grid.

With a battery, some of that energy can be stored and used later when you return home.

This can increase your solar self-consumption and reduce the amount of electricity you need to buy from the grid.

For many households, this is particularly valuable because electricity is generally more expensive to buy from the grid than the amount you receive for exporting surplus generation.

Hanchu ESS: Our Main Battery Storage Solution

At SolarTherm UK, Hanchu ESS is now our main battery storage solution.

Hanchu offers flexible energy storage designed for residential applications, with its 9.4kWh battery providing a useful starting point for many UK homes. The system uses LFP battery chemistry and supports remote monitoring and energy management.

Hanchu also offers hybrid inverter options, allowing the battery and solar PV system to work together as part of an integrated energy storage solution.

For homeowners looking for a practical, flexible battery system without automatically moving into the premium price bracket, Hanchu ESS can be an excellent option.

The right configuration will depend on your solar array, household consumption and future energy requirements.

Tesla Powerwall 3

For homeowners looking for a premium, highly integrated battery storage solution, we also offer Tesla Powerwall 3.

Powerwall 3 has a 13.5kWh nominal energy capacity, with up to 11.04kW of on-grid power depending on local conditions. It also has an integrated inverter and can be expanded with additional Powerwall 3 units.

This makes Powerwall 3 particularly interesting for homes with higher electricity demand, larger solar PV systems or homeowners who want a substantial amount of storage and a sophisticated energy management system.

Powerwall 3 can also provide backup power during a grid outage when installed with the appropriate configuration.

Sigenergy SigenStor

For homeowners looking for a highly modular, future-focused energy system, Sigenergy SigenStor offers another option.

SigenStor is a 5-in-1 energy storage system, combining the energy controller, battery storage, power conversion and energy management functions into an integrated system, with an optional DC EV charging module.

Its modular design means battery capacity can be increased as your energy requirements change.

SigenStor battery modules are available in different capacities, with the current system supporting up to six modules per stack. The UK system can therefore be configured to suit a wide range of household requirements.

It can be particularly attractive if you have an EV, are considering an EV in the future or want a system that can integrate more of your home’s energy technology into a single platform.

Hanchu ESS vs Tesla Powerwall 3 vs SigenStor

There is no single “best” battery for every homeowner.

The right choice depends on what you want your battery to achieve.

Battery system	Best suited to	Key advantage
Hanchu ESS	Most homes looking for flexible battery storage	Practical, scalable energy storage
Tesla Powerwall 3	Higher-demand homes and homeowners wanting a premium integrated system	13.5kWh capacity and high power output
Sigenergy SigenStor	Tech-focused homes, EV owners and future expansion	Modular 5-in-1 energy system

The battery capacity is only part of the decision. The inverter, power output, tariff compatibility, backup requirements and future expansion options can all affect which system is most suitable.

Should I Get a Bigger Solar Battery?

Not necessarily.

A larger battery isn’t automatically better.

If your solar panels rarely generate enough surplus electricity to fill a large battery, you could end up paying for storage capacity that you don’t regularly use.

Equally, if you have a high electricity demand, an EV, a heat pump or a large solar PV system, a battery that is too small may regularly reach full capacity and leave surplus solar electricity being exported.

The ideal system aims to strike a balance between:

• Solar generation
• Household electricity consumption
• Battery capacity
• Battery power output
• Electricity tariffs
• Export payments
• Future energy requirements
• Installation cost
• Expected savings

What If My Energy Usage Increases?

It’s worth thinking about the future when choosing your battery.

Your electricity consumption could increase if you:

• Buy an electric vehicle
• Install a heat pump
• Work from home more often
• Add an extension
• Replace gas appliances with electric alternatives
• Add more solar panels
• Increase the size of your household

This is where a modular battery system can be particularly useful.

Rather than installing substantially more storage than you need today, it may be possible to choose a system that can be expanded as your requirements change.

Hanchu ESS and Sigenergy SigenStor both offer scalable approaches to energy storage, while Tesla Powerwall 3 can also be expanded with additional units.

Do I Need a Battery If I Have Solar Panels?

Not necessarily, but battery storage can significantly change how you use your solar electricity.

Solar panels generate electricity primarily during daylight hours, while many households use a significant amount of electricity in the evening.

A battery helps bridge that gap.

For example:

During the day:
Solar panels generate electricity → your home uses what it needs → surplus electricity charges the battery.

In the evening:
Solar generation falls → your home uses stored battery energy instead of immediately buying electricity from the grid.

This can help increase your solar self-consumption and reduce your reliance on grid electricity.

Can My Battery Charge From the Grid?

Depending on the battery and system configuration, yes.

Some battery systems can be configured to charge from the grid as well as from solar.

This can be particularly useful with time-of-use tariffs, where electricity prices vary throughout the day.

For example, your battery could potentially charge during a cheaper period and then supply electricity to your home during a more expensive period.

However, tariff compatibility and the most financially beneficial charging strategy depend on the specific system and tariff.

What About Battery Backup During a Power Cut?

If backup power is important to you, this needs to be discussed when your system is designed.

Not every battery installation automatically provides whole-home backup.

The system may require additional equipment or a specific configuration, and the amount of power available during an outage can depend on the battery, inverter, electrical supply and loads you want to operate.

If you want your battery to keep important appliances running during a power cut, tell your installer before the system is designed.

So, What Size Battery Should I Choose?

For many homeowners, a battery around 8–10kWh can be a sensible starting point, but there is no universal answer.

A smaller home with lower energy consumption may need less.

A larger home with high electricity usage, an EV, a heat pump or a larger solar PV system may benefit from considerably more storage.

The most important thing is to avoid choosing a battery based on a simple rule such as “one kWh of battery for every kWp of solar”.

Those rules can be useful as rough starting points, but they don’t account for how your household actually consumes electricity.

At SolarTherm UK, we look at your solar generation, electricity consumption, existing system, tariff, future plans and desired level of backup before recommending a battery size.

Get the Right Solar Battery for Your Home

Choosing the right battery isn’t simply about buying the biggest capacity available.

It’s about finding the right balance between capacity, power, solar generation, household consumption and cost.

At SolarTherm UK, we offer a carefully selected range of battery storage solutions, including Hanchu ESS, Tesla Powerwall 3 and Sigenergy SigenStor.

Whether you’re looking for a cost-effective and flexible Hanchu ESS system, the premium performance of Tesla Powerwall 3 or the modular 5-in-1 technology of Sigenergy SigenStor, we can design a system around your property and energy requirements.

Contact SolarTherm UK for a free, no obligation quote and design, tailored to your property, usage and future energy needs. No hard sell, just honest, expert advice – and the time you need to make an informed decision.

Your home. Your power. Your future.

Frequently Asked Questions