Sync Energy Flow Battery Storage Buying Guide: 3.6kW vs 6kW, Battery Capacity and Solar Options

The Sync Energy Flow battery storage range is a modular home energy management system designed to store electricity for use when it is needed most.

It can be used with solar panels, without solar panels, or as part of a future-ready installation where solar PV or EV charging may be added later.

This buying guide explains the difference between the 3.6kW and 6kW all-in-one systems, how to choose the correct battery capacity in kWh, when to use the modular battery stack, and whether optional accessories such as the solar power diverter are needed.

The most important thing to understand is the difference between kW and kWh. These are often confused, but they describe two different parts of a battery storage system.

kW measures power. This tells you how quickly the inverter can charge or discharge energy at one time.

kWh measures energy storage capacity. This tells you how much electricity the batteries can store.

For example, a 6kW inverter can deliver more power at once than a 3.6kW inverter, but the amount of stored energy depends on the number of battery modules installed.

Quick recommendation

For most new installations, choose one of the all-in-one systems first.

The Sync EV Flow All-in-One 3.6kW Battery Storage System is best for smaller homes, lower-demand properties and entry-level off-peak energy storage.

The Sync EV Flow All-in-One 6kW Battery Storage System is recommended for higher-usage homes, EV-ready installations, electric heating and larger battery capacities.

Both all-in-one system kits can be ordered with 5.12kWh, 10.24kWh or 15.4kWh battery capacities.

If you are building a system from separate components, use the modular listings.

Choose a Sync EV Flow Hybrid Inverter in either 3.6kW or 6kW, then choose a Sync EV Flow Modular Battery Stack with 5.12kWh, 10.24kWh, 15.4kWh or 20.5kWh storage capacity.

It is important to note that the battery stack on its own is not a complete home battery system.

A compatible hybrid inverter is required to charge the batteries, discharge power into the home or connect the system to solar PV.

What is Sync Energy Flow?

Sync Energy Flow is a modular battery storage system for domestic energy management.

It allows electricity to be stored in LiFePO4 battery modules and used later, either to reduce peak-rate electricity use or to store surplus solar energy.

The system can be used with solar panels to store surplus solar energy for later use.

It can also be used without solar panels, allowing the battery to charge during cheaper off-peak periods and discharge during peak-rate periods.

It can be installed as a solar-ready system, with battery storage fitted now and solar PV added later.

It is also EV-ready, allowing battery storage to be combined with an EV charger and a time-of-use tariff to make better use of cheaper overnight electricity.

The range includes all-in-one systems, modular battery stacks, standalone hybrid inverters and optional energy management accessories.

All-in-one systems vs modular components

There are two main ways to buy Sync Energy Flow.

An all-in-one system includes the hybrid inverter and battery modules in one stacked system. This is best for most new domestic battery storage installations.

Modular components use a separate hybrid inverter and separate battery stack. This route is best for installer-led builds, system expansion or more flexible project design.

The all-in-one systems are the simplest route for most customers because they combine the inverter and battery storage within one product family.

The modular route is useful when the inverter and batteries need to be ordered separately, or where an installer is designing the system around specific requirements.

Choosing battery capacity: 5.12kWh, 10.24kWh, 15.4kWh or 20.5kWh

Each Sync Energy Flow battery module provides 5.12kWh of storage capacity.

Adding more battery modules increases the amount of energy that can be stored.

A 5.12kWh option uses one battery and provides 5.12kWh total capacity, with approximately 4.61kWh usable capacity at 90% depth of discharge.

A 10.24kWh option uses two batteries and provides 10.24kWh total capacity, with approximately 9.22kWh usable capacity at 90% depth of discharge.

A 15.4kWh option uses three batteries and provides 15.4kWh total capacity, with approximately 13.86kWh usable capacity at 90% depth of discharge.

A 20.5kWh option uses four batteries and provides 20.5kWh total capacity, with approximately 18.45kWh usable capacity at 90% depth of discharge.

The all-in-one systems are available with one, two or three batteries, giving up to 15.4kWh of storage.

The separate modular battery stack listing also includes a four-battery option up to approximately 20.5kWh.

For smaller homes and lighter usage, 5.12kWh or 10.24kWh may be enough.

For higher electricity usage, electric heating, EV-ready homes or customers trying to reduce peak-rate grid import, the 15.4kWh option is usually the more serious choice.

3.6kW vs 6kW inverter: what is the difference?

The inverter controls how quickly the battery can charge and discharge.

This is different from battery capacity.

A 3.6kW inverter can charge or discharge at up to 3.6kW.

A 6kW inverter can discharge at up to 6kW and has a higher charging rate.

This matters because larger homes often use more than 3.6kW at once, especially when appliances, electric heating, EV charging or hot water loads are running.

The 3.6kW all-in-one system is best suited to smaller homes, lower loads and entry-level battery storage.

The 6kW all-in-one system is best suited to larger homes, electric heating, EV-ready installations and higher loads.

Adding more batteries increases storage capacity, but it does not increase the inverter output.

A 3.6kW system with three batteries still has a 3.6kW inverter limit.

This means the system may store plenty of energy, but it can only release that energy at up to 3.6kW.

This is why the 3.6kW version is best treated as an entry-level system.

It can be a good option for smaller properties and projects where lower output is acceptable, but it becomes limiting if the customer plans to expand battery capacity or run higher household loads.

For most higher-usage homes, the 6kW Sync EV Flow All-in-One Battery Storage System is the better choice because it offers a more future-proof solution.

How fast can the battery charge during off-peak electricity?

Charging speed is an important buying point, especially for customers using a time-of-use tariff with a short off-peak window.

For example, if your off-peak electricity period is 00:30 to 05:30, that gives a five-hour charging window.

The basic calculation is inverter charge rate multiplied by charging hours, giving the maximum energy charged.

A 3.6kW system charging at 3.6kW can charge a maximum of 18.0kWh over five hours.

A 6kW system charging at up to 5.2kW can charge a maximum of 26.0kWh over five hours.

In simple terms, the 3.6kW version can charge a 15.4kWh battery stack within a five-hour off-peak window, but it uses most of the available time.

A 5.12kWh battery takes approximately 1.42 hours to charge with a 3.6kW system, or approximately 0.98 hours with a 6kW system charging at 5.2kW.

A 10.24kWh battery takes approximately 2.84 hours to charge with a 3.6kW system, or approximately 1.97 hours with a 6kW system charging at 5.2kW.

A 15.4kWh battery takes approximately 4.28 hours to charge with a 3.6kW system, or approximately 2.96 hours with a 6kW system charging at 5.2kW.

These are simplified calculations and do not allow for charging losses, battery management, temperature, charge limits or tapering.

However, they show why the 6kW version is more flexible. It can recharge the battery more quickly, leaving more room in the off-peak window for other high-demand loads such as EV charging or electric heating.

What happens if EV charging, electric heating and battery charging run together?

This is one of the most important checks before buying a battery storage system.

Many homes have a limited single-phase supply.

If several large loads run at the same time, the total demand can become very high.

An EV charger may use around 7.4kW, which is approximately 32A at 230V.

A Sync 6kW system charging may use around 5.2kW, which is approximately 23A at 230V.

Electric heating may use 8kW to 10kW, which is approximately 35A to 43A at 230V.

A background load of 1kW is approximately 4A at 230V.

In this example, the total demand could be around 21.6kW to 23.6kW, which is approximately 94A to 103A at 230V.

That can be close to, or above, the available supply capacity for some properties.

A 100A main switch in a consumer unit is usually an isolator, not the device that trips for normal overload.

RCDs are designed for residual current or earth leakage protection, not normal load management.

If the total property demand is too high, the issue may involve individual MCBs or RCBOs, the service fuse, meter tails, consumer unit design, DNO limits, or the load management settings on devices such as EV chargers and battery inverters.

Before installing battery storage, solar PV or an EV charger, a qualified electrician should check the main fuse rating, meter tails, earthing arrangement, consumer unit rating and layout, RCD or RCBO protection, DNO notification or approval requirements, whether load management is required, and surge protection requirements.

For high-usage homes, load management can be very important.

It allows devices such as EV chargers or battery systems to reduce their charging rate automatically when the rest of the house is using a lot of power.

How does Sync Energy Flow compare with Tesla Powerwall 3?

Tesla Powerwall 3 is a premium battery storage system with high output power.

On many UK installations, Powerwall 3 can provide much higher discharge power than the Sync Energy Flow 3.6kW or 6kW models.

Tesla Powerwall 3 has 13.5kWh battery capacity, approximately 11.04kW discharge power on many UK installations, integrated battery system technology and solar-ready capability.

The Sync Energy Flow 6kW with three batteries has 15.4kWh battery capacity, 6kW discharge power, a modular LiFePO4 battery stack and solar-ready capability with a hybrid inverter.

Tesla Powerwall 3 is best suited to premium, high-output battery storage.

Sync Energy Flow 6kW with three batteries is best suited to cost-effective modular battery storage.

The key difference is output power.

The Sync 6kW system has strong battery capacity, especially with three batteries, but it does not match the Powerwall 3 for maximum discharge power.

This is why the 3.6kW Sync system should not be presented as a direct Powerwall 3 alternative.

It is a good entry-level battery storage system, but it becomes limited as property demand increases.

The 6kW version is the better Sync Energy Flow option for customers comparing against Tesla Powerwall 3.

Which items should I order?

Complete new installation: smaller home or entry-level storage

Choose the Sync EV Flow All-in-One 3.6kW Battery Storage System.

Then select the battery capacity.

The 5.12kWh option is suitable for entry-level storage.

The 10.24kWh option is better for more daily usage.

The 15.4kWh option provides larger storage, but is still limited to the 3.6kW inverter output.

This option is best for smaller homes, lighter loads, lower-demand installations and customers who want a lower-cost route into battery storage.

Complete new installation: higher-usage home, EV-ready or electric heating

Choose the Sync EV Flow All-in-One 6kW Battery Storage System.

For battery capacity, 10.24kWh is suitable for many homes with moderate usage.

The 15.4kWh option is recommended for higher-usage homes and Powerwall alternative comparisons.

This is the version to choose for larger homes, electric heating, future EV charging, larger battery storage and customers who want a stronger alternative to entry-level battery systems.

Modular system build: separate inverter and battery stack

Choose a Sync EV Flow Hybrid Inverter in either 3.6kW or 6kW, and a Sync EV Flow Modular Battery Stack from 5.12kWh to 20.5kWh.

This route is best for installer-led designs, system expansion or projects where the inverter and battery storage need to be ordered separately.

For most higher-usage installations, the 6kW inverter should be considered first.

The 3.6kW inverter is better suited to lower-demand properties and smaller projects.

Adding more battery capacity

Use the Sync EV Flow Modular Battery Stack.

Adding more batteries increases the amount of energy that can be stored, but it does not increase the inverter output.

For example, adding more batteries to a 3.6kW system does not turn it into a 6kW system.

If the customer may need larger loads, EV charging support or faster charging during off-peak periods, it is usually better to choose the correct inverter size at the start.

Solar PV installation

For a solar-ready battery installation, choose either the 6kW All-in-One Battery Storage System for a complete inverter and battery solution, or a Hybrid Inverter and Modular Battery Stack for a modular system build.

The hybrid inverter is the key component that allows the system to work with solar PV.

A solar diverter is not automatically required.

Do I need the Sync EV Flow solar power diverter?

In most battery storage installations, no, you do not automatically need the solar diverter.

The Sync EV Flow Solar Power Diverter is an optional accessory.

It is not the main inverter and it is not required to make the battery system solar-ready.

The priority for most homes should be to use solar energy directly in the home, store surplus solar energy in the battery for later, and export only when there is no better use for the energy.

A solar diverter can be useful where the property regularly has surplus solar generation and the customer wants to divert energy to hot water, battery storage or EV charging.

However, it is not always the best investment.

If the home already heats water cheaply with gas, diverting solar energy into hot water may not save as much money as using that electricity to avoid peak-rate grid import.

Electricity stored in the battery can often be more valuable when it is used later to power the home during expensive peak periods.

The solar diverter should be treated as an optional energy management accessory, not a required part of the core battery storage system.

VAT: supply-only vs installed battery systems

VAT treatment can depend on how the system is supplied.

For domestic installations, qualifying battery storage installed as part of an energy-saving materials installation may qualify for zero-rated VAT under the current rules.

However, supply-only sales of energy-saving materials are normally standard-rated.

This means customers should check VAT treatment carefully with their installer or accountant before ordering.

Product prices on a supply-only ecommerce website may not be treated the same way as a full installed domestic energy-saving system.

Best Sync Energy Flow alternative to Tesla Powerwall 3

For customers looking for a Tesla Powerwall 3 alternative, the closest Sync Energy Flow option is the Sync EV Flow All-in-One 6kW Battery Storage System with 15.4kWh battery capacity.

This gives a strong balance of battery capacity, inverter output and value.

It does not match Tesla Powerwall 3 for maximum discharge power, but it provides more battery capacity than a single Powerwall 3 and may be a more cost-effective option for customers who do not need the full Tesla ecosystem.

The 3.6kW version is not the best Powerwall alternative because the inverter output is much lower.

It is still useful as an entry-level option, but customers planning to expand storage or run higher household loads should usually consider the 6kW version first.

Summary: which Sync Energy Flow system should you choose?

For a small home, lower usage or entry-level battery storage, choose the 3.6kW all-in-one system.

For a larger home, higher usage or future EV charging, choose the 6kW all-in-one system.

For a Powerwall alternative, choose the 6kW all-in-one system with 15.4kWh battery capacity.

For an installer-led modular build, choose a Hybrid Inverter and Modular Battery Stack.

For adding more storage to a compatible system, choose the Modular Battery Stack.

For surplus solar hot water or wider energy diversion, the Solar Power Diverter is optional only.

For most customers, the decision should be made in this order: choose the inverter size, choose the battery capacity, check the property supply capacity and whether load management is needed, decide whether solar PV or EV charging will be added now or later, and only add the solar diverter if the installation has a clear use for surplus solar energy.

The safest general recommendation is simple: choose the 3.6kW system for smaller, lower-demand homes, and choose the 6kW system for higher-usage homes, EV-ready installations, electric heating and anyone comparing Sync Energy Flow against Tesla Powerwall 3.

For more information on Sync Energy Flow Battery Storage Buying Guide: 3.6kW vs 6kW, Battery Capacity and Solar Options talk to Expert Electrical Supplies Ltd