Storing energy

Home energy storage systems make the most of electricity and heat by storing it so you can use the energy when you need it.

They are particularly useful for people with home renewable energy systems who can use more of the clean energy they generate at home.

If you already have home renewable energy, an energy storage system could reduce your fuel bills and carbon emissions.

The fuel bill savings are dependent on the system installed and how it is used.

For some new energy storage technologies, there isn’t currently enough independent evidence available to estimate typical savings.

Ask installers to calculate savings for you based on your home and circumstances and to explain how these calculations are done.

Most energy storage systems offer smart operation. This allows you to keep track of your energy use online and to decide when to charge your storage unit and when to draw energy from it.

Heat storage systems fall into two categories – thermal stores and heat batteries.

Thermal stores are highly insulated tanks that can store heat as hot water for many hours. Thermal stores can vary in size from a common hot water cylinder of around 120 litres up to very large stores of 500 litres or more. Thermal stores can have a single heating input or can have multiple heat inputs.

If you have a renewables system, you can make the best use of the free renewable energy by putting any excess energy you generate into a thermal store to be used later. This reduces the need to use other costly heating sources when your renewables system isn’t generating. Thermal stores are commonly used with several renewables systems, including biomass heating systems, solar water heating, heat pumps, solar PV, and wind or hydro turbines.

Find out how thermal stores can be integrated with different renewable energy systems.

The cost of a 500 litre thermal store is around £2,500, and installation costs can be up to £450.

Heat batteries are a new technology for storing either spare heat or electricity generated by renewable energy systems. They work on the principle that heat is stored when a material changes phase from a liquid to a solid. Spare heat or electricity from a renewable energy system is used to charge the phase change material inside the battery. When the heat is needed, the phase change material is changed into liquid with a release of heat, which is used to provide hot water.

Heat batteries are generally smaller and lighter than (filled) thermal stores, and it is claimed that they don’t lose performance over time compared with electrical batteries. A heat battery could supply a significant proportion of your heat demand.

There is currently only one supplier of home phase change heat batteries, Sunamp, and a 5kWh heat battery unit has a list price of £1,300 (excluding installation). The type of heat battery you need (and its cost) would depend on your heating needs (hot water, space heating or both) and on the heating system already present at your property.

Electricity batteries help you make the most of renewable electricity from a solar PV system, wind turbine or hydroelectricity system. For example, your solar PV system will generate electricity during the day, which can then be stored in your electricity battery for you to use for cooking, heating or watching TV in the evening.

The capacity of a typical home battery storage system could be up to 16kWh, but there are also other ‘stackable’ or bespoke systems if more capacity is required.

A typical 4kWh system would be able to power the kettle 37 times.

If your home is connected to the grid, an electricity battery will help you make the most of your renewable electricity, meaning your electricity bills will be cheaper and your carbon emissions will be lower. In an off grid home, battery storage can reduce your reliance on an alternative fossil fuel electricity generator.

The cost of electricity batteries currently ranges from £4,000 to £6,000 for a fully integrated 4kWh system.

The feed-in tariff (FIT) scheme closed to new applications on 31 March 2019, but details about the scheme are still available here.

If you currently receive FIT payments for an existing renewable electricity system, and you add an electricity storage system, then your generation payments should be unaffected. Before you go ahead, check with your FIT supplier that the storage installation does not affect your eligibility.

Your export payments are probably currently deemed at 50% of generation, and this will not change with the addition of storage, even though actual exports will be reduced. However, when you get a smart meter fitted this will operate as an export meter. All your export payments from then on should be based on actual metered export, and these payments will reduce if you fit storage.

Payments under the domestic Renewable Heat Incentive (RHI) are expected to be unaffected by using home energy storage.

Most energy storage systems offer smart operation, allowing users to track energy usage online.

As well as storing renewable energy generation, energy storage technology can also be used to store electricity bought from the grid at cheaper times of the day, such as Economy 7 tariffs.

As Economy 7 electricity is supplied overnight, you can charge your battery with it and benefit from its power during the day.

The Microgeneration Certification Scheme’s (MCS) battery storage standard outlines the installation requirements for MCS-certified installers who supply, design and install electrical battery storage systems. You can search the database for MCS-certified battery storage installers.

The Renewable Energy Consumer Code (RECC) and BRE National Solar Centre (NSC) have jointly issued some guidance on electricity batteries.

For all energy storage systems, talk to more than one installer for different approaches, system options and quotes. When you’ve decided what system to go for, we recommend getting at least three written quotes to make sure you’re getting the best value for money.

It is recommended that you get your heating system, including any energy storage technology, inspected every year.