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Energy storage

Energy storage systems, also known as batteries or thermal stores, allow you to capture heat or electricity when it is readily available, typically from a renewables system, and save it until a time when it is useful to you.

What are the benefits of home energy storage?

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 can 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 power from it. 

Heat Storage

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

Thermal stores

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. 

What are the benefits of thermal stores?

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 a number of renewables systems:

Biomass or wood-fuelled heating systems

Thermal stores can increase the efficiency of wood-fuelled heating systems, particularly log boilers which are designed to burn logs in larger batches rather than small quantities throughout the day. Thermal stores store hot water from the last time the stove or boiler was lit, so you don’t need to wait as long for water to heat up.

Solar water heating

Thermal stores capture the heat from the solar panels and can also be used to allow excess solar heat to be used for heating rooms as well as heating water. They can be designed to prioritise solar heating above all other sources. However, using a solar water heating system for space heating as well as hot water means the system won’t be eligible for the domestic Renewable Heat Incentive (RHI).

Heat pumps 

An air source heat pump or ground source heat pump is typically linked to a thermal store. This allows it to work more efficiently, with less wear on the pump and compressor, by removing the need for it to continually ‘short cycle’ on and off when the demand for heat is low.

Solar PV and wind or hydro turbines

When combined with smart controls, thermal stores can also work with renewables systems which generate electricity rather than heat, such as wind turbines or solar PV systems. Instead of exporting unused electricity to the grid, the spare electricity generated is used to power an immersion heater, warming water in the thermal store. 

How much does a thermal store cost?

The cost of a 500 1 thermal store is around £2,500, and installation costs can be up to £450. 

Heat batteries

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.

What are the benefits of heat batteries?

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.

How much do heat batteries cost?

There is currently only one supplier of home phase change heat batteries, Sunamp, and a 5kWh heat battery unit has a list price of £1300 not including installation or VAT. This cost should come down as the market grows. 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 

Electricity batteries help you make the most of renewable electricity from a solar PV system or wind or hydro turbine. For example, your solar PV system will generate electricity during the day when you’re out at work, and this can be stored in your electricity battery for you to use 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.

Read our blog on the potential revolution in the electricity market from the development of domestic solar plus battery storage.

What are the benefits of electricity batteries?

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.

How much do electricity batteries cost?

The cost of electricity batteries currently ranges from £4,000 to £6,000 (VAT included) for a fully integrated 4kWh system, but this is expected to fall in the future.

Feed-in Tariff payments and energy storage

The FITs scheme closed to new applications on 31 March 2019, but details about the scheme are still available here.

If you currently receive Feed-in Tariff (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, you go ahead, you should 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.

Storing grid electricity

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.

How do I choose a system and installer? 

As home battery storage is an emerging sector there are currently no specific government or industry body-set standards for installation, although discussions are currently taking place.

Some guidance on electricity batteries has been issued by the Renewable Energy Consumer Code (RECC) along with BRE National Solar Centre (NSC). 

For all energy storage systems, talk to more than one installer for different approaches, system options and quotes.

Some product manufacturers have a list of approved installers.

When you’ve decided what system to go for, get at least 3 written quotes to make sure you’re getting the best value for money. 

Make sure any gas-related works are done by an engineer registered with Gas Safe.

For electricians and plumbers, check their qualifications and professional body membership as well as their experience of energy storage. It is recommended that you get your heating system, including any energy storage technology, inspected every year.

You could get a specialist renewable energy engineer to check your entire system including any renewables systems.

Next steps

Energy storage guide

A helpful factsheet with further information on energy storage is available to download.

Download now

Renewable energy

Discover more information about the benefits of installing of home renewables system.

Learn more

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