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.
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 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 a number of renewables 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.
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).
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.
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.
The cost can be around £450 for a single heat source thermal store including installation, up to £1900 for a multi heat source thermal store. A larger system can cost around £500 more than this.
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 £1,700 with installation on top. This cost should come down as the market grows.
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.
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 £5,000 for a fully integrated 4kWh system, but this is expected to fall in the future.
Feed-in Tariffs (FITs) payments are calculated on the basis that 50% of the electricity you generate is exported back to the grid. Even if you store spare electricity you generate, export payments will still be calculated on this 50% basis. This may change as the UK Government are looking to base FITs export payments on actual meter readings after the smart meter roll-out.
It is becoming more likely that people with energy storage devices will benefit from payments or reduced tariffs in the future for providing smart services to the grid – for example, allowing their energy storage device, including hot water cylinders, to be used to store excess electricity on the grid.
If you store energy, you’ll still currently get your Feed-in Tariffs export payments for eligible solar PV systems and wind turbines, even if you’re exporting less electricity back to the grid. 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.
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.
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