Is domestic battery storage the answer to the energy crisis?.

Original Article
April 25th, 2023


Sava’s Johnnie Leather discusses the prospect of using domestic battery storage to power our homes and how they can help combat the ongoing energy crisis.

The use of batteries in our society is now an everyday occurrence from torches to cars. However, the concept of using batteries to power our homes may seem a strange thought. Yet this is fast becoming a reality with companies like Tesla and Moixa producing their own domestic energy storage units. In this article we explore the use of batteries in the home.

Why domestic energy storage batteries?

Using batteries for domestic energy storage has two key benefits. They can provide a clean alternative to grid supplied electrical energy, and they have the potential of offering considerable economic advantages to consumers via savings on energy bills. Domestic batteries are most effective when used in conjunction with solar PV panels as they can store excess electricity generation. With domestic energy demand patterns not always matching that of solar generation, a battery can store excess electricity when generation is high, but demand is not. This energy can then be used when demand is high, but generation is low, like at night-time, maximising the generated electricity. This not only saves an occupier money on their energy bill by reducing their use of grid electricity, but it is also far greener than grid electricity as it comes direct from solar generation.

New time-of-use tariffs can also be used to optimise the benefits of batteries. Like economy 7 tariffs, time-of-use tariffs charge different electricity prices at different times of the day, reflecting the wholesale cost. Households can then utilise the prices offered by the tariff, charging up their battery at the cheapest times to use at their convenience, offering great economic advantages. As renewable energy is the cheapest form used by the grid, electricity during the lower costing periods tends to be less carbon-intensive too, creating another environmental benefit to battery use.

Despite clear financial and environmental benefits, the uptake of batteries in domestic properties has been limited by high upfront costs. Whilst this is starting to change with the rising adoption of Electric Vehicles (EVs) helping to bring down the price of modern lithium-ion (Li-ion) batteries, for many, domestic batteries are an unrealistic expense in today’s circumstances.

What are domestic energy storage batteries?

The most common types of domestic energy storage batteries are lead acid. A lead acid battery is a type of rechargeable battery that uses a chemical reaction between lead, water, and sulfuric acid to store electrical energy. The technology is not new, and the batteries are proven to be robust, reliable, and cheap to make and use. While lead acid batteries can still be a good choice, newer lithium batteries technologies are rapidly improving with the benefit that the batteries are likely to become more convenient and compact.

An important driver of Li-ion technology uptake is the establishment of a good recycling market. Currently, due to the relative infancy of large Li-ion batteries there is yet to be a robust recycling market for them. Whilst there are some companies carrying out recycling services like GS Yuasa Corporation, it is a fragmented market with no overly dominant figures. As the use of Li-ion batteries continues to rise, the recycling market will also grow as this will create more demand for it. This will result in the cost of Li-ion batteries dropping further, making them more accessible and increasing their uptake.

Batteries vary in size, weight, and storage requirements between brands. However generally, batteries can operate at temperatures from -20°C to 50°C degrees, require access to the home’s electrical wiring, weigh anywhere from 100 to 250kg and are often floor-mounted and fixed against a wall.

Batteries have similar noise levels to a fridge, and it is recommended they are kept inside for optimal operation and to avoid risk of vandalism. For all these reasons, the ideal storage space for a battery is in a garage or a utility room. As a garage or utility room is not an option for everyone, there is also potential to keep batteries on the wall in rooms like the kitchen or living room. Whilst this only really works with smaller battery systems, as domestic batteries become more common and the technology more compact, this could be the norm, with batteries consciously designed to incorporate with the interior of homes. This is a direction Moixa seem to be heading in, with pictures on their website displaying wall-mounted batteries assimilating with their surroundings.

Technology development

Looking to the longer term there is an array of emerging energy storage technologies such as flow batteries, metal air batteries, supercapacitors, flywheels, and hydrogen batteries to name but a few. As many of these are currently used on an industrial scale, it is likely we will have different, even more effective types of domestic energy storage batteries in the future.

Batteries and energy security

Batteries have an important role to play in improving the UK’s energy security by reducing grid demand. The UK’s energy supply is partially reliant on importing electricity, which makes us susceptible to the volatility of international energy markets. This limits the security of both our energy supply and pricing, but with greater use of domestic battery storage, there is an opportunity to reduce import requirements, support grid balancing and increase security.

One way batteries reduce grid demand is by storing excess solar PV generation which allows homes to utilise their own generation and reduce their reliance on grid electricity. This gives heightened supply security to both battery owners, who can rely on their own generation, and the UK, by cutting overall grid demand and therefore importation requirements.

A slightly more complex way in which batteries can increase energy security is by assisting with grid balancing schemes. As part of many tariffs offered to battery owners, energy companies are allowed to take energy from batteries when supply is struggling to keep up with demand. This is known as grid balancing and will be especially important this winter with fears of energy supply shortages caused by Russia constraining its gas
supply to Europe.

Another interesting feature of domestic batteries is that they can power homes in an outage. Due to the current size of most systems, it is unlikely they will be able to power everything, with essential and non-essential loads normally separated. But it still offers another form of security, which, unfortunately, may be needed this winter if the UK’s supply is not properly managed.

Available options

Tesla is probably the most familiar of the modern residential battery options because of the success of the Tesla EV. But, like the cars, they come at a premium. The Tesla Powerwall 2 costs between £6,700 to £8,700, has a capacity of 13.5kWh, a peak power output of 7kW and a continuous power of 5kW. This means they are not necessarily a cheap alternative to grid electricity, although with the cost of Li-ion batteries constantly declining and the cost of fuel on the up, it is likely they could reach price parity soon.

Moixa, however, provides cheaper alternatives, offering three different capacity systems. Their cheapest option, the 4.8kWh ‘smart battery’ comes in at £4,450, whilst their larger system the ‘optimised battery’ comes in either 7.2 kWh or 9.6 kWh systems, costing £5,250 or £6,250 respectively. All of which are cheaper but also lower capacity than the Tesla Powerwall 2.

When it comes to batteries, bigger does not always mean better. An oversized battery can be an unnecessary expense as it will be more costly than a smaller battery and the extra storage space is redundant if not used. On the other hand, too small a system will mean a house can’t store all its excess solar generation and will have to export it to the grid. It is, therefore, important that the battery is an appropriate size for the specific house, their usage levels, and the amount of solar energy they generate.

Policy context

Unlike other energy-saving green technologies like PV panels and heat pumps, there is currently no government policy to solely support the uptake of domestic batteries. One way the government could fit batteries into their net zero plans is via community battery schemes. These work by splitting the costs and benefits of PV’s and larger centralised batteries between members of the local community. By sharing the system, the individual risk and cost drops which could encourage uptake. The government could further increase these kinds of schemes by partially funding them through grants or loans. This would have a multitude of benefits for the UK, from reducing emissions, to creating energy-secure community ‘microgrids’ and even providing more energy storage units to aid grid balancing programmes.

Although the government is yet to fully utilise batteries in their net zero strategy by supporting consumers to enter the market, the energy saving properties of batteries are now recognised in SAP. SAP version 10.2 rewards new homes with a battery in conjunction with PV panels with a higher SAP rating.

In the current climate of high energy bills, supply insecurity and empty net zero targets, domestic battery storage units are part of the solution to many of the energy problems the UK is facing. Equally, with the price of Li-ion batteries constantly dropping, it is a technology we can expect to see more of in our homes.

Living with a battery

Whilst this all sounds promising on paper, to get a feel for what it is like living with a battery, I spoke to Andy and Rob, who recently moved into a property with a fully integrated system. The four-bed, based in Gosport, Portsmouth, is on a new development built by the award-winning Elite NuGEN, who are renowned for prioritising sustainable practices in their work.

Their fully integrated Wondrwall system includes solar PV panels, a 6.5 kWh battery, an inverter, roof fitted heating panels, and smart switches which automatically adjust the heating and lighting to match the households use patterns. Pair this with the homes near-Passivhaus level of insulation and it makes for an extremely energy efficient home, estimated to have 75% lower running costs than an average house.

Andy and Rob praised the energy efficiency of the building, paying only £3.15 for a day’s electricity on average in summer. A price that gets even lower when the £20.79 earned for exporting excess electricity to the grid in August is taken off the couple’s bill.

Now it is winter and there is less solar gain, Andy and Rob have switched over to a time-of-use tariff. This was done automatically by their energy provider, Octopus, as part of their exclusive Octopus Go tariff which automatically switches customers to the best deal for them. Here, Octopus works with the system to understand their usage patterns and ensures their battery is never drained when they need it. This is one feature Andy and Rob were especially fond of, as it means they get the cheapest electricity, with no risk of being left without.

Although there were no complaints raised about the cheaper energy bills afforded by the battery and its fully integrated system, the same cannot be said for the usability of the system. Completely controlled by an app, Andy and Rob noted the complexity of setting up the system, which they would have struggled to do had it not been for a Wondrwall representative being on hand to assist. They also expressed difficulty trying to set their own heating and lighting controls rather than using the settings suggested by the system’s AI. Having previously lived in a property with a similar system but a different app, Andy and Rob expressed their old Newheat system was far less complicated. However, they did also mention that the Wondrwall app is new so expect it to become more user friendly as it develops.

This article was taken from Sava Technical Bulletin 42. To be informed when the next Technical Bulletin is published, you can sign up here. Alternatively, to view past issues of our Technical Bulletin, you can sign up Sava Edge, our free online library of practical and technical information and other resources for residential property professionals.

This article was written by Johnnie Leather. Johnnie is a Public Policy Researcher with an MA in Social and Public Policy and carries out research on energy policy and sustainability in the built environment at Sava.