Batteries FAQs

A home battery system is a large battery that you have installed at home, which can store excess electricity – usually that which is generated by your solar PV system and isn’t needed at the time – for use in your home at a time when energy can’t be generated such as night-time or on days with poor weather. This reduces your demand on the grid, because your home can use the energy stored in the battery instead.  It helps you make savings on your electricity bills and ensure that more of the energy you are using is renewably generated.

There are several key reasons why homeowners are looking at battery storage.

• Self-sufficiency. In general, we see that people want to be more self-sufficient and to run their homes off the electricity thy have produced themselves
• To run their car on sunshine. Even if you are out during the day, you can still use solar electricity to run your car.  Store your generated electricity in a home battery, and then discharge this into your vehicle when you return home.
• To help the grid. Using a home battery reduces electricity demand at peak times (weekdays 16:30-19:30).  That makes the UK’s overall system easier and cheaper to run.  Peak demand also determined how many power stations we need – so if we can reduce demand at peak times we simply don’t need to have as many fossil fuelled power stations anymore
• Riding through power cuts. Some models of batteries allow you to use your stored electricity in the event of a power cut.
• Getting the cheapest electricity. A home battery can allow you to store cheap night-time electricity for use at other times.  It means you always access the cheapest possible electricity, whether from solar or the grid.

The simple answer is that the home battery system stores electricity for use in your home at another time. The demand for energy within the home isn’t at one level all day, especially if there are periods when some or all of the family are out of the house. This means that for some periods of the day, the electricity being generated by their solar panels isn’t being fully utilised. Of course, when the sun goes down or the weather is particularly bad, the solar PV can’t generate electricity, and you need to draw from the grid to power your home. A home battery means that you have solar energy stored to use before you need to take from the grid. A much more detailed explanation of how home battery storage systems work can be found here.

If you currently receive feed-in-tariff (FiT) payments for the electricity you generate with your solar PV, they will not be affected if you install a home battery system. The FiT scheme was discontinued for new home solar PV systems installed on or after 1^st April 2019, but existing qualifying households won’t lose any of these payments for the contract term (usually 20 years from installation) if they do install a home battery system.

Different home battery storage systems may come either ‘AC coupled’ of ‘DC coupled’. A DC coupled battery system, locates the battery between your panels and the inverter (which converts DC electricity to AC electricity for use in the home.  DC coupled systems are more thermodynamically efficient, as you only convert DC to AC electricity once.An AC coupled battery system has a separate inverter in the battery itself.  Solar DC electricity is converted to AC electricity for use in the home, and if it goes into the battery is converted to DC again.  This is thermodynamically less efficient, but much more flexible.  It allows batteries to be charged from any source, not just solar.  They can be charged from the grid, for example when electricity is cheap, typically when there is a lot of wind power on the national grid.  So it allows you to take advantage of cheap low carbon electricity no matter where it is generated.

It also means that the battery doesn’t need to be installed physically close to your solar PV inverter, which makes installation more flexible. For these reasons, the market is moving towards AC coupled systems as standard.

Regardless of whether you choose a DC or AC coupled battery storage system, it should be possible to install it with an existing solar PV system, when using an experienced approved installer like Joju Solar.

If your household has very high energy requirements in the evenings, especially during longer winter nights, smaller battery storage systems may not be able to hold enough power for all of your needs all night. For example, if you wanted to run several ‘thirsty’ appliances at once in the evening, such as kettles, microwaves, washing machines, along with TVs, lights, fridges etc, your battery would discharge at a much quicker rate than that of a less busy household with lower energy demands. Home battery systems are also limited to the amount of electricity output they can give at any one time. It’s important to choose a battery storage system for your home which is best matched to your household’s needs. We can help you to find the best home battery solution for your individual circumstances – contact us today for more information.

The size of home battery system that you need will depend on the size and energy requirements of your home. The average household uses between 8-10 kWh of electricity per day. Home storage batteries start at around 2.5-5 kWh in capacity for small systems, up to the larger systems which offer around 13-15 kWh of energy storage.We would typically size a system by following a two step approach:

• Economically, the ideal size for a battery is one that would cover your evening and night-time usage (with a little to spare, just in case). Your electricity demand will empty the battery by next morning, meaning it has the maximum possible space to capture the next day’s sunshine.
• We then sense check this against the size of your solar PV system. Obviously, there’s no point having a large battery if your generation is small – as you’d never be able to fill it.

So in practice, some home battery systems are sized to the demand of the home, but in some cases they are sized to what the solar PV system can produce.  Getting this right is complex, which is why our expert engineers are on hand to help you find the right system for your home.

You will need to bear in mind that home storage batteries might well not receive enough energy to charge every day (depending on the weather and how much solar electricity your home generates and uses).  Find out more about how this can work around the year here.

With a correctly-sized battery system for your home in the UK, you should ideally have enough energy waiting to meet your evening and overnight needs for the majority of the year, but are likely to need to draw electricity from the grid in the winter months.

With home battery systems that you use your solar PV system to charge, there are two ways to answer this question.The amount of time that the solar battery can run your home for will depend on the capacity of the battery system and the level of charge. Some home batteries, like the Tesla Powerwall 2, could potentially power your home for more than 24 hours from a full charge, because the capacity of the battery is more than the average daily household usage of electricity. However, if it is only partially charged, or if you have a battery system with less capacity, the energy won’t last as long when powering your home.

In terms of the life span of a home battery system, this can vary; depending on the make and model of your battery and the way that you use it. Whilst these types of batteries are designed and optimised to undergo frequent charging and discharging, eventually, over many thousand cycles, the batteries will start to lose a small percentage of capacity. Professionally installed home battery systems will always come with a warranty, which are usually around 10 years, and are guaranteed to maintain a certain level of performance e.g. the Tesla Powerwall 2 has a warranty for 10 years for 80% of the original capacity; so, if your battery isn’t storing at least 80% of the energy it did when new within 10 years, Tesla will replace it.

From our own experience of these products and the very slow degradation of the types of batteries used in the home battery systems, the likelihood is that a home battery system will usually significantly outlast the warranty.  It is the same as any other electronic product in this respect – if you bought a TV with a 5 year warranty, you would reasonably expect it to last for 10+ years.

We can advise on the best home battery system for your needs and make sure that all warranty information is clearly understood, on all aspects of the installation. Get in touch today for more information.

We would never use or install a brand of home battery that doesn’t come with a warranty. All of the major manufacturers of these systems offer a warranty, usually around 10 years in length, although there are some restrictions and caveats on usage for some products. If you choose Joju Solar to install your home battery system, we can match the best type of system, with a warranty that you’re comfortable with, to your home.

The cost of a home battery system will vary, depending on the make and model of system that you choose. You will also need to consider installation costs, which can also vary, depending on the complexity of the work that needs to be done. For example, some of our customers choose to upgrade their solar array and/or install an EV charging point at the same time as we install the home battery system, which can mean a big saving on having these three things done separately. Some installations may require a separate inverter be fitted and some will be able to use the same inverter as your solar panels. We can offer expert guidance as to the best system for your existing setup and home.The cost of a home battery system will depend not only on the brand of product, but also the size/capacity of the battery itself. Currently, the Tesla Powerwall 2 offers great value per kWh of storage, but if you are a smaller or less busy household then you may be better off with a smaller and cheaper system with less energy storage capacity.

If you’re getting a home battery that works with your solar PV system, you will need to ensure that your installer has the necessary experience to carry out the installation properly, so that all of the necessary elements communicate properly with each other. It is advised that you use an installer with years of experience in both solar PV installations and home battery systems.We are fully signed up to the Renewable Energy Consumer Code, which enforces high consumer protection standards, following the consumer journey from start to finish, for businesses who are selling or leasing renewable energy generation systems to domestic consumers.

Get in touch with us for more information on installations.

Some home batteries can be installed either indoors or outdoors, depending on which system you opt for. Many homeowners choose to install their battery system in their garage, which offers some protection from the elements. The Tesla Powerwall 2 and some other models can be installed either inside or outside, as the UK’s climate makes extremes of temperature unlikely. You would need to ensure that a battery system installed outside is kept clear of significant debris like leaves and an accumulation of snow, and that it is safe from potential flooding.

It’s very difficult to say how much a home battery will save you, as it is highly dependent on both how much you personally use and how much you can generate.Our analysis has shown that a battery can actually improve the payback of a solar PV system in some circumstances.  Where the solar PV system is large, the battery can be filled from solar PV for a greater proportion of the year, which improves the overall economics of the home generation system.

We also know that where this is not possible, having the ability to top-up with cheap grid electricity when solar is not available, also massively improves the return on investment.

Overall, battery paybacks tend to sit in the 10-15 year range – this is above the warrantied lifetime, but within the lifetime that you might expect the product to last, as we have noted above.  We therefore consider battery storage systems as a broadly cost-neutral way for you to increase your own self sufficiency, and to be less reliant on more polluting grid electricity.

Some home battery systems can power your home in the event of a power cut, but not all products of this type are designed with this capability. You can find out more about which battery storage products can work in a power cut here.

Whilst most people use home battery systems to help make the most of the solar energy being generated by their PV system at home, it can be possible for some home battery systems to be used in households that don’t have a solar array fitted. Not all products will have this capability, but some, e.g. the Tesla Powerwall 2, can be set up to do this.Rather than the battery system being charged by solar energy, it can instead be charged with ‘cheap’ electricity from the grid (for those homes on a tariff that provides cheaper off-peak energy, usually overnight), which is then used in the home during peak times so that they don’t need to draw as much ‘peak-rate’ energy from the grid. This can mean savings on your electricity bills.

If you have any more questions about home battery storage systems or want advice on which might be the best choice for you, get in touch with us today!