The short answer
Yes. Almost any home with solar panels can have a battery added, even if the panels were fitted years ago by another company.
Without a battery, most of the electricity your panels make during the day is exported to the grid for a few pence. A battery stores that spare energy so you can use it in the evening, when you would otherwise be buying electricity at full price.
At Eco Systems Group, we have been installing solar panels and battery storage since 2012. We are MCS-certified and have completed the Fox ESS installer programme. We fit Fox ESS, Sigenergy and Tesla Powerwall batteries to new and existing solar systems across London, the South East and the East of England.
This guide explains how adding a battery works, what affects the choice of system, and what to expect from the installation.
Two ways to add a battery
There are two main ways to add a battery to an existing solar system. Which one suits you mostly depends on the age and type of your current inverter.
| Option 1: Keep your inverter (AC-coupled) | Option 2: Replace it with a hybrid inverter | |
|---|---|---|
| How it works | The battery comes with its own inverter and connects alongside your existing system | A new hybrid inverter runs both your panels and the battery |
| Best for | Newer systems where the existing inverter is working well | Older systems, or where the inverter is due for replacement anyway |
| Disruption | Your existing solar set-up is left as it is | Your old inverter is removed and replaced |
| Good to know | Simple, and leaves your current system untouched | Gives you a new inverter warranty at the same time |
Inverters typically last 10 to 15 years, so if yours is getting on, replacing it with a hybrid inverter at the same time can save a second visit later. We will check your system during the survey and recommend the right option.
What to consider before adding a battery
What size battery do I need?
The right size depends on how much electricity you use in the evening and overnight, and how much spare solar your panels produce. Most homes we work with choose a battery between 5kWh and 24kWh. We look at your system, your bills and how you use energy before recommending a size, so you do not pay for capacity you will not use.
Which batteries do you install?
We install batteries from three leading brands:
- Fox ESS. We have completed the Fox ESS installer programme. Fox batteries are modular, so storage can be added in stages, and Fox inverters suit both AC-coupled and hybrid set-ups.
- Sigenergy. A modular, all-in-one system that combines inverter and battery, with room to expand storage later.
- Tesla Powerwall. One of the best-known home batteries, with a simple app for monitoring your solar, battery and usage.
We will recommend the brand and size that best suit your home, your existing system and your budget.
Can I charge it from the grid at night?
Yes. Many energy suppliers now offer time-of-use tariffs with cheaper overnight electricity. A battery can charge at the cheap rate and power your home through the expensive evening peak. In winter, when your panels produce less, this is where much of the saving comes from.
Will it work in a power cut?
Not automatically. Most batteries switch off during a power cut for safety. If backup power matters to you, ask about a system with a backup or emergency power function, and we will explain what it can and cannot run.
Where will the battery go?
Safety guidance for home batteries (PAS 63100:2024) sets out where they should and should not be installed. Batteries should not go in lofts or roof spaces, bedrooms, or on escape routes such as hallways, landings and stairs. Common locations are a garage, an outbuilding, a utility room or an outside wall. We will agree the best location with you at the survey.
I get Feed-in Tariff payments. Can I still add a battery?
Usually, yes. The battery must be connected so that your generation meter only records electricity made by your panels. We will check how your system is set up and explain what, if anything, you need to tell your Feed-in Tariff supplier.
Is there VAT on a battery?
Currently, no. Since 1 February 2024, batteries added to existing solar panels in homes have qualified for 0% VAT. This relief currently runs until 31 March 2027 (HMRC guidance).
Do I need permission?
You do not normally need planning permission for a battery inside your home or garage. Your local electricity network operator must be notified, and in some cases asked for approval, before a battery is connected. As your MCS installer, we handle this paperwork for you.
How a battery retrofit works with Eco Systems Group
- Enquiry. Call us or fill in the quote form. Tell us roughly when your panels were fitted and, if you know it, the make of your inverter.
- Free survey. We check your panels, inverter, consumer unit and the best place for the battery, and look at how you use electricity.
- Written quote. You get a clear quote with the recommended battery size and option, with no obligation.
- Installation. Most battery retrofits are completed in a single day. We set up the app so you can see your solar, battery and usage.
- Handover and paperwork. We explain how everything works, register the installation and handle the network operator notification.
Areas we cover
We are based in Harold Wood and install solar panels and batteries across London, the South East and the East of England, including Essex, Kent, Hertfordshire, Surrey, Sussex, Suffolk, Cambridgeshire and Norfolk.
Frequently asked questions
Can I add a battery if another company installed my solar panels? Yes. We regularly add batteries to systems we did not originally install. We check the existing set-up at the survey first.
How long does it take to install a battery? Most battery retrofits take one day. If the inverter is being replaced as well, it may take a little longer.
Can I add more battery storage later? Many modern batteries are modular, so extra capacity can be added later. We will tell you whether the system we recommend can be expanded.
Does a battery need maintenance? Very little. The system monitors itself, and you can check its performance in the app. We are on hand if anything needs looking at.
Will a battery save me money in winter? Yes, especially if you charge it on a cheaper overnight tariff and use that energy during the evening peak.
Get a free battery survey
Thinking about adding a Fox ESS, Sigenergy or Tesla Powerwall battery to your solar panels? Call Eco Systems Group on 0203 411 4885, email info@ecosystemsgroup.co.uk, or request a free, no-obligation quote online. We cover London, the South East and the East of England.
