Adding Battery Storage to Existing Solar

Can You Add Battery Storage to Existing Solar Panels?

If you already have solar panels but no battery, you are almost certainly exporting a significant amount of solar electricity to the grid during the day and then buying it back at full price in the evening. Adding battery storage to your existing system captures that surplus generation for use when you actually need it, dramatically increasing your self-consumption rate and reducing your electricity bills further.

At ALPS Electrical, retrofit battery installations are one of our most requested services. Many customers who installed solar panels in the Feed-in Tariff era are now looking to add storage to maximise the value of their existing arrays, especially as electricity prices have risen sharply since their original installation.

AC-Coupled vs DC-Coupled: Which Do You Need?

When adding a battery to an existing solar system, the key technical decision is whether to use an AC-coupled or DC-coupled approach. This depends on your existing inverter type and what you want the battery system to do.

AC-Coupled Battery (Most Common for Retrofit)

An AC-coupled battery connects to your home's electrical system on the AC side, independently of your existing solar inverter. This means your existing solar inverter continues to operate exactly as before, and the battery system is a completely separate addition. AC coupling is the most common approach for retrofit installations because it works with any existing solar inverter, requires no changes to your existing solar setup, and can be installed in a single day in most cases.

Popular AC-coupled battery options include the Tesla Powerwall 3 (which can also be used in AC-coupled mode), GivEnergy AC-coupled systems and Fox ESS AC batteries.

DC-Coupled Battery (Inverter Replacement)

A DC-coupled approach involves replacing your existing solar inverter with a new hybrid inverter that handles both the solar panels and the battery. This can be more efficient (fewer conversion steps) and is often the better long-term choice if your existing inverter is ageing or near the end of its warranty period. Hybrid inverters from Fox ESS, GivEnergy and Sigenergy all support this approach.

The downside is that replacing the inverter adds cost and complexity. However, if your original inverter is 8-10 years old and will need replacing soon anyway, combining the inverter replacement with a battery addition makes excellent financial sense.

Best Batteries for Retrofit Installation

Based on our experience fitting dozens of retrofit battery systems, these are the options we most commonly recommend:

Tesla Powerwall 3: 13.5kWh capacity, seamless backup capability, excellent app. Ideal for customers who want a premium, all-in-one solution.
GivEnergy Gen 3: Available in 5kWh, 9.5kWh and larger sizes. Flexible sizing, competitive pricing, excellent scheduling capabilities for tariff arbitrage.
Fox Cube: Modular 5.76kWh stacking modules. Start small and add capacity later. Excellent value for money.
Sigenergy: New entrant with impressive full-home backup capability. Competitive with Tesla Powerwall on features.

What Does Retrofit Installation Involve?

A typical retrofit battery installation takes 1-2 days and involves mounting the battery unit on an internal or external wall, installing a new dedicated circuit from the battery to your consumer unit, fitting a CT clamp to monitor your grid import and export in real time, connecting the battery system (AC or DC coupled as appropriate), commissioning and configuring the battery management system, and testing all protection devices and verifying safe operation.

If you are also replacing the inverter (DC-coupled approach), the existing solar panels remain on the roof but are disconnected from the old inverter and reconnected to the new hybrid unit. This adds approximately half a day to the installation time.

How Much Does It Cost?

Retrofit battery installation costs depend on the battery capacity and whether you are replacing the inverter:

AC-coupled 5-6kWh battery: £3,000-4,500 installed
AC-coupled 10-13.5kWh battery: £5,000-9,000 installed
DC-coupled with hybrid inverter replacement + 10kWh battery: £5,500-8,000 installed
Tesla Powerwall 3: £9,000-12,000 installed (includes built-in inverter and backup gateway)

All residential battery installations qualify for 0% VAT, and the savings from tariff arbitrage and increased self-consumption typically deliver a payback period of 5-8 years.

Get a Retrofit Battery Quote

If you have existing solar panels and want to add battery storage, contact ALPS Electrical for a free assessment. We will evaluate your current system, recommend the best battery option for your setup and provide a fixed, all-inclusive quote. We install all major battery brands and can advise impartially on which system best suits your needs.

Watch Related Installations

See real installations from our team that demonstrate the topics covered in this article.

Frequently Asked Questions

1 How much does battery storage cost?

Battery storage costs in the UK range from £2,500 for a small 5kWh unit to £12,000+ for premium systems like the Tesla Powerwall 3 (13.5kWh). A mid-range system like the GivEnergy Gen 3 with 9.5kWh storage typically costs £4,000-£6,000. Prices include installation and are subject to 0% VAT when installed alongside or added to an existing solar panel system.

2 Can I install a battery without solar panels?

Yes, battery-only installations are increasingly popular. By charging your battery overnight on cheap tariffs like Octopus Go (7.5p/kWh) and using that stored energy during the day when rates are 24p+/kWh, you can save hundreds of pounds per year. Our Fox Cube battery-only installation video on YouTube demonstrates the savings potential in detail.

3 Tesla Powerwall 3 vs GivEnergy — which is better?

Both are excellent systems. The Tesla Powerwall 3 has a built-in inverter (simplifying installation), 13.5kWh capacity, backup gateway capability and the polished Tesla app. GivEnergy Gen 3 offers more flexible sizing, a strong community following, open API access and typically lower cost per kWh of storage. We install both and recommend based on your specific needs, budget and whether you want full home backup capability.

4 How long does a solar battery last?

Modern lithium-ion solar batteries typically last 10-15 years, or 6,000-10,000 charge cycles. Tesla Powerwall comes with a 10-year warranty. GivEnergy offers a 12-year warranty on Gen 3 batteries. After warranty expiry, batteries continue to work but with gradually reduced capacity, similar to a mobile phone battery. Most batteries retain 70-80% of original capacity after 10 years.

5 What is the difference between hybrid and AC-coupled batteries?

A hybrid (DC-coupled) battery connects directly to the solar panels via a hybrid inverter, converting energy once and achieving higher efficiency (typically 95-97%). An AC-coupled battery connects to your home electrical circuit and works independently of the solar inverter, making it easier to retrofit to existing solar installations. We install both types and recommend based on whether this is a new installation or an addition to an existing system.