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BatteriesAC versus DC coupled batteries, explained simply
There are two ways to wire a battery into a house. One suits a retrofit, one suits a fresh install, and the efficiency difference between them is smaller than almost everyone assumes.
Updated 4 August 2026 · from the OVO Solar & Battery team
The short answer
If you already have solar panels that work, your battery will almost certainly be AC coupled. It brings its own inverter, connects on the alternating current side of your system, and leaves the solar inverter you already own exactly where it is. If you are fitting solar and a battery at the same time, DC coupling through a single hybrid inverter is usually the better build.
The rule of thumb
Adding a battery to solar that already works means AC coupling. Buying solar and a battery together means DC coupling. The exception is an existing solar inverter that is near the end of its life, in which case replacing it with a hybrid unit can make sense.
What coupling actually means
Solar panels produce direct current. Battery cells store direct current. Your house runs on alternating current. So somewhere in the system, electricity has to be converted, and coupling is simply the word for where that conversion happens and how many times.
DC coupled: one inverter, two jobs
In a DC coupled system the panels and the battery share a single hybrid inverter. Solar electricity can go straight into the battery as direct current without being converted to AC first and back again. Fewer conversions means fewer losses, one box on the wall instead of two, and one set of wiring and commissioning to pay for.
AC coupled: the battery brings its own
In an AC coupled system the battery has its own inverter and charger built in, and it connects to the house on the AC side, downstream of whatever solar equipment is already there. Your existing solar inverter carries on doing its job untouched. The battery can also be sited wherever suits the property rather than wherever the solar wiring happens to land.
| DC coupled | AC coupled | |
|---|---|---|
| Inverters | One hybrid unit shared by panels and battery | Two units, one for the solar, one for the battery |
| Round trip loss | Roughly 6 to 8% | Roughly 8 to 10% |
| Solar you already own | Usually means replacing the existing inverter | Leaves the existing inverter exactly as it is |
| Battery with no panels | Not applicable | The only option |
| Where it can be sited | Tied to the solar wiring | Anywhere sensible, including away from the panels |
| Best fit | Solar and battery installed together | Adding a battery to solar that already works |
Round trip figures are typical UK market ranges for a full grid charge and discharge cycle, not a guarantee for any one product.
The efficiency gap, in money
Two percentage points sounds like a reason to choose. Put it through a year and it stops being one. A battery cycling around 5 kWh a day moves roughly 1,825 kWh in a year, so two extra percentage points of loss is about 36 kWh. At the 26.11p capped unit rate for July to September 2026, that is under £10 a year. Cycle a larger battery harder at 10 kWh a day and the gap is still under £20 a year.
The tariff gap dwarfs the conversion loss
Buying a unit overnight instead of paying 26.11p at teatime saves you roughly 13p on the 13p off peak rate we model across this site, and more on the cheapest published windows, which ran from 6.99p to 9p per kWh on 3 August 2026 and nearly all ask for an electric vehicle or a charge point. Losing an extra 2% of that unit in conversion costs you about a quarter of a penny. Coupling is a build decision about what is already on your wall, not the thing that decides whether a battery pays. The strategy behind those numbers sits on the strategy page.
Why a retrofit is usually AC coupled
- Your existing inverter stays. It works, it may still be in warranty, and pulling a healthy inverter off the wall to save half a penny a unit is poor value.
- Siting is flexible. The battery goes where the house has room and access, rather than being tied to the solar cable runs in the loft.
- Microinverters and optimisers change the picture. Systems that convert to AC up on the roof leave no DC to tap into, so AC coupling is the only sensible route. Our guide to optimisers, microinverters and string inverters explains which you have.
- No panels at all means AC coupling by default. A battery on its own has nothing to share a hybrid inverter with, and it still earns from the gap between off peak and standard rates.
- The loss is smaller than the alternative. Roughly two percentage points a year against the cost of a new hybrid inverter and a second commissioning visit.
Not sure what is on your wall, or what it would take to add a battery to it? The free 45 minute video design call works that out from photos and your meter data, and you get a written quote on the call.
Get your free quote →The retrofit detail people miss: your network operator
Adding a battery with its own inverter adds capacity to your grid connection, and your Distribution Network Operator has a say in that. The G98 process covers up to 16A per phase, about 3.68 kW on a single phase supply, and allows the work to be fitted first and notified within 28 days. Above that you need a G99 application, approved before installation, with up to 45 working days for a response. The assessment is on inverter rating rather than battery capacity, and it is cumulative, so a 3.5 kW solar inverter already fitted plus a 3.5 kW battery inverter puts the property at 7 kW and into G99 territory. That is a lead time rather than a barrier, and it is one of the first things checked on your design call.
When DC coupling is the better call
You are buying solar and a battery together
One hybrid inverter, one set of cable runs, one commissioning visit and one network application. It is the cheaper and tidier way to get both, which is why it is the standard build for a new installation.
Your existing inverter is already due replacement
Solar inverters do not last as long as the panels they serve. If yours is approaching the end of its working life, swapping it for a hybrid unit at the same time as the battery goes in deals with two jobs on one visit.
You want the fewest boxes on the wall
A hybrid inverter does the work of two separate units. In a tight utility room or a small garage, that difference is more practical than the efficiency figure behind it.
Your local OVO expert will tell you which arrangement suits your property before you commit to anything. Check the coverage page to see who covers your postcode, then book the free 45 minute design call and get the answer, and the price in writing, without anyone visiting the house.
Get your free quote →Coupling questions, answered
Can I add a battery to solar panels I already have?
Yes, and it is one of the most common jobs in the industry. The battery is normally AC coupled, which means it arrives with its own inverter and charger and connects downstream of your existing solar equipment. Your current inverter is not touched. The main things to check are where the battery can be sited and whether the added inverter capacity pushes your connection from G98 into G99, which we explain in our guide to the two processes.
Is DC coupling worth replacing my inverter for?
On efficiency grounds alone, no. The difference is roughly two percentage points of round trip loss, which on a normal household cycle is worth under £20 a year. Replacing a working inverter costs a great deal more than that. It changes if your inverter is already near the end of its life, because then you are paying for a replacement you needed anyway and getting the hybrid capability with it.
What is a hybrid inverter?
A single unit that manages both the solar array and the battery, rather than having a separate inverter for each. It is what DC coupling relies on. It converts the panels' direct current for use in the house, sends surplus direct current straight into the battery without a round trip through AC, and manages when the battery charges and discharges.
Does the coupling type affect what happens in a power cut?
No. Both AC and DC coupled systems shut down in an outage unless you have extra hardware, because of a safety rule called anti islanding that stops your house re energising a cable someone may be working on. Keeping the lights on needs a gateway or a dedicated backup circuit, which we cover in our guide to gateways and whole home backup.
Will a retrofit battery change my export rate?
OVO's SEG Install Exclusive rate pays 20p per kWh where OVO installs both your solar and your battery, and 15p per kWh for solar only. The exclusive rates require you to take your electricity supply from OVO and apply to systems under 30kW. Rates were correct at July 2026 and are subject to change. If your panels were fitted by someone else, ask your local OVO expert what your specific setup would qualify for, and see our Smart Export Guarantee page for how the scheme works.
Do I pay VAT on a retrofit battery?
Not at the moment. Battery storage installed in a home in Great Britain attracts 0% VAT, and that covers batteries retrofitted to existing solar and standalone batteries with no solar at all, not just new solar and battery systems together. The relief is scheduled to run until 31 March 2027, after which the rate is due to return to 5%.
How much does a retrofit battery cost?
Across the UK market, installed battery prices run at roughly £400 to £900 per kWh, a wide band because it stretches from a small retrofit to a large system with backup hardware. Our own figure is published rather than quoted on the day: £2,444 for 5.2 kWh usable, about £470 per usable kWh, fitted and commissioned. Full pricing is on the costs page.
Figures and specifications in this guide are sourced below and were checked on the date shown. Rates and product specifications change; we confirm the current picture on your free design call.
Sources
- AC coupled and DC coupled home batteries, retrofit behaviour and round trip efficiency comparison greenreachenergy.co.uk
- AC and DC coupling explained for UK homes, including microinverter systems jojusolar.co.uk
- Hybrid inverter DC coupling, conversion losses and cost for new installations kilowatts.uk
- Decision rule for AC versus DC coupling on retrofit and new installations saveenergyuk.co.uk
- G98 and G99 thresholds, cumulative inverter assessment and network operator response times capture.energy
- Ofgem, energy price cap 1 July to 30 September 2026, unit rate 26.11p per kWh ofgem.gov.uk
- Published overnight off peak rates of 6.99p to 9p per kWh, checked 3 August 2026, most of them conditioned on an electric vehicle or charge point supplier tariff pages
- Zero rate VAT on domestic battery storage, including retrofit and standalone, to 31 March 2027 solarenergyuk.org
- Installed cost per kWh benchmarks for UK home battery storage, 2026 kilowatts.uk
- Anti islanding behaviour of grid tied solar and storage in a power cut viablepower.co.uk
- OVO Solar and Battery published pricing, battery specification and SEG Install Exclusive rates ovosolarandbattery.co.uk
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