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BatteriesAC coupled or DC coupled? The 60 second answer
It sounds like an engineering detail and it is, but it decides whether you keep your existing inverter, how much energy you lose on every cycle, and what the installation actually costs.
Updated 4 August 2026 · written by the Clearline guidance team
The answer, before the reasoning
If you already have solar panels that work and an inverter with life left in it, you want an AC coupled battery. If you are buying solar and storage together, or your existing inverter is old and due replacement anyway, you want DC coupling through a hybrid inverter. That covers the large majority of UK homes.
Retrofit means AC, fresh install means DC
AC coupling adds a battery with its own inverter alongside whatever you already own, so nothing existing has to be touched. DC coupling replaces the inverter with a hybrid unit that handles panels and battery together, which is cheaper and slightly more efficient when you are buying both at once.
- Solar inverter
- Integrated, 3 MPPTs
- Efficiency, solar to home or grid
- 97.5 per cent
- Efficiency, solar to battery to home
- 89 per cent
What the two actually mean
Solar panels produce direct current. Your house runs on alternating current. Batteries store direct current. The question is how many times the electricity crosses between the two on its way from the roof to the battery to your kettle, and where those conversions happen.
AC coupled
The battery sits on the AC side of the system with its own inverter and charger built in. Solar generates DC, the existing solar inverter converts it to AC, the battery's own inverter converts it back to DC to store it, then converts it to AC again on the way out. Three conversions for a solar charge cycle.
The upside is independence. The battery does not care what brand your panels are, what inverter you have, or how old the array is. It also does not have to live next to the panels, which matters when the loft is full or the only sensible battery location is a garage on the other side of the house.
DC coupled
A single hybrid inverter handles both the array and the battery. Solar DC goes straight into the battery as DC with no conversion at all, and only converts to AC when the house actually draws it. One inverter instead of two, fewer conversions, and less kit on the wall.
| AC coupled | DC coupled | |
|---|---|---|
| Best for | Retrofit to working solar, microinverter systems, battery only homes | New solar and battery together, or replacing an old inverter |
| Existing inverter | Stays where it is | Replaced by a hybrid unit |
| Round trip loss on grid charge and discharge | Roughly 8 to 10% | Roughly 6 to 8% |
| Number of inverters | Two | One |
| Physical placement | Can sit away from the array | Tied to the array wiring |
| Cost on a fresh install | Higher, two inverters | Lower, one inverter |
Efficiency figures are for grid charge and discharge cycles. Specifications checked 3 August 2026.
How much the efficiency gap is worth
The honest answer is: less than the brochures imply. The difference between an 8 to 10% round trip loss and a 6 to 8% one is roughly two percentage points on every stored unit.
Put a number on it. A household cycling 10 kWh a day through the battery loses around 0.9 kWh on AC coupling and around 0.7 kWh on DC, a difference of about 0.2 kWh a day. Valued at the 26.11p capped unit rate for July to September 2026, that is a little over 5p a day, or under £20 a year. It is real, it is worth having when the choice is free, and it should never be the reason to rip out a functioning inverter.
Compare the whole job, not the efficiency line
Replacing a working solar inverter to gain two percentage points of round trip efficiency will not pay for itself. The DC advantage is genuine when you are buying an inverter anyway. It is not an argument for creating that purchase.
The cases where the rule flips
- Microinverter systems. If each panel has its own microinverter, there is no central DC bus to tap, so AC coupling is the only sensible route. The Enphase IQ Battery 5P is AC coupled by design and pairs naturally with Enphase microinverter arrays, while still working alongside non Enphase solar.
- Battery only homes. With no array at all, there is no DC generation to couple to, so the battery runs AC coupled off the grid connection.
- An old or failing inverter. If the existing unit is near the end of its life, replacing it with a hybrid and going DC coupled turns a repair you were going to pay for anyway into an upgrade.
- Physical constraints. Where the only viable battery position is a long way from the array, AC coupling avoids running new DC cable across the property.
What each approach means on the DNO application
This is where retrofits catch people out. Your Distribution Network Operator assesses the connection on inverter rating, not on how many kWh the battery stores, and it assesses cumulatively. Adding a 3.5 kW AC coupled battery inverter to an existing 3.5 kW solar inverter takes the site to 7 kW, which is well past the 3.68 kW single phase G98 threshold and into G99 territory.
G98 means you can install and then notify the network operator within 28 days. G99 means applying and waiting for written approval before the work happens. Ofgem's connection guaranteed standards give the operator 45 working days to issue a quotation for a low voltage generation connection, and type tested systems under 50 kW are usually decided faster than that in practice. A DC coupled hybrid replacing the existing inverter can land differently, because the old inverter comes out as the new one goes in. Our guide to adding a battery to existing solar covers that trap in full.
A free remote design call works out which coupling your specific setup needs, and whether it pushes you into a G99 application.
Get your free quote →What to ask on a quote
- Is this AC or DC coupled, and why was that chosen for my property?
- If DC coupled, what happens to my existing inverter, and is its removal priced in?
- What is the cumulative inverter rating after the work, and does that need a G98 notification or a G99 application?
- What is the usable capacity, as opposed to the nominal capacity?
- Does the chosen configuration still support the backup specification I asked for?
Product choice narrows quickly once coupling is decided. Sunsynk's ECCO hybrid inverters at 3.6 kW and 5 kW single phase are built for the DC coupled route, Fox ESS EQ modules work with both hybrid and AC inverters in the Fox range, and Enphase sits firmly on the AC side. The battery storage guide covers the landscape, and every county page in our coverage area carries a local calculator.
Clearline gives independent guidance and a free remote design call. Installations are carried out by an MCS-certified installation team for your area.
Coupling questions, answered
Which is better, AC or DC coupled?
Neither is better in the abstract. DC coupling is more efficient and cheaper when you are installing solar and a battery at the same time, because one hybrid inverter does both jobs. AC coupling is the right answer when you already have working solar, because it leaves the existing system alone.
Can I add a DC coupled battery to my existing solar?
Only by replacing your existing solar inverter with a hybrid one. That is a sensible move if the inverter is near end of life, and poor value if it has years left. Most retrofits go AC coupled for exactly that reason.
How much energy does AC coupling lose?
A grid charge and discharge cycle on an AC coupled battery loses roughly 8 to 10% round trip, against roughly 6 to 8% for DC coupling. On a 10 kWh daily cycle that difference works out at around 0.2 kWh a day, worth a little over 5p at the July to September 2026 capped rate.
What is a hybrid inverter?
An inverter that handles solar generation and battery charging and discharging in one unit, rather than needing a separate battery inverter. It is the piece of hardware that makes DC coupling possible, and it is why DC coupled systems have one box on the wall where AC coupled systems have two.
Does coupling affect whether I can have backup?
It affects which backup options are available, because the backup circuit is provided by the inverter or by a gateway sitting alongside it. Both approaches support backup, but the specification needs to be agreed at design stage rather than assumed. Our gateway guide covers what each tier requires.
Will an AC coupled battery work with any brand of solar panel?
In practice yes, because it connects on the AC side and never sees the panels directly. That is precisely why it is the standard retrofit answer, including for arrays whose original manufacturer no longer exists or whose inverter brand has no battery product of its own.
See the numbers next: Tesla Powerwall 3, installed, or what a battery costs.
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 batteries retrofit to existing solar without replacing the inverter and can sit away from the array greenreachenergy.co.uk
- AC and DC coupled battery comparison for UK homes jojusolar.co.uk
- DC coupling: shared hybrid inverter, fewer conversions, higher efficiency, cheaper for new installs kilowatts.uk
- Round trip efficiency: roughly 8 to 10% AC coupled versus 6 to 8% DC coupled greenreachenergy.co.uk
- Decision rule: AC for retrofit, microinverter and battery only systems; DC for new installs and inverter replacement saveenergyuk.co.uk
- Enphase IQ Battery 5P is AC coupled and works with existing non Enphase solar switchtogether.co.uk
- Sunsynk ECCO hybrid inverters at 3.6 kW and 5 kW single phase sunsynk.org
- Fox ESS EQ compatibility with Fox hybrid and AC inverters fox-ess.uk
- G98 and G99 thresholds, notification periods and cumulative inverter assessment capture.energy
- Ofgem connection guaranteed standards: 45 working day quotation timescale for a low voltage generation connection, £80 failure payment connections.nationalgrid.co.uk
- Ofgem price cap 1 July to 30 September 2026: 26.11p per kWh ofgem.gov.uk
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