Should your business retrofit an AC- or DC-coupled battery?

AC coupling joins a battery to the site's AC circuits, while DC coupling connects storage on the solar DC side. A laboratory study models 2 layouts and shows why the connection point affects conversion and clipping [S1]. For existing business solar, check retained equipment, simultaneous output, metering and network acceptance before selecting a design. Checked October 2026.

Last checked 18 October 2026

How do AC-coupled and DC-coupled battery retrofits differ?

The coupling point is where your battery joins the solar installation. With alternating-current (AC) coupling, solar and storage have separate conversion paths joined on the building’s AC side. With direct-current (DC) coupling, the battery connects on the solar DC side, commonly sharing an inverter [S1].

For an existing photovoltaic (PV) array, that distinction affects which equipment you retain and how electricity reaches storage. The flow below describes the energy paths modelled in the national laboratory’s technical study [S1]. It is not a wiring design.

Read commercial solar inverters for the shared inverter basics. Here the question is how to add storage to an installation already operating at your premises.

Can you keep the existing solar inverter?

An AC-connected battery uses dedicated power electronics, so its electrical architecture can leave the original PV inverter in place. A DC-connected design requires a compatible path on the solar side [S1], [S2]. Neither label establishes compatibility with your particular installation.

Ask the designer to inspect the existing inverter model, electrical drawings, panel strings and available connection space. Request a marked drawing showing what remains and what changes. If the proposed DC route involves replacing the solar inverter, identify that replacement explicitly in the scope.

Historic England describes packaged storage with specified input and output conditions and stresses matching the package to generation, loads and supply [S3]. A battery-ready description therefore needs supporting equipment and operating details, rather than an assumption that any storage can be attached later.

Obtain written confirmation of compatibility, commissioning responsibilities and effects on existing warranties. Ask who will investigate a fault spanning the old solar installation and the new storage.

Does avoiding extra conversion always make DC coupling worthwhile?

DC coupling can avoid passing solar charging energy through the PV inverter before storage. AC coupling requires that conversion first [S1]. However, a conversion-path advantage is not an annual operating result.

The following is an illustration, not a quote. Every numerical input is an assumption for comparing paths at the same starting boundary: 100 kWh of solar energy on the DC side, all intended for storage and later use. Kilowatt-hours (kWh) measure energy; kilowatts (kW) measure the rate at which it moves.

Arithmetic: AC = 100 × 0.97 × 0.96 × 0.95 × 0.97. DC = 100 × 0.98 × 0.95 × 0.97. Results are rounded. These selected efficiencies are not measurements or technology benchmarks. Auxiliary consumption, standby demand, clipping, capacity restrictions and direct solar use are excluded.

For a real proposal, request measured or modelled system efficiencies at the same boundaries and operating loads. Then apply them to the energy that will actually pass through storage. Do not apply the example’s difference to all annual PV generation.

Can a DC-coupled battery recover inverter clipping?

Clipping occurs when potential solar production exceeds the inverter’s conversion limit. The laboratory’s DC-coupled model can divert energy to storage before that bottleneck, while an AC-connected battery receives solar energy after the original inverter [S1].

Recovery still depends on available battery capacity, charging power and control settings. The laboratory’s hybrid modelling also imposes inverter constraints on combined solar and storage output [S2]. Moving the charging point does not remove every power limit.

Distinguish clipping from export curtailment. Export limitation controls power leaving the premises; it is not simply the solar inverter rating [S4]. Ask the designer to identify each cause of reduced production in the generation records before estimating what a battery might recover.

Require an energy breakdown for direct use, storage, export, inverter clipping and export-related curtailment. Ask where recovered energy would go if the battery were already full.

What changes at the grid connection?

Your distribution network operator (DNO) manages the local electricity network. Storage guidance directs installations outside specified smaller-system arrangements through G99, the technical requirements for generation operating in parallel with that network [S5].

An export limitation scheme controls the net export at the connection. The DNO’s guidance says such schemes must meet G100, the engineering recommendation for limitation arrangements, and relevant power-quality requirements [S4]. A retained solar inverter does not establish that the changed combined system is accepted.

Ask the installer to show the existing and proposed generation capacity, battery converter rating, import requirement and requested export limit. Include operating cases where solar and storage discharge together. Use G99 applications and export limitation for the detailed paperwork. Check the applicable process separately for Northern Ireland.

What this means for your site

Compare layouts against your existing installation and operating needs. This is a technology comparison; the decision should follow a documented assessment of your roof, controls and connection.

For Feed-in Tariff installations, Ofgem’s storage guidance distinguishes layouts and metering arrangements because eligible generation must remain identifiable [S6]. Follow adding a battery to business FIT solar for that specific issue. This is separate from deciding which conversion path suits your premises.

Ask for monitoring that records PV generation, battery charging and discharge, grid imports and exports. Keep clocks and measurement boundaries consistent so the totals can be reconciled. Historic England recommends monitoring inverter performance and retaining maintenance records [S7]. Require a handover demonstration of the measurements and control limits used in your proposal.

What should you do next?

Gather your existing drawings, inverter details, grid approval and generation records. Take those to the cut energy costs hub and site check, then get matched with an installer that covers your area.

Piggy Pineapple Ltd operates the referral service. We refer enquiries to installer partners and may be paid a fee. Our owner holds shares in at least one partner. We identify the proposed partner and disclose any shareholding our owner holds in it before passing on your details.