Solar Battery Installation

Adding storage: what a battery installation involves

If you already have solar panels — or you are speccing a new system and wondering whether storage earns its place — a battery is the piece that changes how much of your own generation you actually use. A solar array without storage typically self-consumes around 35–50% of what it generates, with the rest exported for modest rates; a well-sized battery lifts that to roughly 70–85%, and each shifted unit is worth the gap between your import price (around 26p) and your export rate (roughly 12–16p/kWh on leading Smart Export Guarantee tariffs as at mid-2026). Typical domestic storage runs 5–15 kWh alongside 3.5–8 kWp of PV.

But a battery installation is not a plug-in accessory, and this page exists because the three decisions that define a good one — how it couples to your array, where it physically goes, and when the grid paperwork is filed — are precisely the three that rushed installers get wrong. The hardware is the least interesting part. The design is the job.

DC or AC: the coupling decision that shapes everything

Every battery installation takes one of two electrical routes, and which one applies to you is mostly decided by whether you already own an array.

DC-coupled means a hybrid inverter manages both the panels and the battery as one system. The battery charges directly from the array’s DC side before conversion losses, making this the more efficient route — and since one hybrid device replaces separate units, it is the natural choice when battery and panels are installed together. Fitting a hybrid inverter to an existing array means replacing the inverter you already own, which is why DC coupling is mostly a new-system decision.

AC-coupled means the battery has its own inverter-charger and connects on the house side, leaving your existing solar system untouched. It bolts onto any array regardless of age or brand, which makes it the standard retrofit route: no warranty disturbance on the original install, no inverter swap. The cost is a little round-trip efficiency — energy converts DC to AC and back again — accepted in exchange for retrofit freedom.

The honest guidance: buying solar and storage together, DC-coupled hybrid is usually the better engineering; adding storage to a working array, AC-coupled retrofit usually wins. An installer proposing to scrap a healthy inverter to force a hybrid route should be asked to justify the arithmetic.

Where the battery goes — and where it must not

Siting is now a safety standard, not a preference. PAS 63100:2024, the British Standards Institution’s specification for electrical energy storage in dwellings, steers domestic batteries away from lofts, escape routes and bedrooms. The proper homes are a garage, a utility room, a plant cupboard or a suitable external wall: cool, ventilated locations with a solid wall or floor fixing and clearance around the unit.

This is the differentiator between installers who follow current guidance and those who follow the shortest cable run. A battery in the loft was common practice for years because the cable route from the roof was convenient — and it is exactly what PAS 63100 now steers against: lofts are warm (batteries age faster and perform worse in heat), hard to inspect, and above your escape routes. A bedroom cupboard fails the same test. If an installer proposes the loft, that is not a difference of opinion; it is a corner being cut against current safety guidance, and worth pushing back on or walking away from.

Physically, expect each unit to occupy somewhere between a suitcase and a small fridge, wall-mounted or floor-standing. Cold is a milder enemy than heat — some chemistries derate below freezing, so an external-wall or unheated-outbuilding siting should come with the manufacturer’s temperature range checked, not assumed.

Installation day, step by step

A battery installation — retrofit or alongside new PV — is a one-to-two-day electrical job when properly planned, and the planning is most of it.

Survey first, boxes later

The survey settles the design before anything is ordered: the coupling route (hybrid versus AC retrofit), the siting location against PAS 63100 with fixing surface and clearances confirmed, the consumer-unit position — spare ways, earthing arrangement, whether surge protection (SPD) needs adding — and the grid-connection arithmetic. That last item has a hard sequencing rule covered in the next section: most solar-plus-battery combinations need DNO approval before they are switched on, so the application belongs at survey stage, not after delivery.

Mounting and wiring

On the day, the installer mounts the unit — batteries are heavy, so wall fixings go into masonry or engineered supports, never plasterboard alone — and builds the electrical connection: DC cabling to the hybrid inverter on a DC-coupled job, or the battery’s own inverter-charger tied into the consumer unit on an AC-coupled one. Expect consumer-unit work either way: a dedicated circuit, isolation, and SPD provision where the design calls for it, all to BS 7671. A current-transformer clamp goes around the meter tail so the system can see household import and export in real time — it is what lets the battery charge from surplus solar rather than blindly.

Configuration is where the value lives

Commissioning covers the electrical tests (insulation resistance, polarity, functional checks) and then the part that actually earns money: configuration. Charge and discharge windows, tariff integration, backup behaviour if fitted, app setup, and — critically — registering the system to work with a smart tariff. The installer should leave you with the monitoring app running, the battery visibly responding to solar surplus, and the tariff logic explained in plain terms. A battery commissioned with factory defaults and no tariff setup is a filing cabinet: installed, but not doing the job.

Paperwork

Handover matches the MCS pattern: certification under MIS 3012 (the MCS battery standard) where applicable, the Electrical Installation Certificate for the consumer-unit and circuit work, DNO evidence — G98 notification or, far more often with storage, the G99 approval — and warranty registrations. Battery warranties are typically expressed in years and throughput (cycles or total energy); knowing both numbers tells you what the guarantee actually covers.

G99 first, energise second

Grid paperwork is where battery projects go wrong administratively. The thresholds: up to 16 A per phase (about 3.68 kW of inverter output), the G98 route applies — connect, then notify the District Network Operator within 28 days. Above 16 A per phase, a G99 application must be submitted and approved before the system is energised. A battery changes the arithmetic because the DNO assesses the combined export capability of everything on the connection: most solar-plus-battery combinations exceed the G98 threshold even when the original array alone did not.

The practical consequence is sequencing. The G99 application belongs at survey stage — before the kit is ordered, weeks before installation day — because approval takes weeks and the DNO can impose conditions, including export limitation. “We’ll sort the paperwork after fitting” on a G99-scale system inverts the legal order and is how people end up with systems forced to run export-limited, or waiting de-energised for retrospective approval. Ask any battery quoter one question: who submits the G99, and when? The answer tells you whether they run this process properly.

Costs, and what actually moves the payback

Retrofit battery-only installations run £2,500–£7,000 depending on capacity and coupling; combined solar-plus-battery systems land at £9,000–£15,500 for typical domestic sizes. Since February 2024, retrofit battery-only installations qualify for the 0% VAT rate alongside solar — a genuine dated saving until 31 March 2027, when the rate reverts to 5%. Detailed pricing sits on the cost guide, and the VAT and export positions under grants and funding.

Two levers move the payback more than the hardware price. First, self-consumption: lifting it from around 35–50% to 70–85% converts export-rate units into import-rate units, worth roughly the 10–14p/kWh gap between the two at current dated rates. Second — and underestimated — smart tariffs: charging the battery on cheap overnight units and discharging through the evening peak often does more for winter economics than summer solar does, because it works every day of the year regardless of weather. A battery installation that includes the smart-meter and tariff setup unlocking this is a different financial product from one that omits it, at the same hardware cost. Combined, a well-designed system models around a nine-year payback; the same battery installed without tariff configuration can model years longer.

Scenario: a 9.5 kWh retrofit to an existing 4 kWp array

A modelled scenario, not a client project. A household with a three-year-old 4 kWp array self-consumes about 40% of its 3,600 kWh annual generation — the working household is out during the sunniest hours. The design: an AC-coupled 9.5 kWh battery, leaving the existing solar system and its warranties untouched, sited in the garage on an external masonry wall in line with PAS 63100 — expressly not the loft the household first suggested. The combined system exceeds G98 limits, so the G99 application goes in at survey and returns approved, without export limitation, before installation day.

The install itself takes a day and a half: mounting and circuit work, CT clamp on the meter tails, SPD added during the consumer-unit work, then commissioning and tariff configuration onto an off-peak overnight rate. Modelled self-consumption rises to around 80%, and winter arbitrage — overnight charging at the off-peak rate, discharging through the evening peak — adds value the panels alone never could. The combined annual benefit models in the £550–£750 range against a mid-range installed cost, for a payback inside the battery’s warranted decade. The two decisions that made the numbers work were the coupling route and the tariff setup — neither of which appears on a spec sheet.

Battery installation FAQs

Where should a home battery be installed?

Following PAS 63100:2024: a garage, utility room, plant cupboard or suitable external wall — cool, ventilated, solidly fixed, with clearance around the unit. Not lofts, not escape routes, not bedrooms. An installer proposing the loft because the cable run is short is cutting a corner against current safety guidance.

Can I add a battery to my existing solar panels?

Yes — that is exactly what AC coupling is for. The battery brings its own inverter-charger and connects on the house side, leaving your existing array, inverter and warranties untouched. Expect £2,500–£7,000 installed depending on capacity, currently at 0% VAT (until 31 March 2027), plus a G99 application in most cases before switch-on.

Do I need DNO permission for a battery?

Usually, yes — in the sense that most solar-plus-battery combinations exceed the 16 A per phase G98 threshold, which triggers a G99 application that must be approved before the system is energised. The application should be submitted at survey stage. Below the threshold, the installer notifies within 28 days of commissioning instead.

How long does a battery installation take?

One to two days on site for a typical domestic retrofit: mounting, circuit and consumer-unit work, then commissioning and tariff configuration. The full programme runs longer — typically several weeks — because the G99 approval belongs before installation, and that timeline is set by the DNO, not the installer.

Will a battery work during a power cut?

Only if it is specified for backup — many standard installations shut down in an outage, by design, to protect engineers working on the network. Backup capability needs the right hardware and wiring for some or all circuits, adds cost, and should be an explicit line in the quote, not an assumption. If outage cover matters to you, say so at survey.

Related pages

If the array itself is still to be built, the pitched-roof solar installation page covers the standard roof method a DC-coupled system pairs with — and for shaded or unsuitable roofs, a ground mounted solar installation feeds a battery just as well from the garden. Then see how much it costs, review grants and funding routes, or request a quote and get the G99 arithmetic done at survey, where it belongs.