Many existing solar PV systems were installed before battery storage became a practical option. They were designed for maximum generation, not maximum self-consumption. Every kilowatt-hour of surplus midday generation that a household cannot absorb in real time is typically exported to the grid at Smart Export Guarantee rates - while the same home imports electricity back at a considerably higher unit rate in the evening. An AC-coupled battery retrofit addresses this directly. Using AC-coupling technology, we connect a Tier-1 battery system to your existing installation at the AC supply level - no changes to your panels, no work on your roof, no replacement of your existing inverter. Your array continues operating as it does today. The battery stores surplus generation that would otherwise be exported and makes it available for evening and overnight use when household demand is highest. Self-consumption typically improves significantly, though the exact uplift depends on your array size, household usage profile and the battery capacity specified. The next step is a review of your existing inverter and export data to confirm compatibility. For an overview of the full battery range, visit our battery storage hub. If you are planning solar and battery together from the start, see solar and battery systems designed together. For payment and finance routes, see our smart financing page.
AC-coupled battery technology connects to your existing installation at the AC supply side of the consumer unit. It has no physical contact with your existing solar inverter, your DC wiring, or your panels. Your existing system continues operating identically. The battery simply monitors AC supply conditions, detects surplus generation from your array, and charges itself from that surplus before it reaches the export meter. This works with any brand of solar inverter, any age of installation, and any panel configuration. There is nothing to uninstall, no scaffolding required, and no disruption to your existing MCS warranty. The entire retrofit takes place within your property - typically in a day.
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A Surrey solar installation without storage typically exports the majority of its generation at 4 to 6p/kWh and imports at 25 to 35p. For example, on a 4kWp array generating 3,600 kWh annually with 65 percent export, this structural inefficiency could cost in the region of 620 GBP per year in avoidable grid purchases. A correctly sized battery retrofit can capture 60 to 70 percent of that export - recovering in the region of 500 to 550 GBP per year in retained generation value, plus additional Octopus Intelligent overnight arbitrage cycles during winter months when solar generation is lower. For larger Surrey estates with 8 to 12kWp arrays, the annual recovery figure can be higher still. These figures are indicative and confirmed through individual system modelling. A potential 0% VAT position on retrofit installations, where eligible, can add to the financial case, subject to confirmation at quotation stage.
Battery storage retrofitted to existing solar may qualify for the same 0% VAT rate as a new combined installation, where eligible under current HMRC rules and confirmed at quotation stage. On a 9.5kWh GivEnergy retrofit costing approximately 7,000 to 8,500 GBP all-in, this could save in the region of 1,400 to 1,700 GBP at invoice, with the exact figure confirmed at quotation stage. Beyond the potential VAT saving, the retrofit creates an integrated energy platform: your existing array, the new battery, and the grid are co-ordinated by a single management system. Octopus Intelligent overnight charging, Smart Export Guarantee registration optimisation, and future EV charger or additional battery capacity can all be layered onto this platform without structural rework.
We request your existing MCS certificate, current inverter generation data, and DNO export arrangement. We analyse your half-hourly Smart Meter export profile to quantify how much generation is currently being wasted to the grid and model the battery capacity required to capture the majority of it.
We select the AC-coupled battery platform for compatibility with your existing inverter brand and Octopus API integration. Capacity is sized against your generation surplus profile and evening demand curve simultaneously, optimising for maximum solar capture and overnight arbitrage return.
Our qualified engineers install the battery and AC-coupling equipment entirely within your property, with certification handled by appropriately qualified professionals where required. No scaffolding. No roof access. No disruption to your existing panels or inverter. All cabling is concealed through building structure to the same standard as the original solar installation.
We commission the AC-coupling, verify solar surplus capture is operating correctly, configure Octopus Intelligent scheduling, and issue the appropriate VAT invoice and manufacturer warranty documentation before engineers leave. Your system is live from the same day.
No roof work, no inverter replacement, no disruption to your existing warranty - the battery connects to the AC side of your circuit, completely independently of your solar equipment.
A standard string inverter has no battery port and was not designed to interact with storage. AC-coupling bypasses it entirely, connecting the battery at the consumer unit level. A current transformer sensor detects surplus solar generation about to leave the property and activates the battery to absorb it - with any solar brand, any inverter age, any panel configuration.
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The correct battery capacity is determined by your actual export surplus, not your array size - and we model it from your real Smart Meter data before any recommendation is made.
We retrieve your half-hourly Smart Meter records for the preceding 12 months and map your generation surplus by season. A 4kWp south-facing Surrey array may export 12 to 15 kWh on a clear summer day, but only 1 to 2 kWh in December. Optimal sizing balances summer solar capture against year-round arbitrage cycling - not just the peak scenario.
Solar surplus capture in summer, grid arbitrage in winter - combined, the battery can generate value most days of the year, depending on tariff rates and household usage.
Between November and February, Surrey solar averages 1.5 to 2.5 kWh per day. Without a grid arbitrage layer, the battery's value to the household falls seasonally. Octopus Intelligent helps offset this: the battery connects to the Octopus API and charges overnight at 7 to 9p/kWh automatically, then deploys during daytime and evening peak rates of 25 to 35p/kWh.
Since October 2023, battery storage retrofitted to existing residential solar may qualify for 0% VAT, subject to current HMRC rules, which where eligible can represent a saving in the region of 1,400 to 2,000 GBP applied at invoice on a typical retrofit, confirmed at quotation stage.
The zero rate applies to all hardware and labour with no minimum concurrent solar purchase required. Most residential AC-coupled retrofits qualify as Permitted Development, requiring only a G98 DNO notification rather than a full G99 application. We manage all compliance documentation as part of the installation programme.
"We had a 4kWp array installed in 2018 and were exporting most of our midday generation. Adding a Tesla Powerwall 3 via AC-coupling transformed the economics completely. The installation took a single day with no roof access required. Our existing SolarEdge inverter was not touched. Self-consumption jumped from around 30 percent to over 82 percent in the first monitored month."
"We had a 6kWp array on our Surrey property that was performing well but exporting heavily every day. The GivEnergy AIO retrofit was completed in one day with completely concealed cabling and no scaffolding. The Octopus Intelligent configuration was set up at commissioning and the battery has been cycling automatically since. Combined solar capture and overnight arbitrage savings are running at over 900 GBP per year against the pre-commitment model's projection of 850 GBP."
Most Surrey homeowners with solar installed before 2020 are exporting 55 to 70 percent of their annual generation at Smart Export Guarantee rates of 4 to 6p/kWh. On a 4kWp array generating 3,600 kWh per year, 2,000 to 2,500 kWh of that generation is currently being sold for 80 to 150 GBP. With a battery retrofit, the majority of that generation is retained for use at full grid value of 25 to 35p/kWh - recovering 500 to 900 GBP per year that is currently leaving the property for pennies. We model your specific export profile from Smart Meter data before any recommendation is made.
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No. An AC-coupled battery retrofit makes no changes to your existing solar panels, DC wiring, or solar inverter. The existing installation continues operating identically. The battery connects only to the AC side of your electrical supply at the consumer unit, which is outside the scope of your existing solar warranties entirely. We review your existing MCS documentation before the retrofit to confirm this and provide written confirmation of no warranty impact with the pre-commitment specification.
A battery retrofit for an existing Surrey or SW London solar installation can achieve an indicative payback in the region of 6 to 9 years, combining solar surplus capture recovery and Octopus overnight arbitrage - the actual figure depends on system cost, household usage and tariff structure, and is confirmed through individual modelling. Where eligible, a 0% VAT position can reduce the effective capital cost compared with a standard-rated installation, which may improve the payback timeline. Modular battery systems allow capacity to be expanded when an EV is added, which can further improve the economics without requiring a full system replacement.
In virtually all cases, yes. AC-coupled battery systems work with any brand of solar inverter and any age of installation - from a 2010 SMA string inverter to a 2023 SolarEdge system. We assess your existing inverter generation data, current DNO export arrangement, and consumer unit capacity before specifying the retrofit. An existing G99 export-limited system is the main factor affecting approach, in which case the battery specification is designed to respect your existing DNO permission. We review your MCS certificate and DNO notification as part of the standard pre-installation audit.
No. An AC-coupled battery retrofit requires no access to your roof, no changes to your existing panels, and no modification of your solar inverter or DC wiring. The entire installation takes place within your property at the consumer unit level, typically completed in a single day with minimal disruption.
A typical Surrey solar installation without storage achieves around 28 to 35 percent self-consumption. A correctly sized battery retrofit can lift this significantly by capturing midday surplus for evening and overnight use. The exact improvement and any associated saving depend on array size, household usage pattern and battery capacity, and are modelled from your Smart Meter data before any recommendation is made.
Following the October 2023 UK legislation update, battery storage retrofitted to an existing residential solar installation may qualify for 0% VAT under HMRC energy-saving materials legislation, subject to current HMRC rules and confirmation at quotation. Where a project qualifies, the zero rate applies to battery hardware, inverter, mounting, cabling, and installation labour. For example, on a 9.5kWh GivEnergy retrofit costing in the region of 7,000 to 8,500 GBP, this could save approximately 1,400 to 1,700 GBP compared with a standard-rated purchase where eligible - the exact figure is confirmed at quotation stage. We confirm eligibility and issue the appropriate VAT invoice on commissioning day.
Your existing solar array has been generating free electricity for years. A battery retrofit recovers the portion of that generation that has been silently exported at 5p/kWh while you imported at 30p in the evening.
Our premium retrofit delivers:
"A battery retrofit can turn years of exported generation into smarter, lower-cost self-consumption working in your favour."