Build Your Own Power Station · Nationwide energy consultancy · Fully Funded Electrical & Structural Surveys · 0115 647 3822
KMM Energy SolutionsBuild Your Own Power Station
Battery Storage · sub-service

Solar Battery Retrofit UK 2026: Cost & Process

Already have solar but no battery? A battery retrofit lifts self-consumption from ~38% to 75%+ and pays back in 6-9 years on current tariffs. Here is the cost and process in 2026.

Updated 6 July 20266 min readReviewed by Steve Moran

What battery retrofit costs in 2026

Adding a battery to an existing solar PV system in 2026 costs £3,500-£9,500 fitted depending on battery size and whether your existing inverter is hybrid (DC-coupled retrofit) or string-only (requires AC-coupled inverter alongside the battery).

Pricing is bespoke per site — talk to our consultants. Get a tailored quote →

The process

  1. Site visit — we check your existing inverter make and model, your consumer unit capacity, your meter type and your usage pattern.
  2. Sizing recommendation — bound proposal showing size, brand, installation cost and projected payback.
  3. G99 application if the combined system exceeds 3.68kW per phase (which it usually does for any retrofit on existing solar).
  4. Installation — 1 day for AC-coupled, 1-2 days for DC-coupled with inverter swap. Solar continues to generate normally during the install.
  5. Commissioning — battery configuration, app pairing, performance verification.

What battery retrofit changes

  • Self-consumption rises from ~38% to ~75% on a typical 4-bed family home with 4kWp solar
  • Year 1 savings increase by £350-£550/yr on a typical install
  • Outage resilience — if your inverter supports EPS (most hybrid inverters do), the battery powers critical home circuits during power cuts
  • Time-of-use savings if you switch to a tariff like Octopus Cosy — charge from 7p/kWh overnight, discharge during 28p peak

FAQs

Will I need a new inverter?
Only if your existing inverter is string-only and you want a DC-coupled retrofit. AC-coupled retrofits work with any existing inverter — the battery has its own inverter built in.
Can I add a battery to a non-MCS solar install?
Yes — the original MCS status of the solar does not affect battery eligibility. The battery itself does not require MCS for SEG, but you do need G99 approval before commissioning.

Request a Fully Funded Electrical & Structural Survey

Tell us about your roof, your bills and your goals. KMM runs a fully funded electrical & structural survey, designs a system, runs the numbers and tells you honestly whether solar makes sense for you. No deposit, no pressure.

Fully Funded Survey → 0115 647 3822
KMM bee Fully Funded Electrical & Structural Survey →