Summary

Home battery storage has grown rapidly alongside rooftop solar PV. As grid export tariffs (Smart Export Guarantee) have made selling surplus solar more attractive, and as time-of-use tariffs have created arbitrage opportunities by charging at off-peak rates, battery storage is now a mainstream retrofit product across the UK. However, the technology carries real fire risk, and poorly installed systems have caused house fires and voided home insurance policies.

The electrical installation requirements for battery storage are considerably more demanding than for simple PV systems. The battery management system (BMS), inverter type, DNO notification, and fire separation requirements all need to be correctly specified and installed. The 18th Edition of BS 7671 (IET Wiring Regulations) — most recently Amendment 4 (BS 7671:2018+A4:2026, published 15 April 2026) — introduced the first dedicated chapter for battery storage installations (Chapter 57) that every electrician in this space must know.

This article covers both the technical installation requirements and the safety considerations that protect homeowners and tradespeople. Battery storage done right will safely operate for 10–15 years; done wrong, it presents a serious fire risk that is difficult to extinguish and can spread rapidly through a dwelling.

Key Facts

Quick Reference Table

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Chemistry Energy Density Thermal Stability Typical Brands Cost Premium
NMC (LiNiMnCoO₂) High Lower Tesla (older), LG Chem Lower
LFP (LiFePO₄) Moderate High GivEnergy, BYD, SolarEdge Higher
NCA (LiNiCoAlO₂) Very high Lower Some EV-derived systems Variable
LMO (LiMn₂O₄) Moderate Moderate Older systems N/A

Detailed Guidance

DNO Notification: G98 vs G99

The choice between G98 and G99 notification depends on the export capacity of the system:

G98 (ENA Engineering Recommendation G98)

G99 (ENA Engineering Recommendation G99)

Most residential battery storage systems are installed under G98. A 13.5kWh Powerwall connected to a 3.68kW inverter falls under G98. A 10kW hybrid inverter system would require G99.

Practical steps for G98:

  1. Install the system
  2. Set inverter parameters to comply with G98 (frequency trip, voltage trip, reconnection delay)
  3. Submit G98 notification form to the local DNO within 28 days
  4. DNO confirms registration; add to Microgeneration Certificate Scheme (MCS) if applicable

BS EN IEC 62619 Safety Requirements

BS EN IEC 62619:2022 (2nd edition, superseding the 2017 edition) defines the safety requirements for secondary lithium cells and batteries. Key requirements relevant to residential installers:

Installers should verify that any battery they purchase carries a CE mark and BS EN IEC 62619:2022 certification on its documentation. Batteries without this certification should not be installed.

PAS 63100:2024 and BS 7671:2018+A4:2026 Chapter 57

Amendment 4 to BS 7671:2018 (published 15 April 2026) introduced Chapter 57, the first dedicated set of regulations for stationary secondary battery installations, covering domestic battery storage paired with solar PV as well as commercial and grid-connected systems. Regulation 570.6.7.203 requires domestic installations to also comply with PAS 63100:2024 (BSI's specification for fire protection of battery energy storage systems in dwellings, sponsored by the UK government).

Key requirements installers must now work to:

Fire Safety and Separation Requirements

Lithium-ion battery thermal runaway is a serious hazard. When a cell enters thermal runaway, it generates intense heat, toxic gas (including hydrogen fluoride, carbon monoxide, and hydrogen cyanide from NMC cells), and in many cases self-sustaining fire that cannot be extinguished with water.

Location requirements:

Detection:

Cable separation:

AC-Coupled vs DC-Coupled Systems

Feature AC-Coupled DC-Coupled
How it works Separate battery inverter; battery charges from AC bus Hybrid inverter; battery on DC side with solar panels
Retrofit? Yes — can be added to any existing PV system Requires replacing existing PV inverter
Efficiency Lower (AC-DC-AC conversion losses ~10%) Higher (DC-DC conversion ~97%)
Typical use Adding battery to existing solar New solar + battery systems
Examples Tesla Powerwall, SolarEdge + StorEdge GivEnergy hybrid, SolarEdge HD-Wave
Cost Lower if existing solar PV in place Better value for new installations

Smart Export Guarantee (SEG)

Under the Smart Export Guarantee (introduced January 2020), licensed electricity suppliers must offer a tariff for exported solar energy. Key rules relevant to battery storage:

Installers must configure the battery to comply with SEG rules. Exporting grid-charged energy is a breach of the SEG contract and can result in termination of the tariff.

Building Regulations Part P Compliance

Battery storage requires a new circuit from the consumer unit (dedicated 16A MCB minimum for the battery inverter). This is notifiable work under Part P. Options for compliance:

  1. Self-certification — if the installer is registered with an approved competent persons scheme (NAPIT or NICEIC — ELECSA was retired as a separate scheme, with ELECSA-registered installers transferred to NICEIC by late 2022), they can self-certify the work and issue a Part P certificate
  2. Building Control — if the installer is not registered, notify Building Control before starting work; an inspector will visit and certify completion

An Electrical Installation Condition Report (EICR) is not a replacement for a Part P certificate. Both documents may be needed when the property is sold.

Frequently Asked Questions

Can a battery storage system be installed in a loft?

No. As of BS 7671:2018+A4:2026 (Chapter 57, referencing PAS 63100:2024), loft and roof space installations are formally prohibited, not just discouraged. This codifies what was already best practice: loft spaces are difficult to access, present severe thermal management challenges (they can exceed 70°C in summer, accelerating battery degradation), and cable routes through habitable spaces create fire risk. Most manufacturers explicitly void warranties for loft installations. Bedrooms and unprotected escape routes (landings, staircases, corridors) are also prohibited locations. A garage, utility room with adequate fire separation, or dedicated external cabinet is required.

Does battery storage affect home insurance?

Yes. Homeowners must inform their insurer before installing a battery storage system. Failure to notify is a common grounds for claim denial in the event of fire or related damage. Most standard home insurers will cover battery storage if it is installed by a registered competent person (MCS-certified installer for combined solar + storage), the Part P certificate is in place, and G98 notification has been submitted.

What is the lifespan of a home battery?

Manufacturers typically guarantee 10 years or a specified number of charge cycles (e.g. Tesla Powerwall: 10 years, unlimited cycles, 70% capacity retention guaranteed). LFP batteries generally outlast NMC chemistry. Real-world degradation depends heavily on charge rate, depth of discharge, and ambient temperature.

Do I need MCS certification to install battery storage?

MCS (Microgeneration Certification Scheme) certification is required to be eligible for the Smart Export Guarantee and BUS (Boiler Upgrade Scheme — not relevant here). Battery-only installations without solar PV do not require MCS certification for the installation itself, but the customer cannot claim SEG without MCS documentation for the whole system.

What cable size is needed for a battery inverter?

For most 3.68kW AC-coupled inverters (single phase, 16A): 2.5mm² T&E on a dedicated 20A MCB with RCD protection (Part P compliant consumer unit). For larger hybrid inverters (5–10kW): 6mm² on a 32–40A MCB. Always check the manufacturer's specification — some inverters require four-core cable for L/N/E and a separate PE.

Regulations & Standards