Home Battery Storage Systems: Installation, DNO Registration and Fire Safety

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) — particularly Amendment 2 (2022) — introduced specific requirements for battery storage installations 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

• Lithium-ion NMC (Nickel Manganese Cobalt) — most common chemistry in early residential batteries; higher energy density but greater thermal runaway risk
• Lithium-ion LFP (Lithium Iron Phosphate) — increasingly preferred for residential; lower energy density but significantly better thermal stability and safer chemistry
• Typical residential capacity — 3.6kWh (entry level) to 15kWh (premium); popular systems: Tesla Powerwall 2 (13.5kWh), GivEnergy (5.2–13.5kWh), Victron (modular)
• G98 notification — Engineered Recommendations G98; applies to microgeneration ≤16A per phase; complete within 28 days of connection
• G99 approval — pre-approval required before connection for systems >16A per phase or any three-phase system >11kW; approval process takes 45 days typically
• BS EN 62619:2017 — Safety requirements for secondary lithium cells and batteries for use in industrial applications; the key safety standard for residential battery packs
• BS 7671:2018 Amendment 2 — IET Wiring Regulations 18th Edition Amendment 2 (2022); introduced Section 722 covering EV charging and updated Section 557 for battery systems
• 500mm minimum clearance — from battery system to combustible materials (timber, soft furnishings, curtains)
• AC-coupled inverter — a separate inverter added to an existing PV system, storing grid or solar energy; Powerwall and SolarEdge Storage use this approach
• DC-coupled inverter — hybrid inverter replacing the existing PV inverter, with battery connected on the DC side; more efficient but requires inverter replacement
• Smart Export Guarantee (SEG) — right to be paid for surplus energy exported to grid; SEG licences require SMETS2 smart meter; battery must not export grid-charged energy (Ofgem rule)
• BMS — Battery Management System; monitors cell voltages, temperature, and state of charge; essential safety feature; must not be bypassed or modified
• Part P — Building Regulations Part P; battery storage installation is notifiable as a new circuit from the consumer unit is required

Quick Reference Table

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)

• Applies to single-phase inverters ≤16A (up to approximately 3.68kW per phase)
• Notification to the DNO within 28 days of energisation
• No prior approval required; installer notifies after the fact
• Must comply with all G98 technical requirements (anti-islanding, reconnection delay, voltage/frequency settings)
• Installer must register with the ENA's EREC G98 self-certification scheme or use a DNO-approved installer

G99 (ENA Engineering Recommendation G99)

• Applies to systems >16A per phase, or any system where the export capacity exceeds the G98 threshold
• Prior application and approval required before installation
• DNO assessment takes up to 45 working days
• May require distribution network reinforcement at the homeowner's cost
• Three-phase installations always require G99 even if below 16A per phase

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 62619 Safety Requirements

BS EN 62619:2017 (and its IEC equivalent IEC 62619) defines the safety requirements for secondary lithium cells and batteries. Key requirements relevant to residential installers:

• Battery must have a compliant BMS that monitors cell voltage, temperature, and state of charge
• Overcharge protection: BMS must prevent charging above the manufacturer's upper voltage limit
• Over-discharge protection: BMS must prevent discharge below the lower voltage limit (protects cell longevity and prevents thermal instability)
• Temperature monitoring: BMS must monitor battery temperature and shut down at the manufacturer's thermal limit
• Short circuit protection: integral fusing or electronic protection required

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

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:

• Never install in a habitable room — always in a utility room, garage, or dedicated external enclosure
• 500mm minimum clearance from all combustible materials
• Install on a non-combustible surface (concrete, brick, or steel plate)
• Ensure the space is ventilated to outside air — gases from a failing battery must not accumulate
• Garage installations: if attached garage, fire separation wall must be maintained (Part B); cable penetrations must be fire-stopped

Detection:

• Smoke alarm in the battery room (interlinked with rest of dwelling under Building Regs Part B)
• Heat detector preferred over optical smoke detector for battery rooms (optical detectors may not respond early enough to thermal runaway gas release)
• Some systems (e.g. Powerwall 3) include self-monitoring with remote alerts

Cable separation:

• DC cables from battery to inverter must be rated for DC use (double-insulated, appropriate DC voltage rating)
• Cable routes must not pass through sleeping areas without fire-rated enclosure
• DC isolators on both the battery and inverter side are required; accessible without moving the battery

AC-Coupled vs DC-Coupled Systems

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:

• Only energy generated by the solar panels can be exported — grid-charged battery energy cannot be exported under SEG
• Compliant battery systems have a "non-export" mode or grid-charge lockout to prevent exporting grid energy
• SEG requires a SMETS2 smart meter to be installed; older SMETS1 meters may not support SEG
• Rates typically range from 1p/kWh to 24p/kWh depending on supplier

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, NICEIC, ELECSA), 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?

Generally not recommended and often prohibited by manufacturers. 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. A garage, utility room, or dedicated external cabinet is always preferable.

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

• Building Regulations Part P (2013) — electrical safety in dwellings; battery storage installation is notifiable work

• BS 7671:2018 Amendment 2 (2022) — IET Wiring Regulations 18th Edition; Section 557 (battery storage systems) and Section 712 (photovoltaic installations)

• BS EN 62619:2017 — Safety requirements for secondary lithium cells and batteries for use in industrial applications; the principal product safety standard

• ENA Engineering Recommendation G98 — Requirements for the connection of generating plant to the distribution systems of licensed distribution network operators; covers systems ≤16A per phase

• ENA Engineering Recommendation G99 — Requirements for systems >16A per phase; requires prior DNO approval

• Smart Export Guarantee Regulations 2019 — Ofgem rules on export tariffs and SEG-compliant metering

• ENA Engineering Recommendation G98 — Energy Networks Association

• ENA Engineering Recommendation G99 — Energy Networks Association

• IET Guidance Note: BS 7671 Section 557 — Institution of Engineering and Technology

• Ofgem: Smart Export Guarantee — Office of Gas and Electricity Markets

• MCS Certification Scheme — Microgeneration Certification Scheme

• solar pv installation — PV system installation requirements and DNO registration

• consumer units — consumer unit replacement and RCD requirements

• heat pump wiring — heat pump electrical connections and DNO notifications