What Are the Regulations and Installation Requirements for Solar PV and Battery Storage?

Summary

Solar photovoltaic (PV) installation has become one of the most in-demand electrical installation types in the UK, driven by high energy prices, improving battery storage economics, and government incentive schemes. For electricians, it represents a significant revenue stream — but the regulatory framework is complex, with overlapping requirements from BS 7671 (18th Edition, Section 712), the MCS scheme, DNO grid connection rules (G98/G99), and planning regulations.

MCS certification is the key commercial prerequisite for most domestic solar installations. While it is not strictly legally required to install a solar PV system, MCS certification is required for the homeowner to access the Smart Export Guarantee (SEG) — the payment scheme through which energy suppliers pay homeowners for surplus electricity exported to the grid. Without MCS-certified installation, the homeowner cannot receive SEG payments, which significantly affects the financial case for installation.

Battery storage has introduced additional complexity. Lithium-ion batteries (the dominant technology) store significant energy density, create fire risk, and require specific installation and fire safety considerations that are not covered in traditional electrical installation training. Electricians entering the battery storage market need familiarity with BS EN 62619, fire compartmentation principles, and battery management system (BMS) integration.

Key Facts

• MCS (Microgeneration Certification Scheme) — Industry quality standard; required for SEG eligibility; installer must be MCS-certified; system must be installed per MCS standards; completion certificate issued at handover
• G98 — Engineering Recommendation for connection of micro-generators (single-phase, up to 16A per phase = 3.68kW); notification to DNO within 28 days after commissioning; no prior approval required
• G99 — Engineering Recommendation for connection of larger generators; prior application and approval from the DNO required before commissioning; applies to systems above 3.68kW per phase or three-phase installations
• DNO (Distribution Network Operator) — The company responsible for the electricity distribution network in the local area (e.g., UK Power Networks, Western Power Distribution, SP Energy Networks); DNO must be notified/applied to for all grid-connected generation
• BS 7671 Section 712 — Wiring Regulations for solar photovoltaic power supply systems; covers DC cabling, isolation, earthing, protection, and integration with the AC installation
• DC cable sizing — PV DC cables are sized differently from AC cables; maximum short-circuit current from the array, open-circuit voltage, temperature derating, and shade conditions must all be considered; do not size DC cables using standard AC tables without adjustment
• DC isolators — Required at the array, at each inverter input, and at the meter tails (AC side); isolators must be rated for DC voltages, which are significantly more hazardous than AC at the same nominal voltage (DC arcs do not self-extinguish)
• Rapid shutdown — In larger systems and commercial applications, a rapid shutdown system (often referred to as "arc fault isolation") is increasingly specified; not yet universally mandated in UK domestic regulations but best practice
• Earthing — PV array frames must be earthed in compliance with BS 7671; the earthing of the array and the earthing of the inverter must be coordinated; details depend on the inverter type (transformerless inverters have different earthing requirements)
• Battery storage — BS EN 62619 — Standard for secondary lithium cells and batteries for use in stationary applications; covers safety requirements including thermal management, BMS, and protection
• Fire compartmentation for battery storage — Lithium-ion batteries can undergo thermal runaway, producing flammable gas and posing significant fire risk; installation location (usually the garage, utility room, or dedicated cabinet) must consider fire spread and the ability for occupants to escape; guidance from BRE GD 814 and insurer requirements apply
• Smart Export Guarantee (SEG) — Statutory obligation on larger energy suppliers to offer SEG tariffs to micro-generators; SEG requires MCS-certified installation and a smart meter; export rates vary by supplier
• SAP (Standard Assessment Procedure) — The method used to calculate the energy performance of dwellings for EPCs; solar PV installed on a property improves the SAP rating and can affect the EPC band, which is relevant for mortgage lenders and rental compliance

Quick Reference Table

Detailed Guidance

G98 vs G99 — Which Applies?

The determining factors are:

1. Connection voltage — Single-phase (standard domestic) or three-phase
2. Inverter output current — Per phase, in amps
3. Total installed capacity — The aggregate export capacity of all generation on the connection

G98 (single-phase, ≤16A per phase = ≤3.68kW): The most common route for standard domestic installations (3–3.5kW systems). The installer notifies the DNO using the G98 notification form within 28 days after connection. The DNO does not need to approve in advance. The notification triggers the DNO to update their network records.

G99 (above G98 thresholds, or three-phase): The installer or customer submits a G99 application to the DNO before the system is commissioned. The DNO assesses the impact on the local network and issues (or declines) an approval. The process can take 8–65 working days depending on the DNO and the network constraint level. Do not connect a G99 system without written approval — this is a breach of the licence conditions and can result in the installation being disconnected.

G100: For small-scale generation connected to LV networks on simplified terms, some DNOs use a G100 process. Check with the specific DNO.

MCS Certification Process

MCS is an industry-managed quality scheme, not a government regulator, but it is required by OFGEM as a condition of SEG eligibility. The MCS scheme covers both the product (panels, inverters, and batteries must be on the MCS Product Register) and the installer (who must hold MCS certification from an accredited certification body such as RECC, HIES, or NAPIT for microgeneration).

The MCS installation process:

1. System design: The system must be designed using the MCS installation standard (MIS 3002 for solar PV) and must comply with the relevant technical standards
2. Products: Only MCS-registered products may be used (check the MCS Product Register at mcscertified.com)
3. Installation: Carried out by an MCS-certified installer to the installation standard
4. Handover: Customer receives an MCS Installation Certificate, plus evidence of DNO notification/approval
5. Guarantee: MCS requires a workmanship warranty and the installation must be reported to the scheme register

BS 7671 Section 712 — Key Requirements

Section 712 of BS 7671 (18th Edition Amendment 2) is the specific section covering solar PV. Key requirements include:

712.411 — Provides for isolation of the PV array from the supply and from the installation on the AC side. An AC isolator is required adjacent to the inverter.

712.531 — Requirements for DC isolators; must be suitable for DC operation (AC isolators are not suitable for DC isolation); must be placed in accessible positions.

712.553 — Where the PV supply is connected in parallel with the public supply, protection must ensure that the system cannot energise the public supply when the public supply is disconnected (anti-islanding protection). All grid-connected inverters must have anti-islanding protection certified to BS EN 62116.

712.413 — Additional protection; earth fault protection for the DC circuit is increasingly required in modern practice to detect faults that could cause fire.

Earthing: The earthing of transformerless inverters is particularly important and complex. Transformerless inverters (which are the dominant type due to higher efficiency) must not have their PV negative or positive conductor bonded to earth in a way that contradicts the inverter's internal design. Always follow the inverter manufacturer's earthing instructions and verify compliance with BS 7671.

DC Cable Sizing — Key Differences from AC

DC cables in a PV installation carry continuous current at voltages that may be up to 1000VDC (for standard residential string inverters) or higher. The hazards are:

• Higher voltage: 1000VDC can cause fatal electrocution; DC arcs do not self-extinguish
• Solar circuit is always live: The array continues to generate as long as there is daylight — the DC circuit cannot be de-energised by switching off the supply; isolators must be used
• Short circuit current: The maximum short-circuit current of each string must be used for cable sizing, derated for the installation method and ambient temperature

Use DC-rated cable specifically designed for PV applications (typically twin-core 4mm² or 6mm² with UV-resistant sheathing to EN 50618). Do not use standard building wiring cables for DC string runs.

Battery Storage — Safety and Fire Considerations

Lithium-ion battery storage (BESS) is increasingly installed alongside solar PV and as standalone home energy storage. Key safety considerations:

Thermal runaway: Lithium-ion cells can enter thermal runaway — a self-sustaining exothermic reaction — due to overcharge, over-discharge, internal fault, or physical damage. Thermal runaway releases heat, flammable gas, and potentially toxic products. Once initiated, it is very difficult to suppress with standard firefighting equipment.

Installation location: The BRE Fire Safety Report (BRE GD 814) and guidance from fire engineers recommend:

• Batteries should not be installed on primary escape routes or in habitable rooms
• Garages or external enclosures are preferred installation locations
• Where batteries are installed inside the dwelling (utility room, under stairs), fire compartmentation of the installation space should be considered
• Minimum clearances from combustible materials should be maintained
• The installation space should have ventilation to the outside to allow gas to escape if venting occurs

BMS (Battery Management System): All lithium-ion batteries used in domestic applications have a BMS that monitors cell voltage, current, and temperature. The BMS provides protection against overcharge, over-discharge, and thermal runaway initiation. Only install battery systems with a certified BMS — do not modify or bypass BMS settings.

BS EN 62619 — The UK/European standard for safety requirements for secondary lithium cells and batteries for use in stationary applications. Products must comply and should be listed on the MCS Product Register.

SAP Calculation and EPC Impact

When a solar PV system is installed on a dwelling, the building's energy performance (SAP rating) improves because some or all of the electrical demand is met from on-site generation rather than the grid. This improvement:

• Raises the EPC band — potentially from D to C, or C to B, which is increasingly important for mortgage lenders and rental compliance
• May affect eligibility for energy efficiency grant schemes (some schemes require a minimum EPC band)
• Should be reflected in a new EPC issued after installation; MCS-certified installations automatically trigger a recommendation to update the EPC

Frequently Asked Questions

Does a solar PV system require planning permission?

In England, most domestic rooftop solar PV installations are permitted development (no planning application required) under Schedule 2 Part 14 of the Town and Country Planning (General Permitted Development) Order 2015. Conditions include: panels should not protrude more than 200mm above the roof slope, and must not be installed on a wall that fronts a highway in a Conservation Area. Listed buildings and some conservation areas require full planning consent. Check with the local planning authority before quoting on listed or conservation area properties.

Can I install battery storage without a solar PV system?

Yes. Standalone battery storage (charged from the grid at off-peak rates and discharged at peak times) is a legitimate installation. It does not require G99 approval if the battery inverter does not export to the grid. If the battery system is capable of grid export, G98 or G99 requirements apply. Always verify the inverter's export capability with the manufacturer before connection.

Do I need to be MCS-certified to install solar PV?

You do not need MCS certification to install solar PV from a legal perspective — it is not a statutory requirement in the way that Gas Safe registration is. However, without MCS certification, the customer cannot access SEG payments, which significantly reduces the value of the installation. Most customers specifically require an MCS certificate at handover. NAPIT and NICEIC both offer MCS certification pathways for registered electricians.

What is the G99 application process and how long does it take?

Submit the G99 application to the DNO (using the DNO's online portal or paper form) before starting installation. Include: system specifications, proposed location, one-line diagram, and anti-islanding protection details. The DNO assesses the impact on the local network — in areas with low generation penetration (little existing solar), approval is usually straightforward. In areas where the network is already constrained, the DNO may impose export limitations (a "controlled export" condition) or require network reinforcement. Processing time: 8–45 working days for standard applications; longer for complex or constrained networks.

Regulations & Standards

• BS 7671 18th Edition (Amendment 2) Section 712 — Requirements for solar photovoltaic power supply systems; the primary electrical installation standard

• Engineering Recommendation G98 — Connection of micro-generators ≤16A per phase to the public LV network; G98 notification procedure

• Engineering Recommendation G99 — Connection of generating plant above G98 thresholds; G99 application and approval process

• MCS 3002 (MIS 3002) — MCS Installation Standard for solar PV; product and installation requirements for MCS certification

• BS EN 62116 — Test procedures for anti-islanding protection; required certification for grid-connected inverters

• BS EN 62619 — Safety requirements for secondary lithium cells and batteries for stationary applications

• MCS (Microgeneration Certification Scheme) — Installer certification, product register, and installation standards

• Energy Networks Association — G98/G99 connection documents — Official G98 and G99 engineering recommendations

• NICEIC / NAPIT — Solar PV competency — Certification pathways for electricians

• BRE — Fire safety of home energy storage systems (BRE GD 814) — Battery storage fire safety guidance

• OFGEM — Smart Export Guarantee guidance — SEG eligibility and tariff requirements

• ev charger — EV charger installation, OZEV grants, and smart charging requirements

• battery storage — Battery storage systems in detail

• testing commissioning — Electrical testing and certification for new installations