The UK now has more than one million residential solar PV installations, with commercial and public sector deployment growing steadily. As the number of installations increases, so do the questions customers have about safety — and rightly so.
Research published by QBE, based on Freedom of Information requests to UK fire services, recorded 91 fires involving solar panel systems in 2022, rising to 131 in 2023, 155 in 2024, and 212 in 2025 — a 133% increase over four years. Over the same period, the number of solar installations increased by approximately 52%. The rate of fires is growing faster than the number of installations, and that points to installation quality, equipment selection, and workmanship rather than to solar technology itself being inherently unsafe.
It is important to keep these numbers in perspective. Set against the total number of solar installations in the UK, the absolute rate of incidents remains low. Solar PV is not an inherently dangerous technology when it is designed and installed to an appropriate standard. But any electrical system that generates direct current whenever there is daylight — regardless of whether the occupier wants it to — deserves the same engineering discipline as any other electrical installation. The consequences of cutting corners are not hypothetical.
A solar PV installation is an electrical generating system. Understanding what can go wrong — and what professional installers do to prevent it — helps customers make informed choices about who they trust with that work.
What Actually Causes Fires in Solar PV Systems?
High-Resistance Electrical Connections
The most common underlying cause of electrical fires — in solar installations and in electrical systems generally — is a high-resistance connection. When electrical current passes through a connection that is loose, poorly made, contaminated, or corroded, the resistance at that point converts electrical energy into heat. The amount of heat generated depends on both the resistance and the current flowing through the connection.
At first, a high-resistance connection may only produce warmth. Over time, however, the heat causes insulation materials to degrade and soften. This can lead to further contamination of the connection, increased resistance, and greater heat — a progressive deterioration that may eventually result in the insulation igniting or the connection arcing.
In a well-made connection, resistance is negligible and the temperature at the connection point stays close to ambient. In a poorly made connection, even a small elevation in resistance — not enough to be obvious during a basic inspection — can lead to localised temperatures sufficient to ignite surrounding materials. This is why small installation details that appear trivial have disproportionate importance when something goes wrong.
DC Connectors
PV DC connectors deserve particular attention, because they are one of the most common sources of problems in solar installations. Most solar PV systems use click-together DC connectors — often referred to generically as MC4-type connectors, after the original design developed by the connector manufacturer Staubli. These connectors look simple from the outside. They are not.
Problems associated with PV DC connectors include:
- Incorrect crimping. The conductors inside the connectors are attached by crimping — a mechanical compression process. A correctly crimped connection achieves excellent electrical contact and will not pull apart under normal mechanical loads. A poorly crimped connection — made with the wrong tool, the wrong die, or without following the manufacturer's procedure — may appear satisfactory but will have elevated contact resistance and may fail in service.
- Use of incorrect or generic crimp tools. Connector manufacturers specify which crimp tools are compatible with their products. Using a generic or mismatched tool is a known source of problems. A correct-looking crimp is not necessarily a correct crimp.
- Incomplete connector engagement. MC4-type connectors must be fully engaged to achieve their rated contact resistance and mechanical lock. A half-mated connector that appears connected but has not fully clicked into position may pass initial testing but fail in service.
- Incompatible connector types. Two MC4-type connectors from different manufacturers may physically mate — they can be pushed together — but that does not mean they are electrically or mechanically compatible. Differences in contact geometry, material, and tolerances between manufacturers mean that cross-mated connectors can have elevated contact resistance, inadequate sealing against water ingress, and reduced mechanical retention. European research has suggested that DC connectors were implicated in around 24–27% of solar-related fires, and incompatibility between brands is a recognised contributing factor.
A professional contractor uses compatible connectors throughout a system — typically matching the module manufacturer's specified connector type — and uses manufacturer-approved crimp tooling. Simply pushing together connectors from different manufacturers because they physically mate is not acceptable practice.
DC Arcing
In an alternating current (AC) supply, the voltage and current pass through zero 100 times per second. This zero-crossing means that an arc in an AC circuit naturally extinguishes with each cycle. Direct current does not have a zero crossing. Once established, a DC arc can sustain itself as long as a sufficient voltage is present — and in a solar PV system, the DC voltage across the array is present whenever there is sufficient light, regardless of whether any isolator is open or whether the property's occupants are aware that anything is wrong.
Standard overcurrent protective devices (fuses and miniature circuit breakers) protect against excessive sustained current flow. They are not designed to reliably detect and interrupt all arcing faults, particularly series arcs, where the arc develops within an otherwise complete circuit. This is why installation quality — particularly the quality of DC connections, cabling support, and connector assembly — is of fundamental importance in solar PV systems. The best protection against DC arcing is ensuring that the conditions for arcing do not arise in the first place.
DC Cabling
DC cabling in a solar PV system carries relatively high voltages and operates in an outdoor or semi-outdoor environment for the life of the installation. Problems that arise in DC cabling include:
- Cables trapped beneath modules. A cable that is partially compressed between a solar module and a roof surface may suffer insulation damage from abrasion or mechanical loading — damage that is not visible without removing the module.
- Cables rubbing against metalwork. A cable that rests against a rail, clip, or roof covering edge and is subject to thermal movement or wind loading may have its insulation abraded over time.
- Inadequate mechanical support. DC cables should be secured at appropriate intervals and routed to avoid unsupported spans, hanging, or contact with surfaces that may damage the insulation.
- Unsuitable cable in UV-exposed locations. Not all cables are rated for prolonged outdoor UV exposure. Solar PV DC cables should be specifically rated for the environment in which they are installed.
- Cables resting in standing water. Low points in a cable run can collect water. Permanent immersion or repeated wetting is not an appropriate condition for cable joints or connectors.
- Poorly positioned joints. DC cable joints should be avoided wherever possible. Where they exist, they must be positioned accessibly, made with appropriate connectors, and protected from mechanical damage.
- Cable entry into buildings. Where DC cabling enters a building, the entry point must be adequately sealed and the cable must be protected against mechanical damage and water tracking into the building.
Much of the DC cabling in a solar installation is located beneath the modules and is not visible once the installation is complete. This means that the quality of the cable routing, support, and connection work is determined at the time of installation — and cannot be readily inspected or corrected afterwards without removing modules.
DC Isolators
A DC isolator is a switching device that allows the DC circuits of a solar PV system to be isolated — typically to allow inverter maintenance, emergency isolation, or to permit safe working. Their purpose is straightforward. The problems associated with them are not.
DC isolators have been responsible for a significant proportion of solar PV fires in the UK and internationally. Investigations have identified a range of contributing factors:
- Inadequate product quality. Components that fail to maintain adequate contact pressure over time, or that are not rated for sustained DC loads at the voltages and currents they encounter, can develop high contact resistance and fail.
- Incorrect wiring. Terminating cables incorrectly within an isolator — reversing polarity, using inappropriate cable sizes, or not achieving adequate contact with the terminals — produces poor connections from the outset.
- Loose terminals. Terminals not tightened to the manufacturer's specified torque may loosen over time due to thermal cycling, resulting in progressive deterioration of the connection.
- Water ingress. An isolator with an inadequate ingress protection rating, incorrectly installed cable glands, or a degraded enclosure seal may admit moisture — leading to corrosion, tracking faults, and ultimately arcing.
- Unsuitable location. Isolators installed on south-facing surfaces in direct sunlight, or in positions exposed to driving rain, face more demanding conditions than isolators in sheltered positions.
The design of a solar PV system determines whether rooftop DC isolators are required and, if so, their number and location. The point here is not that every system needs the same configuration, but that the isolators specified must be of appropriate quality and correctly installed.
Inverter Installation and Location
The inverter converts the DC power from the array into AC power for use within the property and the electricity network. Inverters contain power electronics that generate heat in normal operation. If that heat cannot be dissipated effectively, problems can arise.
Common issues that can lead to inverter overheating or reduced service life include:
- Inadequate clearance. Most manufacturers specify minimum clearances around the inverter for ventilation. An inverter installed closer to walls or other equipment than the manufacturer requires will run hotter than it should.
- Inappropriate location. Inverters should not be installed where the ambient temperature is already elevated — for example, directly beneath a south-facing roof covering in summer, in an unventilated loft space, or adjacent to a boiler.
- Restricted cooling paths. Blocking the vents or installing an inverter in a way that prevents airflow through its cooling system reduces its ability to manage temperature.
- Loose terminations. Both DC and AC connections at the inverter must be made to the manufacturer's requirements. A loose connection causes localised heating which can damage the connection and surrounding equipment.
- Ignoring manufacturer instructions. Inverter manufacturers publish installation manuals specifying location requirements, clearances, mounting orientation, environmental ratings, and wiring requirements. Deviating from them voids the warranty and may create unsafe conditions.
Loft spaces, understairs cupboards, and small utility rooms are common inverter locations. These locations are not inherently unsuitable, but they require careful assessment of temperature, ventilation, access, and moisture — and strict adherence to the inverter manufacturer's specific requirements for that installation.
Battery Storage and Electrical Energy Storage Systems (EESS)
Battery storage systems — used to store solar-generated electricity for later use, or to provide backup power — are now commonly installed alongside solar PV systems. Their fire behaviour is fundamentally different from the connector, cabling, and isolator faults discussed above.
Most domestic and commercial battery storage systems use lithium-ion chemistry. Under normal conditions — within their designed operating parameters, correctly charged and discharged, within their temperature limits — they are safe. Problems arise when these parameters are not maintained.
Thermal runaway is the critical failure mechanism of lithium-ion batteries. It occurs when a cell begins to generate heat internally faster than it can dissipate it. As the cell temperature rises, the rate of heat generation accelerates — in some chemistries rapidly — until the cell reaches temperatures at which it releases flammable gases and may ignite. The heat from a cell in thermal runaway can trigger adjacent cells, creating a cascading failure across a battery module. Battery fires can be extremely difficult to extinguish and may reignite after apparently being brought under control.
The triggers for thermal runaway include:
- Internal cell failure due to manufacturing defects
- Physical damage to the cell or battery module
- Overcharging beyond the cell's designed voltage limit
- Excessive discharge below the minimum voltage limit
- Operation at excessively high or excessively low temperatures
- Water ingress into the battery enclosure
- Incorrect electrical connection, inadequate terminations, or polarity errors
- Failure to commission the battery in accordance with the manufacturer's instructions
The Battery Management System (BMS) is an electronic control system integrated into every modern battery storage unit. Its functions include monitoring individual cell voltages, monitoring battery temperature at multiple points, managing charge and discharge currents, maintaining the battery within its safe operating range, and shutting down the battery if abnormal conditions are detected. A functioning BMS is an important safety layer. However, a BMS cannot compensate for a battery that is physically damaged, installed in an unsafe location, or operated in conditions beyond its design envelope.
Location Requirements for Battery Storage
The question of where a battery storage system can be installed has received significant regulatory attention in the UK, with the position clarified in 2024 and 2026.
PAS 63100:2024 — published by the British Standards Institution in March 2024 — sets out requirements for fire-safe installation of small-scale battery storage systems in domestic dwellings. Under PAS 63100:2024, batteries must not be installed in rooms in which persons sleep, or in routes used as a means of escape. For externally mounted systems, a minimum separation of 1 metre from windows, doors, and ventilation openings is recommended.
BS 7671:2018+A4:2026 — the fourth amendment to the 18th Edition IET Wiring Regulations, published April 2026 with a mandatory compliance date of 15 October 2026 — introduces a dedicated new Chapter 57 covering stationary secondary battery storage systems. Under Chapter 57, battery storage installations in lofts are prohibited, as are installations in locations that form part of a means of escape. For externally mounted systems, a minimum clearance of 1 metre from windows, doors, and ventilation openings applies.
Professional battery storage design considers far more than whether the chosen location has enough wall space to mount the unit. The location, environmental conditions, proximity to escape routes, manufacturer requirements, and the requirements of PAS 63100:2024 and BS 7671 Chapter 57 all inform where a battery storage system can and cannot go.
The Small Details That Prevent Big Problems
A completed solar and battery installation looks comparatively simple from the outside. What is not visible — buried beneath modules, routed behind cladding, enclosed within distribution boards and isolator enclosures — is the engineering that determines whether the system will operate safely over its intended lifetime.
The details that prevent problems include:
- Calculating cable sizes correctly for the voltages, currents, temperature conditions, and installation methods applicable to each circuit
- Selecting connectors from the same manufacturer throughout a string, using manufacturer-approved crimp tooling, and following the manufacturer's assembly procedure
- Stripping cables to the correct length — not so short that insufficient conductor is within the connector body, not so long that bare conductor is exposed
- Verifying polarity before connecting strings
- Tightening all electrical terminations — at connectors, isolators, inverter terminals, and distribution boards — to the torque specified by the equipment manufacturer
- Using cable glands of the correct size and ingress protection rating, tightened correctly to achieve the required seal
- Securing DC cables at appropriate intervals, routing them away from edges that may cause abrasion, and ensuring they are not trapped beneath modules or compressed by mounting hardware
- Protecting DC cables against mechanical damage at penetration points
- Maintaining appropriate bend radii in cables, particularly at entry points to equipment enclosures
- Keeping connectors clear of surfaces where standing water may collect
- Observing manufacturer clearances for inverters, batteries, and all electrical equipment
- Using fire-rated cable supports where required
- Applying correct earthing and bonding throughout the installation
- Providing appropriate electrical protective devices for each circuit
- Labelling the installation correctly to assist future inspection and emergency services
Good solar installation is electrical engineering applied to a generating system. It is not the task of fitting panels to a roof and connecting them to a box.
Testing and Commissioning
A solar PV and battery installation must be tested before it is placed into service. Testing is not a formality — it is the process by which an installation is verified to be safe and correctly assembled. Faults that testing identifies before the system operates will not cause problems in service. Faults that are not identified before the system operates may.
A responsible contractor tests and verifies:
- Visual inspection of all components, connections, cabling, and equipment
- Protective conductor continuity
- Insulation resistance testing where applicable
- Polarity of all DC circuits before connection to the inverter
- String open-circuit voltage (Voc) measurements for each string, compared against the calculated design values
- String current measurements where equipment allows
- Confirmation that measured values are consistent with the system design and with the manufacturer's published module data
- AC electrical testing in accordance with BS 7671
- Verification of all protective devices
- Inverter commissioning in accordance with the manufacturer's instructions
- Battery commissioning in accordance with the manufacturer's instructions
- Grid protection settings and verification
- Export limitation or G100 settings where applicable
- Confirmation of remote monitoring setup
- Completion of all required documentation, including the MCS Installation Certificate and the Electrical Installation Certificate
Testing is not the same as commissioning. Testing verifies that the installation is electrically safe and correctly assembled. Commissioning verifies that the equipment operates correctly and that its settings comply with the applicable requirements. Both are necessary.
Thermal Imaging as a Diagnostic Tool
Thermal imaging — using an infrared camera to identify unusual temperature distributions — is a valuable additional diagnostic and maintenance tool for solar PV and battery systems. It is not a replacement for proper electrical testing.
An infrared camera detects the heat radiated by surfaces. Where an electrical connection, a protective device, a terminal, or a distribution board component is running at an abnormal temperature relative to surrounding equipment, this can be identified from the thermal image. Sources of elevated temperature that may indicate a developing problem include high-resistance connections at inverter DC and AC terminals, distribution board and consumer unit connections, isolators, and cable termination points.
Useful thermal inspections are normally carried out while the system is operating under meaningful load — for example, during a period of good solar irradiance. An inspection carried out when the system is generating negligible output will not detect thermally abnormal connections because insufficient current is flowing to reveal them.
Thermal imaging provides an additional layer of confidence about the condition of accessible electrical components. It cannot provide information about connections and cables that are concealed beneath modules or within sealed enclosures. This is a service offered by the Omni3 electrical services team.
The Value of Monitoring After Installation
Modern solar and battery systems provide remote monitoring — either via an app, a web portal, or both — that records generation, consumption, battery state, and system fault status. Monitoring is not only commercially useful; it can provide early indication of developing problems.
Monitoring may alert the system owner to:
- Inverter faults or repeated restarts
- Unexpected shutdowns
- Unexplained reduction in generation performance
- Individual string underperformance compared to the rest of the array
- Battery faults or communication failures
- Abnormal operating conditions outside the system's normal parameters
Repeated fault notifications, persistent generation underperformance, or error messages that do not clear should not be ignored. Abnormal conditions in an electrical generating system require investigation by a competent person — not repeated dismissal of alert messages in an app.
What Is the Industry Doing to Improve Solar Fire Safety?
The UK industry and regulatory framework have moved significantly in recent years to address solar PV and battery storage fire safety.
BS 7671:2018+A4:2026 — the current version of the IET Wiring Regulations, mandatory from 15 October 2026 — represents the most significant update to the technical framework for solar PV and battery storage installations in the UK. It introduces Chapter 57 with dedicated requirements for battery storage systems, including the prohibition on loft installations and requirements for location clearances. It also updates requirements for PV system design and protective devices.
PAS 63100:2024 provides a detailed specification for fire-safe installation of domestic battery energy storage systems, setting out requirements for battery and fault management, installation location, separation distances, and documentation.
RC62 — the Joint Code of Practice for fire safety with PV panel installations, developed by the RISC Authority and the Fire Protection Association in collaboration with MCS and Solar Energy UK — provides fire safety guidance primarily focused on commercial and industrial rooftop-mounted PV systems.
MCS standards — specifically MIS 3002:2025 for solar PV installation and the MCS battery storage installation standard — set out the technical requirements that MCS-certified installers must follow, addressing system design, component selection, installation, testing, and documentation.
On arc fault detection devices (AFDDs): under BS 7671:2018+A4:2026, AFDDs conforming to BS EN 62606 are mandatory for single-phase AC final circuits supplying socket outlets in specified higher-risk premises — including high-rise residential buildings, care homes, houses in multiple occupation, and student accommodation. For other premises, the standard provides a recommendation. The specific mandatory requirements relate to AC circuits in particular premises types; they do not apply universally to all solar PV installations. For DC arc fault detection specifically, current guidance discusses the topic but does not yet mandate DC AFDDs across all PV installations. Follow the current version of BS 7671 as the authoritative reference.
The IET Code of Practice for Electrical Energy Storage Systems — now in its third edition — provides detailed technical guidance for specifying, designing, installing, and maintaining battery storage systems alongside PAS 63100:2024. Batteries installed in the UK market are required to meet BS EN IEC 62619 for safety requirements of secondary lithium cells and batteries for stationary applications.
What Should a Responsible Solar Installer Be Doing?
A responsible installer approaches each project as an engineering task, not simply a product installation. In practice, this means:
- Surveying the property properly before designing the system — assessing the roof structure, condition, orientation, and shading; the existing electrical installation; the available locations for inverter, battery, and metering equipment; and the customer's energy use and objectives.
- Designing the electrical system — calculating string configurations, DC voltages and currents, AC circuit requirements, fault levels, protective device ratings, cable sizes, and earthing arrangements. Not simply selecting the maximum number of panels that fit on the available roof area.
- Calculating appropriate cable sizes for all circuits, taking into account installation method, ambient temperature, and grouping.
- Selecting compatible, reputable equipment — modules, inverters, batteries, connectors, isolators, and mounting systems — from manufacturers with appropriate product certifications.
- Following all manufacturer installation instructions for every component.
- Using correct PV DC connectors throughout a system, from the same manufacturer and connector family, assembled using manufacturer-approved crimp tooling.
- Routing, supporting, and protecting DC cabling correctly throughout the installation, particularly in the areas beneath modules and at penetration points.
- Avoiding unnecessary DC cable joints.
- Tightening all electrical connections to the torque specified by the equipment manufacturer.
- Selecting sensible inverter and battery locations that comply with manufacturer requirements, BS 7671 Chapter 57, and PAS 63100:2024.
- Considering heat, ventilation, moisture, physical access, and proximity to escape routes when choosing installation locations for all electrical equipment.
- Carrying out comprehensive testing of the completed installation before it is placed into service.
- Commissioning the inverter and battery storage system in full accordance with the manufacturer's instructions.
- Verifying grid connection settings, including G98 or G99 notification, export limitation, and G100 compliance where applicable.
- Photographing all electrical connections and concealed cabling during installation as a record of what was done and where.
- Providing the customer with all required documentation, including the Electrical Installation Certificate (EIC), the MCS Installation Certificate, and all manufacturer documentation.
- Setting up monitoring, explaining it to the customer, and confirming that they understand what the key indicators mean and when to seek advice.
- Being available to investigate faults and abnormal conditions — not simply referring every question back to the equipment manufacturer.
Why the Cheapest Solar Quote Is Not Always the Cheapest System
Two quotations that appear to describe the same system — "12 solar panels, inverter, battery" — can conceal significant differences in what the customer actually receives: the quality and rating of DC connectors and whether manufacturer-approved crimp tools are used; the routing, support, and protection of DC cabling; the quality of DC isolators and their installation; the selected locations for the inverter and battery; the testing carried out before handover; the time spent on commissioning; the level of documentation provided; and the availability of aftercare.
These differences are not visible in the quotation document, and they are not obvious to a homeowner comparing two proposals on the basis of price and panel count. They become significant if something goes wrong — or if a future inspection reveals workmanship that does not meet current standards.
Customers who want to make an informed comparison between installers should consider asking:
- Who carries out the electrical installation work, and what qualifications do they hold?
- What connector system is being used, and how is it assembled?
- How will the DC cabling be routed, supported, and protected?
- Where will the inverter and battery be installed, and how were those locations chosen?
- What testing will be completed before the system is handed over?
- What documentation will I receive?
- Who deals with a fault or concern after installation, and how quickly can they respond?
An installer who cannot answer these questions clearly, or who is reluctant to discuss the technical details of the work, is giving you information about the standard of installation you can expect.
The Omni3 Approach
Omni3 designs and installs solar PV systems, battery storage and EESS, EV charging, and electrical installations across West Sussex and the South East. We are MCS certified for Solar PV and Battery Storage, NICEIC Approved Contractor, RECC member, and ECA member.
At Omni3 we regard a solar and battery installation as an electrical generation and energy-storage system first, and a renewable-energy product second. That distinction matters — it means we approach every installation with the same engineering discipline that we bring to any electrical project.
In practice, this means:
- Every system is electrically designed — not simply sized for roof area. We calculate cable sizes, circuit protection, voltage rise, and system configuration before we specify equipment.
- We specify components from reputable manufacturers with appropriate product certifications, and we use compatible connector systems assembled with the correct tooling.
- We route and support DC cabling to a professional standard, and we keep records — including photographs — of all concealed cabling and connections.
- We carry out comprehensive electrical testing before any system is placed into service, and we provide the customer with a full documentation set including the Electrical Installation Certificate and MCS Installation Certificate.
- We commission every inverter and battery to the manufacturer's procedure and verify grid connection settings.
- We set up monitoring and make sure customers understand how to use it.
- We are available for ongoing support, fault investigation, and maintenance — not just for the day of installation.
Good engineering and professional workmanship are about identifying, understanding, and controlling foreseeable risks throughout the design and installation process. That is what our customers are paying for, and it is what we deliver on every project.
Sources
- QBE Insurance (2025). Solar panel fires increasing at more than double the rate of installations. Freedom of Information research into UK fire service statistics, 2022–2025.
- British Standards Institution / IET (2026). BS 7671:2018+A4:2026 — Requirements for Electrical Installations (18th Edition, Amendment 4). Published 15 April 2026; mandatory from 15 October 2026.
- British Standards Institution (2024). PAS 63100:2024 — Electrical installations: Protection against fire of battery energy storage systems for use in dwellings. Published March 2024.
- IET (2023). Code of Practice for Electrical Energy Storage Systems, 3rd Edition.
- MCS (2025). MIS 3002:2025 — The Solar PV Installation Standard.
- Fire Protection Association / RISC Authority. RC62: Recommendations for fire safety with PV panel installations.