The short answer
Good commercial solar maintenance rests on four things:
- Monitoring that someone actually watches, so faults are spotted in days rather than months.
- Regular visual inspections of panels, fixings, cables, connectors, DC isolators, inverters and the roof around the array.
- Periodic electrical testing and thermography to find faults the eye cannot see.
- Safe roof access planned in advance, because most maintenance happens at height.
Cleaning, bird proofing and inverter replacement are added as the site needs them. An O&M contract can cover all of this, but you should know what you are buying and check it against what your insurer expects.
Why maintenance matters on a commercial roof
A commercial system that underperforms can cost thousands of pounds a year, and nobody notices, because the building simply draws more from the grid. A failed inverter or a tripped string makes no noise.
There are also safety reasons. Rooftop PV carries direct current at high voltage whenever the panels are in daylight, and faulty connectors, damaged cables and water in DC isolators are known causes of fires. The roof itself has been penetrated or loaded, and its condition needs watching over the decades the panels are there. Insurers are aware of these risks and increasingly ask owners how they manage them.
Monitoring: the first line of defence
Almost every commercial inverter can report its output to an online portal. Monitoring is only useful if:
- it stays connected (a lost internet link or a changed router password stops it reporting)
- alerts go to a named person or an O&M provider, not an unused inbox
- someone compares output with what the system should be producing
- inverter error logs are reviewed, not just headline totals
String-level or optimiser-level monitoring shows faults more precisely than inverter totals. On larger systems an irradiance sensor or satellite irradiance data lets you separate a dull month from a real fault.
Performance ratio in general terms
Performance ratio compares the energy a system actually produced with the energy it could have produced given the sunlight that fell on it. Because it adjusts for the weather, it is a fairer measure than raw kWh. A falling performance ratio over several months suggests a problem, such as soiling, shading from new growth, a failed string or an inverter running hot.
Treat it as a trend to watch rather than a single number to hit. Compare like periods with like, because temperature and low winter sun affect the result. Where an O&M contract guarantees a performance ratio or availability figure, check exactly how it is calculated and what is excluded.
Routine inspections
A visual inspection by a competent person typically covers:
- Panels: cracked glass, discolouration, delamination, burn marks, broken frames and heavy soiling
- Mounting and fixings: loose clamps, corrosion, missing ballast, movement after storms
- Cables: cables lying on the roof surface, chafing on sharp edges, UV damage, loose ties
- Connectors: damage, overheating, and mismatched connector brands, which can cause faults
- DC isolators and enclosures: water ingress, condensation, cracked housings and correct labelling
- Inverters: ventilation, dust build-up on fans and heat sinks, error history and firmware
- The roof: seals around penetrations, drainage paths kept clear, ponding on flat roofs, fragile areas
- Signage and records: warning labels, firefighter information and an up to date layout drawing
Inspections are also needed after storms or unusual weather, and after any other contractor has worked on the roof.
Cleaning
UK rain keeps many pitched arrays reasonably clean. Low-pitch and flat roof systems collect more dirt because water drains off them slowly, and some sites soil faster than others: farms, sites near busy roads or quarries, buildings with flour or dust from production, and roofs where birds roost.
Clean when monitoring or an inspection shows it is needed, not on a fixed timetable by default. Use purified water and soft brushes, and follow the panel manufacturer's cleaning instructions, because harsh chemicals, pressure washers and walking on panels can damage them and may affect the warranty. Cleaning contractors need the same safe access arrangements as any other roof work. Our farms page covers the particular soiling issues on agricultural buildings.
Thermography
Infrared thermography shows faults as hot spots: cells or panels with internal damage, failed bypass diodes, poor connections and overheating connectors. It is usually carried out with a handheld camera or a drone, in strong sunlight so the array is working hard enough for faults to show.
It is also worth extending thermography to the AC side, including inverters, isolators and the switchgear where the system connects to the building. A report should identify each fault by location so it can be found and fixed, and should be carried out by someone trained in PV thermography who knows the difference between a real fault and a reflection.
Electrical testing
Solar PV is part of the building's electrical installation, so it falls within periodic inspection and testing under BS 7671. The IEC 62446 series covers testing, documentation and maintenance of PV systems specifically, including DC side tests such as insulation resistance and string voltages and currents.
The right interval depends on the installation, its use and its condition. The inspector who completes each periodic report recommends when the next one is due, and your insurer or O&M contract may set its own requirement. Keep every certificate and test report with the system records.
TODO for the site owner: confirm the inspection and testing intervals currently recommended for commercial PV in IET guidance and in the latest edition of RC62 before adding any specific periods to this page.
Bird proofing
Pigeons and other birds like the sheltered space under panels, especially on pitched roofs. Nests and droppings can soil panels, block drainage, damage cables and create a fire risk from nesting material near electrical parts. Mesh guards fitted around the array edge are a common solution, ideally at installation.
Nesting wild birds are protected under the Wildlife and Countryside Act 1981, so active nests must not be disturbed. Plan proofing work outside the main nesting season, or take ecological advice if birds are already present.
Roof access and safety
Most maintenance is work at height, covered by the Work at Height Regulations 2005. Before anyone goes up, the plan should address:
- Fragile surfaces: fibre cement sheets and rooflights can give way. Never assume a roof is safe to walk on. See our pages on metal roofs and asbestos roofs.
- Edge protection: permanent guardrails, temporary edge protection, or fall restraint systems on suitable anchors.
- Access route: fixed ladders, roof hatches or platforms, kept clear and maintained.
- Electrical isolation: the DC side remains live in daylight even when the inverter is isolated, so only trained people should open DC equipment.
- Site controls: permits to work, inductions, and coordination with site operations below.
Designing safe maintenance access at the start, with clear walkways and anchor points, makes every later visit safer and cheaper.
Inverters and planning for replacement
Panel performance warranties are commonly 25 to 30 years, but inverters are often replaced once in that period, typically after 10 to 15 years. Budget for it, keep the inverter warranty documents to hand, and ask whether an extended warranty is worth buying. Keep inverter firmware up to date and check that replacement models will be compatible with your monitoring. Our guide to commercial solar panel lifespan covers long-term performance in more detail.
O&M contracts
O&M contracts vary widely. Most fall roughly into three levels.
| Level | Typically includes | Suits |
|---|---|---|
| Monitoring only | Remote monitoring, alerts and a periodic performance report | Smaller systems with an engaged facilities team |
| Preventive | Monitoring plus scheduled inspections, thermography and electrical checks | Most commercial rooftop systems |
| Comprehensive | Preventive work plus corrective repairs, spares, and sometimes an availability or performance guarantee | Large systems, multi-site estates, or owners who want one point of responsibility |
Questions to ask before signing:
- What is included in the fixed fee, and what is charged as extra work?
- What are the response and repair times, and are they measured from the alert or from your call?
- Are cleaning, bird proofing and thermography included?
- Who supplies spares, and is labour for warranty claims included?
- How is any performance or availability guarantee calculated, and what is excluded?
- How does the contractor manage roof access, permits and safety?
- What reports will you receive, and how often?
If your system is funded through a power purchase agreement, the provider usually owns and maintains it, but check the agreement for your obligations on access, roof maintenance and notification of faults.
What insurers expect
Insurers increasingly ask about rooftop PV at renewal. Many refer to RC62, which includes recommendations on design, installation, inspection and maintenance. In practice, insurers often want to see:
- that the system was installed by a competent contractor with certificates on file
- a documented inspection and maintenance regime, including thermography and DC isolator checks
- remote monitoring with alerts acted on promptly
- clear isolation points and information for the fire service
- records of faults found and fixed
Talk to your insurer before agreeing an O&M scope so the two match. Our guide to solar fire safety and insurance covers RC62 in more detail.
An illustrative maintenance calendar
This is an illustrative starting point only. The installer's O&M manual, the last periodic inspection report and your insurer's requirements take priority.
| When | Task |
|---|---|
| Continuously | Remote monitoring and alerts |
| Monthly | Review generation against expected, check monitoring is connected |
| Each year, typically | Visual inspection of array, roof and DC equipment; thermography; inverter checks |
| As needed | Cleaning, bird proofing, vegetation management for shading |
| After storms | Check fixings, ballast, cables and the roof |
| At the interval on the last report | Periodic electrical inspection and testing |
| Typically after 10 to 15 years | Plan inverter replacement |
Budgeting for maintenance
Include O&M costs in your financial case from the start. A system that saves a lot in year one but has no maintenance budget will drift down in performance. Our solar payback guide shows where maintenance sits in the sums, and our guide to choosing an installer lists the O&M questions to raise at quote stage.
Frequently asked questions
How often should commercial solar panels be cleaned?
There is no single right frequency. Rain keeps many pitched arrays reasonably clean, while flat and low-pitch systems, farms, sites near roads or quarries and roofs where birds roost soil faster. The best approach is to clean when monitoring shows a drop in output or an inspection finds heavy dirt. Use purified water and soft brushes, and follow the panel manufacturer's instructions to protect the warranty.
Do we need an O&M contract?
Not necessarily, but someone must take responsibility for monitoring, inspection, testing and repairs. A facilities team with electrical support can manage a smaller system with a monitoring only arrangement. Larger systems and multi-site estates usually benefit from a preventive or comprehensive contract with defined response times. Check your insurer's expectations first, as they may require a documented maintenance regime.
What does a thermographic survey find?
Thermography uses an infrared camera, often on a drone, to show parts of the system running hotter than they should. It finds damaged cells, failed bypass diodes, loose or poor connections and overheating connectors, many of which cannot be seen by eye. It should be done in strong sunlight by someone trained in PV thermography, with each fault located on a plan so it can be fixed.
Who maintains the panels under a power purchase agreement?
Under most power purchase agreements the provider owns the system and is responsible for monitoring, maintenance and repairs, because they are paid for the electricity it produces. You will usually still have obligations, such as giving safe access, maintaining the roof and reporting damage. Read the agreement for who pays to remove and refit panels if the roof needs repairs.
Is it safe to switch off the inverter and work on the panels?
Not by itself. Isolating the inverter stops AC output, but the panels and DC cables remain live whenever light falls on them, and DC faults can cause arcing. Only people trained in PV systems should open DC isolators, connectors or junction boxes. Facilities staff should know where the isolation points are, but leave work on the DC side to a competent PV contractor.
Related pages
- Fire safety and insuranceRC62 in plain terms, insurer questions, DC isolation, cable routing, separation from rooflights and fire breaks, and inspection regimes for commercial rooftop solar.
- Solar panel lifespanProduct and performance warranties, degradation, inverter replacement, roof life, end of life recycling and how lifespan affects payback and lease length.
- Choosing an installerCertification by system size, insurance, warranties, design documents, yield assumptions, questions to ask and red flags, with a table for comparing quotes like for like.
Solar paybackA worked payback example for a 100 kWp system, the factors that move the result most, the effect of tax relief, and a calculator to try your own figures.
Flat roofsHow membrane type, ballasted or fixed mounting, east-west layouts, parapets, drainage and roof loading decide whether a flat roof suits solar.