Taking on an unfamiliar commercial solar system: what a takeover survey should cover

A provider asked to maintain a system they did not install is taking on unknown risk. A takeover survey turns that unknown into a baseline, which is why a sensible provider will not quote a maintenance price down the phone for a system they have never seen. It matters most when you have bought a building with an array already on it, when the installer has gone, or when the array has simply run for years with nobody looking. If your installer has ceased trading, our guide on what happens when a solar installer goes bust covers the warranty and paperwork side that runs alongside this.

A good provider works to published guidance rather than a checklist of their own invention. Solar Energy UK — the trade association, which describes itself as representing over 400 member companies across the UK energy sector — publishes Rooftop O&M Guidelines 3.0, issued in December 2025. It covers the safe maintenance, cleaning and monitoring of domestic and commercial rooftop PV, organised around safety principles including professional training and working at height, inspection activities, maintenance and cleaning, monitoring, common issues, site security and warranties. It stresses that every installation is unique and encourages consulting qualified solar professionals rather than treating any checklist as universal.

SolarPower Europe’s Operation & Maintenance: Best Practice Guidelines Version 6.0, released in February 2025, added new chapters on electrical safety and on common tests and inspections, and states that its practices are relevant to solar PV systems of all sizes. Neither document is a legal standard, and neither replaces the electrical standards a qualified provider works to. But if a prospective provider can map their survey against those headings, that is a good sign. The sections below follow the same order.

The survey starts on the ground, with how anyone gets onto the roof and moves around it. HSE defines work at height as work anywhere that, without precautions, a person could fall far enough to be injured — explicitly including a fall through a fragile roof. Its approach is to avoid work at height where reasonably practicable, then prevent falls using a place of work that is already safe or the right equipment, then minimise the distance and consequences of a fall, preferring collective protection such as guardrails over harnesses.

The duty is not only the contractor’s. HSE states the regulations apply to anyone who controls work at height, "for example facilities managers or building owners who may contract others to work at height", and that work must be "properly planned, supervised and carried out by competent people". So the survey should record what safe-access provision the roof already has — guardrails, walkways, ladder access, anchor points or a lifeline — and whether it is in date, since anchors and lifelines need periodic inspection to stay valid.

Two HSE points carry into any commercial roof: "All roofs should be treated as fragile until a competent person has confirmed they are not", and fragile rooflights need barriers or secured, labelled covers. On older industrial roofs with cement sheet or aged rooflights between the panel rows, that is not a formality. Where there is no safe access provision, that finding comes first, because it governs the cost of every future visit. Our rooftop solar safety and safe-access page covers arranging an assessment.

The visual inspection of the modules needs doing row by row, not from one corner. The surveyor is looking for cracked or shattered glass, delamination where the laminate layers have separated, discolouration or browning of the encapsulant, snail trails, burn marks or discoloured cells suggesting hot spots, damaged junction boxes, and the condition of the backsheet underneath — chalking, cracking or splitting there is a safety issue as well as a performance one. Soiling, moss along the lower edge and new shading from plant or an adjacent extension all get noted.

Underneath, the mounting and roof interface matter just as much and get looked at far less: penetrations and their weathering details on a pitched or membrane roof, the condition and distribution of ballast on a flat roof, whether clamps and rails are still torqued and correctly placed, corrosion at fixings, and any evidence of movement such as rails out of line, panels sitting proud, scuffing or ponding. Water ingress in the building below the array is a finding in its own right. Where the array sits on a roof near the end of its own life, that needs saying plainly, because it changes the economics — our page on solar panel removal and reinstallation covers what happens when the roof underneath needs work.

This part must be done by a competent, qualified person, and it is where a proper survey separates itself from a walk-round with a camera. Inspection and testing should cover the DC and AC wiring, string voltages and currents against expected values, insulation resistance, continuity of protective and equipotential bonding, earthing arrangements, the operation of protective devices, and the integrity of every DC and AC isolator including whether water has got into any of them. String-by-string results are what tell you whether one part of the array is underperforming.

Cable management is a genuine weak point on inherited systems: cables resting on the roof rather than clipped, chafing against rail ends or sharp edges, UV-degraded or missing containment, perished cable ties, and connectors of mismatched brands mated together. Then look under the array, because that space is warm and sheltered — nesting material, droppings and rodent or bird damage to DC cabling are frequent findings, and are a fire risk as well as a generation one. Our bird proofing page covers closing that gap off.

Be clear what you should end up holding. The survey is a condition assessment; the electrical work should produce a formal report against the relevant standards, recording what was tested, the results, and any observations coded by severity. That document has your name on it and becomes the reference point for the next inspection. Our solar electrical testing and EICR page covers arranging it with a qualified provider — PPA Funding does not carry out or certify testing.

Inverters work every daylight hour and are usually the first major component to need replacing, so on an inherited system they deserve close attention. The survey should record make, model, serial numbers, manufacture and commissioning dates, firmware version, and the full fault and event log rather than just the current status — a log full of repeated grid or insulation faults tells a story the display does not. Physical checks cover ventilation and cooling, fan and filter condition, dust ingress, heat damage or corrosion on DC and AC terminations, and whether the unit is mounted somewhere it can actually be serviced.

The question most often missed is the commercial one: is this model still supported, and can you still get parts? An inverter that is out of production, or whose manufacturer has withdrawn from the UK market, is a different proposition from an identical-looking unit that is still current. If a failure means a long lead time or a full replacement rather than a board swap, you want to know before signing a maintenance contract, not eighteen months later with the array offline. A survey that flags "supported, spares available" or "obsolete, no spares" against each inverter is doing its job.

Monitoring gets treated as an afterthought and should not be. The survey needs to establish four things: whether monitoring is live and reporting, who owns the portal account, whether the historic data is complete or full of gaps, and whether actual yield matches what a system of that size, orientation and pitch should produce in that location. Solar Energy UK’s guidelines treat monitoring as a distinct topic alongside inspection and maintenance, for the obvious reason — an array with no monitoring is one whose faults are found by accident.

Account ownership is what catches people out on inherited systems, because the portal is often registered to a company that no longer exists. Establishing that at survey stage rather than at the first fault is worth a lot. Where data does exist, comparing modelled against actual output, and strings against each other, points straight at the underperforming part of the array. Where the gap is unexplained, a thermal imaging survey is the usual next step for hot spots and dead strings a visual inspection misses.

Alongside the physical inspection, the survey should review whatever records exist and list plainly what is missing. The set worth chasing is: DNO correspondence and the G99 acceptance or connection agreement; the electrical installation certificate and any later condition report; the commissioning and handover pack with string test results, as-built drawings and a single-line diagram; module and inverter makes, models and serial numbers; warranty certificates and registrations; any existing O&M or monitoring agreement; the roof or structural sign-off and wind-loading calculation; and an MCS certificate if one was issued. Solar Energy UK’s guidelines treat warranties as a topic in their own right, and with good reason — a claim usually stands or falls on the records behind it.

The output should be a written condition report you keep, not a verbal summary and a quote. It should say what was inspected and tested, with photographs; list findings ranked by priority, with safety items clearly separated from performance ones; give an honest view of remaining life on the major components; and recommend a maintenance interval. Crucially it should answer the question owners have but rarely ask out loud: is this array worth maintaining at all? On a tired system with an obsolete inverter, degraded cabling and a roof nearing replacement, the honest answer may be that repowering or removal makes more sense. A provider willing to say so is worth more than one who is not.

PPA Funding is an independent introducer operated by DVC Group Ltd in Shrewsbury. We do not survey, test or maintain systems, and we do not run a standing panel of firms. Tell us the array size, the building and roof type, how the roof is accessed and what records you hold, and we will source and vet a suitable specialist for your site and pass your enquiry on. The provider carries out the survey and contracts with you directly. Our solar O&M takeover page is the place to start.