Solar Photovoltaic (PV) Systems

A solar photovoltaic system generates electricity from sunlight. It comprises modules (panels) on mounting frames, DC cabling and connectors, DC isolators, inverters (string inverters, microinverters or optimisers with a central inverter) that convert DC to AC, AC connection to a switchboard, metering, monitoring, and often batteries. Systems on roofs interact with the roof covering, structure, lightning protection and fire-fighting access.

Ownership varies. Arrays may be owned outright, leased, or installed under a power purchase agreement with a third party that owns the equipment and holds rights over the roof; these arrangements constrain re-roofing and sale.

What shortens life:

• Poor installation: mismatched connectors, cables on roof surfaces, isolators exposed to sun and water.
• Heat on inverters mounted in sun or in hot rooms.
• Coastal exposure on frames and fixings.
• Shading and soiling that cause hot spots.
• Wind on poorly fixed or ballasted arrays.

DC connection and isolator fires

DC circuits on roofs carry high voltages that arc when a connection is poor. Mismatched connectors from different manufacturers, poorly crimped connectors, and rooftop DC isolators that take in water have caused roof fires. In Australia, rooftop DC isolators were a known fire source and are no longer mandatory under the current PV array standard.

Inverter failure

Inverters are the commonest failure: electronics fail from heat, surges and age, typically within 10 to 15 years. A failed inverter stops generation without any visible sign on the roof.

Module degradation and defects

Modules lose output slowly; defects accelerate it: hot spots from cell cracks or shading, potential-induced degradation, delamination, moisture ingress, junction box failures, and microcracks from hail or foot traffic.

Roof interaction

Penetrations for mounting leak if poorly flashed; frames trap debris and water; roof coverings under arrays cannot be inspected or maintained; re-roofing requires removal and reinstatement of the array. Arrays add load the roof structure must carry, and ballasted arrays can shift in wind.

Frame and fixing corrosion

Dissimilar metals, poor fixings and coastal air corrode frames and clamps; modules can come loose in wind.

Battery risks

Lithium battery systems can enter thermal runaway, producing fire and toxic gases; location, separation and ventilation rules apply.

Grid compliance and export limits

Inverters must meet grid connection standards and network settings; older inverters may not meet current requirements, and export limits may constrain output.

Bypass diode and junction box failures

Bypass diodes in module junction boxes let current pass shaded or damaged cells; when they fail, sections of a module overheat or stop producing. Junction boxes that lose their seal let in water and can arc.

Soiling, birds and debris

Dust, bird droppings and leaves reduce output and create hot spots; birds nesting under arrays damage cabling and block drainage on the roof below.

Fire-fighting constraints

Arrays generate DC voltage whenever there is light, so fire-fighters cannot simply isolate them. Without rapid shutdown, labelling and clear access pathways, fire services may limit roof operations on buildings with arrays.

On the roof

• Discoloured, cracked or burnt modules; hot spots on thermal imaging.
• Cables lying on the roof surface; connectors in water.
• Burnt or discoloured DC isolators and connectors.
• Corroded frames and clamps; loose modules.
• Debris and bird nesting under arrays.
• Leaks below mounting penetrations.

At the inverter

• Error lights and fault codes.
• Inverter in direct sun or a hot room.
• Monitoring showing zero or reduced generation.

In the records

• Generation data against expected output.
• Installation certificates and compliance documents.
• Roof structural assessment for the array.
• Power purchase or lease agreements.
• Battery installation and compliance records.

Comparing strings tells you more than the total: one weak string points to a fault in that string; uniform decline points to soiling, degradation or the inverter.

Findings are graded by what they demand: safety (can hurt someone now), failure (failed and damaging the building), condition (distress present and progressing), lifecycle (renewal due on age and exposure), deadline (a regulator or ordinance sets the date), check (investigate before sizing works) and nil (cosmetic or stable).

A licensed solar installer or electrical engineer.

• Generation analysis against expected output for the system size, orientation and weather.
• Visual and thermographic inspection of modules, connectors, isolators, cabling and frames.
• String testing: open-circuit voltage, current, insulation resistance.
• Inverter inspection and fault history.
• Roof inspection: penetrations, covering under the array, structural capacity.
• Compliance check against grid connection and installation standards.
• Contract review: ownership, leases, PPAs.

• Electroluminescence imaging where cracks or hail damage are suspected.
• Earth fault and insulation testing of DC circuits.
• Battery inspection: location, separation, ventilation, detection and the battery management system's fault history.
• Fire service access: rapid shutdown, labelling and roof pathways where required.

The report should state generation performance against expectation, safety defects, roof and structural effects, compliance, and the remaining life of inverters and modules.

• Replace connectors and isolators with matched, correctly installed parts.
• Inverter replacement.
• Module replacement for defective modules.
• Cable management off roof surfaces.
• Frame repairs and refixing.
• Cleaning.
• Array removal and reinstatement for re-roofing.
• Battery relocation or separation to meet rules.

Interactions: re-roofing under an array means removal, storage and reinstatement by a licensed installer, recommissioning, and often updating to current standards; batteries may need relocation; lightning protection must bond the array.

• Labelling and shutdown: labels for fire services and rapid shutdown where codes require it.
• Monitoring with alerts so failed inverters are found within days, not months.

• Bird proofing around array edges to stop nesting and cable damage.

Inverter replacement is priced per inverter and recurs at 10 to 15 years, so it belongs in the register as a recurring line. Module replacement is per module, often limited by matching availability. Connector, isolator and cabling remediation is priced per string. Array removal and reinstatement for re-roofing is a lump sum that can be a large share of a re-roofing project and should sit in the roof line. Monitoring and cleaning recur. Batteries are replaced on their own cycle.

Inverter and battery replacement are lifecycle; DC fire-risk rectification is immediate; repairs and cleaning are repairs and maintenance. Under a power purchase agreement, many of these costs sit with the system owner, and the register should say so.

• Australia. AS/NZS 5033 governs PV array installation, and its current edition no longer requires rooftop DC isolators; AS/NZS 4777.1 and 4777.2 cover inverter installation and grid performance; AS/NZS 5139 covers battery installation and location; installers must be accredited under the national solar accreditation scheme; network service providers set export limits and connection requirements.
• United Kingdom. BS 7671 Section 712 covers PV installations; the IET Code of Practice for grid-connected solar PV sets practice; MCS certification is needed for most incentive schemes; connection follows Engineering Recommendations G98 and G99; fire-safety guidance addresses PV on roofs.
• United States. NFPA 70 Article 690 governs PV systems, including rapid shutdown at the roof to protect fire-fighters; UL 61730 lists modules and UL 1741 inverters; IEEE 1547 sets interconnection; the International Fire Code sets rooftop access pathways and setbacks.

• Installation certificates, single-line diagrams and compliance documents.
• Generation monitoring data since installation.
• Inverter, module and workmanship warranties.
• Roof structural assessment for the array.
• Ownership, lease or power purchase agreement terms, including roof access and re-roofing provisions.
• Network connection approval and export limits.
• Battery installation compliance and location records.
• Maintenance and cleaning records.