Solar Panel Repairs and Fault Finding

Diagnosis before parts

The most expensive way to repair a solar system is to replace components until it works. We test first, and we tell you what the test found.

Most systems that come to us fall into one of four groups: nothing at all, one string missing, a gradual decline nobody noticed for two years, or water appearing somewhere it should not. Each has a characteristic set of causes.

Nothing at all

A system reporting zero is not necessarily a failed inverter, though that is where most people start.

Working outwards, the usual culprits are the AC side first — a tripped breaker or RCD, or an isolator someone switched during unrelated work and never switched back. Then the DC isolators, which are a well-known weak point: a plastic enclosure on a roof, full of water after a decade, with corroded contacts inside. Then the array itself, where a single failed connector opens the string.

Only after all of that has been eliminated does the inverter become the likely answer, and by then the diagnosis is evidence rather than assumption.

One string missing

An array split across two roof faces, or two strings on one face, will often carry on quietly producing half of what it should. Without monitoring, nobody notices for months.

The cause is nearly always at a joint. Plug-in DC connectors are reliable when both halves are the same manufacturer and both were crimped with the right tool. Mixed-brand pairings — a common shortcut — do not have the correct contact geometry, resistance rises, the joint heats under load, and eventually it fails. The failure signature is a discoloured, sometimes melted, connector body.

Rodents are the other frequent cause. DC cable in a loft or under a ground-mounted frame is chewable, and the damage is often visible only when the cable is followed by hand.

Gradual decline

Slow losses are the hardest to spot and the most rewarding to find. Causes we see regularly:

• Failed bypass diodes in a junction box, which take a third of a panel out of service permanently.
• Hotspots and cell damage from earlier physical stress, often from someone having walked on the array.
• Optimiser or microinverter failure on one position, invisible without per-panel monitoring.
• Falling insulation resistance as water finds its way into a damaged cable, which the inverter may respond to by derating or by refusing to start on damp mornings.
• Shading that has grown, which is not a fault at all but is worth measuring before spending money.

Water where it should not be

Two distinct problems get reported the same way.

A leak into the building near the array may come from the array fixings, or it may come from the covering and simply appear there. Correctly installed roof hooks bolt into the rafter with the tile above dressed to sit back down over them, and they weather as well as the roof does. Fixings screwed into battens, or driven straight through a tile and sealed with mastic, do not, and mastic has a much shorter life than a roof.

Water inside electrical equipment — a rooftop isolator, a junction box, an inverter enclosure — is a different and more urgent matter. It gets isolated first and diagnosed second.

After the repair

Any repair we carry out is retested and documented. You get the test results, an updated certificate covering the work, photographs of what was found, and a plain explanation of the cause. Where the fault points at something systemic in the original installation, we will tell you that too, even when the answer you get is not the one you wanted.