When an inspector fails a solar system, the crew usually gets the blame. Sometimes that is fair. But a share of solar installation defects are built exactly as drawn. The drawing left out a detail, so the crew guessed. This guide sorts the common defects by where they really start, so you can fix the ones that begin on the plan set.
Quick answer. The most common solar installation defects fall into four groups: wiring and connector faults, mounting and attachment faults, earthing and bonding faults, and disconnect or isolation faults. Australia’s Clean Energy Regulator named these same four as the top causes of substandard systems in its 2024 to 2025 inspections. Many start as design gaps: no connector rule, no attachment detail, no bonding path, or a missing isolator rating.
TL;DR
- In 2024 to 2025 inspections, 18.6 percent of Australian rooftop systems installed in 2024 were rated substandard.
- On utility sites, Raptor Maps measured 4.46 percent average power loss at commissioning in 2025.
- Connectors are a known fire source. Cross-mating different brands is a common field fault.
- For each defect, ask one question: did the drawing tell the crew what to do?
This guide is for EPC quality managers and design leads. It is the field-side companion to our list of solar design mistakes. That post covers errors inside the design. This one starts from what inspectors find on site and works back to the drawing.
How common are solar installation defects?
Two recent public data sets give a clear picture, one for rooftop and one for utility scale.
| Data set | Scope | Key finding | Source |
|---|---|---|---|
| Clean Energy Regulator, Inspections Update No. 24 | 2,586 rooftop PV inspections, Australia, 2024 to 2025 | 18.6% of 2024 installs substandard; 0.4% unsafe | CER (2025) |
| Raptor Maps Global Solar Report, 2026 edition | 373 GWdc of assets analysed | 5.08% average power loss in 2025; 4.46% at commissioning | Raptor Maps (2026) |
The Clean Energy Regulator (CER) defines “substandard” as a system that does not meet key clauses of the standards. It may fail early, but it is not an immediate safety risk. “Unsafe” means a hazard, such as exposed live parts or panels not securely mounted.
The Raptor Maps figure matters for EPCs. A 4.46 percent loss at commissioning means the defects were built in, not caused by age. Raptor Maps sells inspection services, so read its figures as one vendor’s data set.
Which defects do inspectors find most often?
The CER lists the top causes of substandard rooftop systems in 2024 to 2025 as wiring, PV array mounting, PV array earthing, and disconnection points. The table below links each to the design gap that often sits behind it.
| Defect group | What the inspector sees | Design gap that often causes it | Drawing fix |
|---|---|---|---|
| Wiring | Loose or unsupported cables, mixed connectors, poor entry seals | No cable management detail; no connector rule | Cable support detail; connector make and model on the BOM |
| Mounting | Wrong attachment spacing, missing fixings, damaged roof | No site-specific attachment layout | Attachment plan with spacing and zones |
| Earthing | Missing bonds, wrong conductor size, broken paths | Bonding method not shown | Earthing and bonding detail with sizes |
| Disconnection | Wrong isolator rating, poor location, water ingress | Isolator rating and location not specified | Device ratings, locations, and enclosure ratings on the SLD |
Not every defect is a design fault. Poor crimping or a dropped fixing is workmanship. The point is to remove every defect that a better drawing would have prevented.
Wiring and connector defects
Wiring is the largest group in the CER data. On utility sites, Raptor Maps found that string and combiner faults made up 26.89 percent and 21.51 percent of observed power loss in 2025.
Connectors deserve their own check. A 2022 connector safety guide from Kiwa PVEL and HelioVolta reports that connectors caused 27 percent of 58 UK fires started by PV systems from 2010 to 2017. In Germany, connectors were blamed for 24 percent of 180 PV fires from 1995 to 2012, per the Kiwa PVEL and HelioVolta guide (2022).
The same guide warns against cross-mated connectors unless they are tested and certified together. An MC4 connector from one maker and a look-alike from another may not be rated to mate.
What the drawing should say:
- The connector make and model, matched to the module leads.
- A note that field connectors must match the module connector or be certified for intermating.
- Cable support spacing and how cables clear the roof surface.
- Entry and gland details for every enclosure.
Mounting and attachment defects
Mounting faults are the second group in the CER data. Panels not securely mounted are an automatic “unsafe” rating.
Most of these start with a generic layout. If the drawing shows modules but not where each attachment goes, the crew picks spacing on site. In high wind zones, that guess can be wrong.
What the drawing should say:
- Attachment spacing for each roof zone, from the structural calculation.
- The fixing type, size, and embedment.
- Rail span and cantilever limits.
- The flashing or waterproofing detail.
Our civil and structural engineering service produces site-specific attachment layouts and calculations.
Earthing and bonding defects
Earthing faults are the third group. They are easy to miss because the system works without them, until a fault happens.
The common design gap is a plan set that says “bond per code” without showing how. The crew then chooses a method, a lug, or a conductor size. Our guide on grounding vs bonding in a solar plan set explains what each term covers.
What the drawing should say:
- The bonding method for modules and rails (listed clip, lug, or integrated bonding).
- The equipment grounding conductor size and route.
- The connection to the building earthing system.
Disconnect and isolation defects
Disconnection points are the fourth group. The CER also lists water damage to DC isolators as an automatic “unsafe” trigger.
Isolator problems often come from the single-line diagram (SLD). If the SLD does not state the voltage and current rating, the enclosure rating, and the location, the crew fits whatever is on the van.
What the drawing should say:
- Rating of each DC disconnect and AC isolator against the string or inverter values.
- Enclosure rating for outdoor devices, and the mounting position to keep water out.
- Required labels and their locations.
How do you catch design-led defects before site?
Run this five-step review on every plan set before it goes to the crew.
- Read the drawings as an installer. For each item, ask: could a crew build this without guessing?
- Check the BOM against the details. Every connector, fixing, and isolator on the drawings should match a BOM line.
- Check site-specific values. Attachment spacing, wind zone, and cable lengths should come from this site, not a template.
- Check the SLD ratings. Each device rating should match the calculated voltage and current.
- Feed defects back. Log every site defect against the sheet that caused it, and update the template.
After construction, close the loop with infrared thermography and the tests in our commissioning checklist. Record any field changes in as-built drawings. Storage adds its own failure modes, covered in our post on hidden BESS defects.
FAQ
What is the most common solar installation defect?
In the CER’s 2024 to 2025 rooftop inspections, wiring issues were the most common cause of substandard ratings. Mounting, earthing, and disconnection points followed.
Are installation defects the installer’s fault or the designer’s?
It depends on the defect. Poor crimping is workmanship. A wrong attachment spacing on a generic drawing is a design gap. Trace each defect to the sheet before you assign it.
Can drone thermography find installation defects?
It finds many electrical faults, such as hot connectors, failed strings, and inactive modules. It does not find missing fixings or wrong bonding methods. Those need a physical inspection. Our drone survey guide for solar projects covers what each sensor can and cannot detect.
Do these figures apply to India or the US?
The CER figures are from Australia and the Raptor Maps data covers its global client sites. Use them to rank defect types, not as rates for your market.
Fix the drawing, then train the crew
Crew training matters. But if the drawing leaves a decision open, a better crew will still guess. Close the gaps on the plan set first, then audit the build against it.
Our Solar Post-Design service produces construction-ready drawings with these details shown. To review a current plan set or a defect pattern, contact our team. We reply within 1 business day.