A guide to addressing fire risks in rooftop solar


Whether you’re a homeowner looking to cut back on your electricity bill or a corporation seeking ways to reduce your carbon footprint, it’s likely that you have looked into or have already installed rooftop solar. And you wouldn’t be alone.

The global rooftop solar market size was valued at $62.4 billion in 2019 and is projected to progress at a compound annual growth rate (CAGR) of 6.9%from 2020 to 2025, according to one recent report.

CEA engineer performing a rooftop inspection.

Image: CEA

The benefits of rooftop solar are enormous. With PV prices low enough to compete with grid prices, impacts from climate change on the rise, the energy and carbon savings easily calculated, and your rooftop likely unused real estate, there has never been a better time to incorporate solar.

However, due to inconsistent installation practices, intense manufacturer competition, and sometimes-conflicting motives between operations and maintenance (O&M) providers and end-owners, the risk of fires on rooftop installations is uncomfortably common.

Based on a sample of hundreds of commercial scale rooftop inspections performed by Clean Energy Associates (CEA) globally, more than 90% of inspected rooftops had significant safety and fire risks.

One need only perform a simple Google search to find examples of these risks turning into actual fires and causing costly damage, business disruptions, store closures, data center interruptions, and so on. Thankfully, despite the prevalence of the risks, the causes, identification, and the remediation and resolution are surprisingly straightforward.

Three common fire risks

Let’s start with the causes. The three most common gating issues (that is, issues that pose a potentially immediate fire risk) include:

  • Wires on sharp edges
  • Poor terminations in inverters / heavy scoring on wires
  • Improperly made or mismatched/crossmated connectors
Wires on sharp edges will degrade faster due to the cables expansion and contraction associated with thermal expansion/contraction and rooftop vibrations. This poses the risk of a ground fault and potential fire if not remediated.

Each of these issues pose potentially immediate fire risks. But many systems can operate fine for years without incident before causing a fire. Thankfully, these “ticking time bombs” can easily be identified by performing an in-depth system-off (de-energized) visual inspection, and typically are also easily fixed. So, how do these relatively trivial issues come about in the first place, and why are they so prevalent across the industry worldwide?

Primary causes

The answer to this question falls into three categories: inconsistent and widely varying installation practices, inaccurate or incomplete connector information, and conflicting motives between O&M providers and system-owners.

The first issue is fairly straightforward and self-explanatory. Typically, companies contract out the installation to one or more third-party installation groups. Commercial-grade rooftop solar is still a relatively new field with solar jobs outpacing the overall job growth rate in the U.S. by 5x over the past decade. Incomplete or inconsistent training is understandably associated with this type of rapid industry expansion and is one of the leading causes of fire risks on commercial rooftops.

Mismatched and cracked field-made connectors are another fire hazard.

The second, and more significant, cause of these fire risks is incomplete and sometimes inaccurate information regarding solar module connectors.

In brief, rooftop solar modules are typically installed in strings of modules connected in series (usually between 18 to 20 modules for commercial/industrial systems) before they ultimately are connected to an inverter at the end. The distance from one module to the next on a string is standard. As a result, the module-to-module wire harness connections on the string are factory-made.

However, because the distance from the end of the string to the inverter varies, those connections (module to inverter and inverter to panel board) are typically “field-made” connectors that are assembled on site instead of in the factory.

Incomplete or inconsistent training is one of the leading causes of fire risks on commercial rooftops.

If the field-made connections use different hardware than the module-to-module connectors on the string, or if they are not assembled and installed per the manufacturer’s specifications, then there a significant risk exists of a hotspot developing. This, in turn, may lead to a fire. Mismatched or improperly made connectors are a common cause of rooftop solar fires; in some cases they account for 100% of an installation’s connectors.

There’s always a risk of an installer creating field-made connectors without realizing that they’re mismatched. But the larger industry issue contributing to improperly made connectors is the inconsistent and inaccurate information from manufacturers regarding which connectors are compatible with each other.

An important resource is the update to the National Electrical Code (NEC) on this issue, which states, “Where mating connectors are not of the identical type and brand, they shall be listed and identified for intermateability, as described in the manufacturer’s instructions.”

However, without proper training, the problem of improper field-made connections is likely to persist.

Improper wire trimming can increase the rise of fire.

With the rise of connector manufacturers, companies may list their connector as “X-connector compatible” in their marketing literature but without the UL listing or documentation to support such a claim. This leads installers to think the mismatched connectors are compatible, when in fact they are not. In terms of seriousness, this is a global issue and the leading cause of fire risks found from our inspectors.

The third common cause of fire risks not being promptly identified and resolved is the complicated nature of agreements between an O&M company and a system end-owner. As these agreements typically are written, an O&M is required to fix known issues as well as perform yearly or bi-annual inspections. Here, too, the inspectors sent to conduct these inspections may have widely varying experience.

More importantly, however, they may be disincentivized to spend much amount of time looking for issues they would ultimately be liable to resolve.

Rather than performing a relatively time-intensive row-by-row inspection that could easily identify issues such as wires on sharp edges, heavy scoring, and mismatched connectors, O&M inspectors may instead opt to run system performance tests and only inspect a sample of the modules.

Identifying and resolving fire risks

Understanding how we got to this point is important. But site owners need to understand how they can check their current installations for fire risks and resolve them as quickly as possible. The good news is that the identification and resolution of these issues is a relatively simple one.

Step 1: De-Energize a Site:  With a group of licensed professionals, follow proper de-energization procedures and ensure the system is in a safe system-off state.

Step 2: Perform an In-Depth Visual Inspection and System-Off Tests: Due to the seriousness and prevalence of these fire risks, qualified inspectors are recommended to perform an in-depth (system off) visual inspection. This inspection should examine things like mismatched or improperly made connectors, wires resting on or hanging near sharp edges, poor terminations at inverters, and heavy wire scoring or improperly landed and torqued terminations

The system-off test should also include DC Insulation Resistance Test (DC IRT) to check the current leakage on the AC cables, and a continuity test to ensure proper component grounding.

Engineers from CEA inspect a rooftop installation.

Step 3: Perform System-On Inspections: After resolving the safety issues found during the visual inspection and system-off tests and eliminating the safety risks posed by those, re-energize the site and perform system-on thermal imaging of the components (inverters, field made connectors, factory-made connectors, load centers, combiner boxes, central and string inverters, and so on).

In all thermal scans, look for a change in temperature (ΔT), with a large enough variance from a determined average temperature of other identical components onsite. Lastly, confirm that the inverters are running properly without irregularities or faulting, and the monitoring capabilities are hooked up and running properly.

Inspect today

According to a Yale University study, about 70% percent of commercial buildings in the U.S. — or 600,000 sites — are potential targets for solar projects. At best, only a few tens of thousands of those commercial rooftops are currently equipped with solar. With rising demand and the expected growth of the rooftop solar industry, the issue of fire and other safety risks is likely to only get worse without remediation, so it is imperative to ensure that your system is installed properly and not operating with risks.

Join pv magazine and CEA for this free webinar, “Understanding PV Fire Risk: Is Your Commercial Rooftop Safe?” Register here.

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Finding and resolving safety risks on your rooftop solar installations is straight-forward, and performing the due-diligence up-front can save significant costs (both real and reputational). If your site has been energized for more than five years, then there is an increased threat that these issues are present. Relying on the trained eye from a certified installer is the best way to check your rooftop for fire risks.

Check that you are using an installer with a good track-record and put the due diligence into your O&M contract up front to ensure regular and proper maintenance and inspections. Bringing in a third party to validate the results of your O&M inspectors or provide an unbiased extra level of scrutiny can help ensure that safety risks are found and that a remediation plan is drawn up to resolve them.

Glenn Shellenberger is project manager and technical sales engineer at Clean Energy Associates. CEA has performed more than 8 GW of third-party inspection and engineering services work for some of the largest global EPCs, O&Ms, and corporate solar sites. 

The views and opinions expressed in this article are the author’s own, and do not necessarily reflect those held by pv magazine.

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