11 Apr
2025
Energeks
Let’s start with a strong statement: solar project fires are rare. But when they do occur—they’re never random.
They are the consequence of oversights, system tension (both literal and figurative), and... a lack of awareness that fire safety begins at the design stage, not at detection.
This article will help you understand the most common causes of fire hazards in PV installations and show you how to design systems that don’t just generate energy—but do so safely, for years.
What will you find in this article?
The most common causes of fires in PV projects
What rodents, DC sheets and overheating inverters have in common
The role of proper installation and thermal management
What you can do to prevent—rather than just react
Reading time: 4 minutes
What most often causes fires in PV projects?
In our experience in the power engineering sector, we’ve noticed several recurring causes. None of them are “random incidents”—each one originates in design, execution, or operation. These are the ones that show up most often:
1. DC arc faults – connections and cables to blame
A barely visible spark. A quiet flicker between contacts. And yet, a DC arc fault is one of the leading causes of photovoltaic system fires worldwide. This phenomenon doesn’t occur suddenly—it’s the result of a slow, invisible erosion of safety that can persist for weeks or months. Unlike AC systems, where alternating voltage extinguishes arcs at each zero crossing of the sine wave, DC systems have no such natural “off switch.” Once an arc starts, it can last longer than it takes a kettle to boil water—and reach temperatures exceeding 3000°C.
From our fieldwork, we’ve found that as much as 74% of DC arc cases originate from installation errors—most often loose MC4 connectors, broken cable ends, or poor contact between copper strands and terminals. In theory, simple actions. In practice, tasks requiring meticulousness, torque tools, and awareness of how tension affects insulation.
Field example: During an inspection of a 4 MW solar farm in southern Poland, we observed recurring thermal anomalies at DC splitters. A thermal camera revealed localized hotspots reaching 128°C at connectors that looked perfect “to the eye.” Upon disassembly, it turned out the cable had been pinched at a 45° angle, causing micro-movements and, ultimately, arcing.
Why is this so dangerous?
Arc sparks can persist in air across gaps of just 1–2 mm—all it takes is oxygen and dry air.
At over 250°C, most PVC and XLPE insulation begins to decompose, releasing flammable gases.
Combined with dust, dry grass or PUR insulation—you have the perfect recipe for ignition.
Engineering solutions:
High-grade MC4 connectors with TUV, VDE and UL certification, tested for at least 25 years of durability
Arc Fault Circuit Interrupters (AFCIs) installed in combiner boxes and inverters
Use of photovoltaic cables such as H1Z2Z2-K, resistant to UV, water, and thermal variations (operating range: –40°C to +90°C)
Regular thermographic inspections during seasonal transitions (spring/fall), when temperature gradients increase tension risk
Arcs don’t ask for permission. They don’t wait for your inspection. If you ignore them—they won’t ignore you.
2. Inverter failures – overheating and design flaws
If a photovoltaic system were a living organism, the inverter would be both its heart and brain—it translates signals from DC to AC, adapts parameters to grid requirements, and monitors if everything runs smoothly. But just like any heart, the inverter has its limits. High temperatures, excessive load, and design flaws can lead to situations where the device, instead of enabling power flow, becomes the source of uncontrollable energy release. In extreme cases, this leads to melted components, short circuits, or fires exceeding 1000°C.
Overheating – the inverter’s stealthy enemy
During summer, especially on PV farms in southern Europe or central Poland, inverter cabinet temperatures can exceed 70°C if the device:
is installed in direct sunlight with no shading,
placed in a container without active ventilation (or with inadequate airflow),
lacks proper clearance from nearby heat sources or walls (no convection paths).
According to manufacturers (e.g. SMA, Fronius, Huawei), inverter efficiency drops by 20–25% once temperatures exceed 60°C. But more troubling are the long-term effects of chronic overheating, which include:
Reduced capacitor life – every 10°C above nominal shortens it by half
Loss of PCB insulation integrity
Melting of plastic elements and insulators in the power stage
Design oversights – where the fire really starts
Contrary to what many think, fires don’t start on-site—they start with poor design decisions. In the past three years across Central Europe, we’ve observed a 37% increase in inverter failures in PV projects rushed through subsidy programs, where:
inverters were selected right at the edge of their nominal capacity (e.g. 100 kW for 99.5 kW of PV DC),
local thermal conditions were ignored (e.g. south-facing steel containers),
mandatory servicing every 12 months was skipped (filter cleaning, torque checks, fan diagnostics).
Add cost pressure—cheap models without AFCI protection, low IP ratings (IP20 instead of IP65), no short circuit analysis—and you’ve got a system that might start up just fine, but won’t survive the first summer.
Case study: fire in a 1.2 MW inverter container
In 2023, a fire broke out at a large PV farm in central Poland. Technical risk analysts determined:
The inverter was housed in a steel container with poor ventilation
No thermal sensors or smoke detectors were installed
No inspections were conducted for 18 months
On the day of the incident, the ambient temperature was 34°C. Internal cabinet temperature was recorded at over 92°C just before the fire. The damage included inverters, cable channels, and part of the support structure. Losses were estimated at over PLN 320,000.
Smart design and operation practices
To minimize the risk of inverter failure and fire:
Choose inverters with a power margin: at least 10–15% over the PV DC capacity
Install devices in ventilated, shaded spaces (e.g. climate-controlled containers or open-frame shelters)
Include active cooling and thermal sensors at critical system points
Plan regular servicing and component replacement (e.g. fans, air filters)
Use online monitoring with early overload detection for systems above 500 kW
Engineering is precision—not guesswork
A good design isn’t about compromise—it’s the result of hard data, standards, and experience. Inverters that process tens of kilowatt-hours daily must operate within strict thermal boundaries. If those limits are crossed, the question isn’t “if” something happens—but “when.”
3. Improper installation – tensioned connections
Installing a PV system might seem like a routine task—pull the cables, plug the connectors, mount the structure. But the danger doesn’t lie in the obvious—it hides in micro-strains. It’s there, in a seemingly solid cable bent at a 35° angle, in an overstretched wire that “somehow fits,” where conditions quietly arise that, over the course of months, evolve into... a fire hazard. Improper installation is a silent saboteur—it works slowly, invisibly, yet with ruthless precision.
Micro-strains that become major problems
Cables in PV systems—especially on the DC side—operate under dynamic conditions:
They expand and contract daily, exposed to temperature ranges from –20°C in winter to +70°C in summer
They are subject to wind-induced movements, structural vibrations, and localized mechanical stress
They endure pressure when bent, twisted, or routed against sharp edges
From a materials science perspective, every such stress—even minor—leads to:
Insulation fatigue (creep and microcrack phenomena)
Gradual weakening of connector contact zones (e.g. MC4 terminals)
Micro-movements of conducting strands, which can loosen under temperature cycling
In practice, this means one thing: a connection that appears secure today may generate localized overheating in six months—or, in the worst case, a DC arc.
Installation errors – the 4 most common culprits
According to an analysis by TÜV Rheinland based on over 500 PV installations across Europe, 42% of all fire-risk incidents stemmed directly from poor installation. The most frequent errors included:
Overtightened cables with no thermal expansion loops (missing so-called service loops)
MC4 connectors forced together without proper clicking or contact grease (or with non-original parts)
Cable crushing against sharp metal frame edges (no PVC sheaths or protective wraps)
Uneven torque on terminal screws in junction boxes (variations up to 60%, no torque wrench used)
A comparison: a strained cable is like a branch under snow
Imagine a DC cable as a thin tree branch in a forest. When it snows, the branch bends, but it holds. If, however, it was already under tension—say, covered in heavy frost—then just a small drop in temperature can snap it. The same happens to overstressed PV cables: if installed under strain, sudden weather changes (e.g. nighttime cooling or strong sun after rain) can cause tiny cracks in the insulation and begin material erosion. And that’s step one toward ignition.
Impact of faulty installation on system performance
This isn’t only about safety. Poor cable layout and connections also lead to:
Increased transmission losses (up to 1–2%)
Higher junction temperatures (reducing component lifespan by as much as 30%)
Greater difficulty during inspections and repairs (lack of visibility, inaccessible routes)
What’s more—many monitoring systems won’t detect these issues in real-time. A lack of alerts for overvoltage or overload doesn’t mean all is well. In a system where a connector reaches 90°C under full sun, your safety margin is razor-thin. And any warning may arrive... too late.
Best practices in installation – precision from the start
To avoid these risks:
Use service loops of at least 30 cm to absorb thermal strain
Stick to original connectors, matched to wire types and current profiles
Protect cable routes with shielding wraps and mechanical guards
Measure torque when tightening connections (preferably with a calibrated torque wrench)
Run thermographic and impedance tests before system commissioning
The biggest enemy of PV safety isn’t lightning or harsh weather. It’s underestimating the consequences of small mistakes. Installing a solar system isn’t just about connections—it’s the art of managing micro-strains, hidden forces that can turn a quiet day on the farm into a sudden fire alarm. That’s why designers, installers, and auditors must think like engineers—with foresight, precision, and respect for physics.
4. Lack of thermal management in dense installations
At first glance, everything looks flawless: tidy panel rows, perfectly laid cable trays, inverters housed in rhythmic, containerized units. But beneath that symmetry hides a force you can’t see—heat. Or rather, the lack of a way to release it. Even the most advanced PV system loses performance (and safety) if it can’t effectively dissipate the heat it creates.
On tightly packed solar farms—and there are more and more of these, especially in industrial zones or highway corridors—space is at a premium. Distance between panel rows is minimized, inverters are stacked close, and cables are laid in layers. The result? A system that feels more like a thermos than a power plant.
Where does the heat come from?
Every component in a PV system generates heat—it’s pure physics. For example:
A DC cable of 6 mm² carrying 20 A emits about 8–10 W/m of power loss, which means up to 3 kW of heat over a 300-meter stretch
A 100 kW inverter operating at 97.5% efficiency releases about 2.5 kW as pure heat
Transformers, disconnectors, and voltage regulators also emit heat depending on load and insulation class
Now add direct sun exposure, no airflow, and minimal spacing between devices—and you get a local thermal microclimate, where temperatures can exceed 65–70°C by 11:00 a.m.
What happens when the system can't breathe?
The effects of poor thermal management are multi-layered:
Overheated cables have higher resistance, increasing power losses by 2–4%, and accelerating insulation degradation (every 10°C above nominal reduces insulation life by half)
Inverters without airflow lose cooling capability for internal components—capacitor, IGBT, and heatsink temperatures rise, leading to accelerated aging or failure (especially when junction temperature exceeds 100°C)
Thermal faults in connectors can create hotspots over 250°C—which, in the presence of dust and oxygen, becomes a serious fire risk
To illustrate: a 1 MW PV system can generate up to 35 kW of thermal energy under high irradiance. That’s equivalent to three home electric heaters running full blast in a closed room.
Case study: logistics hall rooftop installation
In 2022, Energeks’ technical team investigated a failure in an 800 kW rooftop PV system installed on a logistics center. The system stopped working in under two years. The reasons?
Layered cable trays routed between roofing panels and the ceiling
String inverters housed in a metal cabinet with only one ventilation slot
No temperature sensors, no forced ventilation
During a heatwave, the inverter cabinet temperature exceeded 85°C, leading to the failure of three out of five inverters and partial melting of DC wires. Estimated losses: over PLN 180,000 and six weeks of downtime.
How to design with heat in mind?
One takeaway: thermal management must be part of the design—not an afterthought. Follow these engineering principles:
Maintain at least 1.2x panel height between rows to allow airflow and reduce ground-level heat build-up
Install inverters in containers with active ventilation or passive gravity cooling—don’t allow temps to exceed 60°C
Use temperature sensors in strategic spots (MC4 connectors, DC boxes, inverters)
Lay cables in a single layer or spaced apart, never jammed into tight ducts
Use PV cables rated H1Z2Z2-K or EN 50618 for high thermal resistance
Also consider Computational Fluid Dynamics (CFD) simulations for energy containers—they show where heat stagnates and what airflow strategies will work best.
True efficiency starts with a cool head
We often hear that “orientation and panel output are the most important.” But the truth is—any energy surplus can be consumed by heat if there’s no safe path for it to exit. That’s why at Energeks, we design PV systems like ecosystems—each element breathes, each has its space, each operates within its thermal limits. And that engineering awareness is what makes the difference between a system that lasts for years and one that ends up in a fire investigation report.
5. And sometimes… nature has its own plans
When we talk about the causes of fires in PV installations, we usually focus on humans: design flaws, poor installation choices, or lack of maintenance. But sometimes, the unpredictable and wild—the natural environment—steps in and becomes the main risk factor. And we’re not talking about storms or hail. We mean rodents, birds, and insects that find PV systems to be the perfect place to settle. Unfortunately, not always without consequence.
Rodents – small saboteurs of large systems
Mice, voles, martens, and sometimes even rats—these aren’t creatures we associate with fire. But when these small mammals find their way into a PV system:
They gnaw through DC cables, causing insulation gaps and arc faults
They build nests inside junction boxes or inverter cabinets, often near high-current connectors
They create short circuits by bridging conductors with their bodies (especially dead rodents, which can conduct currents of 15–20 A)
For instance, a 2021 report by a German technical firm showed that 7% of inverter-related incidents involved animal interference. In one case, rainwater entered an enclosure and mixed with a mouse nest and fur remnants—creating a conductive environment that led to a short circuit and fire within 2 minutes.
Birds and insects – subtle enemies of insulation
Birds may seem too big, and insects too small, to pose real threats. But the reality is different. When sparrows or pigeons nest on PV support structures or under panels, their droppings—rich in organic acids—accelerate the degradation of protective coatings. Within a single season, this can lead to:
Accelerated oxidation of aluminum PV panel frames (especially in non-anodized installations)
Penetration of cable sheaths by acidic contaminants and moisture
Insects like hornets and wasps often build nests in the gaps of inverter or DC box enclosures. Their activity can:
Block ventilation channels (raising internal temps by 15–20°C)
Mechanically jam relays, sensors, or fans
Create conductive paths between terminals (e.g. a dead insect wedged between DC pins)
In one 2023 case we analyzed, a wasp stuck between two DC connector pins inside a combiner box caused a short circuit that led to a fire in under 90 seconds—on a day when the ambient temperature was just 23°C.
How to protect against nature?
It’s not about fighting nature—it’s about designing with nature in mind. Here are some proven solutions:
Protective meshes (metal or polymer) around cables and junction boxes to keep rodents and birds away
Sealed cable entry points using water-resistant materials (e.g. EPDM inserts)
Motion and animal presence sensors (PIR + IR), integrated into the SCADA monitoring system
Annual thermographic checks and endoscope inspections in hard-to-reach places
Ultrasonic repellent systems to deter martens and mice—especially near transformer stations
It’s also worth designing systems to avoid open voids between components and the ground or wall surface—empty spaces become ideal nesting grounds for many species.
Animals don’t know voltage—but engineers should
Responsible design that considers not only people but also the natural environment determines whether a PV system lasts a decade—or falls victim to a rodent’s instinct or a bird’s nesting habit. Let’s treat nature with respect—and with foresight. Because what today is just a paw print in the sand—tomorrow could be the start of a spark.
If this topic caught your attention…
…then you’ll likely also appreciate this article:
👉 10 causes of transformer explosions - how to avoid these disasters?
Before anything reacts – make sure your system knows what to do
PV system safety doesn’t begin with a reaction—it begins with intent. With a design that understands physics better than a product catalog. With a team that sees the flow of heat, current, and responsibility.
Protections don’t act by chance. Their effectiveness comes from understanding the grid as an organism—dynamic, disturbance-prone, but also capable of adaptation. Fires that show up in incident reports aren’t sensor failures. They’re the consequence of systems unprepared for reality.
Because in solar—just like in transformer networks—it’s not only the rated power that matters, but engineering awareness: – Will your cable retain integrity when the sun raises the temperature by 20°C in 8 minutes?
– Will your inverter react faster than the arc can destroy the insulation?
– Do you even have time to wait for a warning?
If you’ve read this far, you’re clearly not after shortcuts. You’re after solutions that work. You know predictability is a form of engineering respect for the future—and it’s thanks to specialists like you that solar energy can be not only green, but also safe.
And if you're now considering equipment that meets your standards—
check out our offer, or go straight to see which transformers are in stock now with full documentation and technical support.
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And remember—the best protection is the one that activates exactly when it should. Not sooner. Not later.
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