24-07-2025
DC Cable: The Overlooked Risk Of The $2 Trillion Solar Sector
Joern Hackbarth, CTO, Ampyr Solar Europe, leads design, procurement, construction, & asset management of utility-scale PV & BESS.
Global solar photovoltaic (PV) capacity surpassed 2.2 TWp in 2024. That's over 2.2 trillion watts of generation capacity, equivalent to roughly $2 trillion in installed value. By comparison, this places the global solar base near the GDP of Russia or Canada, and above that of Spain.
Despite the massive investment, solar modules are now priced as low as €0.08/Wp. This cost efficiency masks deeper challenges: as prices fall, safety and system integrity risks grow, especially on the DC side of the system.
Solar DC cables, though just 1.2% of CAPEX, carry 100% of the energy and the exposure. Their reliability is the foundation of the system. And yet, this is often where engineering decisions are de-scoped or delegated without a full understanding of the risk.
Why DC Is Inherently Riskier Than AC
Solar cells generate direct current (DC), which is harder to isolate than alternating current (AC). AC crosses zero volts 50 or 60 times per second, naturally extinguishing faults. DC has no such zero crossing. When a fault occurs, current continues to flow if sunlight is present.
DC faults don't clear themselves. They can ignite, arc or persist unnoticed, making disconnection and protection much more critical than in AC systems.
The traditional protection logic designed for AC systems, such as fuses and circuit breakers, often cannot detect or react to low-current DC arc faults. The result is that dangerous conditions can exist silently until thermal damage, fire or insulation failure occurs.
How Cable Topology Amplifies Risk
Large-scale PV systems use a rule of thumb of 15 km of DC cable per MWp installed. With 2.2 TWp globally, that's an estimated 30 million kilometres of energised DC cable. Most of this is 6 mm² (about 10 AWG) and operates at higher than usual DC voltage with significant environmental exposure—exceeding the voltage used in railway DC traction systems and many data centre DC bus architectures.
Each meter of that cable—on rooftops, in trenches, across mounting rails—is a potential ignition point if not properly protected, installed and maintained. And each failure can result in loss of yield, insurance claims or, even worse, a major fire.
Overvoltage, Cold Weather And Fuse Limitations
Tier 1 module N-type can be strung in series up to 28 units. At 25°C, 28 modules generate around 1480 VDC. In cold weather, voltage increases further due to the negative temperature coefficient, easily pushing systems over 1500 VDC.
This overvoltage can cause thermal runaway, and most fuses are ineffective at low current faults. This places heavy reliance on insulation integrity and correct voltage margin planning.
The inability of conventional protection to detect early-stage faults means that damage can accumulate slowly, particularly in sites with extreme temperature swings, fluctuating irradiance or poor connector management.
Material Quality And Fire Prevention
Electron-beam cross-linked (EBXL) insulation provides superior fire and tracking resistance. Unlike chemically cross-linked compounds, EBXL avoids degradation, prevents rodent attraction and withstands higher temperatures.
Rodent attacks, insulation creep, UV degradation and thermal fatigue are real-world causes of DC arc faults. These are not rare events; they are daily risks across global solar farms.
Fire classification matters (e.g., CPR Cca-rated cable or higher, self-extinguishing, low smoke, halogen-free) should be the minimum standard to protect assets such as inverters.
Connector Mismatch And Mechanical Stress
MC4 connectors must be precisely matched to cable geometry and crimped correctly. If thermal cycling or vibration loosens a connection, or if insulation swells from heat and moisture, the result can be a resistive arc fault.
Incorrectly torqued glands, fluctuating insulation jackets or incompatible connector inserts lead to failure points. Yet these are often overlooked in procurement and installation.
The visual inspection of a connector cannot reveal internal crimp deformation, oxidation or micro-movement. These issues only surface when it's too late, often during peak irradiance and load.
Backfeed And Inverter Blind Spots
Modern inverters allow up to 24 strings in parallel. That's 48 cables (positive and negative) per unit. If one string faults, current can backfeed from healthy strings, sustaining a fault even if the inverter shuts down.
MPPT tracking does not eliminate the risk. In fact, it may mask it. Without module-level isolation or arc suppression, faults remain live if there's sun.
This makes string cable layout and parallel current modelling critical. Uneven aging, partial shading or connector failure in just one string can affect the entire array, even during normal operation.
Systemic Scale: NREL's 75 TWp Net Zero Forecast
According to NREL, "The increasing acceptance of PV technology has prompted the experts to suggest that about 75 terawatts or more of globally deployed PV will be needed by 2050 to meet decarbonization goals." That implies over 1 billion kilometres of DC string cable.
At this scale, even rare events become statistically frequent. Without system-level and module-level protection, the risks grow faster than the grid.
As more projects come online, the density of installed DC cable increases exponentially.
Executive Takeaway: DC Safety Is a Strategic Asset Risk
DC cable is not a commodity. It is the circulatory system of the entire $2 trillion solar asset base and has a growing annual installation rate projected to exceed 500 GWp, with total deployment needing to reach 3 TWp per year to meet NREL's Net Zero scenarios.
To mitigate risk:
The future isn't just fossil-free—it's DC-heavy. In order to prevent risks, we need to ensure we build it with precision.
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